Understanding Fan

 

EN G IN EERIN G LETTERS The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60521 -5530

NUMBER

SUBJECT

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

System Calculation Fan Laws and System Curves Understanding Fan Performance Curves Temperature and Altitude Affect Fan Selection Fan Performance - The System Effect Increasing Fan Performance Field Testing of Fan Systems Proper Selection of Pressure Blowers Pneumatic Conveying Fans and Blowers for Combustion Process Selection Criteria for Fan Dampers Fan Acoustics Fan Balance and Vibration Stainless Steel Specifications for Fan Equipment Practical Limits of Spark-Resistant Construction Corrosion-Resistant Coatings for Fan Equipment Coating Surface Preparation Specifications Corrosion Resistance of FRP Fans

19 20 21 22 23 24 25 E G

 nyb  FRP Fans Design and Construction of  nyb Accessories and Construction Modifications for FRP Fans Surface Veil for FRP Fans Integral Motors for Centrifugal Fans Electric Motor Codes and Standards Fundamentals of Steam Industrial Steam Heating Systems Miscellaneous Engineering Data Engineering Letter Glossary

 Click on a Subject to open the corresponding Engineering Letter

 

ENGINEERING LETTER

1

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60527-5530

S YS T EM C A L C U L A T I O N INTRODUCTION

The velocity through a system can be determined the ACFM is known. The relationship between velocity andonce airflow is defined by the equation:

A fan system is anyetc., combination of ductwork, hoods, filters, louvers, collectors, that relies upon a fan to produce airflow. When the air moves past each of these components, resistance is created which must be considered in system calculations. It is also important to remember that fans are rated independently of a system and that fan performance will vary depending upon the accuracy of the system calculations. This Engineering Letter will explain some of the basic fundamentals of system design and calculation.

Q = VA where: Q = ACFM V = velocity in lineal feet per minute A = cross-sectional area in square feet To determine the airflow requirement, the cross-s cross-sectional ectional area is multiplied by the required r equired velocity.

SYSTEM DESIGN

System design is really a matter of defining the required work in terms of volume or velocity and then sizing and selecting the necessary system components to accomplish that work. Of course, this must be done within the economic and space constraints of the installatio installation. n.

The purpose of the system will dictate the design criteria to be used. Generally they will fall into one of the following two categories: Velocity Velocity   is typically the primary consideration in dust

collection, dilute pneumatic conveying, fume removal, and contaminant applications. In these applications, a capture velocity is required to redirect the flow of airborne materials into the duct syste system. m. In addition, a minimum conveying velocity is necessary to maintain the flow of the materials within the system.

DETERMINING SYSTEM RESISTANCE

System resistance is the sum of the resistance through each component within the system. The system depicted in Figure 1 may appear complex, but dealing with each component separately provides an orderly process for determining the overall resistance.

Given these velocity requirements, system components can be selected to maintain the appropriate air volume and required velocity through the syste system. m.

HOOD LOSS

Air Mass Mass   is the primary consideration in many drying, combustion process, and ventilating applications. These applications generally require a certain amount of air mass, usually measured in pounds of air, to support the application. Because fan manufacturers publish fan capacities in actual cubic

To determine hood or entrance losses, resistance calculations must be made for both the acceleration loss and the entry loss. Since the air or atmosphere surrounding the hood must be accelerated from a state of rest, energy will be required to set the air in motion. This energy en ergy is equal to the velocity pressure at the entrance to the duct. Assuming the hood in this example

feet per minute (ACFM), cubic the mass required must be converted from standard feet of perairminute (SCFM) to ACFM.

empties into a 7" diameter duct, the required 1165 ACFM results in a velocity of 4363 FPM: V=Q÷A where: Q = 1165 CFM

Figure 1 – Typical System

 

 

A =

(3.5 in. radius)2 x 3.1416 144 in.2 /ft.2 

The hood in this example is most similar to item 2 in Figure 3. Therefore, the entry loss from atmosphere into the hood is .90 times the entering air velocity pressure at 1000 feet per minute or:

= .267 ft.2 

therefore: V = 1165 CFM ÷ .267 ft. 2 = 4363 FPM The velocity pressure (VP) at 4363 FPM is calculated by: VP =

(

Velocity 4005

)

2

Entry Loss = .90 x

therefore: Acceleration Loss =

(

4363 4005

)

2

The same result can be obtained by interpolating from the data in Figure 2.

Outlet Velocity 

Velocity Pressure 

Outlet Velocity 

Velocity Pressure 

800 1000 1200 1400 1600 1800 2000 2200 2400 2600

.040 .063 .090 .122 .160 .202 .250 .302 .360 .422

2800 3000 3200 3400 3600 3800 4000 4200 4400

.489 .560 .638 .721 .808 .900 .998 1.10 1.21

4600 4800 5000 5200 5400 5600 5800 6000 6200

1.32 1.44 1.56 1.69 1.82 1.95 2.10 2.24 2.40

= .06" W.G.

The total hood loss in the example is the acceleratio a cceleration n loss added

The entry loss of a hood is a function of its efficiency. The efficiencies of several common entry conditions are shown in Figure 3. The relative efficiencies are expressed as losses in  percentage of the duct velocity pressure. Consequently Consequently,, the lowest percentage is actually a ctually the most efficient. Velocity Pressure 

2

This loss could have been reduced to .5 VP by simply adding a flange to the bottom edge of the hood as indicated by item 3 in Figure 3.

= 1.19" W.G.

Outlet Velocity 

1000 (4005 )

to the entry loss: Hood loss = .06" + 1.19" = 1.25" W.G. PRIMARY BRANCH

The duct loss from the hood to the branch junction can be determined by using the equivalent length method. This run of duct includes 62' of 7" diameter duct and one 4 piece 90° elbow of R/D = 2. According to Figure 4, the elbow has a loss equal to 12 diameters of 7" duct, or 7'. Thus, the total equivalent length of straight duct is 69'.

Figure 2 – Acceleration Loss

Figure 4 - Loss in 90° elbows of round cross-section

Chart I on page 4 indicates a 4.0" loss for every 100' of 7" diameter duct handling 1165 CFM. The loss for this run can be determined as: Duct Loss =

69 ( 100 )

x 4.0 = 2.76" W.G.

Therefore, the total resistance of the hood branch to the junction is: Branch Loss = 1.25" + 2.76" = 4.01" W.G. SECONDARY BRANCH

A secondary branch is calculated in the same manner as the main branch. For example, a grinder hood handling 880 CFM through a 6" pipe results in a velocity of 4500 FPM, which has a 1.26" VP. According to item 1 in Figure 3, a grinder hood has a .6 VP loss, so the total hood loss will be: Figure 3 - Entrance Loss Percentage

Hood Loss = 1.26" + (.60 x 1.26") = 2.02" W.G. Page 2

 

 

Chart II on page 4 indicates a resistance of 3.3" for every 100' of 9" diameter duct handling 2045 CFM. According to Figure 4 the two elbows are equal to another 18' of duct, so the total equivalent length is 68' between the junction and the fan.

The duct branch from the grinder hood to the junction consists of 27' of 6" pipe and (2) 4 piece 90° elbows of R/D = 2. With an equivalent length of 39' (27' + 6' + 6') the duct loss for this run is: Duct Loss =

39 ( 100 )

Duct Loss =

x 5.2 = 2.03" W.G.

39 ( 100 )

x 3.3 = 2.24" W.G.

 Note that all the losses to this point, up to the fan inlet, are expressed as negative pressure. Also that only the branch with the greatest loss is used in determining the total.

See Chart I on page 4, 4 , which indicates a 5.2" loss for every 100' of 6" diameter duct handling han dling 880 CFM. The total resistance of the grinder branch to the junction is: Branch Loss = 2.02" + 2.03" = 4.05" W.G.

Therefore:

 Note that the resistance in both branches is nearly n early equal. This is  because the pressures in converging branches must be equal during operation or the system will automatically equalize by adjusting the flow different than the design point. If the variation in resistance between any two converging branches exceeds 5%, further design is required to balance the loss in  both branches. Where Where necessary necessary,, balancing can be accomplished accomplished  by altering duct lengths, duct diameters, diameters, or ai airr volumes.

SP inlet = (-4.05") + (-.25") + (-2.24") = -6.54"W.G. Assuming the same size duct from the fan to the collector, the 30’ of duct and the one elbow will have a loss equivalent to the following: Duct Loss =

The main duct resistance calculations begin with the selection of the appropriate duct diameter. Assuming a minimum conveying velocity of 4500 FPM and an airflow requirement of 2045 ACFM (880 + 1165) in the main, a 9" diameter duct will suffice

SP outlet = 1.29" + 2.0" = 3.29" W.G. FAN SELECTION

with a resulting velocity of 4630 FPM. The junction itself represents a loss due to the mixing effect of the converging branches. The ratio of the CFM in the branch (1165 ÷ 880 = 1.3) can be used to determine the loss in percent of VP in the main. Interpolating from the data in Figure 5 results in: 4630 2 Junction Loss = .19 = .25" W.G. 4005

At this point enough information is known about the system to  begin fan selection. Because fans are rated independent of a system, their ratings include one VP to account for acceleration. Since the system resistance calculations also consider acceleration, fan static pressure can be accurately determined as follows:

)

Fan SP = SP outlet - SP inlet - VP inlet In this example with 4630 FPM at the fan inlet, and a 1.33" VP

LOSS IN MAIN AT JUNCTION WITH BRANCH. (BASED ON 45° TEE & EQUAL MAIN & BRANCH VELOCITIES.) 

CFM in Upstream Main ÷ CFM in Branch  1 2 3 4 5 6 7 8 9 10

Fan SP = 3.29" - (-6.54") - 1.33" = 8.5" W.G.

Loss in Main in % of Main V.P.  .20 .17 .15 .14 .13 .12 .11 .10 .10 .10

For this example, a fan should be selected for 2045 ACFM at 8.5" SP and have an outlet velocity of at least 4500 FPM to  prevent material settling. This presumes a standard airstream density of .075 lbs./ft.3 If the density were other than standard, the system-resistance calculations calculations would have been the same but the resulting fan SP would have been corrected. Refer to Engineering Letter 4 for density correction procedures. This example also assumes that the fan inlet and outlet connections are aerodynamically designed. Fans are sensitive to abrupt changes in airflow directly adjacent to the fan inlet or outlet. The effects of abrupt changes and other “system effect”  problems are discussed discussed in Engi Engineering neering Letter 5.

CORRECTION FACTORS FOR OTHER THAN 45° TEE.  Tee Angle  0 15 30 45 60 75 90

x 3.3 + 1.29" W.G.

The pressure drop across the dust collector, like coils or filters, must be obtained from the manufacturer of the device. Assuming a 2.0" loss for this example, the resistance at the fan outlet is:

MAIN DUCT

(

39 ( 100 )

CONCLUSION

45° Loss X Factor  0 0.1 0.5 1.0 1.7 2.5 3.4

It is the responsibility of the system designer to ensure that there th ere are adequate air flows and velocities in the system and that the selection of duct components and fan equipment has been optimized. While computer programs do the bulk of system calculations today, set this Engineering Letter should help to  provide a common of methods and terminology to assist in that effort.

Figure 5

  Page 3

 

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Form 507 DJK

 

 

ENGINEERING LETTER   2 The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60521-5530

FAN LAWS AND SYSTEM CURVES INTRODUCTION

The purpose of this Engineering Letter is to explain the basis and application of the rules used to predict fan performance in a given given sys system. tem. With a basic basic un unders derstan tanding ding of these these rul rules, es, the  performance of a fan can be quickly calculated for various conditions. SYSTEM REQUIREMENTS

The three three fun fundam dament ental al rul rules es governi governing ng fan perform performanc ancee are common com monly ly call called ed the “fan “fan laws laws.” .” These These rules rules are only valid valid within a fixed system with no change in the aerodynamics or  Figur Figuree 1 - Sys System tem Cur Curve ve airflow airf low cha charact racteris eristics tics of the sys system. tem. For the purpos purposee of this this discussion discu ssion,, a   system   is the combin combinatio ation n of ductwo ductwork, rk, hoods, hoods, The same calculation using any number of varying CFM ratings filters,, grills, collecto filters collectors, rs, etc., throug through h which air is distributed. would result in a plotted curve as shown in Figure 1. Therefore, Therefo re, these rules can also be referred to as “system laws.” Regardless of fan type, fan size, or volume of flow through a VOLUME AND PRESSURE PRESSURE The motion of any mass causes friction with its surroundings. The movement of air through a system causes friction between the air mol molecu ecules les and their their su surrou rroundi ndings ngs (duct (duct walls, walls, fil filter  ter  media, etc.) and any other air molecules. Energy is required to overcome this friction, or resistance. The faster the air moves the greater the resistance to flow and the more energy is required required to push or pull the air through the system.

This energy is stated in terms of pressure. The portion of the  pressure that results in air velocity is described as velocity  pressure (VP). The portion necessary to overcome friction in the air and in the system is described as static pressure (SP). The sum of the two is described as total pressure (TP). The law of physics, for motion, is expressed algebraically as: V =   √2gh

V2 = 2gh

or

system,, itself system the relation relationship shipinofsome CFMway. to SP not change unless system is altered SPwill always varies as the the square of the change in CFM. The only exception to this rule is found in a laminar flow characteristic where VP is of far greater  importance than SP. Such circumstances are not typical of fan systems. FAN LAWS

In air movement systems, it is the fan wheel that does the work. In a sense, the fan wheel acts like a shovel. As it revolves, it dis disch char arge gess th thee same same vo volu lume me of air air wi with th each each revo revolut lution ion.. Working within a fixed system, a fan will discharge the same volume of air regardless of air density, (disregarding the effects of compression at high pressures). If the fan RPM is increased, the fan will discharge a greater  volume of air in exact proportion to the change in speed. This is the first “fan law.” 1.

where where V = veloc velocity ity of flow flow g = fo forc rcee of gr grav avit ity y h = pre press ssur uree ca caus usin ing g flow flow

CFM varies varies in direct proporti proportion on to change change in R RPM PM CFM (new) =

RPM (new) x CFM (old) RPM (old)

As can be seen seen from the equ equati ation, on, the pressur pressuree nec necess essary ary to cause flow is proportional to the square of the velocity. In a system, this means that SP will vary as the square of the change in velocity or volume expressed in cubic feet per minute (CFM). This makes it possible to predict all possible combinations of SP at the the corre corresp spon ondin ding g CF CFM M gi give ven n any on onee su such ch ca calcu lcula lated ted relationship of SP and CFM for a fixed system. For example, a system is calculated to require a static pressure equal to 2" water gauge at an airflow rate of 1000 CFM. If it is desired to increase the flow to 1500 CFM without any physical changee in the system, the required SP would be: chang 2

(1500 ÷ 1000) x 2” = 4.5” SP CFM new (  CFM old   )

2

=

SP new SP old

Figure 2 - A fan wheel is a constant volume device.

 

As shown earlier, in a system, the SP varies as the square of  the change change in CFM. CFM. Sin Since ce CFM varies varies directl directly y with with RPM, RPM RPM ca can n be subs substit titut uted ed fo forr CFM CFM in the the sy syst stem em eq equa uati tion on.. Therefore, SP varies as the square of the change in RPM. This is the second “fan law.” 2.

The following are examples of how the fan curve can be used to calculate changes to flow and pressure requirements.

2

SP varies varies in prop proportion ortion to the change change in ((RPM) RPM) SP (new) =

(

RPM (new)   RPM (old)

 )

 2

Example 1: A fan has been selected to deliver 35,530 CFM at 8" SP. The fan runs at 1230 RPM and requires 61.0 BHP.

x SP (old)

The efficiency of a fan is a function of its aerodynamic design and point of operation on its SP/CFM curve (see Figure 3). As the fan speed changes, this relative point of operation remains unchanged as long as the system remains unchanged. Thus, the fan brake horsepower varies proportionally as the cube of the change in RPM. This is the third “fan law.” 3.

If the the fan fan sp spee eed d is incr increa ease sed d or decr decrea ease sed, d, the the poin pointt of  operation operat ion will will mov movee up or down down the exi existi sting ng sys system tem cur curve. ve. This is shown in Figure 4.

BHP va varies ries iin n proportio proportion n to tthe he ch change ange in (RPM) (RPM) BHP (new)  =

RPM (new)

(   RPM (old)   )

 3

After installation, it is desired to increase the output 20%. At wh what at RPM RPM must must the the fan fan ru run? n? Wh What at SP wi will ll be deve develo lope ped? d? What BHP is required? 1. CFM varies varies as R RPM PM (1230) (1.20) = 1476 RPM

3

x BHP (old)

It is impo importa rtant nt to reme rememb mber er that that ea each ch of thes thesee “f “fan an law law”” rel relat atio ions nshi hips ps take takess pl plac acee simu simult ltan aneo eous usly ly an and d ca cann nnot ot be considered independently independently..

2. SP varies varies as (RPM)2 2 (1476/1230) (8) = 11.52" SP 3

3. BHP varies varies as (RPM) 3 (1476/1230) (61.0 (61.0)) = 105.4 BHP Example 2: A fan was originally installed to deliver 10,300 CFM at 2 1 / 4 " SP and to run at 877 RPM, requiring 5.20 BHP.

FAN CURVE AND SYSTEM CURVE

As stated previously, a system curve can be plotted to show all  possibl  possible combinati combinations onsonofthat SPsystem and CFM for a given fixed system.e Any fan used must operate somewhere on that system curve. Fan perform performanc ancee is determ determine ined d by lab laborat oratory ory testin testing g and is  presented  present ed graphical graphically ly in the form of fan curves. Unless it is  physically altered in some way, a fan must operate somewh somewhere ere on its SP/CFM curve. The relative shape of that curve will not change, regardless of fan speed. Because the fan and system can each only operate somewhere on their own respective curves, a fan used on a fixed system can only have one point of operation. The point of operation, as shown in Figure 3, is the intersection of the system curve and the fan SP CFM curve.

After Aft er instal installat lation ion,, it is fou found nd that that the system system only deliv delivers ers 9,150 CFM at 2 1/2"  SP and uses 4.70 BHP. This indicates the original calculations were in error, or that the system was not installed according to plan. What fan RPM and BHP will be ne nece cess ssary ary to deve develo lop p the the de desi sire red d 10, 10,30 300 0 CFM? CFM? Wh What at SP should have been figured? 1. CFM varies varies as R RPM PM (10,300/9,150) (877) = 987 RPM 2

2. SP varies varies as (RPM) (987/877) 2 (2.50) = 3.17" SP 3. BHP varies varies as (RPM)3 3 (987/877) (4.70) = 6.70 BHP CONCLUSION

Figure 3

Figure 4

Use of the “fan laws” is based on a fixed system and a nonmodified fan. Adding or deleting system components such as dampers, or incurring density changes, will create completely new system system cu curves rves.. Changi Changing ng fan acc access essori ories es suc such h as inlet inlet  boxes, evases, or inlet damper damperss will alter the fan’s performance curve from standard. These variables must be considered before the fan laws can be applied. During the pro During proces cesss of syste system m des design ign,, the fan law lawss can be hel helpfu pfull in det determ ermini ining ng altern alternate ate per perfor forma mance nce crit criteria eria or in developing a minimum/maximum range. If “safety factors” are applie app lied d to syste system m calcul calculati ation ons, s, it shoul should d be recogn recognize ized d that that a 10% factor on volume will result in an increase in horsepower  of 33% according to the third fan law. An evaluation should be ma made de weigh weighing ing the necess necessity ity of the safety safety factor factor ver versu suss the cost penalty incurred. Form 607 GAW

 

ENGINEERING LETTER   3 The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60521 -5530

U N D E R S T AN D I N G F A N P E R F O R M AN C E C U R V E S INTRODUCTION

One of the most important documents customers request from fan fa n man manuf ufac actur turer erss is pe perf rform orman ance ce cu curv rves es.. In ad addit dition ion to graphically depicting the basic fan performance data of CFM, RPM, and SP (on the static pressue curve) and BHP (on the  brake horsepower curve), these curves also illustrate the  performance characteristics of various fan types, like areas of  instabi instability lity,, or the rate of change change between between flow and pres pressur sure. e. With some basic knowledge of performance curves, decisions can be made concerning fan selection, fan and system alterations, or the advisability of using a fan in a modulating system, for  example. Except for very large fans, Except fans, perf perform ormanc ancee curve curve informa information tion is generated by connecting the fan to a laboratory test chamber. Very specific test procedures are followed as prescribed in the Air Movement and Control Association’s Standard 210 to assure uniform unif orm and acc accurat uratee reading readings. s. Dat Dataa points points are collec collected ted at a given RPM while the flow is slowly modulated from full closed Figure 1 - Static Pressure Pressure Curve to full open. The information gathered is then used to develop computer selection programs and published capacity tables for  Assuming this same fan was intended to operate at 1200 RPM, the use by system designers and end users. fan laws can be applied to obtain performance at this lower speed. 1. CFM varies varies as R RPM PM

STATIC PRESSURE CURVE

The static pressure pressure curve provides provides the basis for all flow and  pressure calculations. This curve is constructed by plotting a series series of static static pressu pressure re poin points ts ver versus sus specific specific flow rate ratess at a given test speed. While the static pressure curve depicts a fan’s  performance at a given speed, it can be used to determine the fan’s pressure capability at any volume.

CFM CFM (n (new ew)) RPM RPM (n (new ew))  = CFM (old) RPM (old) Therefore: CFM (new) =

1200   (8750) (8750) 1750

= 60 6000 00 CF CFM M

2. SP v varie ariess as (RPM (RPM))2 In addition, it is also possible the to approximat approximate thelaws: fan’s performan performance ce at other speeds by applying following followingefan

SP (new) = P (old)

1. CFM varie variess as RPM

PM (new) (   RRPM (old)   )

 2

Therefore: 2. SP varies varies as (R (RPM) PM)

2

3

3. BHP varies varies as ((RPM) RPM)

SP (new) =

1200

( 1750  )

2

(12) = 5.6” SP

To locate locate a fan’s fan’s point point of operatio operation, n, first first locate locate the requ required ired BRAKE HORSEPOWER CURVE static pressure on the SP scale at the left of the curve. Then draw a horizontal line to the right, to the point of intersection with the Once the CFM and SP have been determined, a BHP rating can SP curve. Next, draw a vertical line from the point of operation  be established. An accurate BHP rating is necessary to properly to the CFM scale on the bottom to determine the fan’s flow size the motor or to determine the operating efficiency of one fan as compar compared ed to anothe another. r. Performa Performance nce curves conta contain in a BHP capability capabi lity for that SP at the given speed. curve from which the BHP rating can be determined for specific capacities. To determine BHP at a specific point of operation, a As shown in Figure 1, the performance for this fan is 8750 CFM hor oriz izon onta tall lin line is dr draw awn n to the the righ rightt from from the the poin pointt of  and 12" SP at 1750 RPM. intersection inters ection of the vertic vertical al CFM line and the BHP curve.

 

Figure 2 - Performance Performance Curve

Figure 3 - Performance Performance Curve with System Lines

As shown in Figure 2, the fan operating at 8750 CFM and 12" SP at 1750 RPM is rated at 30 BHP. By employing the third fan law, the BHP rating can be determined for operation at 1200 RPM. 3.

BHP va varie riess as (RPM) (RPM)3 BHP (new) = BHP (old)

Therefore: BHP (new) =

(

RPM (new) RPM (old)

  (   1200 1750 )

3

 

 3

) (30) = 9.67 BHP

SYSTEM LINES

Let’s Let’s assu assume me th that at a tach tachome omete terr readin reading g ind indic icat ates es th thee fan fan is running at 1200 RPM instead of 1750 RPM, because of mistakes in motor speed or drive selection, and an airflow check indicates only 6000 CFM. These These readin readings gs con confirm firm that the syste system m was calcula calculated ted correc correctly tly and that the fan speed must be correct corrected ed to 1750 RPM as originally specified to achieve the desired 8750 CFM. If the tachometer reading indicates the proper speed but the airflow reading is down, additional system resistance beyond that originally calculated is indicated. This additional resistance could be caused by partially closed louvers/dampers louvers/dampers,, changes in duct sizing from the original design, system effect losses, or just an error in the system-resistance calculations. The deficiency can usually be corrected by either altering the system or increasing the fan speed.

Since fans are tested and rated independently from any type of  system, a means of determining the fan’s capabilities within a given system must be provided. The fan laws apply equally to any system; therefore, CFM and SP variations within the system are predictable. This enables system lines to be superimposed on  performance curves to simplify performance calculations. The system line is nothing more than the sum of all possible CFM and SP combinations within the given system. Any combination of fan and system must operate operate somewhere aalong long that system lline. ine.

Often Often,, pe perf rform orman ance ce cu curv rves es fo forr on onee spee speed d mu must st be us used ed to determine the performance of a fan for use on systems requiring mo more re air air or highe higherr pr pres essu sures res.. A pe perfo rform rman ance ce cu curve rve such such as Figure 4 can be used to determine fan performance beyond the SP scale shown by using the fan laws to obtain a reference point of  operat ope ratio ion n on th thee sy syste stem m line. line. This This can be accom accompli plish shed ed by ap apply plying ing som somee suita suitabl blee facto factorr to th thee requi required red CF CFM M and th thee square of that factor to the required SP.

Because a fan must operate somewhere along its SP curve and since the system has a known system line, their intersection is the point of operation. If the fan speed is changed, the point of  operation must move up or down the system line. If the system is changed in some way, the point of operation must move up or  down the SP curve. In practice, these principles can be used to check the accuracy of fan performance and system design.

For example, the performance curve shown in Figure 4 can be used to determ determine ine fan perform performance ance requiremen requirements ts for a system calculated at 15,000 CFM and 23.5" SP, even though that point is bey beyond ond the cu curv rve. e. By det deter ermi minin ning g a suita suitabl blee ref refere erenc ncee capacity using the fan laws, that falls within the curve data, fan  performance requirements can be obtained at the curve speed and then projected up to the system requirements using the fan laws once again.

USING PERFORMANCE CURVES

Figure 3 illustrates the point of operation of a fan selected for  87 8750 50 CF CFM M and and 12 12"" SP opera operatin ting g at 17 1750 50 RP RPM. M. In Incl clud uded ed in Figure 3 are a number of different system lines. If the system

The required 15,000 CFM and 23.5" SP is on the same system line as 10,000 CFM at 10.4" SP which intersects the fan’s SP curve drawn for 1750 RPM and has a corresponding BHP of  33.0 at 1750 RPM. Therefore:

does properly start-up,performance measurements can be taken not andoperate compared againstupon the available curve.

RPM (new) = BHP (new) =

Page 2

15000 10000   (1750)

(   15000 10000   )

 3

= 2625 RPM

(33.0) (33. 0) = 111 BHP

 

FAN PERFORMANCE CHARACTERISTICS

The per perform formanc ancee cha charac racteri teristic sticss of a fan can be determ determine ined d from the performance curve at a glance. These characteristics include such things as stability, increasing or non-overloading BHP, and acceptable points of operation. Fan performance is based on certain flow characteristics as the air passes over the fan wheel blades. These flow characteristics are different different for eac each h gen generic eric fan or wheel wheel type, type, (i.e. (i.e. rad radial, ial, forward-curved, forward -curved, backw backwardly ardly-inc -inclined, lined, radial-tip, and axial).

Static Pressure

Brake Horsepower 

Thus, theeral performanc performance characteris tics different each of  thes these e gen general fan types. typees.characteristics Furth Further, er, these the sewill performa perfbe ormance nce charact chafor racterist eristics ics may vary from one manufacturer to the next depending upon the particular design. The characteristics described in this letter  are based on nyb  fan equipment. The performance curves presented in Figures 1 through 4 are typic typical al of fa fans ns with with radia radiall-bla blade de wh whee eels ls.. The The SP cu curv rvee is sm smoot ooth h and and st stab able le fr from om wi wide de op open en to close closed d off off.. Th Thee BHP curve clearly indicates that the BHP increases steadily with the volume of air being handled as shown in Figure 4.

CFM in 1,000’s Figure 4 – Typical Radial-Blade Fan Performance Curve

Fans with forward-curved wheels, such as shown in Figure 5, also have a BHP curve that increases with the volume of air   being handled. The SP curve differs significantly from the radial since it exhibits a sharp “dip” to the left of the static  pressure peak. This sharp dip (shaded area) indicates unpredi unp redicta ctable ble flow cha charac racteri teristi stics. cs. Tho Though ugh not techni technicall cally y accurate, accura te, this region is often referred to as the the “stall” region. It indicates that at these combinations of pressure and relatively low volumes, the airflow characteristics across the wheel blades change or break away so that the fan performance point is no longer stable. Any fan with this characteristic SP curve should not be selected for operation in the unstable area. As shown in Figure 6, the SP curve for a backwardly-inclined fan has a sharp dip to the left of the static pressure peak. This indica indicates tes an area of ins instabi tability lity.. How Howeve ever, r, the bac backwa kwardly rdly-inclined SP curve is generally steeper than that of the forwardcurv curved ed whee wheell indic indicati ating ng its de desi sira rabil bility ity fo forr use use in highe higher  r   pressure systems. Therefore, variations in system resistance will result in smaller changes in volume for the BI Fan when compared to the FC Fan. Ev Even en thou though gh Ne New w Yo York rk Blow Blower er ce cent ntri rifu fuga gall fa fans ns with ith ® AcoustaFoil wheels are stable in the area left of the peak, the majority of fans with backwardly-inclined wheels exhibit an SP curve similar in appearance to that of the forward-curved fan. The SP curve shown (in Figure 7) for fans using AcoustaFoil (airfoil, backwardly backwardly-incl -inclined) ined) wheel wheelss exhibits exhibits a much smoother  depression to the left of the static pressure peak. This indicates that th at th thee ov over eral alll fan fan desi design gn is su succh that that inte intern rnal al fl flow ow charac cha racteri teristi stics cs remain remain desirab desirable le or pr predi edicta ctable ble even even in the region left of peak and that performanc performancee in this region is stable. stable.

Static Pressure

Brake Horsepower 

CFM Figure 5 – Typical FC Fan Performance Curve

Brake Horsepower 

Static Pressure

CFM AcoustaFoil  ® is a trademark of The New York Blower Company.

Figure 6 – Typical BI Fan Performan Performance ce Curve

Page Page 3

 

The BHP curve for all backwardly-inclined fans is the major  difference between them and all other fan types. As shown in Figures 6 and 7, the BHP curve for backwardly-inclined fans reaches a peak and then drops off as the fan’s volume increases. With this “non-overloading” BHP characteristic, it is possible to establish a maximum BHP for a given fan speed and select a motor that can not be overloaded despite any changes or errors in 3 system sys tem design design.. Bec Becaus ausee BHP varies varies as (RPM (RPM)) , this this no nonnoverloa ove rloadin ding g cha charac racte terist ristic ic does not apply apply to increas increases es in fan speed, but it is very useful for motor protection against errors or  changes in system calculations and installation. Figures 5 and 6 indicate certain unacceptable selection areas on the SP curve. Although stability or performance may not be a  problem, a point of operation down to the far right on the SP curve should be avoided. Selecting a fan that operates far down to the right, eliminates the flexibility to compensate for future system changes. Also, the fan is less efficient in this area as compared to a larger fan operating at a slower speed. Figure 7 shows the best selection area on the SP curve and the area in which the majority of capacity tables are published.

CFM Figure 7 – Typical AcoustaFo AcoustaFoil il Fan Performance Curve

As is evident in Figure 8, the radial-tip fan design combines the  backwardly-inclined  backwardly -inclined SP curve characteristics with the radial fan’s BHP curve. The radial tip is often more efficient than radial fans and typically best applied in high-pressure applications. As a result of its efficienc efficiency y and dust-han dust-handling dling capabilities capabilities,, the radial-tip fan can can al also so be appli applied ed to lowe lowerr pre press ssur uree ma mate teria riall co conv nvey eying ing systems. The term term axia axiall fa fan n is us used ed to de desc scrib ribee va vario rious us prope propelle ller, r, vaneaxial, tubeaxial, and duct fans. The performance curves of  thes thesee fa fans ns are chara charact cter eriz ized ed by th thee ab abili ility ty to de deliv liver er large large volumes of air in relatively low pressure applications. As can be se seen en in Fi Figu gure re 9, the the ax axia iall flow flow fa fan n is di dist stin ingu guis ishe hed d by a drooping BHP curve that has maximum horsepower at no flow or  closed-off closed -off conditi conditions. ons. The axial fan SP curve exh exhibits ibits an area of  extreme instability to the left of the “hump” in the middle of the curve. Depending upon the severity, axial fans are normally only selected to the right of this area.

CFM Figure 8 – Typical Radial-Tip Fan Performance Curve

CONCLUSION

A good working knowledge of performance curves is necessary to understand the performance characteristics and capabilities of  dif diffe feren rentt fan equipm equipmen ent. t. Use of pe perfo rform rman ance ce cu curv rves es in th thee selection of fan types and sizing will assure stable and efficient operation as well as future flexibility.

CFM Figure 9 – Typical Axial Fan Performance Curve Form 607 GAW

 

ENGINEERING LETTER   4 The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60521 -5530

TEMPERATURE RATURE AND ALTITU ALTITUDE DE AFFEC AFFECT T FAN SELECTION TEMPE INTRODUCTION

Fan performa performance nce chang changes es with the den densit sity y of the gas being handled. Therefore, all fans are cataloged at a standard condition defined as: 70°F. air, at sea level, with a gas density of .075 3 lb./ft. at a bar barome ometric tric pressure pressure of 29.92 29.92"" Hg. At any oth other  er  condition condi tion,, the fan’s hors horsepow epower er requiremen requirementt and its abili ability ty to develop pressure will vary. Therefore, when the density of the 3 gas stream is other than the standard .075 lb./ft. , correction factors must be applied to the catalog ratings in order to select the correct fan, motor, and drive. In add additio ition, n, the maximum maximum safe safe spe speed ed of a wheel wheel,, sh shaft, aft, or  Figure 2 - With hot gas, there there is less weight to shovel. shovel.  bearing can change due to an alloy becoming too brittle or too  pliablee at temperat  pliabl temperatures ures other than 70°F. Tempera Temperature ture derate fac factors tors must be app applie lied d to the fan’s catalog catalog ma maxim ximum um safe safe Example 1. A fan handling standard density, 70°F. air, delivers speed to ensure against overspeed situations. 12,400 CFM against 6" SP (static pressure) requiring 14.6 HOW TO CALCULATE ACTUAL FAN PERFORMANCE AT OTHER THAN 70 DEGREES FAHRENHEIT

As illustrated in Figure 1, a fan wheel is similar to a shovel. In a given system, it will move the same volume of air regardless of the air’s weight. If a fan moves 1000 CFM at 70°F., it will also move 1000 CFM at 600°F.

BHP (brake horsepower). If the system and fan RPM are not changed, but the inlet airstream temperature is increased to 600°F., how will the fan perform? The fan will will still still delive deliverr 12, 12,400 400 CFM, but s ince ince the air at 600°F. weighs half as much as the air at 70°F., static pressure and horsepower will be cut in half. The fan will generate only 3" SP and require only 7.3 BHP. A typical fan specification based on hot operating conditions is illustrated in Example 2. Example 2.  Required: 11,000 CFM and 6" SP at 600°F. (This me means ans the actua actual, l, mea measur surabl ablee sta static tic pre pressu ssure re of the fan at 600°F. will be 6 inches of water.)

The fan’s catalog performance tables are based on 70°F. air at .075 density. The specified SP must be corrected by the ratio of the standard density to operating density. Since densities are inversely inve rsely proportional proportional to absolute absolute temperatu temperature re (degr (degrees ees F. + 460): Figure 1 - A fan wheel is like a shovel.

However, air at 600°F. weighs half as much as it does at 70°F. Theref The refore ore,, the fan requir requires es just just half half the horsep horsepow ower. er. (See (See Figure 2.) Likewise, since the air weighs half as much, it will create only half the static and velocity pressures. The reduction in static pressure is proportional to the reduction in horsepower, thus the overall fan efficiency will remain unchanged.

Total Efficiency =

CFM x Total Pressure 6356 x Brake Horsepower 

6”

460 + 600

1 0 60

(   60 + 70   ) = 6” (   530   )  = 12”

The fan mu must st be select selected ed fro from m the rating rating tab tables les for 11, 11,000 000 CFM at 12" SP. The BHP obtained from the table should be multiplied by the ratio of operating density to standard density in order to obtain the BHP at 600°F. If the rating table showed 30.0 BHP, the operating BHP would be 30.0 (530/1060) = 15.0 BHP. In most “hot” systems, the fan is required to handle cold air  un until til the system system reache reachess tem temper peratu ature. re. A goo good d exampl examplee is in oven exhaust systems.

 

If Example 2 were such a case, the fan would require 30.0 BHP when when op opera eratin ting g at 70 70°F °F., ., an and d 15 15.0 .0 BHP BHP wh when en the oven ha had d warmed to 600°F. Very often a damper is furnished with the fan so that, during the warming-up period, the fan can be dampered to reduce the horsepower. Without the damper, a 30 HP motor  would be needed. Confusion can be avoided if the SP is specified at the temperature it was calculated. In Example 2, the specifications should read either: 11,000 CFM and 6" SP at 600°F., or  11,000 CFM for operation at 600°F. and 12" SP at 70°F. Tablee 1 gives Tabl gives correction correction facto factors rs used to conver convertt from a non non-standard density to a standard density of 70°F. air. These factors are mer merely ely the ratios ratios of abs absolu olute te tempera temperatur tures. es. Mult Multiply iply the actual static pressure by the specific temperature/altitude factor  so standard catalog rating tables can be used. Divide the brake horsepower from the catalog rating table by the temperature/altitude factor to get BHP at conditions. Table 1 - Corrections for Temperature Air Temperature °F.

Factor

Air Temperature °F.

-50 -25 0 + 20 40 60 70 80 10 0 12 0 14 0 16 0 18 0 20 0 22 5

0. 77 0. 82 0. 87 0. 91 0. 94 0. 98 1. 00 1. 02 1. 06 1. 09 1. 13 1. 17 1. 21 1. 25 1. 29

275 300 325 350 375 400 450 500 550 600 650 700 750 800 900

1. 39 1. 43 1. 48 1. 53 1. 58 1. 62 1. 72 1. 81 1. 91 2. 00 2. 09 2. 19 2. 28 2. 38 2. 56

25 0

1. 34

10 00

2. 76

Factor

Table 2 - Corrections for Altitude Altitude Feet Above Sea Level

HOW TO CALCULATE ACTUAL FAN PERFORMANCE AT OTHER THAN SEA LEVEL

A fan operating at an altitude above sea level is similar to a fan operating at air temperatures higher than 70°F.; it handles air  less dense than standard. Table 2 gives the ratio of standard air  density densi ty at sea level to dens densities ities of 70°F. air at other altitud altitudes. es. Example 3.   Required: 5800 CFM at 6" SP at 5000 ft. altitude. 70°F. air at sea level weighs 1.20 times as much as 70°F. air at 5000 Ft. Therefore, at sea level, the SP is 1.2 x 6 = 7.20" SP. The fan would need to be selected for 5800 CFM at 7.2" SP at

70°F. .075 density. When both heat and altitude are combined, the density of the air  is modified by each, independently, so that the correction factors can be multiplied together. Example 4.  Required: 5800 CFM at 6" SP at 5000 ft. altitude at 600°F. Air at 70°F. at sea level weighs 2.00 x 1.20 = 2.40 times as much as 600°F. air at 5000 ft. altitude. At sea level and 70°F., SP = 2.40 x 6 = 14.4" SP. Select a fan for 5800 CFM at 14.4" SP. Divide the brake horsepower in the rating table by 2.40 to obtain horsepower at 600°F. and 5000 ft. If the fan is to start cold, it will still be at 5000 ft. altitude. Therefore, to get the “cold” “co ld” hor horsep sepowe owerr requ requirem irement ent,, divide divide by 1.20, 1.20, the alti altitud tudee factor only.

DENSITY CHANGES FROM OTHER THAN HEAT AND ALTITUDE

Fan densities densities may vary from standard for other reason reasonss than heat and altitude. Moisture, gas, or mixtures of gases (other than air) are a few possibilities. In these cases, it is necessary to obtain the actual density of the airstream gas by some other reference material. A similar factor, as shown in Table 1, is then created using the standard density of air .075 lb. per cubic foot divided by the new density. 3

Factor =

.075 lb./ft. special gas density

ACFM-SCFM DEFINITION

The terms ACFM and SCFM are often used in design work and cannot be used interchangeably. SCFM is Standard Cubic Feet per Minute corrected to standard density conditions. To determine the SCFM of the volume used in Ex Exam ampl plee 2, wh which ich was 11 11,00 ,000 0 CF CFM M at 60 600° 0°F., F., we woul would d multiply the CFM by the density ratios.

Factor

Altitude Feet Above Sea Level

Factor

0 500 1000 1500 2000 2500 3000

1. 00 1. 02 1. 04 1. 06 1. 08 1. 10 1. 12

5000 5500 6000 6500 7000 7500 8000

1. 20 1. 22 1. 25 1. 27 1. 30 1. 32 1. 35

This indicates that if the weight of air at 600°F. were corrected to standard conditions its volume would be reduced to 5500 CFM

3500 4000 4500

1. 14 1. 16 1. 18

8500 9000 10000

1. 37 1. 40 1. 45

work work wh wher eree bo both th qu quan antit tities ies ne need ed to be kn know own. n. It shou should ld be remembered, however, that since a fan handles the same volume of air at any density, ACFM should be used when specifying and selecting a fan.

11000 x

.037  = 5500 SCFM .075

ACFM stands for Actual Cubic Feet per Minute. It is the volume of gas flowing flowing thro through ugh a system system and is not depen dependen dentt upo upon n density. The terms ACFM and SCFM are often used in system design

Page 2

 

FAN SAFE SPEED AND TEMPERATURE TEMPERATURE

Whenever a fan is used to move air at temperatures substantially above or below 70°F., care must be taken to ensure that the safe speeds of wheel and shaft are not exceeded, and that bearing temperature and lubrication are satisfactory. The maximum safe speed of a particular fan must be determined  by calculations or actual tests. Safe speed depends entirely upon the the wh whee eell and and sh shaf aftt as asse semb mbly ly’s ’s ab abil ility ity to with withst stan and d th thee ce cen ntr trif ifug ugaal fo forc rcees cre created ated by its its own own weigh eight. t. Hi High gher  er  temperatures can affect the wheel and shaft assembly’s ability to withstand these forces and therefore must be considered. Mostt me Mos meta tals ls be becom comee weak weaker er at hi high gher er tem tempe pera ratu tures res.. Th This is weakness is measurable in terms of yield and creep strength. It can be translated into formulas that accurately determine the safe sp spee eed d of a whee wheell and and sh shaft aft asse assemb mbly ly in rel relati ation on to its tested tested maximum speed at standard conditions. Manufacturers provide safe speed reductions in their catalogs based on the alloy that was used to manufacture the wheel and/or shaft.

Arrangement 4 centrifugal fans, where the fan wheel is mounted on the motor shaft, should should not be use used d abo above ve 180 180°F., °F., unless unless special provisions are made (i.e., a shaft cooler or heat shield) to keep kee p heat heat radi radiated ated from the hou housin sing g from increa increasin sing g mot motor  or   bearing and winding temperatures. When fan bearings are located outside of the airstream, as in Arra Arrang ngem emen entt 1, 8, an and d 9 centri centrifug fugal al fans fans,, hi high gher er airs airstre tream am tempera tem perature turess are possib possible. le. Tab Table le 4 lists lists som somee typical typical max maximum imum rec recomm ommend ended ed operati operating ng tempera temperatur tures es for fans fans using using ball or  roller bearings. A conventional fan using standard bearings and standard lubricant ca can n no norma rmally lly be op oper erate ated d to a maxim maximum um of ap appro proxi xima mate tely ly 30 300°F 0°F.. Wit With h th thee ad addi ditio tion n of a shaf shaftt co coole olerr (Fig (Figur uree 3), this temper tem peratu ature re limi limitati tation on can be extend extended ed to 650 650°F. °F. The shaft shaft cooler has the effect of absorbing and dissipating heat from the shaft while circulating air over the inboard bearing. Table 4 - Maximum Fan Inlet Temperatures Arrangement 1 and 8 (Overhung Wheel)

Some metals withstand heat better than others. Certain grades of  stainless steel can be substituted to increase temperature limits. On the other hand, fan wheels constructed of aluminum should never be operated above 200°F. For inform informatio ation n regard regarding ing fibe fibergla rglass ss reinforc reinforced ed plasti plasticc fan equipment, consult the appropriate product bulletin. Table 3 gives an indication of the speed derate factors for several different alloys. These are listed for   reference purposes only. For a specific fan, consult the appropriate product bulletin.

M i ld ld S t e ee el

70 200 300 400 500 600

1. 0 . 97 . 95 . 94 . 93 . 92

800 1000

. 80 --

A lum lum iinum num

300°F. 650°F. 800°F. 1000°F.

Arrangement 3 (Wheel Suspended Between Bearings) Standard Construction   200°F. Arrangement 4 (Wheel on Motor Shaft)

Standard Construction

Table 3 - RPM Derate Fac Factors tors By Mate Material rial Temperature °F.

Standard Construction With Shaft Cooler  With Shaft Cooler and Heat Gap With Shaft Cooler, Heat Gap, Stainless Wheel, and Alloy Shaft

Enclosed Bearing Fans (Axial Fans)

Stainless Steel

1. 0 . 97 -----

304L 304L 1. 0 .88 .82 .78 .75 .73

31 316L 6L 1. 0 .95 .92 .89 .86 .84

347 347 1.0 .95 .93 .90 .90 .90

---

---

.79 .75

.86 .83

180°F.

Arrangement 4 Arrangement 9 ith Special V --B Belts with 2.0 S.F. Arrangement 9 Duct Fan With Heat-Fan Construction

105°F. 120°F. 200°F.  

600°F.

Plenum Fans

Arrangement 3 Arrangement 4

105°F.  

The limiting temperature on any fan is the highest temperature that any component of the fan assembly will reach during any operating cycle. A fan in a process oven application may handle air several hundred degrees above the highest temperature the oven reaches, especially during start-up. On such applications, a tempe tem pera ratu ture re indic indicato atorr sh shou ould ld be locat located ed in th thee fa fan n inl inlet et to control the heat source and to keep the fan within its maximum safe safe tem temper peratur ature. e. Thi Thiss is part particu icularl larly y true where where burner burnerss are located on the inlet side of the fan. In all cases, the fan should remain in operation until the air is cooled to 180°F. or less to  preventt “heat soaking”  preven soaking” of the fan shaft which cou could ld cause sagging. sagging. Bearings must be kept cool; otherwise standard lubricants lose their effectiveness and bearing failures are likely. For axial fans, where the bearings are located in the airstream, care must be tak taken en to ens ensure ure prop proper er lubrica lubrication tion.. Spe Specia ciall fan and bearing bearing designs, as well as high temperature lubricants, are available to extend the operating range to higher temperatures.

Page 3

Figure 3 – Shaft Color

105°F.

 

With the addi With additio tion n of a he heat at ga gap p (F (Figu igure re 4) th thee tempe tempera ratu ture re limitation can be extended to 800°F. since the fan pedestal is isolate isolated d from the hot fan housing housing.. For specif specific ic applica applicatio tions, ns, consult consu lt the appropriate product bulletin. Also, recognize that these these lim limitat itations ions apply only to bea bearin rings gs and that whe wheel el and shaft limitations must be treated independently. All of the foregoing is based on the use of standard lubricants. When Whe n high-t high-temp empera erature ture lubrica lubricants nts are requ required ired,, the type type of  lubricant and the frequency of relubrication are normally much more critical. When the fan shaft is heated to the point that it expands more than the structure to which it is attached, one expansion bearing and one fixed bearing should be furnished. The fixed bearing is located on the drive end of the fan while the floating bearing is located loca ted next to the fan. This arran arrangem gement, ent, however, however, is not critical and may vary by manufacturer. When the fan is handling air below 70°F., there is the possibility of other problems. Below -30 to -50°F., ordinary steel is too  brittle. Aluminum wheels or wheels of steel containing at least 5% nickel must be used, and shafts must be made of nickel-

 bearing steel. In addition, lubricants  bearing lubricants become become stiff, or even solid in these low -temperature -temperature applicati applications. ons. Exact op operatin erating g conditions should be given to the fan manufacturer to relay to the bearing supplier for proper selection. CALCULATING “HOT” RESISTANCE FOR SYSTEMS

Figure 5 shows a system that operates at the same temperature throughout. If the inlet temperature is known, the fan may be selected from the fan capacity tables and the rated horsepower and static static pres pressur suree corr correct ected ed by the tem tempera perature ture correct correction ion factor  factor  from Table 1. However, what happens to the system that the fan was operating against? If a fixed system, which originally was calculated for standard air, was subjected to the same temperature increase as the fan, then system static pressure will change and be identical to the fan static pressure change. The result is that if a fan and system operate together the flow will remain unchanged. (Seee Figure (Se Figure 6.) Unfortu Unfortunat nately ely,, this exam example ple assum assumes es th that at th thee entire system is being subjected to the same temperature change, which is not always the case.

FiguFigure Figure re 4 4“Heat Gap” betwe between en ffan an and – “Heat Gap” between bearin bea rin . fan and bearing.

Fi ure 5

Figure 6 – Fan-system curve rel relationship ationship with fan and system at the same temperature.

A s stem stem with the same same te tem m eratur eraturee th thro rou u hou hout. t.

Page 4

 

Figure 7 shows a system in which different temperatures are involved. The fan will not handle the same volume of air when operating hot as it does when cold. If the burner is on, the fan will handle 1430 ACFM against an actual static pressure of 1.2 inches. This is arrived at by adding the filter, burner, and nozzle resist resistanc ance, e, neg neglec lecting ting for the sake sake of simplic simplicity ity any ext extern ernal al resistance from additional ductwork. The fan would be selected fro from m the capa capaci city ty table tabless on th thee ba basi siss of 143 1430 0 CFM CFM at 1.7 1.72 2 inch inches es static static pre press ssur uree (300 (300°F °F.. co corre rrect ctio ion n fa fact ctor or times times 1.2 inches).

 be assumed that air expansion takes place after the high ve velo loci city ty sect sectio ion n of the the burn burner er.. The The nozz nozzle less wi will ll vary vary in resistance directly as the density changes and inversely as the square of the flow. The nozzle would then have a resistance cold at 1000 CFM of:

.5” x

( 1000 1430 )

 2

x 1.43 = .35”

Summin Sum ming g these these resista resistance ncess yields yields the cold cold resist resistanc ancee at 100 1000 0 If the burner is turned off while the fan continues to operate at the the sa same me RPM, RPM, it is nece necess ssar ary y to dete determ rmin inee the the sy syst stem em charac cha racteri teristi sticc curve curve and plot its inters intersecti ection on with the fan to determine how much air the fan would move and at what static  pressure. To accomplish this we must assume an arbitrary capacity, such as 1000 CFM at 70°F. The filter louver resistance would be the same, cold or hot, at .3 inches 70°F. The burner  resistance would remain unchanged unchanged with temperature since it must

CFM of then 1 .05"SP. .05" SP. This new syste system m poin point t and correspon corres pondin ding g curve are plotted against a fan curve at standard conditions such suc h that the result resulting ing intersec intersectio tion n will be the fin final al ope operati rating ng  point of tthe he cold system. Using an actual fan as an example, th thee result resultin ing g flow flow wo woul uld d be 122 1220 0 CF CFM M at 1. 1.5 5 in inch ches es stat static ic  pressure. (See ( See Figure 8.)

Figure 8 - Fan-system Fan-system curve relationship relationship with fan at different temperatures.

Figure 7 - A system with different temperatur temperatures. es.

Page 5

 

FAN LOCATION IN HOT PROCESS SYSTEMS

Figure 9 shows how a fan may be located more economically in one part of a system, as contrasted to another. Suppose 10,000 CFM is to be heated from 70°F. to 600°F. Obviously, the heater  will require the same 3-inch 3-inch pressure differen differential tial wheth whether er the fan is to push the air into, or pull the air out of, the heater. A fan pushing air into the heater would be specified to handle 10,000 10, 000 CFM at 70°F 70°F.. aga agains instt 3 inc inches hes of static static pre press ssu ure at 70°F.. One poss 70°F possibl iblee select selectio ion n is a fan with a 27 27-inch -inch wheel wheel diameter, Class I design utilizing a 71/ 2 HP motor.

The alternati alternative ve fan fan,, pul pulling ling air from the heater heater,, wou would ld be specified to handle 20,000 ACFM at 600°F. against 3" SP at 600°F. It would be selected from the capacity tables for 20,000 CFM at 6" SP. One suitable choice is a fan with a 3 6 1/ 2 -inch wheel diameter, Class II design utilizing a 15 HP motor. (Note: 26 HP, HP, fr from om the the tabl tables es,, at 70 70°F °F., ., di divi vide ded d by tempe temperat ratur uree correction factor, is 13 HP at 600°F.) This example illustrates why it is usu usually ally more economi economical cal to locate locate the fan at the coolest part of the system. In this case, the “push” fan might cost half as much as the “pull” fan.

Figure 9 - The importance of fan location.

F o rm 6 0 7 G A W

 

ENGINEERING LETTER   5 The New York Blower Company   ●   7660 Quincy Street, Willowbro Willowbrook, ok, Illinois 60521-5530

F AN PERF ORMANCE -

THE SYSTEM EFFECT

INTRODUCTION

Fans are typically tested and rated in prescribed test configurations defined by the Air Movement and Control Association. This is donee to ens don ensure ure standa standardiz rdized ed procedu procedures res an and d ratings ratings so that that system sys tem des design igners ers can mak makee rea realis listic tic cho choice icess among among vari various ous manufacturers manufa cturers.. Beyon Beyond d the routin routinee sys system tem resista resistance nce calculations calculations,, the location of some common comp components onents and their proximity to the fan inlet or outlet can create additional immeasurable losses commonly common ly called  System Efect.  These losses, if not eliminated or minim minimiz ized ed,, will will ne nece cess ssita itate te fan sp spee eed d an and d ho hors rsep epow ower  er  increases to compensate for the performance deficiencies. This Lette Letterr will will ou outli tline ne so some me of th thee commo common n cause causess fo forr th thes esee deficiencies and provide useful guidelines for more efficient and  predictable air-handling systems.

The four most common causes of system-induced performance deficiencies: 1. 2. 3. 4.

Eccentric Eccentric flow in into to the fan inlet. Spinning Spinning flow into th thee fan in inlet. let. Improper ductwo ductwork rk at the ffan an outl outlet. et. Obstructions Obstructions aatt the fan iinlet nlet or ou outlet. tlet.

ECCENTRIC FLOW

Fans perform correctly when air flows straight into the inlet. Air  should sho uld be drawn drawn into the fan inlet inlet with with an evenly evenly distribu distributed ted velocity profile. As shown in Figure 1, this allows all portions of  the fan wheel to handle an equal air load.

SYSTEM DESIGN

If the air is not drawn into the fan inlet evenly, performance The term  system  refers to the path through which air is pushed will result from the combined effects of turbulence and/or pulled. Since it can be any combination of ducts, coils, deficiencies and uneven air distribution. This is illustrated in Figure 2, where filt filters ers,, etc etc., ., through through which air flow flows, s, a sys system tem can ran range ge in an elbow is installed installed directly on the fan inlet. comp complex lexity ity.. The sy syst stem em ca can n be as sim simple ple as ex exha haus ustin ting g ai air  r  through an opening in the wall of a building, or as involved as a mu multi lti-z -zon oned ed syst system em with with va vary rying ing flow flowss an and d de dens nsiti ities es.. The calculations calcu lations for determ determining ining the performance performance requirements requirements are discus discussed sed in Eng Enginee ineering ring Letter 1. The effec effects ts of the system system design on the actual performance capability of a fan represent separate and equally important considerations. In the the typic typical al proce process ss of sy syst stem em design design,, the perf perform orman ance ce requ requir irem emen ents ts are are ca calc lcul ulat ated ed an and d then then used used to se sele lect ct the the appro appropri priat atee fa fan. n. How Howev ever, er, in many many ca case sess the ef effe fects cts of th thee relationship between the system components and the fan are not considered in the calculation or selection process. For example, the resistance of a given size elbow at a given flow can be easily determin dete rmined ed usin using g the equival equivalent ent len length gth cal calcula culation tion method. method. However, Howeve r, if that elbow is located at the fan inlet or outlet, furt further  her  immeasurable losses will be imposed in addition to the simple loss loss throug through h the elb elbow ow itself. itself. Mos Mostt imp importa ortantl ntly, y, these these losses losses cannot can not be mea measure sured d or eve even n detect detected ed with with fie field ld instrum instrument entss  because they are, in fact, a destruction of the fan performance characteristics.

Figure 1 – Even Air Loadin Loading g

Standa Standardiz rdized ed tes testing ting and rati rating ng method methodss for fan fanss have have been been est establ ablish ished ed by the Air Moveme Movement nt and Control Control Ass Associa ociation tion,, (AMCA). The test methods are described in AMCA Standard 210, titled Test Code for Air Moving Devices. Specifying fan equipm equ ipment ent tes tested ted and rated in strict strict acc accorda ordance nce with AMCA Standard 210 is the best way to ensure accurate fan performance. Howev How ever er,, the the syst system em eff effec ects ts th that at alt alter er or limit limit th thee ultima ultimate te  performance remain the most frequent causes of field  performance problems. pr oblems.

Figure 2 – Uneven Air Loadin Loading g

 

When the system attempts to change the direction of flow, the air hugs the out outside side of the inlet elbow enter entering ing the fan fan.. This This causes uneven, turbulent airflow into the fan. Another common cause of non-uniform flow into the fan inlet is a poorly designed inlet box, such as the one shown in Figure 3. It is important to remember that air has mass.

Pre-spin Pre-sp innin ning g flow flow can can resul resultt fro from m an any y nu numb mber er of co comm mmon on situat situation ions. s. Two elb elbows ows in clos closee prox proximi imity ty to one another another can force the air to make consecutive turns in perpendicular planes to form a corkscrew effect. As shown in Figure 5, air converging tangentially into the main duct or plenum can create an obvious spinning effect. Pre-spinning Pre-spin ning flow can also be induce induced d by suc such h common common air  cleaning devices as a venturi scrubber or a cyclone as seen in Figure 6. In these cases, it is often the very function of the air  cleaning device to create a spinning effect.

Figure 3 – Poorly Designed Designed Inlet Box

SPINNING FLOW

Unintentionally spinning air into the fan inlet can have the same effect on performance as the intentional pre-spin produced by a vortex-type inlet damper. The direction air is flowing when it enters the fan wheel is very important. In order to produce its rated capacity, the fan works on the air by changing its direction and accelerating its velocity. If  the air is spinning in the same direction as the wheel rotation, the fan capacity capacity will be diminish diminished. ed. If the air is spi spinnin nning g in the opposite direction of the wheel rotation, the brake horsepower  and noise of the fan will increase. The static pressure of the fan may also increa increase se slight slightly, ly, but far les lesss than than indica indicated ted by the increased power consumption.

Figure 5 – Spinning E Effect ffect

The evaluation and control of pre-spinning flow is more difficult than eccentric flow because of the variety of system connections or compo components nents that can contribu contribute te to pre-spin. pre-spin. Also, Also, spinni spinning ng often occurs in combination with eccentric flow such as the case with the inlet box shown in Figure 4.

Figure 4 – Eccentric Flow with Pre-Spin

Figure 6 - Fan/Cyclone Fan/Cyclone System

Page 2

 

CORRECTING BAD INLET CONNECTIONS

The ideal ideal fan inlet inlet connec connection tion create createss neithe neitherr ecc eccentr entric ic nor  sp spin inni ning ng fl flow ow.. Wher Wheree an in inle lett duct duct is re requ quir ired ed,, the the be best st connec con nection tion is a long long straig straight ht duct duct wit with h straigh straighten tening ing vanes. vanes. Howev How ever er,, it is us usua ually lly ne neces cessa sary ry to ad adap aptt th thee sy syst stem em to th thee available space. When space becomes the limiting factor, two choices are available: 1. Install Install correc corrective tive de devices vices in the duc duct. t. 2. Increase Increase fan speed to compensat compensate. e. The first choice is preferable, the second islves oftenwill necessary. In many cases, the corrective corrective but devices themselves themse represent represent some resistance to flow. A combination of both choices could be necessary to correct extreme field performance problems. If the fan and system are properly matched, matched, their common point of  operation should fall within the recommended range on the fan Figure 8 – Turning Vanes static-pressure curve. Figure 7 illustrates the recommended range for backwardly-inclined fans. A deleterious system effect could move the point of operation to the left on the pressure curve. This would force the fan to operate at an unstable point. The same To overcome these losses, the fan speed must be increased to the situation can occur with any of the basic fan types that exhibit speed shown in the fan’s rating table at the required volume and a originally riginally calculated: unstable flow characteristics as discussed in Engineering Letter   pressure 21% greater than o 3. When this happens there are three options: alter the system to all allow ow greate greaterr flow flow wit withou houtt inc increa reasin sing g resistance resistance significantly significantly,, (110% ÷ 100%)2 = 1.21 replace the fan with a smaller one, or replace the fan with one that has a stable curve.

Of course the fan’s speed should never be increased beyond the cataloged maximum safe speed! It is important to note that the increased resistance will not be observed on the system. The pressure increase is only for the  purpose of selecting the fan to compensate for the losses associated with the particular system effect.

Static Pressure

Brake Horsepower 

CFM

Figure Figu re 7 - Stati Staticc Pressur Pressuree Curve for Backwardly-Inclined Fan

The fan laws cannot be applied selectively, only simultaneously. According to the fan laws, if the fan speed is increased 10% for a given system, the flow through the system will increase 10%, the sy syste stem m resist resistan ance ce will will incre increas asee 21% 21%,, and and the fan fan BHP will will increase 33%. This represents an obvious waste of energy due to an often avoidable system-related deficiency. In most cases, such a change would require the purchase of a larger motor as well as a new drive. If the fan is a direct-connected arrangement, limited to on onee fixed fixed mo motor tor spee speed, d, the solu soluti tion on be beco come mess ev even en more more expensive. These considerations and horsepower penalties apply to all all the the major ajor caus causes es of sy sysstemtem-in indu ducced perf perfor orm mance ance deficiencies. If the avai availab lable le space dicta dictates tes the nee need d for a turn turn into into the fan inlet, a stand standardized ardized inlet-box design, with predic predictable table losses, should be used whenever possible.

Simple or complex turning vanes, such as those shown in Figure 8, can be used to minimize the effects of both eccentric and/or  spinning flow. The egg-crate straightener, such as the one shown DISCHARGE DUCTWORK  in Figure 6, can be used in the available space to stop pre-spin and improve fan inlet conditions. The connection made to a fan outlet can affect fan performance. An ou outl tlet et du duct ct rang ranging ing in len lengt gth h fro from m 21 21/2 /2 to 6 fan fan whee wheell Mostt of the Mos the inlet inlet conn connec ectio tions ns illus illustra trate ted, d, with with or with without out diameters, depending on velocity, is necessary to allow the fan to corrective correcti ve devices, can produ produce ce losses in perform performance. ance. These losses would be difficult, if not impossible, to predict. Even the inlet  box show shown n in Figure Figure 8, with all the turni turning ng vanes vanes installe installed, d, coul could d still easily represent losses of 10% to 15% of the required flow.

de deve velo lop p its fu full ll rate rated d press pressur ure. e. If th thee out outle lett duc ductt is omi omitte tted d completely comple tely,, a static static pressu pressure re loss loss equ equal al to one half the outlet outlet vel velocity ocity pressure pressure will resu result. lt. The system system resi resistan stance ce calculat calculation ion should include this loss as additional required static pressure.

Page 3

 

Figure 9 - Velocity Prof Profile ile at Fan Outlet

Air is not discharged from a fan with a uniform velocity profile. The main reason for this is the fact that air has weight and is thrown to the outside of the scroll. Figure 9 shows a typical velocity profile.

Figure 10 - Poor Fan Outlet Connections

In a duct with a uniform cross-section, the average velocity will  be the same at all points along the duct. However, where velocity distribution changes (such as the duct adjacent to the fan outlet) the velocities are not typically the same. Since velocity pressure is proportional to velocity squared, the average velocity pressure at the fan outlet will be higher than the average downstream. Since total pressure will be virtually the same, the static pressure cannot be fully developed until some  point 21/2 to 6 duct di diameters ameters downstream. Although duct turns directly at the fan outlet should be avoided, there are times when they cannot. In such cases, the turns should follow the same direction as the wheel rotation. Turns made in the opposite direction of wheel rotation (such as those shown in Figure Figu re 10) can have a pressu pressure re drop beyo beyond nd normal normal system system calculations. Usually the drop is between .5 to 1.5 fan outlet velocity pressures. INLET OR OUTLET OBSTRUCTIONS

System obstructions can be as obvious as the cone-shaped stack  cap which which can have a pres pressur suree drop as high as one velocity velocity  pressure, or as subtle as the installation of a large fan sheave directly in front of the inlet on an Arrangement 3, double-width, double-inlet fan. One of the most common situations is to place a fan inside a  plenum or near some obstruction and fail to account for the effects on the airflow to the fan inlet. The installation shown in Figure 11 is typical of the sort of non-uniform flow that could result in additional losses beyond the normal system calculation. These The se losses losses will increas increasee as the veloc velocity ity increases increases or as the distance between the obstruction and the fan inlet decreases. CONCLUSION

AMCA Publication 201 - Fans and Systems, presents an in-depth discussion of system effect and provides methods for estimating losses associated with many common situations.

Figure 11 - Plenum System System

If system effect situations cannot be avoided, their impact on  performance should be estimated and added to the calculated system resistance prior to sizing or selecting the fan. Ignoring th thee syst system em effec effectt co coul uld d lead lead to di diff fficu icult lt field field perfo perform rman ance ce  problems later. It could be that the installed fan does not have the necessar necessary y spe speed ed reserv reserve, e, or the motor is not of suffici sufficien entt  brake horsepower. The cost of correcting such a field  performance problem pr oblem could escalate rapi rapidly. dly. System designers need to carefully consider the system effect values values pre presen sented ted in AMCA Pub Public licati ation on 201 201.. By accura accurately tely defining the true performance requirements of fans in installed systems, field performance problems can be reduced significantly. Form 607 GAW

 

ENGINEERING LETTER The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60521-5530

I N C R E A S I N G F A N P E R F O R M AN C E INTRODUCTION

Industrial Indus trial proce processes sses and plantplant-vent ventilation ilation systems often need

Chec Ch eck k whee wheell and and inle inlett co cone ne alig alignm nmen ent. t.   See See Figu Figure re 3.

more more ai airr than than or orig igin inal ally ly de desi sign gned ed.. In Incr crea ease sed d pr prod oduc ucti tion on Components may be out of position due to routine cleaning or  requirements, process changes, and facility renovations are a  painting or the wheel could have shifted during shipment. For  few of the major reasons. Additionally, the lack of adequate  backward inclined fans, the relati relation on of wheel to inlet cone is maintenance over time can negatively impact system airflows. ve very ry criti critica cal. l. Even Even a quar quarte terr of an inch inch can can ha have ve a major  major  This letter discusses several procedures that can increase airflow. impact. The fan’s installation and maintenance literature shows CHECK THE FAN’S MECHANICAL CONDITION the proper proper positi positioni oning ng of the wh wheel eel to the inlet cone (“A (“A”” dimension) or inlet plate. Of Ofte ten n ai airfl rflow ow can can be incr increa ease sed d by ad adhe herin ring g to prope properr fa fan n mainte mai ntenan nance ce procedu procedures res as out outlin lined ed in fan instal installat lation ion and maintenance literature. Properly aligned and tightened V-belt drives.  See Figure 1. Fan speed can decrease by as much as 10% to 20% when belts are too loose, with a corresponding loss of airflow.

Figure 3 – Wheel to Cone Alignm Alignment ent

Figure 1 - Poor Drive Alignment and Belt Tension

INSPECT THE SYSTEM The design and maintenance of the system plays a large role in achieving achie ving the overal overalll desire desired d perform performance. ance. Visual inspec inspections tions of ofte ten n reve reveal al so some me easi easily ly rect rectif ifie ied d pr prob oble lem ms that that can can

significantly impair performance. Check for clogged filters or coils.  If the system has not been  properly  properl y maintained, maintaine d, clogged filters filter s or obstruct obstructed ed coils will reduce airflow. The greater the obstruction, the greater the loss in airflow.

Figure 2 – Incorrect Wheel Rotation

leakss in the the ductw ductwork ork wi will ll Eliminate System Eliminate System leaks. leaks.   Any leak contribute contri bute to reduc reduced ed perfo performanc rmance, e, espec especially ially leaks aroun around d  plenum bulkhead bulkheadss that can lead to recircul recirculation ation of air. Worn flexible connectors are a common source of leaks and should  be inspected regularl y.

Clean airstream surfaces.  A fan cannot perform as designed if  Verify that dampers are installed correctly and operating the air flow surfac surfaces es are distorte distorted d by contami contaminan nants. ts. Even in the da damp mper er link linkag agee is out out of adju adjust stme ment, nt, the the properly.   If the larg largee fans fans,, a si sixt xtee eent nth h of an inch inch of bu build ild up ca can n reduc reducee dam damper per may not be ope openin ning g com comple pletely tely,, thereb thereby y red reduci ucing ng  performance.  perfor mance.  performance.  perfor mance. If inlet dampers are used, make sure they are installed so that the air is pre-spun in the same direction as Check fan rotation.   See Figure 2. Centrifugal fans will move wheel rotation rotation.. See Figur Figuree 4. If the air distri distribut bution ion syste system m somee air even som even wh when en run runnin ning g backw backward ards. s. While While som somee ty types pes wheel employs balancing dampers, make sure they are set properly. would use so much horsepower they would trip circuit breakers, other designs could run for years without being detected.

 

Figure 4 – Inlet Damper/Fan Damper/Fan Wheel Rotation

Figure 6 – The effects on brake horsepower, static pressure and loudness when fan speed is increased.

When incr When increa easi sing ng fan fan sp spee eed, d, it is ne nece cess ssar ary y to chec check k the the ma maxim ximum um safe safe spee speed d of th thee fan and make make sure sure th thee mo motor tor is capable of the horsepower required to run the fan at the new speed.  Never run a fan beyond its maximum safe speed. REPLACE E FAN EQUIPME EQUIPMENT NT ADD OR REPLAC Figure 5 – Fan Inlet Connections

On a first-cost basis, adding or replacing fan equipment is the mostt costly mos costly alt alterna ernativ tive. e. How Howeve ever, r, on a life-cycle life-cycle-c -cost ost basis, basis, considering consi dering operatin operating g and maintenanc maintenancee expen expense, se, it can be the leas leastt ex expen pensiv sive, e, as co comp mpare ared d to in incr crea easi sing ng th thee spee speed d of an existing existi ng f an.

For all dampers, make sure there is sufficient clearance for the  blades to open and close completely without hitting the ductwork or other system components. Last, for systems with Someti Sometime mess a seco second nd fan may may be adde added, d, eith either er in serie seriess or  eithe eitherr pn pneum eumat atic ic or el elec ectri tricc co cont ntrol rols, s, ma make ke su sure re dampe damper  r   parallel with the original, although it may be more cost effective actuators are operating properly. to simply upgrade the system with a new fan capable of the required airflow and pressure. Look for system effect.   Sharp changes in the direction of airAdding another fan in series will increase the airflow because of  flow at either the fan inlet or outlet will disrupt the flow through the additional pressure. The operating point of the new system the fan and impair performance. If it is impossible to straighten mo move vess fu furth rther er ou out/u t/up p th thee sy syst stem em cu curv rve. e. Where Where du duct ct size size is the ductwork entering and leaving the fan, the use of inlet boxes adequate to handle the desired amount of air but the existing fan and turning vanes can minimize performance losses as shown in doesn’t provide sufficient pressure, a second fan in series may Figure Fig ure 5. For a more more de detai taile led d ex expla plana natio tion, n, ref refer er to Engin Engineering eering  be the best solution. However, make sure the ductwork can Letter 5, Fan Performance - The System Effect. handle the increase in pressure. INCREASE SE THE FAN SPEED INCREA

Adding another fan in parallel with the first will increase airflow due to the com combin bined ed cap capaci acities ties.. Bec Becaus ausee cap capaci acities ties are bein being g combined instead of pressures, a greater increase in airflow will result for a given system. However, system pressures will also increase and caution is required to avoid the unstable operating area of the combined fan system.

One of the easiest solutions to low airflow problems is speeding up the fan. While airflow is increased by speeding up the fan, so too are static pressure, noise, and power requirements. Figure 6  presents this graphically. Therefore, while increasing the fan’s speed spe ed is an easy proc procedu edure re with low first first cos cost, t, the ad addit dition ional al operati oper ating ng exp expens ensee ove overr time makes it the most cos costly tly solution. CONCLUSION See Engineeri Engineering ng Letter 2 - Fan Laws and Sys System tem Curves, Curves, for  Wh When en mo more re air air is req requi uire red d it is imp import ortan antt to inves investig tigat atee th thee additional information. system system on a step-by step-by-step -step bas basis, is, con consid siderin ering g the leas leastt exp expens ensive ive  possibilities first. For existing systems that seem to have lost  performance, fan and system maintenance is the place to start. Often, Ofte n, simply simply impr improvin oving g the effi efficienc ciency y of exis existing ting com compone ponents nts will suff suffice ice.. For sys systems tems that that require require greate greaterr airf airflow low and/or  and/or   pressure, increased fan speed is generally the first alternative. Howeve How ever, r, when when lar large ge increas increases es in per perform formanc ancee are requ required ired,, there may be no alternative alternative but to purchase a larger fan. Form 607 GAW

 

ENGINEERING LETTER

7

The New York Blower Company ●  7660 Quincy Street, Willowbrook, Illinois 60527-5530 

FIEL D TESTING OF FA N SYSTEMS INTRODUCTION A fan system may require field testing when the system is

For greater convenience, a more compact Magnehelic  pressure gauge may be used with a Pitot tube as a substitut  pressure substitutee for the manometer mentioned earlier. These gauges, illustrated in Figure 4, are available in a variety of pressure ranges.

thought to be malfunctioning, needs modification or requires  balancing of its volume and pressure characteristics. When it has been determined that a field test is required, the test can provide a complete check on fan performance. This includes determination of air volume, fan static pressure and fan brake horsepower. This Engineering Letter details the steps involved in performing a field air test. A field test sheet, which simplifies the recording of test data and the calculation of test results, is provided. A list of safety precautions to be observed while conducting the test is also included.

2.

A clip-on amme ammeter/voltmeter ter/voltmeter is used to obtain a reasonable estimate of fan motor horsepower.

3.

A calibrated hand tachometer is used to determine the fan RPM.

4.

An accurate tem temperature perature probe is used to measure temperature at each test location where volume or static  pressure readings are taken.

INSTRUMENTS REQUIRED

1.

The best method of measu measuring ring both air velocity and sstatic tatic  pressure in the field is with a Pitot tube and manometer. The absence of moving parts, combined with fundamental simplicity, make this set of instruments accurate and nearly foolproof. Both instruments may be used in nearly any atmosphere and require no adjustments except for zeroing the manometer prior to testing. Figure 1 sh shows ows a Pitot tube cross-section. Figure 2 demonstrates how it is connec connected ted to the manometer to indicate pressures by measuring the difference in heights of water columns in the “U” tubes. Most manometers, such as shown in Figure 3, read directly in inches of water column. Some manometers may have have velocity graduations marked directly in feet per minute for use where barometric pressure and temperature corrections are normal (i.e., test conditions assumed to be 70°F. and 29.92 inches of mercury).

Figure 1 – Pilot Tube Cross-Section

Sometimes there are no accessible test duct locations suitable for use with the Pitot tube. In this case, the air volume can be determined at the system entrance or exit, or through a grille or coil by using an anemometer or velometer. This method, however, is not as accurate and readings should only be taken by experienced service personnel familiar with this type of testing. PERFORMING A PITOT TUBE/MANOMETER TEST:

1.

Make a sketch of the system as a record and as a guide for selecting locations for taking test readings. Often this will call attention to poor system-design features. Include dimensions, such as duct diameters or areas, duct length, motor size, motor speed and sheave diameters on belt drive fans.

Figure 2 – Pilot Tube Connection

Figure 3 – Pilot Tube/M Tube/Manometer anometer Test Kit

   

2.

Determine the best poss possible ible location for obtaining the air volume readings via a Pitot tube traverse (set of readings). The traverse location should not be directly after any turns, transitions or junctions. The traverse should be after a minimum of 2 1 / 2 duct diameters of straight duct. To obtain the correct air volume, the Pitot tube and manometer or gauge should be connected to display velocity pressures, not velocities (see Figure 5). The location of the test points within each traverse is shown on the field test sheet included with this letter.

3.

Take static press pressure ure readin readings gs sseveral everal duct diam diameters eters from the fan inlet and outlet to avoid turbulence (see Figure 6). If the fan has either an open inlet or outlet, assume the static  pressure to be zero at the opening. Record the airstream temperatures at each static pressure location.

4.

Record the fan speed after measuring it w with ith the tachometer. If a tachometer is unavailable, make sure you record the motor nameplate RPM and sheave diameters from which the fan speed can be calculated.

5.

Read the voltage and amperes supplied to the motor and

record the values for calculation of fan motor horsepower. 6. Measure the barometric pressure at the fan site with a  portable barometer or obtain the pressure from the nearest weather station or airport. Be sure the barometric pressure is correct for your altitude and that it has not been corrected to sea level reference. 7.

Determine wh whether ether the air bei being ng handled contains contains quantities of moisture, particulates and/or gases other than clean air. If so, obtain the concentrations and densities of the gases or mixture for use in making density corrections. The attached test sheet is used to calculate flow through a fan. For additional information on conducting field tests of fan systems, AMCA Publication 203, Field Performance Measurements of Fan Systems, is recommended.

Figure 4 – Magnehelic Gauge

Figure 5 – Air Flow Pressure

Figure 6 – Static Pressur e Readings Readings

 

Page 2  

CALCULATING FAN PERFORMANCE

The following steps explain how to calculate density, CFM, SP, and BHP using the acquired test data.

This method requires power factor and motor efficiency data, which may be difficult to obtain. Another method is to draw an amps versus horsepower curve, (see Figure 7). This is done by plotting a rough horsepower versus amps curve for the motor as follows:

1.  Determine the density of the airflow through the fan during the test by using the dry-bulb temperature at the fan inlet and the barometric pressure. Density in pounds per cubic foot is determined by: Density

inlet = 0.075

530

( 460 + °F. ) (  

Barometric Pressure 29.92

a.  Establish no-load amps by running the motor disconnected from the fan (point a).  b.  Draw a dotted line through one-half no-load amps, at zero HP, and nameplate amps, at nameplate HP (points b).

)

c.  At one-half nameplate HP, mark a point on this line (point c).

2. Determine the density of the airflow at the CFM test location (if different from inlet density) by: Density

CFM = 0.075

530 460 + °F.

(

)(  

Barometric Pressure 29.92

)

3. Calculate fan inlet air volume in CFM as measu measured red with the Pitot tube and manometer/gauge as follows: First, take the square roots of the individual velocity pressures and compute the average of the square square roots. Then: CFM

inlet

= [ 1096 x test duct area (ft2) ] x

Avg. of Sum of

( √Density

√VP’s 

)   (  x

  CFM test

Density CFM

d.  Draw a smooth curve through the three points (a, c, b). e.  Determine running HP by plotting running amps. Multiply fan horsepower by the “K” density correction factor to determine HP at standard conditions. 6.  Locate volume, static pressure and horsepower on a  performance curve drawn at the fan RPM. Curves can be generated using manufacturer’s fan-selection software at specific densities, temperature and altitude. The test plot values will probably not fall exactly on the curve. If the fan system has been designed and installed  properly, the difference should be small, reflecting test

)

Density Inlet

The above calculation gives air volume in actual cubic feet  per minute (ACFM) which is the conventional catalog rating unit for fans. If standard cubic feet per minute is desired, it may be calculated as follows: SCFM = ACFM x

(

Actual Inlet Density Standard Density

accuracy. If the difference is great, the system should be analyzed as described in the next section. Figure 8 shows a typical fan curve and field test points which fall on the curve.

)

4. Determine the fan static pressure (SP) by the following formula: SP fan = SP outlet

Where:

VPinlet = VPinlet

- SP inlet - VP inlet

CFM inlet   x inlet area in sq. ft.) (1096  

x Density inlet

Figure 7 – Amperes versus Horsepower

 NOTE: Correct inlet and outlet static pressure to standard values by the following formula before summing. SP

standard

= SP

actual

(

Actual Density Standard Density

)

5. Fan motor horsepower m may ay be determined in several ways. The best is to read the volts and amperes supplied to the motor and apply the formula: For single phase motors: Fan BHP =

Volts x Amps x Power Factor x Motor Eff. 746

For three phase motors: Po wer Factor x Motor Eff. x √3  Fan BHP = Volts x Amps x Power

Figure 8 – Typical Fan Curve and Field Test Points

746

Page 3

   

POOR PERFORMANCE TEST RESULTS

If the test results indicate poor fan performance, a number of simple steps can be taken that could improve performance. Be sure that any dampers at the fan inlet or outlet are set to the correct position and that no other system dampers such as fire dampers, smoke dampers or balancing dampers have been inadvertently closed.

determined. Once inserted, slowly twist the tube. The angle at which air is entering the fan can be determined by observing the angle of the tube generating the h highest ighest gauge reading. If the angle deviates noticeably from being parallel to the fan shaft, the air entering the fan inlet may be spinning and therefore reducing fan performance.

A frequent cause of poor fan performance is the presence of poor inlet connections. Sharp elbows, inlet boxes without turning

Another reason for poor performance could be stratification of the air entering the fan. By taking four temperature readings ninety degrees apart in the inlet duct near the fan, the possibility of stratification can be determined. A temperature difference of

vanes and duct configurations causing the air to spin upon entering the fan, are examples of undesirable inlet connections.

10 degrees or more in the readings indicates stratification exists. An illustration of stratification is shown in Figure 10.

Fan performance is also impacted by poor outlet conditions. Examine the outlet connection, keeping in mind that sharp elbows, rapid expansions, reductions or the absence of an outlet connection all together can reduce fan performance.

Refer to Engineering Letters 5 and 6 for more detailed explanations of system effect and improving fan performance. SAFETY PRECAUTIONS

By connecting the Pitot tube and manometer/gauge to read velocity pressure and inserting the Pitot tube through a hole at the inlet connection (as illustrated in Figure 9), pre-spin can be

Figure 9 – Testing Fan Inlet for Spinning Airflow

The included list of safety precautions should be observed whenever testing or servicing fan equipment.

Figure 10 – Condition Causing Stratification

Form 1007

   

FIELD TEST SHEET Fan Owner ______________________________________________________________ _______________________________________ _______________________ Fan Location ____________________________________________________________ Fan Nameplate Data ______________________________________________________ Fan RPM ___________Motor Nameplate Data _________________________________ Motor Test Current _____________________ Voltage ___________________________ Date __________________ Tested by _________________________________________

Traverse Points for Round Duct 

Barometric Pressure

Average SP Inlet

Traverse Points for Rectangular Duct 

Temperature °F. Inlet

Average Static Pressure Outlet

Temperature °F. Outlet

Test * Points 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

SP

VP

√VP 

23 24

Sum of √VP’s  Avg. of Sum of √VP’s 

Density

Density

Density

CFM

VP

fan

) =

lbs./ft.3 

530

Barometric Pressure 29.92

) =

lbs./ft.3 

530

Barometric Pressure 29.92

) =

lbs./ft.3 

0.075 lb. ft.3  x

(  460 + °F. ) x ( 

outlet

=

0.075 lb. ft.3  x

(  460 + °F. ) x ( 

CFM test

=

0.075 lb. ft.3  x

(  460 + °F. ) x ( 

=

(

CFMinlet

outlet

Single Phase BHP

x

(

DensityCFM test Avg. of Sum of √VP’s    x   Density √Density CFM test inlet

) (

)

 =

CFM

2

1096 x Inlet Area

= SP

SP

Barometric Pressure 29.92

=

inlet = 1096 x Duct Area x

inlet

530

inlet

(

)

“ W.G.

x 0.075 =

0.075 Densityoutlet

)

- SP inlet

x

(

0.075 Densityinlet

)

- VP inlet =

fan

=

Amps x Volts x Power Factor x Motor Efficiency 746

Three Phase BHP fan

=

Amps x Volts x Power Factor x Motor Efficiency x √3   746

“ W.G.

BHP

=

=

* A minimum of 24 test points is recommended for round ducts less than 8 feet in diameter and rectangular ducts with areas 24 square feet and less. For larger ducts, more test points are required.

BHP

   

SAFETY PRECAUTIONS A WORD ABOUT SAFETY

MOVING PARTS

Testing, adjusting, and maintaining fan equipment exposes  personnel to potenti potential al safety hazards. Only experienced experience d mechanics, who are aware of the safety hazards created by moving or rotating parts, should be authorized to work on fan equipment. The proper precautions must be followed to  prevent injury from mo ving par parts. ts.

All moving parts must have guards to protect personnel. Safety requirements vary, so the number and type of guards needed to meet company, local and OSHA standards must be determined and specified specified by the u user. ser. Never start a fan without having all safety guards installed. Check regularly for damaged or missing guards and do not operate any fan with guards removed. Fans can also become da dangerous ngerous because of  potential  potenti al “windmilling”, “windmill ing”, even though all electrical electri cal power is

disconnected. Always block the rotating assembly before working on any moving parts. AIR PRESSURE AND SUCTION

In addition to the normal dangers of rotating machinery, fans  present another hazard from the suction created at the fan inlet. This suction can draw materials into the fan where they  become high velocity velocit y project projectiles iles at the outlet. It can also be extremely dangerous to persons in close proximity to the inlet as the forces involved can overcome the strength of most individuals. Inlets and outlets that are not ducted should be screened to prevent entry and discharge of solid objects. ACCESS DOORS

Beginning in June 2012, the above WARNING  signage has  been placed on all nyb  fans, as specified by ISO and recommended by the European Union. Air moving equipment involves electrical wiring, moving parts, and air velocity or  pressure which can create safety hazards if the equipment equipmen t is not properly installed, installed, operated and maintained. To minimize this danger, follow these instructions as well as the additional instructions and warnings on the equipment itself. All installers, operators and maintenance personnel should study AMCA Publication 410 - Recommended Safety Practices for Air Moving Devices, which is included as part of every shipment. Additional copies ccan an be obtained by writing writing to The New York Blower Company, 7660 Quincy Street, Willowbrook, IL 60527-5530 or can be downloaded from our web site at www.nyb.com. ELECTRICAL DISCONNECTS

Every motor-driven fan should have an independent disconnect switch to isolate the unit unit from the electrical supply. supply. It shou should ld  be near the fan and must be capable of being locked by maintenance personnel while servicing the unit in accordance with OSHA procedures. Do not attempt any maintenance on a fan unless the electrical supply has been completely disconnected and locked.

Danger: Do Not Enter/Confined Spaces

The above DANGER decal is placed on all nyb cleanout doors. These doors, as well as access doors to the duct system, should never be opened while the fan is in operation. Serious injury could result from the effects of air  pressuree or suc  pressur suction. tion. Quick-opening doors must have the door handle bolts securely tightened to prevent accidental or unauthorized opening. Bolted doors must be tightened for the same reason. MAXIMUM SAFE SPEED

Safe operating speed is a function of system temperature and wheel design. Do not, under any circumstances, exceed the maximum safe fan speed published in the nyb bulletin, which is available from your nyb field sales representative.

   

ENGINEERING LETTER

8 

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60521-5530 

P R OP E R S EL E C T I ON OF P R E S S U R E B L OW E R S INTRODUCTION

In generalat terms, a pressure blower provides relatively  pressure low volume when compared to other typeshigh of centrifugal fans. For purposes of this letter, fans with volumes to 10,000 CFM with pressures to 80" WG are considered  pressure blowers. Typical applications require constant pressure throughout the system’s operating range. A fan outlet damper or system damper is usually used to control air volume. Consequently, a requirement of pressure blowers is that they  provide stable performance from full-closed to full-open. f ull-open.

POINT OF OPERATION Since typical pressure-blower applications require a constant  pressure, selections are normally near the flat peak of the st static atic  pressure curve. See Figure 2. Because of the flat nature of the  pressure-blower curve, a typical question is, “what keeps the fan’s performance from fluctuating between different points on  on  the fan curve?” The answer lies in the relationship between the fan’s performance curve and the system curve.  curve.  

Figure 3  –  Typical  Typical Pressure Blower and System Curves

Figure 1  –  Dual-Tampered  Dual-Tampered Pressure Blower Wheel

Most pressure blowers employ a radial-blade wheel design.  New York Blower’s research has resulted in a unique wheel design that is not truly radial. The blades are slightly canted  backward and dual tapered from the hub to the blade tip. See Figure 1. This design provides better efficiencies and, as a result, significantly lower noise levels. The volume-pressure characteristics remain the same as radial-blade wheels.

At a given RPM, the fan can only operate on its performance curve. The only way to alter this curve is to either increase or decrease the fan’s speed. Conversely, Conversely, the system can only operate along one system curve. The only way to change this system curve is to increase or decrease the resistance through the system. Since the two curves can only intersect at one  point, the actual performance of the fan can occur only at the intersection of the fan curve and the system curve. This is depicted in Figure 3.

Figure 2  –  Typical  Typical Pressure Blower Performance Curves  Note: Broken lines denote typical system curves.

 

 

Considering that pressure blowers are often selected near the  peak of their pressure curve, dampering usually results in an operation left of the pressure peak. One benefit of radial-blade wheel design is that it delivers stable performance left of peak. Radial wheels bring other advantages to pressure blowers. The radial design delivers greater pressures at a specific RPM than  both the radial-tip and backwardly-inclined designs. The inherent strength of the radial wheel allows for the relatively high wheel tip speeds required for the development of high  pressures. Remember, pressure is approximately proportional to the square of themust change in wheel speed. Therefore, 2 PSI  pressure blower be capable oftip speeds 1.414 times asa fast as a 1 PSI unit. 1.4142 = 2 SINGLE-STAGE VS. MULTI-STAGE  MULTI-STAGE 

Single-stage pressure blowers are the most common and least expensive of the two designs for the range of flows and pressures noted in the introduction. A single-stage pressure blower consists of a single wheel in a volute-shaped housing design, such as shown in Figure 4.

SELECTION PROCEDURES

Selecting pressure blowers or any other type of fan for applications involving relatively high pressure requires some special considerations. Pressure blowers are generally used with the pressure entirely on the inlet or entirely on the outlet. Air is compressed as it passes through the fan, lowering the volume and raising the density. In negative pressure systems, air is rarefied to become less dense. The extent to which the effects of compression and rarefication must be considered depends largely on the degree of accuracy employed in the actual system design and calculation process. During compression there is also a temperature rise associated with the energy expended to overcome the system resistance and fan inefficiency. The rule of thumb is to allow 1°F. temperature rise for every 2" static pressure differential. For example: a supply fan with 40" SP at the outlet will develop a 20°F. temperature rise at the fan outlet, as compared to the air temperature at the fan inlet. To determine the proper air volume for selection purposes, the effect on density of both compression and temperature must be considered. One notable exception to these rules for performance corrections is the combustion-air-supply application. Burner manufacturers use SCFM ratings to arrive at lbs./hr. of air. The air will be compressed through the fan to a proportional lower volume, yet higher density so that the total weight of air in lbs./hr. remains constant and is sufficient for the combustion process. PERFORMANCE CORRECTIONS

Fan performance is based on a standard density of .075 lbs./ft.3  Density corrections for positive or negative pressure are based on changes in absolute pressure. A.  Standard absolute pressure is 408" WG at sea level. B. 

Compressed density for + 40" SP at the fan outlet is:

( C.  Figure 4 - Single-Stage Pressure Blower

Single-stage units are usually far more economical in applications up to about 3 PSI. They are also less complex and easier to maintain than multi-stage pressure blowers. Power consumption is also less because the single-stage blowers are more efficient. It is possible to place two, and sometimes more, single-stage  pressure blowers bl owers iin n series to develop pressure as high as 5 PSI and still represent an economical alternative when compared to the multi-stage units for the same performance. There is the added reliability factor of being able to “limp along” with one unit while the other unit is down for maintenance. When a multi-stage unit is down, the entire system is down. Consult the manufacturer for proper selection and application information when designing pressure blowers for series operation.

 

408 + 40”  40”  408”   408”

) x .075 = .082 lbs./ft.   3

Rarefied density for - 40" SP at the fan inlet is:

(

408 - 40” 40”   408”   408”

) x .075 = .0676 lbs./ft.   3

Density corrections for temperature changes are based on absolute temperature in degrees Rankin (°R). A.  Standard absolute temperature is 530°R., 70°F. (0°F. = 460°R.) B. 

A 20° temperature rise over a fan inlet temperature of 70°F. gives the following density:   460° + 70°

( 460° + 70° + 20° )

x .075 = .072 lbs./ft. 3 

Also refer to the following sample selections

Page 2  

C. 

SAMPLE SELECTIONS

Example 1: No performance correction due to compression.

Density ratio is: 442.6 408

x

460° + 70° = 1.05 460° + 87°

D.  Air density at the burner (B) will be: 075 x 1.05 = .079 lbs./ft. 3 

What actually happens in the system? A.  2300 ACFM at 70°F. at 408" atmospheric pressure enters the pressure blower inlet (A). B. 

ACFM at (B) will be: 2300 ÷ 1.05 = 2190 ACFM

F. 

To get 2300 ACFM at (B), the volume of air entering at (A) must be increased by the density ratio: 2300 x 1.05 = 2415 ACFM

Select the pressure blower for 2415 CFM at 34.6" WG pressure at .075 lbs./ft.3 density. Example 3: Performance correction due to negative pressure.

The pressure reading at (B) is 34.6" gage pressure or 408" + 34.6" = 442.6" absolute. The temperature has increased to 87°F.

( C. 

E. 

34.6 + 70° 2

Density ratio is: 442.6 408

x

)

460° + 70° = 1.05 460° + 87°

D.  Air density at the burner (B) will be: .075 x 1.05 = .0788 lbs./ft. 3  E. 

ACFM at (B) will be: 2300 ÷ 1.05 = 2190 ACFM

F. 

The SCFM equivalent at (B) will be: 2190 x .0788 = 172.6 lbs./minute 2300 x .075 = 172.5 lbs./minute

 Note: The changes in volume and density can be ignored in this case because the proper amount of air by weight will still be available at the burner (B). Select the pressure blower for 2300 CFM at 34.6" WG pressure at .075 lbs./ft. 3 density. Example 2: Performance correction required due to compression.

Given: draw-thru pneumatic conveying, as illustrated. Required: 4800 SCFM at - 34" WG. What actually happens in the system? A.  Air enters at 70°F. at 408" atmospheric pressure at the system inlet (A). B. 

The resistance at the pressure blower inlet (D) is - 34" gage pressure or 408" 34" = 374" absolute.

C.  

Density ratio is:

( 374 408 )

= .92

D.  Air density at (D) will be: .075 x .92 = .069 lbs./ft. 3 

Given: injector conveying system, as illustrated.

E. 

To get - 34" at (D) at .069 lbs./ft. 3 density, the pressure must be increased by the density ratio for proper fan selection: -34" ÷ .92 = - 37" WG.

F. 

Capacity = 4800 ÷ .92 = 5217

Required: 2300 CFM for the velocity required at (B). Resistance is 20 oz. or 34.6" WG.

G.  Select the pressure blower for 5217 ACFM at 37" WG.

What actually happens in the system?

H.  Operating horsepower would be: .92 x rated BHP, corrected for the lower density.

A. B. 

Air enters at 70°F. at 408" atmospheric pressure at the  pressure blower inlet (A). The pressure reading at (B) is 34.6" gage pressure or 408" + 34.6" = 442.6" absolute. The temperature has increased to 87°F.

(  

34.6 + 70° 2

)

 Note: The actual air volume at the fan outlet will be less than the volume at (A) by the density ratio, but the actual air volume at the fan outlet is not important in this system.

Page 3

 

NOISE ATTENUATION

A rising concern in many of today’s industrial applications is OSHA’s criteria for noise levels. To meet these requirements, many pressure blowers require sound attenuation. The  backward-canted and dual-tapered wheel design can result in an 8-10 db noise reduction over the traditional straight blade design. In some cases, this may eliminate the need for a silencer. If attenuation is required, silencers are readily selected based on their connection to either the inlet or outlet of the pressure

 blower. The most common connection is directly on the blower, flange to flange. See Figure 5. Silencers are rated in dynamic insertion loss (DIL) in decibels. These values are subtracted from the pressure blower sound power level’s eight octave  bands. The pressure drop through the silencer must be added to the system requirements, but generally the values are less than 0.2" and are insignificant.

Figure 5  –  Pressure  Pressure Blower Silencer

Form 607 GAW

 

 

ENGINEERING LETTER   9 The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Willowbrook, Illinois 60521 -5 -5530 530

AT T I C C O N V E Y I NG NG PNEUMA INTRODUCTION

DUST COLLECTIO COLLECTION N AND FUME REMOVA REMOVAL L

A well designed pneumatic conveying system is often a more  practicall and economic  practica economical al method of transporting transporting materials from one poin pointt to ano anothe therr tha than n alte alterna rnative tive manual manual or mecha mechanic nical al sy syst stem ems. s. Th This is Engi Engine neer erin ing g Le Lett tter er outl outlin ines es so some me of the the fundam fun dament ental al princip principals als of pne pneuma umatic tic con convey veying ing sys systems tems and explains various special considerations for fan selection.

Dust collection, fume removal, and material conveying systems each have unique characteristics characteristics,, but all three are similar in their  dependence upon proper air velocities.

TYPES OF PNEUMATIC CONVEYING

Pneumatic conveying encompasses numerous different system designs, technologies, and pressure ranges; however, there are only three basic methods for moving material with air. These can be categorized into the following system types: Dilute-ph Dilute -phase ase conveying  is the process of pushing or pulling air-sus air-suspen pende ded d ma mate teria rials ls fr from om on onee lo loca cati tion on to an anoth other er by ma main inta taini ining ng a suffi suffici cien entt ai airst rstre ream am ve velo loci city ty to ca capt ptur uree an and d convey the suspended particles.

Dust collection and fume removal are generally thought of as “housekeeping” systems that usually incorporate a hood at the system entry point. There are many types and styles of hoods in common use, and hood design is a subject in itself. Some state and local codes offer hood design criteria, and there are several ref refere erence nce texts, such as Indu Industr strial ial Ventil Ventilatio ation n - A Manu Manual al Of  Recomm Rec ommend ended ed Prac Practic tices, es, that that can assist assist in the select selection ion and design of hoods. In all cases the hood design should minimize turbulence and offer the lowest possible entrance losses.

Air-film   or   air-float conveying  is a means of moving product along a conveyor on a cushion of air.

Determining the minimum velocity for dust collection or fume removal is often a matter of practical trial-and-error judgment. State and local codes may dictate minimum velocities for certain materials. Where no codes apply, the velocities shown in Figure 1 can be used as conservative estimates. Since these velocities are conser conservat vative ive,, it is ofte often n pos possib sible le to reduce reduce them thro through ugh experimentation. Reducing the velocity to near the settling point will generate the lowest overall operating cost but raises the risk  of system system plug pluggin ging, g, increa increased sed mainte maintenan nance ce cos costs, ts, and lost lost  production.

The use of fans for pneumatic conveying is generally limited to dilute phase conveying and air film conveying.

Dust Collecting and Fume Removal Duct Velocities

Dense-phase conveying  relies on a pulse of air to force a slug of material from one location to another. This form of conveying usually requires positive displacement blowers or compressors to generate the necessary necessary pressure of 1.5 to 30 psig or more.

DILUTE-PHASE CONVEYING

In this this me meth thod od of con conve veyin ying, g, ma mate teria riall is su susp spen ende ded d in th thee airstream. airstre am. Sucti Suction on or vacuum vacuum are not facto factors rs in this type of  system and fan static pressures are no greater than 60" WG. If  the system uses a fan on the exhaust end and the material is collected or separated from the airstream before it reaches the fan, fa n, the the fa fan n its itself elf can be of a mo more re eff effic icien ientt ty type pe such as  backwardly inclined. If the system is designed so that the combine com bined d mat materia eriall and air mixt mixture ure passes passes throug through h the fan fan,, sel select ection ion is limi limited ted to the more rugged rugged but less eff efficie icient nt fan type typess inten intende ded d fo forr ma mate teria riall lade laden n ai airs rstre tream ams. s. A num number ber of  radia radial-bla l-blade de wheel wheel des design ignss are availa available ble to handle handle various various concentrations, sizes, and types of airborne particles. Radial-tip wheel designs are tolerant of airborne contaminants, but radialtip fans are not generally thought of as bulk material handling designs. In all cases, the fan manufacturer should be consulted to determine the most appropriate fan type available to handle the specific material quantity and type, but it must be understood that the fan manufa manufactu cturer rer can nei neither ther control control the variables variables in  pneumatic conveying systems nor provide any guarantee of the service life of the fan itself. service Applications requiring fans for dilute-phase pneumatic conveying fall fall into one of three three bas basic ic cat catego egories ries:: dust dust coll collect ection ion,, fum fumee removal, or material conveying.

Material

 

Velocity in FPM

 

Material

 

Velocity in FPM

1. Grindi nding Dust 2. Foundry Dust

500 5000 4500

20. Jute Dust

3500

3. Sand Blast Dust 4. Wood Flour

4000 2000

21. Grain Dust 22. Shoe Dust

3000 4000

5. Sander Dust

2000

23. Rubber Dust

3500

6. Shavings, Dry

300 3000   24. Rubber Buffings  

4500

7. Shav Shavin ings gs,, Wet Wet

40 4000 00

8. Sawdust, Dry

3000

9. Sa Saw wdust dust,, Wet

400 4000

10. Wood Blocks

4500

11. Hog Waste

4500

27. Oven Hood

2000

12 12.. Buffi uffing ng Lint, int, Dr Dry y

30 3000 00

28 28.. Tail Tail Pipe Pipe Exha Exhaus ustt

3000 3000

13. Bu Buff ffin ing g Li Lint nt,, We Wett

400 4000 0

29. Melt Meltin ing g Pot Pot an and d

14. Metal Turnings

5000

15. Lead Dust

5000

30. Metallizing Booth

3500

16. Cotton

3000

31. Soldering Fumes

2000

17. Cotton Lint 18. Wool

2000 4000

32. Paint Spray 33. Carbon Black

2000 3500

19. Jute Lint

3000

3 34 4. Paper

3500

25. 25. Bake Bakeli lite te Moul oulding ding Powder

3500

26. 26. Ba Bake kellit itee Moul oulding ding Dust

Furnace

Figure 1

2500

2000

 

MATERIAL CONVEYING

Alth Althoug ough h the the diffe differen rence cess betw betwee een n di dilut lutee-phase -phase ma mate teria riall conveying conve ying systems and dust collect collection ion or fume removal systems might appear to be minimal, there are certain distinctions that are critica criticall to the successful successful operati operation on of materialmaterial-conveying conveying systems. system s. These differences differences include the method method of introducing introducing the materia materiall to the hood, hood, the vel veloci ocity ty req require uiremen ments, ts, the duct duct configuration, and the fan type. The introduction of material into a material conveying system can be difficu difficult. lt. The mos mostt impo importan rtantt crit criteri erion on is to fee feed d the material into the airstream evenly. This can be accomplished by means of gravity or by a mechanical device. A hood or hopper can be used as a gravity feeder. Use of these comp compon onen ents ts is lim limit ited ed to dr dry, y, free free-flow -flowin ing g ma mate teria rials. ls. It is important to remember that it is the velocity moving around and  past the material that induces it to flow. If the entry becomes  plugged with material, the required velocity cannot be maintained, significantly impeding air and material flow. A ventur venturii feeder feeder can be use used d to introdu introduce ce materia materiall into the airstre airs tream. am. Like the hoo hood, d, it has no moving moving parts so there there is virtual virt ually ly no mai mainte ntenan nance. ce. Howeve However, r, the des design ign of the ven ventur turii must be tailored to each application and even the best ones can be rather easily blocked if system conditions vary. Typical throat velocities are 2 to 3 times the velocity in the main duct . . . see Figure 2.

Figure 3 – Typical Rotary Valve Fee Feeder der

Since the purpose of a conveying system is to move quantities of material material suspe suspende nded d in air, the ratio of mat materia eriall to air (by weight) is critical. The most common form of reference is to state the ratio according to the combined weight in pounds per  hour. hou r. A conserv conservativ ativee des design ign approa approach ch is to kee keep p the ratio of  matter mat ter-to -to-air -air bel below ow a 1:2 prop proporti ortion. on. How Howeve ever, r, succes successfu sfull systems have been designed using material loadings of 1:1 or  more when when th thee syste system m comp compone onents nts are are well-d well-des esig igne ned d an and d eliminate sharp turns, abrupt junctions, or other potential points of bin bindin ding, g, clog cloggin ging, g, or dropdrop-ou outt an and d th thee mate materia riall being being conveyed is well-defined and consistent. Certain minimum conveying velocities must be maintained to keep the material in suspension and flowing. To some extent these velocities are dictated by, or at least related to, the material-toialto-air air rati ratio. o. For exampl example, e, con convey veying ing sawdust sawdust at a rate of  1800 lbs./hr. through a 6" pipe with a material loading ratio of  1:2 will result in an air velocity of 4073 FPM.

Figure 2 – Typical Venturi Venturi Feeder

1800 lbs./hr. material = 30 lbs./min. 3

60 lbs./min. air ÷ .075 lbs./ft. std. density = 800 CFM. Rotary valves and screw-type (auger) feeders (see Figure 3) are the the mo most st comm common on me mech chani anica call de devi vice cess us used ed to in intro trodu duce ce material into the airstream. Both types offer a controllable flow rate and are readily available in a number of standard designs to handle pressures common to dilute phase conveying. However, there are some precautions. Both are typically more expensive than than grav gravity ity-f -feed eed alte alternat rnatives ives.. Rot Rotary ary valves valves can experie experience nce internal intern al air recirculatio recirculation n which causes a reduction reduction in materia materiall throu through gh-p -put. ut. Th Thee sc screw rew-t -typ ypee fe feed eder er is a re rela lativ tively ely hi high gh mainten main tenanc ancee device device.. In eit either her cas case, e, the manufa manufactu cturer rer of th thee specifi spe cificc fee feeder der sho should uld be con consult sulted ed for sel selecti ection, on, equi equipmen pmentt recommendations, and system limitations.

6" pipe = .1964 ft.2 area inside. 2

800 CFM ÷ .1964 ft. = 4073 FPM. Figure 4 provides conservative minimum conveying velocities to be used for some common materials. The velocity shown for  sawdust is 4000 FPM. If the same 1800 lbs./hr. of sawdust had  been introduced to a system with a 1:1 design ratio and there were no other changes to the system, the resulting velocity would only be half and the material would probably settle and clog. To compensate for the lower ratio, the pipe size could be reduced to 4" 4",, bu butt th this is migh mightt in intr trod oduc ucee ne new w pr prob oble lems ms in feed feedin ing g th thee material to the pipe or transitioning to the fan. In this example, the 1:2 ratio would seem to be ideal.

Page 2  

FAN SELECTION

Material Conveying Duct Velocities  

Material

Velocity in FPM

 

 

Material

Velocity in FPM

1. Wood Chips

4500

12. Cotton

4000

2. Rags

4500

13. Wool

4500

3. Ground Feed

5000

14. Jute

4500

4. Powdered Coal

4000

15. Hemp

4500

5. Sand

7500

16. Vegetable Pulp,

6. Wood Flour

4000

7. Sawdust

40 00

17. Paper

5000

8. Hog Waste

4500

18. Flour

3500

9. Pulp Chips

4500

19. Salt

6000

10. Wood Blocks

5000

20. Grain

11. Cement

 

Dry

4500

 

6000   21. Coffee Beans 22. Sugar 

Just as designing around a velocity that is too low will impede the material conveying capability of the system, unnecessarily high hig h veloci velocitie tiess can also also be detrim detriment ental. al. Sys System tem resist resistanc ancee increases as the square of the increase in velocity. Therefore, additi add itiona onall ene energ rgy y is requ require ired d to ove overco rcome me that that resist resistanc ance. e. Also, the abrasive or erosive characteristics of the material  being conveyed will increas increasee with an increas increasee in velocit velocity, y, shortening the service life of all system components.

 

5000 3500

Only the air volume is considered in determining the velocity. The material volume is ignored to compensate for the periods of inconsistent material loading that occur during start-up and shutsh ut-dow down. n. How Howeve ever, r, the materi material al con conten tentt of the ov overa erall ll airstream mixture cannot be ignored when calculating system resistance or when sizing the fan.

6000

Figure 4

Suffic Suf ficien ientt veloci velocitie tiess mus mustt be ma mainta intaine ined d thr throug oughou houtt the conveying convey ing syste system m to avo avoid id ma mater terial ial settli settling. ng. All airborn airbornee materials, except the finest of dusts or fumes, can settle in a system or even in the fan itself. When settling occurs in the horizontal plane, it is known as  salt ation.  When settling occurs in the vertical plane, it is called  choking. Saltation is probably the most difficult to avoid because even the the sm smal alle lest st ridge ridge or duct duct se seam am ca can n begi begin n the the pr proc oces ess. s. Whenever possible, it is advantageous to employ the aid of  gravity to minimize potential build-up by designing the piping or ductwork with a downward slope. This is particularly true with fine granular materials. Choking in downward movement often occurs in the vertical line as a direct result of saltation in the adjacent horizontal line. Upward movement is often easier to control because all that is needed is sufficient momentum (velocity) to keep the material in suspension. All falling materials simply drop back  into into the airstr airstream eam.. Howev However, er, ch choki oking ng in the upw upward ard flow directly the problems. enou enough gh above ma mate teri rial al fan is discharge fo forc rced ed back baposes ck into inadditional to the the fa fan n wh wher eree If  it recirc recircul ulat ates es,, the the fan fan wi will ll ex exhi hibi bitt prema prematu ture re we wear ar due due to excessive loading.

To mini minimi mize ze the the po poten tenti tial al fo forr sa salt ltat atio ion n or ch chok okin ing, g, it is recommended that some provision be included in the system for bleeding in excess air through adjustable vents or dampers. Se Seee Figu Figure re 3. This This ex exce cess ss air air wi will ll ef effe fect ctiv ively ely incre increas asee velocities in the system to assist material transportation. It is important to remember that the fan selection must account for  the maximum potential excess air, and that handling more air  then the minimum system requirements will result in increased  power consumpti consumption. on.

Fans are consta Fans constant nt vol volume ume machi machine ness that that discha discharge rge a fixed fixed volume of air at a fixed speed. If a fan is required to handle a given volume of air and a given volume of material, it should  be sized to handle the combined volume. Using the previous example, 1800 lbs./hr. of sawdust at an average bulk density of  3 3 11 lbs./ft. results in 164 ft. /hr. or nearly 3 CFM. The fan sh shou ould ld be sele select cted ed to ha hand ndle le 80 803 3 CFM CFM (8 (800 00 + 3). In this this exampl exa mplee the 3 CFM is neg neglig ligible ible.. Howeve However, r, in situat situation ionss where greater material volumes are being handled or when the  bulk material density is much lighter, lighter , the volume cannot be ignored.

The effects effects of the materi material al on syste system m resist resistanc ancee mus mustt be consider consi dered. ed. Sin Since ce mo most st mater material ialss usual usually ly exh exhibit ibit a low lower  er  coefficien coeff icientt of frictio friction n than air, a simp simple le dens density ity correction correction  based on the combined weight and volume of the air/material mixture would result in an unnecessarily high correction. No dependable depen dable methods of determ determining ining the flow resistanc resistancee of  air/materia air/m ateriall mixtu mixtures res have been proven proven,, so only reasonable reasonable estimates are available. Some researchers have theorized that the bulk material content merely acts to reduce the effective area of the pipe or duct and so ignore the density effect by calculating calcu lating air resis resistanc tancee throug through h the resul resulting ting smaller smaller pipe diameter. The best method for determining the resistance of  the air/ma air/materi terial al mix mixture ture is thr throug ough h pilotpilot-pla plant nt testing testing or  experimentation. Figure 5 provides correction factors that can  be used as reasonable starting points for estimating resistance.

FRICTION MULTIPLIER

MULTIPLY FRICTION FOR CLEAN AIR BY MULTIPLIER

CUBIC FEET OF AIR PER MINUTE PER POUND OF MATERIAL

Figure 5 – Resistance Facto Factors rs

Page 3  

Even though Even though the air/ma air/mater terial ial mix mixture ture does does not follow follow the tra tradi diti tion onal al laws laws of fl flui uid d fl flow ow as the they y ap appl ply y to fr fric icti tion on or  resistance, it is suggested that the fan brake horsepower (BHP) will increase according to the bulk density of the mixture. The combined weight and total volume can be used to determine the maximum airstream density for selecting a motor that will handle the fan BHP at the bulk density. Where, 1800 lbs./hr. material + 3600 lbs./hr. air = 5400 lbs./hr. 5400 ÷ 60 = 90 lbs./min. 90 ÷ 803 CFM = .112 lbs./ft. 3  bulk density To determine the approximate approximate BHP for this example, multiply the rated BHP at standard density of .075 lbs./ft.3  by 1.5.

Either positive pressure or vacuum can be used to move the containers. In a pressurized system, air is directed through a drilled or slotted surface, where the air is discharged at a slight angle in the direction of flow. The greater the discharge angle, the higher the velocity from one station to the next. Vacuum ele elevat vators ors are used used to raise raise or low lower er con contai taine ners rs to differe different nt levels in the system by holding them to a moving, perforated  belt. Vacuum transfer devises allow fallen or damaged product to drop drop out of th thee syste system, m, thereb thereby y reduc reducing ing down downtim timee and maintaining efficient high-speed processing. Both techn techniques iques may be employed in different portions of complex conveying systems. The benefits of air film conveying over conventional mechanical conveying include:  

(.112 ÷ .075) = 1.5

 

It is sometimes thought that a larger fan is naturally better than a smaller one. This is far from correct since material is just as liable to settle in a fan as in a duct. If the inlet and outlet velocities of a fan are at least as high as the minimum conveying velocity, no settling should occur in the fan. This is true for   both dust collect collection ion and conveying.

 

       

Increased process speed. Lower maintenance maintenance costs (fewer m moving oving parts). Reduced energy consumption. Reduced noise and safety hazards.

  Reduced downtime from jamming.   Gentler handling of the product.

Many companies in the packaging industry use a combination of  air and mec mechan hanical ical con conveyi veying ng systems systems in their their man manufac ufacturi turing ng  processes.

AIR-FILM CONVEYING

CONCLUSION

This method of pneumatic conveying uses a film or cushion of  air to move items such as cans, boxes, or plastic containers through a plant. Used primarily in the packaging industry, air  film conveying usually requires fan static pressures of no more than 8" WG. In most cases, the system utilizes several smaller  fans as opposed to one large fan. Because the air is clean, variou var iouss fan types can be used used in the these se sys system tems, s, inc includ luding ing  backwardly  backward ly inclined incline d and radial -bladed designs. Selection Selecti on is  based on pressure and flow, but configura configuration tion is equally important.

Pneumatic conve Pneumatic conveying ying systems have limitations limitations,, and alternate manual or mechanical means cannot be ruled out. However,  pneumatic conveying systems usually require less plant space, can be easily installed in the available or wasted space, can be easily eas ily autom automate ated, d, can usual usually ly be eas easily ily altere altered d for fu futur turee change, and usually carry a lower capital cost. Beyond these economic advantages, pneumatic conveying systems can also  be useful in controlling control ling or minimizi minimizing ng product loss, improvi improving ng dust control, and thus improving overall plant conditions.

Form 607 GAW

 

ENGINEERING LETTER   0 The New York Blower Company   ● 7660 Quincy Street, Willowbrook, Illinois 60521 -5530

F A NS A N D B L O W E R S F O R C O M BU S T I O N P R O C E S S INTRODUCTION

The burning of gas, oil, coal, or other combustible material requires air. When the end result of the burning is to be an efficient combustion process, in compliance with Federal and State Clean Air Act requirements, the volume of supply air  must be reliably controlled. Insufficient Insufficient air volume will result in wasted was ted fuel fuel and exc excess essive ive part particu iculate late alon along g wit with h potenti potentially ally explosive gases in the exhaust system. Too much air increases the amount of heat carried up the stack by the excess draft. Either extreme increases the cost and difficulty of controlling exhaust emissions.

Mechanical draft is accomplished in one of two ways: when air is blown or forced into the combustion chamber it is known as as forced  forced draft . . .  see Figure 2; when the air is drawn through the combustion chamber it is called induced called  induced draft . . see .  see Figure 3. When both forced and induced draft are used, the system is ter terme med d a  balanced-draft system.

NATURAL AND MECHANICAL DRAFT

Air can be supplied to the combustion process by   natural   or  mechanical draft. mechanical  draft.  Natural draft simply refers to the use of a chimney or stack to induce an upward flow of air. The stack effect pulls air into the combustion chamber, as shown in Figure 1. The amount of  ai airfl rflow ow depe depend ndss on the the st stac ack’ k’ss heig height ht an and d di diam amet eter er,, the the  prevailing  prevai ling wind velocity, and the resista resistance nce of the burner  mechan mec hanism ism or fue fuell bed its itself elf.. The dem deman and d for air-cle air-clean aning ing apparatus appar atus on comb combustio ustion n syst systems, ems, particularly particularly oil and coal, has increased the overall system resistance to such an extent that natural draft alone is seldom sufficient.

Figure 2 – Forced D Draft raft

Figure Figu re 3 – Induced Dra Draft ft

Figure 1 – Natural Draft Draft

Mechanical draft refers to the use of fans or blowers to create airflow through the combustion area. When mechanical draft is incorp incorpora orated ted,, the chimney chimney or stack stack is used used primari primarily ly to direct the exhaust gases up and away where they will not be a nu nuis isan ance ce.. Beca Becaus usee wi wind nd ve veloc locity ity an and d di dire rect ctio ion n ar aree less less important, the combustion process can be much more carefully controlled.

Generally, the fans or blowers used for induced-draft applications are larger larger and mor moree exp expen ensiv sivee than than thos thosee use used d for similar  similar  forced forced-d -draf raftt ap applic plicati ations ons.. The com combus bustio tion n process process its itself  elf  cre create atess gas gases es and elevat elevated ed tem temper peratu atures res that that exp expand and the exhau exh aust st airstre airstream, am, requirin requiring g fans fans wit with h greate greaterr vol volume umetric tric capaci cap acity ty than wou would ld be requir required ed on the supply supply side side of the combustion process to supply clean, ambient air. Also, the hot exhaust serves to lower the density of the airstream, so density corrections must be applied to the fan static pressure (SP) to overco ove rcome me the actual actual system system resist resistanc ance. e. The fact fact that that the exhaust or flue gases are hot often requires induced-draft fans to  be of a construction construc tion suitable suitabl e for higher temperat temperatures. ures.

 

The first induced-draft fans were applied to hand-fired, solid-fuel  boilers where the combustion chamber had to be at a negative  pressure to permit the op operator erator to shovel in fuel. When oil and gas became primary fuel sources, boiler designers were able to seal the combustion chambers. As a result, forceddraftt fans draf fans became became popula popular. r. The adv advant antage agess were were lower lower fan  power and fans handling clean air (no corrosion or abrasion) abrasion) at ambient conditions. These factors encouraged the use of airfoil fans fa ns,, fu furth rther er reduc reducin ing g pow power er co cons nsum umpti ption on.. Th This is led led to th thee almos alm ostt un unive ivers rsal al us usee of press pressur uriz ized ed firin firing g in ga gas, s, oi oil, l, an and d  pulverized coal boilers by the mid 1 1950s. 950s. However, by the late 1 960s the combustion process industry had learned through experience that it was impossible to maintain an airtight quality in large (approximately 150,000 lbs./hr. and larger) industrial and power boilers. These units (some over 100 feet high) simply had too much thermal expansion. Fly ash and no noxi xiou ouss and and corr corros osiv ivee fu fume mess were were cr crea eatin ting g trem tremen endo dous us maintenance and personnel problems. This led to the development of ba bala lanc nced ed-d -draf raftt sy syst stem ems, s, in which which bo both th fo force rced-dr d-draf aftt an and d induced-draft fans are used. (See Figure 4)

Figure 5 – Pressure Blo Blower wer

Figure 6 sh Figure shows ows a typica typicall bac backwa kwardlyrdly-inc incline lined d air airfoil foil whe wheel el commonly used for forced-draft fans on balanced-draft boilers. Th This is ty type pe of fan is pre prefe ferab rable le be beca caus usee it ty typic pical ally ly is hi high gh volume, medium pressure and is usually the most efficient fan se sele lect ctio ion. n. Some airf airfoil oils, s, such such as the   nyb   AcoustaFo AcoustaFoil, il, are capable capab le of stable operatio operation n through throughout out a comple complete, te, dampered range from wide-open to closed-off so the combustion rates can  be closely closel y controlled with iinlet nlet or outlet dampers. On boilers that use hot, dirty gases for combustion supply, the gas recirculation fan most frequently selected is a radial-blade type. This type of wheel is considered to be the most “rugged” and will run at lower tip speeds. It is therefore less subject to abrasi abr asion on than than radi radial-ti al-tip p or backw backwardl ardly-in y-inclin clined ed whe wheels. els. (See Figure 7)

Figuree 4 - Balanced Figur Balanced Draft - For Forced ced and Induced Induced

Forced-draft fans and blowers are common for cast iron firetube and and sm smal alll wa wate terr tub tubee boile boilers rs.. The The fa fan n or bl blow ower er se serv rves es to  provide the air and the velocity necessary for the fuel-to-air  mixture to enter the actual combustion chamber. When used in con conjun junctio with induced induce draft, the forpr ced-draf draft fan often oftary en call called ed ction the then pr prim imar ary y ai airr dfan fadra n ft, sinc since e itforcedprov ovid ides est the th e is pr prim imar y combus com bustion tion supply supply air. The induce inducedd-dra draft ft fan provide providess the airflow necessary necessary to overcome overcome syste system m resist resistance ance and exhaust exhaust the flue gases.

Figure 6 – Backwardly-Inclined Airfoi Airfoill Wheel

Somee combus Som combustion tion systems systems draw hot, perh perhaps aps dirty air from other processes. Forced-draft fans for such systems are called  ga s rec irc ul a tio n  fans, and must be selected for the rigorous conditions under which they will operate. ALTERNATIVE FAN DESIGNS

Fi Figu gure re 5 sh shows ows a typi typica call Pre Press ssur uree Blowe Blowerr fo forr fo forc rceded-dra draft ft application. This type of unit is normally direct connected to a 3600 RPM motor and develops pressure sufficient to overcome the tota totall sys system tem resista resistance nce on sma small ll com combus bustion tion systems. systems. To minimize motor bearing load and starting current, the wheel is normally fabricated of high-strength aluminum. It is therefore limited to handling clean, often filtered air. Pressure Blowers are commonly used on small firetube boilers.

Figure 7 – General Industrial Whee Wheell (Radial)

Page 2  

Radial-blade fans were at one time commonly used for induceddraft service. However, as pollution requirements have become more stringent and control devices have been added to reduce flue gas particulates (ahead of the induced-draft fan), radial-tip  blade or even backwardly-inclined fans have become popular  popular  du duee to the their hi high gheer eff efficie icien ncies cies an and d hi high gheer vo volu lume metr tric ic charact cha racteris eristics tics.. (See Figures Figures 8 and 9) The exception exception to this is wher wheree hig high h effic efficien iency cy sc scru rubbe bbers rs ar aree us used ed an and d th thee press pressur uree requirements are increased to where the radial-bladed fans are more suited.

explosive gases in the exhaust system. From this viewpoint it is  better to includ includee excess air volume. Some typical excess air   percentages  percen tages are shown in Figure 11 for reference reference only. The amount of air required for theoretically perfect combustion is  based on the portion of the combustible substances carbon (C), hydrogen (H   2),  oxygen (O2), and sulfur (S) contained in fuel. These are the only combustibles found in common fuels. Air Required for Combustion Combustible Substance

Lbs. of Air Per Lb. of Combustible

C

Carbon

11.5

H2

Hydrogen

34.3

O2

Oxygen

--

S

Sulfur 

4.3 Figure 10

Figure 8 – Radial Tip Tip Wheel

The ratio of air required for perfect combustion to a pound of  each element in the fuel is shown in Figure 10. This ratio should  be multiplied multiplied times the percent percentage age of the element in the fuel, times the weight of the fuel to get the required weight of air, and then excess air must be added and the result must be corrected to the corresponding air volume per minute. For example: Assume a fuel oil with 86.1% C, 13.8% H 2  , 0.1% S, and negligible free oxygen. The fuel oil weighs 6.8 lbs./gallon and will be consumed at a rate of 5 gallons each hour. .861 C x 11.5 x 6.8 = 67.3 lbs. air  .138H 2  x 34.3 x 6.8 = 32.2 lbs. air  .001 S x 4.3 x 6.8 = .03 lbs. air  Total = 99.53 lbs. air 

Figure 9 – Flat Blade Blade Backwardly-Inclined Wheel

The combustion of coal and most fuel oils will release sulfur  fumes into the flue gas. If a wet scrubbing or cleaning apparatus is us used ed,, wate waterr va vapor por will will co comb mbine ine wi with th th thee su sulfu lfurr to fo form rm sulfuric acid. This can place severe constraints on the fan types availab ava ilable le to handle handle this this high highly ly corr corrosi osive ve gas stream. stream. For this very reas reason, on, flu fluee-gas-d gas-desu esulfu lfuriza rization tion (FG (FGD) D) equ equipm ipment ent is designed into the pollution control systems of many combustion  processes.  process es. Anothe Anotherr alternativ alternativee to reduce the potential for sulfuric acid in the exhaust system is to mix lime or crushed limestone in a fluidized bed combustion process so the lime will neutralize the sulfur and stabilize the pH of the exhaust gases. FAN SELECTION

Ideally,, the fan in any combustion Ideally combustion process process will will supply supply just just enough air to completely burn all the fuel, and no more. This will help keep heated, but unused, air from going up the stack. Actua Actually lly,, this this ide ideaa is appro approac acha hable ble wi with th ga gass bu burn rners ers bu butt impractical with wood- or coal-fired combustion. Thus, nearly all ai airr volum volumee requi requirem remen ents ts fo forr co comb mbus ustio tion n pro proce cess sses es ar aree calculated to include some margin of excess air. As stated in the introduction, insufficient air volume will result in wasted fuel and excessive particulate along with potentially

99.53 lbs. x 1.10 excess x 5 = 547.4 lbs./hr. air  547.4 ÷ 60 = 9.12 lbs./min. air  In a combustion supply application handling standard density 3 air, this equates to (9.12 lbs./min. ÷ .075 lbs./ft. = 121.6 CFM). Although there are a number of accepted methods for determining combustion air requirements . . . some rules of thumb, some exact exa ct calcula calculation tionss . . . they all rely on the actua actuall port portion ion of  combustion combu stion constitu constituents ents found in the fuel in question. Figure 11 lists some typical examples, but a full, accurate list would be imprac imp ractic tical al as ther theree are hundre hundreds ds of unique unique coal gra grades des.. In  practice,  practic e, the combust combustion ion system design designer er shoul should d determine the actual air volume requirements and the excess air margin based on an analysis of the fuel in questi question. on. In addition to the fundamental volume specifications, combustion  process fans, particularly larger fans, are often specified for two conditions . . . actual and test block. The actual condition is the ca calc lcul ulat ated ed vo volu lume me (inc (inclu ludi ding ng ex exce cess ss air) air) an and d pr pres essu sure re requirements. The test block condition is a theoretical duty that include includess som somee safety safety factor factor beyond beyond the actu actual al vol volume ume and  pressure requirements. The fan selection for the application should be capable of meeting both conditions with good efficiency, economy, and stability. Whenever possible, the actual condition should represent the most efficient point of operation for the fan selected for the application.

Page 3  

Typical Excess Air Range (% Volume)

Fuel

Fuel Oil  No. 1

TypicalPercentage of Combustibles (% Weight)  

Carbon

 

Hydrogen Hy

Oxygen

 

Sulfur

5- 20 86.3

13.7

--

0.3

 No. 2

87.2

12.9

--

0.5

 No. 4

87.9

11.8

--

1.1

 No. 5  No. 6

87.9 88.4

11.3 10.8

---

1.8 2.1

70.6 54.3 85.0 80.0

22.7 5. 6 5. 4 0. 3

1.4 37. 9 5. 8 0. 5

0.3 0. 1 1. 5 0. 6

 Natural Gas Wood, Pine Coal (ref. only) Coke

55-15 15 10- 25 10- 60 10- 30

Figure 11 - Typical fuel analysis of excess air requirements and amount of combustibles.

Typically Typica lly,, dire direct ct-d -drive rive fans fans are pref preferre erred d to belt-driv belt-drivee fan fans. s. Direct-drive fan arrangements used are 4, 7, and 8. To reduce reduce volume volume and pressu pressure re to me meet et the actual actual des design ign or  reduced load reduced load con conditi ditions ons,, inle inlett dam dampers pers or variab variable le frequen frequency cy drives are used. Variable speed offers the most efficient means of perf perfor orm man ance ce redu reduct ctio ion, n, al alth thou ough gh the the init initia iall co cost st an and d equipment maintenance is greater than that of dampers. These mu must st be evalu evaluat ated ed on an indiv individu idual al job basi basiss to de dete termi rmine ne whether the power savings will offset the greater initial price differential and added maintenance costs. Belt-drive fans, Arrangements 1, 3, 9, and 10, can be selected for the most efficient operation at the actual operating conditions. It is usually enough that belted units simply have sufficient speed reserv reservee to mee meett the speed speedss nec necess essary ary to fulfill fulfill the test bloc block  k  condition by means of a change in drive sheaves. The criteria for selecting the fan motor is usually specified per   job. Often, the motor is sized to handle the hot test block  conditions so the fan can be dampered for low load periods such as start-up or shut-down. This reduces the dampering, or turndown, range required under actual conditions.

3.

The enti entire re fa fan n as assem sembly bly shou should ld be rugg rugged ed to w withs ithstan tand d industrial indus trial service. Catalo Catalogs gs or drawin drawings gs should contain contain complete material specifications.

4.

When Whenev ever er possi possibl blee th thee en enti tire re fan, fan, mo motor tor,, and drive drive assemb assembly ly sho should uld be factory factory assemb assembled led,, aligned aligned,, and tes test run to ensu ensure re smoo smooth th oper operat atio ion. n. The The fan fan manu manufa fact ctur urer er shou should ld be capa capabl blee of test test ru runn nnin ing g complete assemblies.

Induced-draft fans have further special requirements: 5.

Where Where fan airst airstream ream temp tempera erature ture eexce xceeds eds 3 300° 00°F., F., the the fan should include a shaft cooler and the bearing base should be separated from the fan housing.

6.

Th Thee fan shou should ld be se sele lect cted ed to ha hand ndle le the the max maximu imum m  particulate loading.   nyb   offers radi radial, al, radi radial al-tip, -tip, and  backwardly-inclined  backwardlyinclined designs in a variety of alloys to handle a wide range of contaminated airstreams.

7.

Fans Fans hand handling ling partic particula ulate te-laden -laden ai airst rstream reamss shou should ld be fu furni rnish shed ed with with shaft shaft seals seals to pr prote otect ct th thee in inboa board rd  bearings. Ceramic-felt shaft seals usually provide the  best protection pr otection in these applications.

FAN CONSTRUCTION

Fans used in combustion processes, whether forced or induced draft, draf t, should should be capabl capablee of meeting meeting the followi following ng minimum minimum requirements: 1.

The fan pressu pressure re curv curves es shou should ld be sta stable ble throughou throughoutt the entire entire ope operati rating ng range range of the syste system m (ac (actua tuall and test  block). Certain fans, such as most radials, the   nyb Pressure Pressu re Blower, and the   nyb   AcoustaFoil, AcoustaFoil, are stable from wid wide-op e-open en to com comple pletely tely closedclosed-off off to off offer er the  broadest possible control range.

8.

Fans Fans hand handling ling partic particula ulate te-laden -laden ai airst rstream reamss shou should ld be furnished with a cleanout door and a drain to facilitate  periodic cleaning. Various quick-opening, bolted, and raised, bolted cleanout doors and drain connections are generally available.

9.

Blade Blade lin liner ers, s, hou housi sing ng lin liner ers, s, and har hard d surf surfac acing ing of   blades and/or inlet cones may be desirabl desirable, e, dependin depending g on the particulate loading.

CONCLUSION

2.

The fan an and d all its comp compone onents nts shoul should d be desi design gned ed to me meet et even even the the test test blo block ck condit conditio ion n wi with thou outt pa pass ssing ing through the first critical frequency of the rotating parts. A com common mon spe specifi cificat cation ion calls calls for the fan shaft’ shaft’ss first first critica crit icall speed speed to be 125% of the maximu maximum m operati operating ng speed.

The proper specification and selection of fans for combustion  processes require a careful communication between the system designer and the fan manufacturer. Given a clear understanding of the the sp spec ecif ific icat atio ion, n, the the fan fan manu manufa fact ctur urer er can can of offe ferr the the appropriate fan type and accessories for the application. Form 607 GAW

 

ENGINEERING LETTER   1 The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60521-5530

SELECTION CRITERIA FOR FAN DAMPERS INTRODUCTION Dampers are the most common volume control

devi device ce use sed d in fan sys systems tems.. Low in cost, ost, dampers dampe rs require little maint maintenance enance,, easily adjust airflow during operation, and need little space. For these reasons, they are often selected over  more complex control systems such as variable frequency drives. To se sele lect ct the the best best da damp mper er for for a part partic icul ular  ar  applica app licatio tion, n, it is necess necessary ary to und unders erstan tand d th thee requirem requ irement entss of the applic applicatio ation n as well well as the capabilities of different damper systems. Since dampers may be placed on either side of  the the fan fan,, the they y are cl clas assi sifie fied d as ei eith ther er inlet inlet or  ou outl tlet et.. Both Both redu reduce ce ai airf rflo low w in pr pred edic icta tabl blee amounts, but by different means. Outlet dampers control the air after it has passed

The horsepower and electrical power savings of this damper make it attractive for systems required to operate at reduced flow rates for extended periods, such as in variab variable-a le-airir- olume system systems. s. While Figure 2 illus illustrates trates an inlet damper’s eff effect ectss on a backwa backwardly rdly incline inclined d fan, fan, the sam samee gen genera erall resu results lts are ach achiev ieved ed using inlet dampers on any type of centrifuga centrifugall fan.

through the fan by changing the resistance the fan fa n is worki working ng again against st.. Fig Figur uree 1 sh show owss th thee effects effects of var various ious outlet outlet dam damper per setting settingss on a  backwardly-inclined fan. It illustrates how the damper dam per con control trolss CFM, static static pre pressu ssure, re, and its impact on fan BHP. As the the ou outle tlett dampe damperr is cl clos osed ed,, th thee po poin intt of  operation moves to the left of the selection point along alon g the fan’s fan’s static static pres pressure sure cur curve. ve. Adding Adding resistance resist ance with the outlet damper also moves the fan fa n ho hors rsep epow ower er to the the left left on its curv curve. e. With With Figure 1 -   Static pressure and brak brakee hors horsepowe epowerr curve curvess for backwardly-inclined backwardly-inclined fan with outlet radia rad iall-bla blade de and and fo forw rwar ard d cu curv rved ed-f -fan ans, s, th thee damper. As the damper closes, the point of operation - brake horsepower and static pressure - moves dampered horsepower will be less than the wide to the left of the original fan selection point to the 90 -degrees (wide open) damper setting. open horsepower as the fan moves to the left on the BHP curves. With backwardly inclined fans, the dampered horsepower may be less, the same, or more ore than its wid idee open hor orssepow power, depending on the original point of operation. For  more information see Engineering Letter 3. Inlet dampers affect the air before it enters the fan. External, internal, internal, or inlet box inlet dampers caus causee the the ente enteri ring ng ai airr to sp spin in in the the sa same me direction as the fan rotation. Because of this, the fan fa n wh whee eell can can no nott de deve velo lop p fu full ll ou outpu tput. t. Th This is res resul ults ts in lower lower vo volum lumee an and d re redu duce ced d BHP. BHP. When Whe n a bac backwa kwardly rdly incli inclined ned fan has an inlet inlet damper, it reacts as shown in Figure 2 as the damper dam per van vanee ang angle le is chan change ged. d. Fo Forr ea each ch ne new w damper vane position, new SP and BHP curves are gen genera erated. ted. The new poi point nt of operat operatio ion n is de defi fin ned by the the sy sysstem tem in whic which h the the fa fan n is installed. The end result is similar to the change that occurs when slowing down an undampered Figure 2 -  Effect of applying inlet dampers to the fan in Figure 1. Separate SP and BHP curves are fan. eveloped for each vane setting. Fan operating points at these settings are determined by system resistance (points where system curve intersects SP and BHP fan curves).

 

TYPES OF OUTLET DAMPERS

The parallel blade arrangement shown in Figure 3 is the simplest, most economical, and most popular type of outlet damper. The cross cro ss-s -sect ectio iona nall area area of a wi wide-op de-open en dampe damperr is no nott gr great eatly ly reduced until the blades have been moved to the 30 degree open  position. Consequently, the outlet damper control arm swings through thro ugh a rela relative tively ly larg largee arc to reduce reduce fan capacity capacity a small small amount. This makes the parallel-blade outlet damper particularly useful usef ul when when installe installed d on a con continu tinuous ous process system where sensitive control of air volume between wide open and 70% or  80% of wide-open is desired. The large control arm swing also allow allowss pr pred edet eterm ermin ined ed se setti tting ngss of ai airfl rflow ow to be repea repeate ted d accu accura rate tely ly.. Thi Thiss dam dampe per, r, be bein ing g th thee leas leastt ex expen pensi sive ve of th thee various designs, also makes it the usual selection for systems that require two position damper operation (either full-open or  full-closed). full-clo sed). Another common applic application ation involves cold starts on a “hot” system requiring a reduction in airflow to reduce BHP until the system reaches temperature. Opposed-blade outlet dampers, as pictured in Figure 4, are used when a straight line relationship between fan volume and control arm swing is desired desired.. In this design, design, alternat alternatee blades blades turn in opposite directions. Therefore, the change in volume, with respect to the damper position, position, is proportional proportional to control arm swing. The oppo oppose sed d-bla -blade de da damp mper er is us usua ually lly se sele lecte cted d wh when en it is necess nec essary ary to main maintain tain an eve even n distribu distribution tion of air immediat immediately ely do dow wnstr nstrea eam m air fr from om the theof da damp er.. Figu Figure re 5versus illu illust stra tess the the downstream pattern anmper opposed-blade arate parallel blade damper. Opposed-blade Opposed-blade dampers cost more than parallel blade models of the same size due to the increased complexity of the linkage required to provide the opposed-blade motion.

Figure 3 - Parallel-Blade Outlet Damper

Figure 4 – Opposed - Blade Outlet Outlet Damper

Figure Figu re 5 - Airflo Airflow w Patterns Patterns through Dampers

TYPES OF INLET DAMPERS

Inlet dampers can provide a substantial horsepower savings for  fans that are operated at reduced capacity for extended periods of time time.. Conc Concer erns ns fo forr en ener ergy gy cons conser erva vati tion on and and redu reduce ced d op opera eratin ting g ex expe pens nsee make make this this featu feature re de desi sirab rable le an and d of often ten mandatory when designing a system. A good example of how inlet dampers are used to accomplish energy savings can be seen in a typical variable volume heatingcooling ventilation system. In this application much less air is needed for winter heating than for summer cooling. In addition, during summer operation, less air is needed for cooling during the nighttime hours than during the peak daytim daytimee hours. Yet, the fan system must be selected for the worst condition/highest air  flow. The inlet damper offers the greatest long term savings in VAV applications due to reduced horsepower requirements at reduced volumes. External Extern al inlet inlet dam dampers pers,, as sho shown wn in Fig Figure ure 6, are mounte mounted d external of the fan structure. The configuration is circular with the damper damper vanes vanes con conne necte cted d to a cen central tral hub throug through h pivot pivot  bearings. The control linkage is also circular and exposed for  easy inspection and maintenance. Generally, Gener ally, this is the most expens expensive ive damper configurati configuration. on. It is also capable of handling higher velocities velocities and pressures than the internal inlet damper.

Figure 6 – Externa Externall Inlet Damper

Page 2  

Figuree 8 – Inlet - Box Damper Mo Figur Mounted unted To Inlet Inlet Box

Figure 7 – Internal Inlet Damper

The internal inlet damper, pictured in Figure 7, is similar to the ex exte tern rnal al in inle lett dam dampe perr wit ith h re resspe pect ct to co con ntrol trolli lin ng fa fan n  performance. The most significant difference is that the internal damper is a self-contained unit furnished as an integral part of  the fan inlet cone. This provides considerable space savings and eases installation. installation. The internal inlet-damper inlet-damper design, design, howev however, er, may tend to create create some resista resistance nce at widewide-ope open, n, due to the control vanes being in the high velocity region of the fan inlet. Therefo Ther efore, re, appropri appropriate ate airf airflow low redu reductio ction n factors factors,, as listed listed in a separate engineering supplement, must be used when sizing a fan with this type of damper. damper. In addition, the dampe damperr control control linkage linkage

Inlet dampers typically improve the stability of most products  because they control the flow through the fan inlet. At extreme dampering, dampe ring, about 30° open, inlet dampers can no longer create a vortex and become essentially essentially a blocking damper. This causes the fan to operate far to the left on its curve. When this happens, happens,aa fan is subject to the same problems of instability as if the point of  rating rati ng was estab establish lished ed by an outlet outlet damper damper or other other system system changes.

is in the airstream on the inside of the fan housing and must be serviced through a cleanout door in the housing.

Occasiona Occasi onally lly it is desira desirable ble to sav savee mor moree pow power er at redu reduced ced capacity while maintaining very sensitive control. In this case, the fan may be equipped with both inlet and parallel-blade outlet dampers dam pers.. With the out outlet let dam damper per set at wid widee-o -open pen,, the inlet inlet damper is set to give just slightly more air than needed. Exact air delivery is obtained by adjusting the outlet damper. Because the outlet damper vanes require a lot of movement to achieve a slight change in air delivery, sensitive control is achieved.

InletInle t-box box dam damper perss (Figure (Figure 8) are paralle parallel-b l-blad ladee rec rectan tangul gular  ar  dampers mounted on an inlet box in such a way that the airflow from the damper produces a vortex at the fan inlet. Inlet-box dampers dam pers are gen general erally ly pref preferab erable le on fan fanss equippe equipped d with with inlet inlet  boxes and have the same general control requirements as standa standard rd inlet inlet dampers dampers.. Bec Becaus ausee the bearings bearings are not in the airstream, inlet-box dampers are often used in airstreams that contain contai n some particulate. particulate. Predicti Predicting ng the exact flow reduction with damper ang angle le varies varies with with damp damper er types types and product products. s.  Normally this is not a requirement since flow should be established using manual reference or feedback from automatic control systems. For all inlet-vane dampers, vane angle versus flow relations relationshi hip p wil willl cha change nge wh when en dampers dampers are applied applied to

COMBINED INLET AND OUTLET DAMPERS COMBINED

PERFORMANCE COMPARISON

Figure 9 shows the effects of damper settings on airflow and  brake horsepower for parallel and opposed-blade outlet dampers, and inlet and inlet-box dampers. These plots represent generalizations of damper effect on fan performance and can be used to compare one type to another.

wheels that have been narrowed to establish specific capacities at direct drive speeds.

Figure 9

Effect of vane setting on airflow and power for various damper types. When a parallel-blade outlet damper is set for 80 percent of  wide-open capacity, the damper setting is 40 degrees, and the fan operates at 85 percent of wide-open horsepower. However, with an inlet damper, operation at 80 percent of wide-open requires a 53 degree damper setting and 72 percent of wide-open horse-power.  Note: These curves are rrepresentative, epresentative, not precise. See text.

Page 3  

Parallel-Blade Outlet Damper

Opposed-Blade Outlet Damper

External and Internal Inlet Dampers

Inlet-Box Damper

Internal - 1.5 to 2.5 times as much as parallel blade. External - 3 to 4 times as much as parallel-blade.

1.3 to 1.4 times as much as paralle parallel-blade; l-blade; combined with inlet box 3 to 4 times as much as  parallel-blade.  parallelblade.

1. Cost

Least costly.

1.1 to 1.2 times as much as parallel blade.

2. Control

Best for full-open or  closed requirements or  for fine control between 80% to 100% full-flow. full-flow.

Same as opposed-blade Best for systems where outlet damper. air volume is changed over a wide range and a straight line relationship of volume to control arm swing is desired.

3. Horsepower 

 

4. Air flow afte terr fan

Used on fan inlet box. Can be used with some  particulate in air airstream. stream.

Depends upon characterist characteristic ic BHP curve; Backwardly Backwar dly incline inclined d - same, more, or les lesss than wide-open, wideopen, FC and Radial – less than wideopen.

Power consumption at reduced air volumes is less than with outlet dampers.

Same as inlet damper 

Thro Throw ws air to one sid idee.

No effect.

No effect.

Distri tribute tess air even enly ly..

Figure 10 - Comparison of Inlet and Outlet Dampers SUMMARY

Each Each sy syst stem em ha hass its ow own n req requi uirem remen ents ts with with re resp spec ectt to th thee control of air volume. System designers must be aware of not only first cost considerations but, more importantly, of the long ter term m operat operating ing savin savings gs that that ca can n be ach achiev ieved ed by a proper properly ly engineered system. Each system also imposes limits on which

dampers can be used with respect to fumes, control sensitivity, an and d temp temper erat atur ure. e. No on onee damp damper er de desi sign gn is best best fo forr all all ap appl plic icati ation ons. s. Figu Figure re 10 pr prov ovid ides es a co comp mpari arison son to help help th thee design des igner er recogn recognize ize some of the factor factorss to be con consid sidere ered d in damper selection. orm 607 GAW

 

ENGINEERING LETTER

12

The New York Blower Company C ompany ● 7660 Quincy Street, Willowbrook, Illinois 60521-5530 

 AN  A N IN INTR TROD ODUC UCTI TION ON TO FA N A CO COUS USTI TICS CS INTRODUCTION Fan Acousticsand is an important consideration in systems. the industrial environment with commercial ventilation The sound generated by some fans can be a potential hazard to  personnel in close proximity to the fan, and the sound can be transmitted, via the ductwork connected to the fan, to all areas serviced by the fan. Because of these concerns, fan manufacturers publish sound ratings for their products to serve as a guide for selecting fans to meet sound specifications, and to assist acoustical consultants in predicting the total noise levels in specific environments. This Letter provides basic information to help understand fan sound ratings and how to apply them. WHY FANS MAKE NOISE Like any mechanical device, fans generate sound, which emanates naturally from the turbulence of moving air, the mechanics of moving parts of the fan, and from vibration. AIR TURBULENCE

Air turbulence within the fan increases the sound coming from the air movement. The noise resulting from air turbulence is a major factor in the sound levels of a fan in a specific application. Further, duct work can transmit this turbulent noise to all areas serviced by the fan.

The next at factor consider isefficiency the fan design. Generally a fan operating peaktomechanical will produce less noise,  because high efficiencies result from minimal air turbulence within the fan. There are four basic centrifugal fan wheel designs - forward curved, backwardly inclined, radial, and radial tip - and a variety of axial flow wheel designs (see Figure 2). Each wheel design has unique sound characteristics due to the way they handle air, and the efficiencies they can achieve. Fan speed does not always determine which fan will be quieter. For example, centrifugal fans have higher amplitudes at lower frequencies, while axial fans exhibit higher amplitudes at the higher frequencies. The amplitude of the blade pass frequency on an axial fan is higher and more pronounced than on backwardly-inclined fans, and commonly will have amplitude peaks at multiples of this frequency.

Factors contributing to air turbulence include the resistance to flow, flow separation along fan surfaces, and shock related to abrupt changes in the direction of airflow, pressure, or velocity. The principal areas where such turbulence is encountered within a fan are shown in Figure 1. A lower noise level can be achieved by reducing air turbulence. This can be done by considering several factors related to air movement when selecting fans. The first factor to consider is the fan’s blade pass frequency, which is a pure tone produced when the blades of the fan wheel (impeller) rotate past the housing cut-off sheet in centrifugal fans, or the turning vanes, in axial fans. The blade pass frequency is calculated by multiplying the number of blades times the rotating speed in revolutions per minute. If this frequency matches the natural frequency of the ductwork, it can excite the ductwork, which can cause it to resonate, thereby increasing the noise level. Because of this possible increase in sound, and because certain  pure tones are irritating to investigated people, the sound the blade  pass frequency should be when output sound of reduction is desired.

Figure 1 - Typical Areas of Turbulence

 

 

Figure 2  –  Various  Various Wheel Types

Of the four centrifugal designs, the backwardly-inclined fans are the most efficient, and therefore, the quietest. Those with airfoil-shaped blades offer the highest efficiencies, for clean air environments, while those with single-thickness blades can  be used iin n appl applications ications where light dust or moisture is present, although the efficiencies are somewhat lower. Certain types of axial fans offer the next highest efficiencies. An excellent example is the nyb Vaneaxial fan that uses airfoil shaped blades in an in-line flow design. This fan is used to handle high volumes of clean air at low pressures, which is a typical ventilation application. Radial fans are typically low efficiency, open designs for special purpose applications, such as bulk material handling, or exhausting/supplying lower volumes of air at higher  pressures.  pressure s. An exception to this is the nyb DH design (Figure 3), which has superior efficiencies for a radial wheel and relatively low sound levels. A radial fan will be much louder than a backwardly-inclined fan operating under the same volume and pressure conditions. Radial-tip fans, commonly used to handle larger volumes of air that contains particles or material, exhibit sound characteristics similar to the radial fans. The sound spectra of radial and radial-tip fans contain amplitude spikes at various frequencies, and a noticeable spike at the blade pass frequency.

Figure 3  –  DH  DH Wheel

components are in the airstream. Motor sound will vary with speed, enclosure, electrical characteristics, and even the manu facturer. Antifriction bearings can be used to reduce bearing noise, and proper drive selection will reduce the likelihood of  belt hop, or slap. Of course, proper maintenance must be employed to keep the moving parts running smoothly, and quietly. VIBRATION

The forward-curved fan design operates at speeds that are much slower than the other fan types, which results in lower noise levels from mechanical operation and vibration. However, because of its modest efficiencies, a forward-curved fan may be noisier than a backwardly-inclined fan when operating at comparable volume and pressure. The sound spectrum of the forward-curved fan shows a slower rate of reduction in amplitudes than the other centrifugal types, and  because of the large number of blades, the blade pass frequency occurs much later in the spectrum and is not  predominant..  predominant

Excessive vibration can significantly add to the overall noise level of an installation. This will occur if the fan or any of its components are not adequately balanced, if the fan is installed on an insufficient foundation, or if the fan is not properly isolated from other system components. For example, it is not uncommon for the fan’s support structure or ductwork to have a have  a natural frequency at the fan’s operating speed or blade pass  pass   frequency, either of which can cause the system to resonate at that frequency, increasing the sound levels, and the possibility of damaging the installation. These risks can be eliminated by changing the speed of the fan, installing appropriate isolation, and/or detuning of the fan or affected system components. components.

MECHANICAL NOISE

NOISE MEASUREMENT

The moving components of the fan - the motor, bearings, and drive - produce sound. This too can be transmitted through the system via the fan structure or shaft, or when these

Overall noise levels sound can be level measured at any installation using a variety of portable meters, or more sophisticated equipment like a frequency analyzer (Figure 4).

 

Page 2

 

Sound Pressure (Lp), is an atmospheric pressure change that is

audible to the human ear, and is measured from a point in space where the microphone or listening device is located. The human ear can perceive a broad range of sound pressures, from the threshold of hearing (2 x 10 - 7 microbar) to the threshold of pain (1 microbar). The threshold of pain is five million times louder than the threshold of hearing. The decibel is used in acoustical work to indicate sound pressure levels  because it condenses this tremendous range of values to a workable range of from 10 dB to 130 dB. A decibel (dB) is a logarithmic ratio of some measured value to some reference value. It is standard international practice to use the sound  pressure at the threshold of hearing as the reference value for the sound pressure level scale. Figure 5 shows the relationship between the sound pressure measured in microbar, and the sound pressure levels measured in decibels.

Often a single sound pressure value is used to represent the total sound spectrum. This is expressed as dBA, indicating i ndicating that the sound pressure, in decibels, has been adjusted to reflect a single number value for a sound pressure, weighted  by the “A” scale.. The “A” scale weighting reduces the effect  scale effect   of lower frequencies, with the intent to establish a value more  proportional  proport ional to the human ear frequency response. dBA is used by OSHA to set maximum allowable noise levels, prescribing a maximum dBA limit for an 8 hour exposure. dBA can be measured with a sound level meter, or calculated by applying the weighted values to the eight octave bands encompassing the range of hearing. Better definition of sound pressure levels is gained by breaking the sound spectrum into discreet ranges. The standard practice is to divide the audio spectrum into eight octave bands identified by the center frequency of each band. Figure 6 shows the octave bands of the audio spectrum as defined by the American National Standards Institute (ANSI) Standard S 1.6, series 2. Series 2 ANSI S1.6 From (Hz)

To (Hz)

45 90 180 355 710 1400 2800 5600

90 180 355 710 1400 2800 5600 11200

Center Frequency (Hz) 63 125 250 500 1000 2000 4000 8000

Band Number 1 2 3 4 5 6 7 8

Figure 6

Figure 4  –  Frequency   Frequency Analyzer

Fan manufacturers generally test and rate fan noise according to Air Movement and Control Association (AMCA) Publication 300 - Test Code for Sound Rating Air Moving Devices, and Publication 301 - Methods for Calculating Fan Sound Ratings from Laboratory Test Data. This testing procedure requires a reverberant or semi-reverberant room with a calibrated reference sound source to determine the room characteristics, and is known as the substitution method. Sound data is acquired in the octave bands shown in Figure 6. The measured sound pressure of a test fan is mathematically converted to a sound power level using predetermined microphone locations. MEASURING FAN NOISE dBA is a useful measurement for evaluating the overall noise level at a particular location, but this measurement takes into account all of the sound sources affecting that particular location, which include the sounds from all equipment in the

Figure 5  –  Sound  Sound Pressure Measurements

area, natural sounds the of environment, other environmental factors. of Some these factorsand are from the current  physical proper properties ties of the air such as temperat temperature, ure, humidit humidity, y, and pressure, whether the location is outside or inside, the size and material of the room. All of these affect the sound 

 

Page 3

 

 pressure experie experienced nced by the listener, listener , and recorded by the sound level meter. Because of this, it is impossible for the fan manufacturer to guarantee sound pressure levels or dBA values. For several years fan manufacturer,s and other makers of industrial equipment, have used Sound Power (Lw) values to test and rate fans. Sound power has been chosen because it is independent of the acoustical environment in which the fan is installed. It is the only value that is specific to the particular fan. Sound power is the total energy emitted from a fan which is a

function of the fan’s speed and point of operation, and is independent of the fan’s installation and surrounding environment. A sound power level is the acoustical power expressed in dB radiating from a sound source. It is defined as: Sound Power (Lw) =

Total sound power can be broken up to inlet sound power and outlet sound power. For all functional purposes, the sound  power that is radiated from tthe he inlet i nlet and outlet of a fan is equal to each other. Because a fan manufacturer can present its sound information in the form of inlet, outlet, and total sound  power, it i t is i s import important ant to clarify the iidentity dentity o off the rating before any comparisons and calculations are made. In general, a fan manufacturers’ sound ratings are at peak  point of efficiency as shown in Figure 8. As stated earlier, fan efficiency and air turbulence contribute to changes in noise levels. Consequently, if a fan is operating at a point of operation outside its maximum efficiency range, the user will have to correct co rrect the manufacturers’ sound ratings as shown in the table on page 5.

10 log (Watts) (10 -12)

Sound power levels can be converted into predictable sound  pressure levels once the acoustical environment surrounding surroundi ng the fan is defined. Sound pressure for a given fan changes with a change in air volume, pressure, or efficiency. Because of this, fans must be tested at several speeds and efficiency points. After a fan’s sound power level has been determined at different speeds and  points of operati operation, on, it is important to remember that these levels will always be the same unless the fan is physically altered. If a fan line is geometrically proportional, the sound  power for other fan sizes can be accurately projected from the  base fan. AMCA Publica Publication tion 301 defines methods for acquir ing such data. FAN SOUND RATINGS The sample table shown in Figure 7 shows a listing of total sound power for a particular fan size and type at several speeds in each octave band. Sound power ratings can also be  presented graphical graphically. ly. Octave Bands Fan RPM

1

2

1100 1300 1500 1700 1900 2200 2600 3000 3400 3800 4200 4600

73 79 85 90 93 96 99 101 105 107 109 111

5000

113

3

4

5

6

7

8

72 74 77 80 83 86 90 93 98 102 106 109

68 75 78 81 83 86 86 88 90 94 97 99

62 67 71 75 78 82 88 90 94 96 98 99

59 63 67 70 73 76 80 83 87 90 93 97

58 62 66 69 71 74 77 79 82 85 88 91

51 57 62 66 69 72 75 78 81 83 86 88

45 50 54 58 61 66 70 74 78 81 84 86

112

102

100

101

93

90

88

Figure 7

Figure 8

Figure 8 shows a fan's point of operation at the intersection of the static pressure and volume range on the curve. Since air volume can be defined by a velocity or velocity pressure through the fan’s outlet area, the fan’s point of operation can  be defined by stating the ratio of velocity pressure to static  pressure, or VP/SP. By using a chart such as the one shown in Figure 9, the user can make the necessary sound corrections for fan operations outside the maximum efficiency range. Published fan sound power ratings and corrections reflect noise created by air turbulence within the Because of the infinite variables, mechanical noise vibration noise are impossible to accurately predict, are not included in the rating.

only fan. and and

Another rating method is described in AMCA Publication 302 Application of Sone Ratings for Non-Ducted Air Moving Devices. A Sone is a ratio of loudness between two sounds. The Sone scale is linear, ranging from soft to loud. Unlike the decibel, two Sones are twice as loud as one Sone. This method will produce reasonably accurate estimates of sound pressure in a free-field condition, and is used by manufacturers of roof ventilators and other non-ducted commercial ventilation  products, but is not suitable suita ble for analytical purposes.

  Page 4  

Fan Speed up to 2500 

over 2500 

VP/SP

Point of Fan Operation

0 to .03 .03 to .10 .10 to .30 .30 and up 0 to .03 .03 to .10 .10 to .30 .30 and up

Peak SP Peak ME 1/2 Peak SP Near Wide Open Peak SP Peak ME 1/2 Peak SP Near Wide Open

Octave Bands 1 5 0 4 2 3 0 4 3

2 3 0 2 2 4 0 2 3

3 0 0 0 2 5 0 0 1

4 1 0 0 1 4 0 3 3

5 1 0 2 3 0 0 3 4

6 0 0 1 3 0 0 3 5

7 -3 0 2 2 0 0 2 3

8 -1 0 2 3 -2 0 1 4

Figure 9 - Typical dB Corrections for Point of Operation

APPLYING SOUND POWER When the sound power for a fan has been calculated at a fixed speed and known point of operation, the sound pressure can be estimated. It should be remembered that sound pressure or dBA  predictions are only estimates based on certain known conditions or assumptions regarding the location of the fan and the physical installation. The Short Form for Sound Calculations shown on page 8 is one way to calculate sound pressure. This is a step-by-step method for estimating sound pressure levels or dBA for a specific installation.

Line 4 - enter the appropriate correction for the type of fan installation. If neither the inlet nor outlet are ducted, no correction is necessary. If either the inlet or outlet is ducted away from the listening location deduct 3 dB. This 3 dB reduction accounts for the assumption that the amplitude of inlet and outlet noise is approximately equal and half the noise is ducted away. Figure 10  provides a graphic depiction of the effects of adding or subtracting noises of similar or like amplitude.

The short form only applies to outdoor installations or to indoor installations the large. listenerSuch is relatively closemay to the and the room is where relatively installations be fan termed “free field.” Even given these assumptions,  assumptions,   reflecting surfaces, inadequate support structures, high-loss ductwork, or flexible duct connections could seriously alter the outcome. Figure 10

For example, the fan corresponding to Figures 7 and 9 might be required to operate at 1500 RPM: Octave Band

1

Center Frequency

63

1. Fan Total Sound Power @1500 RPM

85

77

78

71

67

66

62

2. VP/SP Correction

5

3

0

1

1

0

-3

-1

80

78

72

68

66

59

53

For this example, assume only the outlet noise is ducted to the listening location.

-3

-3

-3

-3

-3

-3

-3

77

75

69

65

63

56

50

6. End Reflection Values

14.5 9.0

4.5

1.5

0

0

0

0

7. Corrected Sound Power (5) - (6)

72.5

68

70.5 67.5 65

63

56

50

20

20

20

20

20

20

52.5

48

50.5 47.5 45

43

36

30

Line 5 - enter the algebraic sum of lines 3 and 4. Line 6 - End reflection is a phenomenon that takes place when a sound wave reaches an abrupt expansion such as the end of an open duct. At this point some of the sound waves are actually reflected back into the duct so that the resultant sound power level is reduced. The effects are more pronounced in lower frequency ranges and in smaller duct diameters as shown in Chart III, page 8. For applications where noise level emitted from the inlet or outlet duct concerns the listening location, the duct diameter must be determined and the appropriate values subtracted from the fan sound power.

3. Fan Sound Power (1) + (2) 90 4. Correction for Insta-3 llation (inlet or outlet) 5. Corrected Sound Power at Fan (3) + (4)

8. Conversion for Sound Pressure, Q=2 9. Sound Pressure at 15 feet

87

2

3

4

5

6

7

8

If the inlet and outlet are both ducted away from the listening location, only the sound power radiated through the fan housing will remain. The appropriate reduction will vary from one fan to another depending upon the specific housing thickness and reinforcements and their attendant transmission loss. Refer to the manufacturers’ rating tables for the appropriate reduction for a specific fan type.

125 250 500 1000 2000 4000 8000

20

20

54

Line 1 - enter the published sound power for each octave band corresponding to the required speed. Line 2 - enter the appropriate VP/SP correction. For For this example, assume VP/SP = .025. Line 3 - enter the algebraic sum of lines 1 and 2.

For this example, assume only outlet ducted noise is available at the listening location and the duct is 15" in diameter. (See Chart III on page 8.) Line 7 - enter the difference between lines 5 and 6. Line 8 - enter the correction for directivity and distance.

  Page 5  

As mentioned previously, the amplitude of a noise level will vary depending upon the installations and the distance between the source and the listening location. The number of reflecting surfaces also determines the sound wave radiation pattern. These  patterns  patter ns are known as directivity directi vity factors (Q) and indicate the type of radiation from the number of reflecting surfaces.

The dBA value is the sound pressure level corrected to the “A” weighting network. This is accomplished  accomplished   by deducting the the proper “A” weighting value from each of the eight octave bands, then using the graph from Figure 10 to combine the results to obtain a single number dBA value that represents the fan and its  particular  parti cular installa installation. tion.  Because decibels are logarithmic values, simple addition cannot be used.

AMCA Publication 303 - Application of Sound Power Level Ratings describes Q = 1 as having spherical radiation with no reflecting surfaces. An example would be an axial fan located in a stack. Q = 2 is used for hemispherical radiation where one reflecting surface is present such as a fan on the floor in the middle of a room. For each additional reflecting surface, the directivity factor is doubled. For example, a fan mounted on the floor directly adjacent to a wall would have a Q = 4 factor.

A simpler method of approximating dBA values can  be found on Chart II on page 8. Using the scale on the left hand side of the graph, plot the sound pressure levels from line 9 directly on to the graph for each octave band. Then the maximum dBA can be derived by finding the band number (center frequency) that exceeds the highest octave band level  by the t he most decibel decibels. s. In I n our example, band number 5 (1000Hz) exceeded the octave band level 40 dBA by 8 dB. This was greater than any other band number. Therefore, the dBA level for this fan would be approximately 48 dBA at 15 feet based on a Q-2 directivity.

The appropriate directivity factor must be used in conjunction with the distance from the noise source to the listening location to obtain the reduction r eduction factor (Lw - Lp) to convert sound power to an estimated sound pressure. Using Chart I on page 8, the listening distance from the source must be plotted on the bottom horizontal graph and a vertical line sho should uld  be drawn at that point. A horizontal line drawn from this vertical line at its intersection with the appropriate directivity line will indicate the (Lw - Lp) reduction. These estimates apply to a listener’s position from the noise source and do not consider outside influences from other machinery or unpredictable obstructions, but produce reasonably accurate estimates of sound pressure in a free field condition or outside installations. For this example, assume a Q = 2 directivity factor at a distance of 15 feet. (See Chart I on page 8.)

Another method is to combine decibels such that a logarithmic addition can be employed in lieu of the tabular method shown in Chart II. Logarithmic addition involves calculating the antilog of each decibel to be added, summing the antilogs, finding the logarithmic sum, and multiplying by 10. This method and the formula are given in AMCA Publication 303. TROUBLESHOOTING To avoid undesirable noise levels in the final installation, the system designer needs to consider many factors. First, an acceptable noise level criteria must be established, based on the activity in the area, the nature of the noise, the relationship of the listening location, noise-criterion curves, and the OSHA  permissible  permissib le noise exposure regulatio regulations. ns. Properly selecting a fan type and operating it at peak

Line 9 - deduct line 8 from line 7 and enter the result. The sound power levels represent the final estimate  based on all tthe he stated stat ed conditions. condi tions. The one remainin remaining g step is to determine the proper dBA value. Correction dBA For Value “A”  by Weighted Octave Network Band

Octave Band 

Sound Pressure From Line 9

1 2

52.5 48

-26.2 -16.1

3 4

50.5 47.5

-8.6 -3.2

44.3

5 6

45 43

0 +1.2

45 44.2

7

36

+1.0

37

8

30

+1.1

31.1

26.3 31.9 41.9

Diff. 

-5.6

mechanical efficiency will assure the quietest possible operation. It is not always possible to select a fan that does not exhibit a predominant blade pass frequency, but an awareness of this will help in selecting acoustical attenuation when necessary.

Factor From III. #10

Factor + Higher Value

1.1

33.0

Factor Factor From + Diff.  III. Higher #10 Value

-13.3 -2.4

2.0

46.3

-.8

2.6

47.6

-5.9

1.0

38.0

.2

Factor Single From Number Diff. III. dBA #10 Value

46.5 

-1.6 

-9.6

.4

48.1 

2.3 

50.4 

  Page 6  

Location of the fan with respect to the listener is very important. The greater the distance, the lower the noise level. The use of absorptive and reflective materials as well as isolation usually control excessive noise. If the final installation seems excessively noisy, an octave  band sound analyzer should be employed to measure the noise level. Because it analyzes the spectrum by octaves, it is helpful in isolating components within the spectrum that are major contributors to the noise problem. Often, the fan is not theor major source of theenvironment noise; manythat times it is nearby machinery the surrounding is louder than the fan. After identifying the noise source, its reduction can be approached from two directions: 1.  Reduce the noise at the source. 2.  Reduce the noise at the listening location. The first approach is usually the most cost effective. To reduce fan acoustical noise, a reduction in sound energy is important. Lining ductwork with sound absorbing material or adding duct silencers will reduce airborne noise within the duct system. Flexible connectors between the fan inlet, outlet, and connecting ductwork will aid in reducing both vibration noise and mechanical noise that may be transmitted through the entire system. Fan noise produced by vibratory forces can be induced by a number of components. Sometimes the source is easily detected from experience and at other times measuring instruments are required. The solution to vibratory noise will depend on where it occurs. Reducing the amount of the vibration, eliminating it by substitution, isolating it, or changing the frequency are all possible solutions.

For example, unbalance is a chief cause of vibratory noise. Consequently, balancing the rotor will reduce the vibration caused by imbalance. Replacing a noisy bearing or drive component will eliminate the source. Installing rubber or spring isolators will prevent transmission of the noise to the mounting structure. Detuning natural frequencies of a structure  by changing the fan speed or the natural frequenc frequency y may eliminate this problem. Using the second approach, the noise level at the listening location can be reduced by increasing the distance of the sound  path. T his can be acco accomplished mplished by movi moving ng either the fan or the listener or by rotating the fan so that the noise is directe directed d away from the listener. Changing the characteristics of the room by adding sound absorbing material will help reduce noise However, the effectiveness of sound absorbing material drops off rapidly at frequencies below 250 Hz.; consequently, this approach is somewhat limited. Enclosing the fan in a sound absorbing room, for example, will aid in reducing noise transmitted from the fan structure but will do nothing about noise within the duct system. Erecting sound barriers or employing some type of ear protection are also alternative solutions. These troubleshooting tips only cover a few possible alternatives. Volumes of reference material are available on the subject, and acoustic consultants are available to assist in the areas of noise abatement and acoustical control. Fan manufacturers can provide assistance in resolving noise issues related to the specific fan but normally do not perform overall acoustical engineering consulting.

  Page 7  

SHORT FORM FOR SOUND CALCULATIONS This form is to be used for the approximate sound pressure level calculation of a fan, assuming that the listener’s position is in the dominant free field. In most cases this can be considered no more than 5 feet in an enclosed room, or an outside installation free from reflecting surfaces. OCTAVE BANDS CENTER FREQUENCIES 1. Fan Sound Power Rating at __________RPM 2. VP/SP Correction 3. Fan Sound Power (1) + (2)

1 63

2 125

3 250

4 500

5 1000

6 2000

7 4000

8 8000

4. Correction for Installation (Inlet, Outlet) 5. Corrected Sound Power at Fan (3) + (4) 6. End Reflection Value (Chart III) 7. Corrected Sound Power (5) - (6) 8. Conversion to Sound Pressure (Chart I) 9. Sound Pressure at ___________ ft. (7) - (8) The estimated dBA value is _______ at _______ ft. (Chart II) CHART I DIRECTIVITY/DISTANCE REDUCTION

CHART II SOUND PRESSURE TO DBA CONVERSION

[Given directivity and distance, Sound Power is converted to Sound Pressure.] Q-1 Q-2 Q-4

UNIFORM SPHERICAL RADIATION with no reflecting surface. Example: Stack discharge. UNIFORM HEMISPHERICAL RADIATION with one reflecting surface. Example: Floor mounted fan. UNIFORM RADIATION over 1/4 SPHERE with two reflecting surfaces. Example: Fan mounted on floor near interior wall. CHART III END REFLECTION VALUES (Decibels) Octave Band Hz 5 10 Duct 15 Diameter 20 Inches   30 40

1 63 23.5 17.5 14.5 12.0 9.0 6.5

2 125 17.5 12.0 9.0 7.0 4.5 2.5

3 250 12.0 7.0 4.5 3.0 1.5 1.0

4 500 7.0 3.0 1.5 1.0 .5 --

5 1000 2.5 1.0 -----

6 2000 .5 ------

7 4000 -------

8 8000 -------

Form 118 JLK

 

 

13

ENGINEERING LETTER

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60527 - 5530 

F A N B A L A N C E A N D VI B R A T I ON INTRODUCTION

Vibration always been a good indicator how well a piece of equipment washas designed, installed, andofmaintained. With sophisticated, computerized, preventative maintenance  programs, vibration vibrati on can now also be used as a precursor precurso r of future maintenance requirements.

 

Because of their inherent wheel geometry, some fans are more susceptible to pulsation when operating to the left of the peak on their static pressure curve. Centrifugal fans utilizing forwardcurved or flat, backwardly-inclined blades are particularly subject to this phenomenon. However, fans with backwardlyinclined airfoil blades, such as the AcoustaFoil   wheel, are designed to be stable left-of-peak. Figure 2 illustrates this area of unstable operation in a typical fan performance table (crosshatch area). These points of operation indicate fan instability. ™

Fans are subject to vibration because they have a high ratio of rotating mass to total mass and operate at relatively high speeds. Unlike most mechanical equipment, there are two major causes for vibration in fan equipment. These are aerodynamic, having to do with airflow, and mechanical, having to do with rotating components, fasteners, and structural Operation left-of-peak may be due to an error in system support. This Engineering Letter will discuss both causes of  pressure calculations, less than optimal system installation, or  poor maintenance practi practice. ce. The fan’s point of operati operation on may vibration and provide guidelines for their reduction. have also changed because the process/system has been modified since installation. For example, a drying system may AERODYNAMIC VIBRATION Aerodynamic vibration, also referred to as aerodynamic  pulsation,  pulsatio n, is one cause of fan-system fan-s ystem vibrat vibration. ion. It occurs when a fan operates to the left of its peak static pressure point. The vibration frequency, when checked with instruments, is at a frequency other than the wheel rotation speed.

have initially been designed to pull air material. Subsequent system changes nowthrough requireaa 2" 6" bed bed of of material with a significantly higher pressure drop. This will cause the fan to operate at a different point on its curve which may be left-of-peak. Refer to Engineering Letter 7 to better understand how to take system measurements to determine a fan’s point of operation.  operation.  

This area of operation is illustrated in Figure 1. In this region the fan wheel does not move enough air to fill the blade passages. Aerodynamic vibration is most easily identified by increasing the volume of air flowing through the fan, thereby moving the fan’s point of operation to the right. If the cause is aerodynamic,   the vibration will usually disappear or be reduced significantly. Increasing the airflow is accomplished by opening dampers, cleaning filters and coils, or as a test, removing a section of duct near the fan. These actions will reduce system pressure

If it is determined that the vibration is aerodynamic, there are several steps that can be taken to restore the fan to an acceptable operating point. If some type of blockage is causing the problem, dampers can be opened, filters and coils cleaned, and the process can be restored to a configuration more closely resembling the initial design. More expensive alternatives include increasing duct sizes, reducing duct lengths, and

and, correspondingly, correspondingly, increase the airflo w.

eliminating abrupt turns.

Figure 1 –  Typical  Typical Fan Static Pressure Curve Cross-Hatch Indicates Areas of Instability ™

AcoustaFoil  is a trademark of The New York Blower Company

1” SP 

2” SP 

3” SP 

4” SP 

CFM

OV

1240 1550 1860

800 1000 1200

1207 1355 1517

0.17 0.23 0.32

1516 1620 1757

.032 0.41 0.52

--2178

--0.97

----

2170 2480 3100 3720

1400 1600 2000 2400

1690 1867 2239 2620

0.42 0.56 0.91 1.40

1904 2065 2405 2765

0.65 0.81 1.22 1.78

2288 2415 2708 3032

1.15 1.35 1.87 2.54

2633 2732 2983 3276

1.70 1.94 2.55 3.32

4340 4960 5580 6200

2800 3200 3600 4000

3007 3401 3797 4196

2.06 2.92 4.01 5.35

3138 3518 3902 4292

2.51 3.44 3 .44 4.58 5.99

3378 3736 4104 4476

3.40 4..45 5.74 7.26

3600 3939 4286 4647

4.29 5 5.47 .47 6.85 8.52

RPM BHP RPM BHP B HP RPM BHP RPM BHP B HP

Figure 2 –  Typical  Typical Fan Performance Table

----

 

 

There are a number of causes for wheel unbalance: Construction - in new fan wheels unbalance exists because of the nature of the fabrication and assembly process. Part and assembly tolerances, material density variations, and warpage during welding all contribute to non-concentric wheel assembly. Balancing compensates for these factors. Material build-up - even a thin layer of dirt can cause a surprising amount of wheel unbalance. Using solvent, wire  brushes, scrapers, etc., wheels can typically be cleaned and restored to a balanced condition.

Figure 3  – Induced Air Recirculation Recirculation

If a redesign of the system is not practical but current air volume is adequate and the fan in question is a centrifugal, it may be possible to eliminate or reduce pulsation by adjusting the fan wheel toward the inlet cone. As shown in Figure 3, by adjusting the wheel so the edge of the cone is inside the wheel front plate, additional air will recirculate in the fan. The fan wheel will now receive a sufficient volume of air, allowing it to perform without pulsating; however, the efficiency of the fan will be reduced. In general, increasing the overlap by a distance equal to 2% of the wheel diameter will eliminate  pulsation.  pulsatio n. Aerodynamic vibration may also be caused by poor inlet connections to the fan. Inlet boxes and inlet elbows should be vaned to reduce losses. When air is forced to flow through a sharp turn as it enters the fan, it tends to load just a portion of the fan wheel. The result is always decreased performance but many times pulsation as well.

Abrasion/corrosion - in material conveying applications or applications handling corrosive fumes, abrasion or corrosion of the wheel will cause unbalance. For safety reasons, this condition is more serious than simple vibration and the fan manufacturer’s representative should be contacted con tacted for repair recommendations,, up to and including wheel replacement. recommendations Drive components - sheaves, belts, couplings, and motors can have their own unbalance resulting in fan vibration. Check components for alignment, examine the grooves of sheaves, and check the surfaces of belts. Replace worn components. Couplings can shift even a few thousandths of an inch in shipment, causing misalignment and vibration.

Several drive components can be easily checked to determine if they are the cause of vibration. Disconnect the drive or coupling and run the motor with one sheave or half-coupling in  place. If this assembly runs rough, remove the sheave or half half-coupling and run the motor alone. It is much more difficult to determine if the fan wheel or the driven sheave/coupling is causing the vibration without removing it and sending it to a balancing facility. Sheaves and couplings should have been dynamically balanced originally. Unless it is important to determine whether the wheel or drive component is out of balance, it is probably best to balance the wheel, shaft, and drive component as an assembly.

The same phenomenon can also develop, though generally to a lesser degree, at the discharge of the fan. Fans do not discharge Fasteners -wheel and drive component setscrews, bearing air at an even velocity across their entire outlet. T hey generally  bolts, and the fan base mounting hardware hardwar e are all subject to operate best when the air is discharged into a long, straight loosening, especially when some vibration is present. Without duct, the minimum being three duct diameters beyond the outlet attention, loose components will add to the overall fan of the fan. vibration magnitude. MECHANICAL VIBRATION

Mechanical vibration is the most common type of fan vibration. It is caused by unbalanced wheels or other rotating fan components. Its negative impact is increased with loose fasteners and poor structural support. Two terms are important in understanding mechanical vibration. Balance primarily refers to the fan wheel or other rotating components. The procedure of balancing involves adding or removing weight in an attempt to move the center of gravity toward the axis of rotation. Vibration primarily refers to the complete fan. Fan vibration is measured during a “run test” and is the vibration amplitude at the fan bearings expressed in units of displacement or velocity. velocity. The vibration level for new fan equipment is a result of the design and construction by the fan manufacturer. For operating fan equipment, the installation and subsequent maintenance  practices can have a major effect on fan vibration.

Structural support - too frequently, fans are mounted on supports that have a natural vibration frequency near that of the fan. At this frequency, the structure will tend to continue to vibrate once it has been set in motion. Under such conditions it is almost impossible to balance all of the rotating components finely enough to prevent an objectionable amount of vibration. Adding mass or stiffeners will move the structure’s structure’s   natural frequency out of the range of the operating fan.

Optimum mounting structures include thick concrete slabs, steel bases supported by isolators, or heavy, all-welded steel structures. Structures must have adequate sway bracing, with no long, unsupported spans. They should be designed to be heavier than if they were designed merely to support a static load. All vertical supports should be directly underneath the fan and the fan should not be located in the middle of beam spans.

Page 2  

Bent shaft - can cause significant vibration which usually results in a vibration magnitude that is proportional to the amount by which the shaft is bent. Using a simple dial indicator, the shaft can be checked for trueness. It should not be out more than one or two thousandths of an inch on a short shaft or two or three thousandths on a longer shaft. If the shaft is bent, it can straightened, replaced, or compensated for trueness by  balancing. BALANCE CRITERIA

Major fan manufacturers balance fan wheels prior to assembly on precision balancing machines (see Figure 4). The balancing  proceduree involves detectio  procedur detection n of and compensation compensatio n for ounceinches of unbalance.

For example, using a Size 264 Series 20 DH wheel: Where: W

= 78 lbs.

 N

= 2280 RPM

G

= 6.3

6.01 x 6.3 x 78 Uper = 2280 Uper = 1.3 oz. oz. –   –  in.  in. VIBRATION CRITERIA

For most HVAC, agricultural, and industrial i ndustrial applications, an ISO balance quality grade of G6.3 is adequate. Using this  balance grade, the permissible residual unbalance is calculated as follows: 6.01 x G x W  N

After wheel installation, assembled fans are “trim balanced” as  as  a complete unit before shipment (see Figure 5). Manufacturers have some limitations on what fans can be run tested based on electrical requirements, test speeds, and customer furnished components.

Uper

=

Uper

= permissible unbalance per balance quality grade (oz.-in.)

W

= wheel weight (lbs.)

 N

= wheel ope operating rating speed (RPM). (RP M).

G

= balance balance quality grade (6.3)

a guarantee of the minimum level of vibration once the fan is installed in the system. To account for this difference in vibration sensitive applications, more and more fans are being mounted on vibration absorption bases. These bases contain springs or rubber-in-shear isolation and may or may not be filled with concrete for additional mass. The purpose of these  bases is to allow the fan to vibrate without transmitting the vibration to the building structure.

Figure 4  – Fan Wheel Balance

Figure 5  – Fan Vibration Run Test

Where:

To perform a vibration run test, the fan is mounted on a rigid  base. The base may be more or less rigid than that which the customer will use. Because of this difference, vibration limits determined from the factory vibration run test cannot be used as

Page 3  

Fi u rre e 6  – Three Axis of Measurement

Fan assembly vibration is typically measured in the horizontal direction with “filter in”.  in”.  Filter in refers to the vibration being measured only at the frequency of interest. This method  provides an accurate measure of wheel unbalance. Transducer orientation may vary by product and/or test stand configuration at the discretion of the manufacturer (see Figure 6). Major fan manufacturers have seismic vibration standards as  part of their manufacturing/qual manufactur ing/quality ity procedur procedures. es. These limits will vary depending upon the fan manufacturer’s test facilities,  facilities,  

CO NCLUSI O N

System designers and specifiers should observe the following specifications to ensure minimum, acceptable levels of fan vibration: 1.  

Wheels should be dynamically balanced prior to installation in the fan assembly to ISO 1940/ANSI S2.19 Quality grade G-6.3.

2.  

Fans should be given a run test and “trim balance” af ter ter wheel installation at the fan manufacturer’s  plantt to decre ase vibr  plan vibratio ation n cause caused d by othe otherr fan components and the overall assembly process whenever whenev er the fan configuration permits it.

3.  

Mounting structures must be rigid and sufficiently heavy to properly support the fan. Structures must have a natural frequency that is well out of the fan’s   operating range.

4.  

For vibration sensitive applications, special consideration considera tion should be given to spring or rubber-inshear isolation, or inertia bases.

5.  

Utilizing computerized fan selection programs and the manufacturer’s representative, fans should be selected to avoid unstable operating points and resulting aerodynamic pulsation.

6.  

Alterations to the overall system design should include consideration of changes in the fan’s point of   of   operation and possible aerodynamic pulsation.

7.  

Proper maintenance practice, including periodic wheel inspections and inspection of drive components and fasteners, will assure reduced vibration levels.

 balancing  bala ncing equi equipment pment,, and a nd ffan an ttype ype a nd si size. ze. As a guideline for fans in HVAC, agriculture, and industrial applications, a peak velocity of 0.15 inches/second at the factory test speed is usually adequate. For those more familiar with using displacement as a measure of vibration, displacement units can be converted to velocity units using the following equation: V =

š x F x D 1000

Where: V = velocity (in./sec.) F = frequency in revolutions per second (RPM/60) D = displacem displacement, ent, peak-to-peak peak-to-peak,, (mils) (1 mil = .001 inch) Example: Convert .6 mils displacement to velocity in in./sec. with the fan running at 1200 RPM. V =

3.1416 x 1200 x .6 60 x 1000

V = .0377 in./sec.

Form 118 JLK

 

 

ENGINEERING LETTER 

  4

The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Illinois 60527-5 60527-5530 530

STAINLESS STAINL ESS STE STEEL EL SPE SPECIF CIFICA ICATIO TIONS NS FOR FA FAN N EQUI EQUIPME PMENT NT INTRODUCTION

Specifiers and users of air-moving equipment are often faced improv improvemen ementt over mild stee steell in abras abrasive ive applicati applications. ons. There with the presence presence of corros corrosive, ive, abrasive abrasive,, or high temperature temperature are, however, special alloy steels classified in the “abrasion resist istant ant”” or “AR” “AR” gro groupi uping. ng. Suc Such h AR ste steels els are us usua ually lly conditi con ditions ons which may be det detrim riment ental al to the service service life of  res standard stand ard mild steel fan equipmen equipment. t. Reco Recognizi gnizing ng the limitless made to a minimum 321 brinell hardness specification where, va varie riety ty of st stai ainl nles esss st stee eell al alloy loyss or poly polyes este terr re resi sin n-bas -based ed for example, 304 stainless steel is rated at only 124 to 147 materi mat erials als of which which fan compon componen ents ts can be fabric fabricate ated, d, an and d  brinell hardness while 316 stainless stainles s steel is only slightly slight ly considering the multitude of special purpose paints and coatings harder. currently curren tly marke marketed ted for such applicatio applications, ns, the specif specification ication and selection of the single best combination can be a difficult task. TEMPERATURE CONSIDERATIONS The purpos purposee of this this Eng Engine ineerin ering g Letter Letter is to pro provid videe some some general guidelines to assist in the process. Refer to Engineering Typically, mild steel’s strength decreases rapidly at elevated Letters 16 and 18 for similar guidelines on corrosion-resistant temperatures, affecting the maximum safe operating speed of  co coat atin ings gs and and fi fibe berg rgla lass ss--re rein info forc rced ed pl plas asti ticc (FRP (FRP)) fa fan n th thee fan fan wh whee eell an and d conse consequ quen ently tly redu reducin cing g th thee effe effecti ctive ve construction.  performance range r ange of the fan. Beyond 800°F. 800°F.,, mild steel and even 304 stainless steel are not well suited for rotating parts. At temperatures up to 1000°F., 316 stainless steel should be STAINLESS STEEL ALTERNATIVES considere cons idered d first because of its cost and availabil availability. ity. Only where 316 stainless steel does not allow adequate speeds at Often, low first cost plays an important role in the selection of a the required temp temperatu erature re shou should ld 347 stainless stainless steel wheel  particular  parti cular type of corrosion-resi corrosion-resistant stant constr construction; uction; specialty specialt y construction be specified. Refer to each fan line’s bulletin coat coatin ings gs us usua ually lly offer offer the the low lowes estt init initia iall co cost st,, fo foll llow owed ed by stainless steel alloy construction, and finally FRP construction. for speed derate factors. However, this method of selection does not take into account life cycle cycle costin costing g tha thatt could could result result in the least ex expen pense se ove overr the service life of the product. Stainless steel and FRP are generally superior to specialty paints or coa coatin tings gs when when it com comes es to cor corros rosion ion resistan resistance. ce. FRP will will usually exhibit the best corrosion-resistant characteristics and will handle certain corrosive agents or reagents that stainless steel will not, and in some sizes is as economical as stainless alloys. How Howev eveer, sta tain inle lesss st steeel al allo loy ys ar aree cap apab able le of hi high gher  er  temper tem peratu atures res and wil willl sta stand nd up much much be bette tterr to the impact impact of  non-abrasive materials. Also, fabrication methods tend to limit the ava availab ilabilit ility y of FRP fan equ equipm ipment ent and certai certain n performance performance requirements may force the consideration of stainless steel alloy constr con struct uction ion as an alte alterna rnate te to the superior superior corros corrosion ion-resista -resistant nt qualities of FRP.

 Neither FRP fan construction nor special duty paints or coatings applied app lied to mil mild d steel steel con constru structi ction on will will prov provide ide any measur measuree of   prolonged  prolon ged service life in an abrasive application applicat ion when compared compar ed to mild steel. Even stainless steel alloys with their seemingly “t “tou ough gh”” cl clos osee text textur ured ed su surf rfac acee fini finish sh pr prov ovid idee negl neglig igib ible le

In all cases, the suitability of a particular fan to operate at the the requ require ired d temp temper erat atur uree is so sole lely ly de depe pend nden entt up upon on the the indivi ind ividua duall fan des design ign and constr construc uction tion.. Max Maximu imum m safe safe operating temperatures for fan equipment range to 1000°F.  but are also dependent upon the proxi proximity mity of motors or   bearings to hot airstream surfaces. Only where the product literature expressly acknowledges the suitability of the basic fan constru construction ction for opera operation tion at the required tem temperatu perature re can stainless steel construction be used to obtain the required safe speeds. STAINLESS STEEL TYPES

As Assu sumi ming ng that that stai stainl nles esss ste steel el is need needed ed fo forr a sp spec ecif ific ic application, the next step is to determine the best stainless alloy to use. There cur There curren rently tly exist exist mor moree than than 100 regist registere ered d gra grades des of  stainless steel. Certainly, not all of these various alloys can be made available for all of the different sizes and types of fan eq equi uipm pmen ent. t. To faci facili lita tate te sele select ction ion,, spec specifi ifica cati tion on,, an and d  production, the availability of stainless steel alloys for fan equipment must be selectively limited.

 

Basically, stainless steel can be divided into three categories; Martensitics - 12% chromium and iron with carbon in balanced  proportion.  propor tion. Ferrit Ferritics ics - with higher chromium chromiu m content and carbon content held low. Austenitics - with nickel added. . . often referred to as 18-8 stainless which is approximately 18% chromium content and 8% nickel content.

construction involves spun-inlet venturi sections or spun wheel components. It may be more economical to furnish all such sp spin inni ning ngss of one one gr grad adee of stai stainl nles esss stee steel, l, allow allowin ing g an inte interc rcha hang ngea eabl blee inve invent ntory ory.. Simila Similarl rly, y, cast casting ingss may may be furnished of one grade of stainless instead of maintaining 3 or  4 various grades and incurring added inventory expense.

Martensitic Martens iticss ha have ve the lea least st ten tende denc ncy y to work work harden harden.. The application of this alloy grouping is usually limited to that of   precisi  prec ision on parts parts suc such h as surgic surgical al inst instrume ruments, nts, sh shear ear bla blades des,, and dies. dies.

Of the Austenitic alloys shown in the summary on page 4, 304, 304L, 316, 316L, and 347 stainless steels provide an adequate variety of corrosion resistance and strength characteristics and

Ferritics exhibit the greatest degree of corrosion resistance in this grouping but work harden quite readily and are usually limited to decorative applications such as interior architectural trim, kitchen trim or utensils, and fasteners. Au Aust sten enit itic icss provi provide de the the be best st co comb mbin inat atio ion n of co corro rrosi sion on res resist istanc ancee and duc ductili tility ty.. The su suita itabil bility ity of these these all alloys oys for  welding and fabrication methods common to the fan industry reflect the standardization by fan manufacturers. The Summary of Austenitic Stainless Steel Types on page 3  present s alloy composi  presents composition, tion, strength characte characteristic ristics, s, and typical applications for the various stainless steel alloys in the Austenitic category. Of the Austenitic alloys shown, some further limitations are  placed on the fan manufacturer manufactu rer due to material availabi availability, lity, inventory needs and costs, and specific production methods. Refer to Engineering Letters 16 and 18 for condensed guides to the corrosion-resistant characteristics of stainless steel alloys.  Note that these are condensed refere references nces and do not present the full extent of the corrosion-resistant characteristics of any grade. gra de. Sin Since ce the inf inform ormati ation on is based based on chemi chemical cally ly pure pure reagents, reage nts, customer in-pla in-plant nt testi testing ng of a particular particular stainless stainless alloy in the actual environmen environmentt is recomm recommended ended to determine determine suitability.

MANUFACTURING CONSIDERATIONS The typ typica icall fan man manufa ufactu cturer rer rare rarely ly has the opport opportun unity ity to  purchase an adequate quantit quantity y of duplicate duplica te parts in the same stainless alloy construction that would warrant direct purchases from the mil mill. l. Instea Instead, d, “pe “perr job” job” purcha purchases ses limit the fan manufacturer to those alloys which are most readily available from steel distributors.

Because of the dissimilar physical and mechanical properties of  the stainless alloys, equipment fabrication methods often vary from the standards established for mild steel construction. For  examp exa mple, le, pro produc ductio tion n equipm equipment ent capabl capablee of handli handling ng 1/ 1/4" 4" carbo carbon n st stee eell ma may y on only ly be ca capa pable ble of hand handli ling ng 3/16" 3/16" th thic ick  k  stainless stain less.. Likew Likewise, ise, the basic fan constructio construction n may involve heavy gauge components cut to size on standard flame burning equipment equip ment,, but when stainles stainlesss steel is requi required red plasma-a plasma-arc rc cutti cuttin ng equi equipm pmen entt be beco come mess ne nece cess ssar ary. y. Typi Typica cally lly,, fa fan n

are readily available from steel distributor stock. These specific stainless steel alloys can be consolidated into versatile 304, 316, and 347 stainless steel construction groupings. Recognizing Recognizin g the avai availabilit lability y of these these vario various us stain stainless less steel constr con struct uction ion classi classific ficati ations ons,, a det determ ermina inatio tion n can be mad madee regard reg arding ing the sui suitab tabili ility ty of a par partic ticula ularr gro group up for a given given application based on the following: 30 304 4 stai stainl nles esss stee steell -   g goo ood d co corr rros osio ion n resi resist stan ance ce at a minimum min imum pric price. e. Und Under er this this all alloy oy gra grade, de, mac machin hined ed part partss such su ch as shafti shafting ng could could be furnis furnishe hed d from 304 stainl stainless ess steel. However, in order to optimize production,   nyb  only offerss 316 stainles offer stainlesss stee steell shafti shafting. ng. Welded parts such as housings or wheels must be fabricated from 304L stainless steel. steel. Bey Beyond ond 800°F., 800°F., the stre strengt ngth h charac characteri teristi stics cs of 304 s t a i nl e s s st ee l ar e no t sufficient to warr an ant recommendation. 316 stainless stainless steel -   better better corros corrosion ion resistance resistance than 304 and good strength characteristics at elevated temperatures. Th Thou ough gh hi high gher er in pri price ce,, this this allo alloy y gr grad adee is the the most most versa versatil tile. e. Wel Welded ded com compon ponen ents ts must must be fab fabric ricate ated d fro from m 316L stainless steel which is a low carbon grade stabilized for welding. 34 347 7 stai stainl nles esss stee steell -   corrosion-resistant characteristics similar to 304 stainless steel but with the highest strength ch chara aracte cteris ristic ticss at eleva elevated ted temper temperatu atures res.. Sin Since ce it is th thee

highestt in initia highes initiall cos costt and most most dif diffic ficult ult to obtain obtain,, 347 stainless steel should only be used where rotating speeds and elev levated ated tem tempe pera ratu ture ress de dem man and d its its use fo forr wheel eel construction.

The corrosion-resistance guide on page 3 provides a reference to the the corr corros osion ion--resi resist stan ance ce cha chara ract cter eris isti tics cs of 304 304 an and d 31 316 6 stai stainl nles esss stee steell allo alloys ys.. For For the the pu purp rpos oses es of this this guid guide, e, the the corrosion-resistance of 347 stainless steel is considered similar to 304 stainless steel and should only be used if high temperature is a factor. Note that this is a condensed reference and does not re repr pres esen entt the the fu full ll exte extent nt of the the co corr rros osio ionn-re resi sist stan ance ce characteristics of any grade. Because this information is based on chemic chemicall ally y pur puree reagen reagents, ts, cus custom tomer er in-pla in-plant nt testin testing g of a  particular  parti cular stainles stainlesss alloy in the actual operating environment is recommended recommen ded to determine suitability.

Page 2

 

CORROSION-RESISTANCE GUIDE Corrosive Agent

Stainless Steel Alloy 304*

Corrosive Agent

316**

Stainless Steel Alloy 30 4*

316**

Acetic Acid Acetic Anhydride Acetone Acetylene Aluminum Acetate

S S E E E

E E E E E

Lactic Acid Magnesium Carbonate Mercuric Chloride Methyl Alcohol Methyl Ethyl Ketone

S E  N E E

E E  N E E

Aluminum Chloride (dry) Ammonia (dry) Ammonia (wet) Ammonium Sulfite Aniline Barium Chloride Benzene Boric Acid Bromine Water  Butane Calcium Chloride Carbon Tetrachloride (dry) Chlorine Gas (dry)

 N E E S E E E E  N E S S S

S E E E E E E E  N E S E S

Mineral Oil Moisture  Naptha  Nitric Acid Ozone Perchloric Acid Phenol Phosphoric Acid Polyvinyl Acetate Potassium Chloride Potassium Cyanide Potassium Dichromate Potassium Hydroxide

E E E E S  N E S E S E E E

E E E E S  N E E E E E E E

Chlorobenzene Citric Acid Copper Sulfate Cyclohexaone Ethyl Acetate Ethyl Alcohol Ethylene Dichloride Ethylene Oxide Ferric Chloride Ferric Nitrate Fluorine Gas (dry) Formaldehyde Formic Acid Gasoline Glycerine Hydrochloric Acid

S E E S S E E S  N E E E S E E  N

S E E S E E E S  N E E E E E E  N

Pyridine Salt Spray Silver Nitrate Sodium Bicarbonate Sodium Chloride Sodium Cyanide Sodium Dichromate Sodium Hydroxide Sodium Hypochlorite Sodium Sulfate Steam Vapor  Sulfamic Acid Sulfur Dioxide (dry) Sulfur Dioxide (wet) Sulfuric Acid Tannic Acid

S S E E S E S E  N E E T S  N  N S

S S E E E E S E  N E E S E S S E

Hyfrofluoric Acid Hydrogen Peroxide Hydrogen Sulfide (dry) Hydrogen Sulfide (wet) Iodine

 N E S  N  N

 N E E S  N

Toluene Trichloroethylene Xylene Zinc Chloride Zinc Sulfate

E S E  N E

E S E S E

E = Excellent

S = Satisfactory

N = Not Recommended

T = Test data not available

* 347 347  stainless stainless  steel steel  is is  considered considered  to to  have have  the the  same same  corrosion-resistance corrosion-resistance  characteristics characteristics  as  as 304 304  stainless stainless  steel. ** Alloy 2205 has similar corrosion-resistance characteristics as 316 stainless steel. SPARK RESISTANCE

A common misapplication of stainless steel is in areas requiring non-s non -spark parking ing mat materia erials. ls. Sin Since ce stainl stainless ess steels steels are basica basically lly alloys of chromium and iron, or of chromium, iron, and nickel,

may be furnished to allow for some types of SRC construction. However, in other cases, all that is available are steps short of  SRC construction which can be added to the fan to minimize

they they are are cons consid idere ered d fe ferro rrous us an and d sp spar arkin king. g. As a re resu sult, lt, th thee availa ava ilabili bility ty of SRC with stainl stainless ess steel steel con constru structi ction on is very limited lim ited.. In some some cas cases, es, a Monel Monel shaft shaft and and/or /or Monel buff buffers ers

the pote potentia ntiall for generat generating ing sparks sparks.. The spe specifi cificc mod modific ificatio ations ns vary depending upon the product, so consult nyb for availability.

Page 3  

SPECIAL ALLOYS

Under the gene Under general ral des descrip cription tion of stainle stainless ss stee steel, l, the there re are many other other spe specia ciall alloys; alloys; som somee mor moree cor corros rosion ion res resist istant, ant, and som somee more abrasion resistant. These specialized alloys require careful consid con siderat eration ionss of costs, costs, avai availab labilit ility, y, des design ign suitabi suitability lity,, and fabrication methods. Therefore, their selection and specification should be left to specific applications. SUMMARY

Any equipment is only as good as its weakest component. If the

specified, 304 or 347 stainless steel should not be substituted  because of limited corrosion resistance. If 304 stainless steel is all all th that at is ne nece cess ssar ary y to co comb mbat at th thee co corr rros osio ion n an and d 31 316 6 sta stainle inless ss steel wheel constru construction ction is adequ adequate ate to obtain the safe speed at the required temperature, there is no reason to substitute the more expensive 347 stainless steel alloy. The 347 stainl stainless ess steel allo alloy y grade grade sho should uld nev never er be spe specifi cified ed  based solely upon its corrosion-resistant characteristics; its only advantage over 316 is higher rotating speeds at elevated temperatures.

corr corros osiv ivee ga gass st stre ream am requ requir ires es that that 316 316 stai stainl nles esss stee steell be SUMMARY OF AUSTENITIC STAINLESS STEEL TYPES

17% % Cr., 7% Ni. gra grade de us used ed pri prima maril rily y in Type 301 Type 301..   17 struct structura urall app applica licatio tions ns and whe where re high high strengt strength h plus plus high high ductility ductil ity is require required. d. Corrosion Corrosion resistance is slightly slightly less than Type 302.

Type 309. Type 309.   A 24% Cr. 12% Ni. steel steel com combini bining ng exc excelle ellent nt resistance to oxidation with high tensile and creep strength at elevated temperatures. It resists oxidation at temperatures up to 2000°F. under normal conditions.

Type 302.   The basic 18% Cr. 8% Ni. possesses excellent corrosion resistance to many organic and inorganic acids and their salts at ordinary temperatures. temperatures. Also has good resis ance to oxid oxidat ation ion at ele eleva vate ted d tem tempe pera ratu ture res. s. Can Can be re read adily ily fabric fabricate ated d by all met method hodss usually usually employ employed ed with carbon carbon steels. Cr-Ni grades are nonmagnetic in the fully annealed

analysis is having sslightly lightly hig higher  her  Type 310.   25% Cr. 20% Ni. analys oxidation resistance and creep values than Type 309. Lower  Coeffic Coe fficien ientt of Exp Expans ansion ion gives gives less less ten tenden dency cy to war warp p and throw scale in fluctuating temperatures.

con conditi dition on Type and cannot can be hard hardene d by precipitation conven conventio tional naldue heat hea treatment. treatm ent. 302not is subje subject ct toened carbide precipi tation tot welding. Type 303.  The basic 18-8 composition with the addition of  one or more more other other ele elemen ments, ts, usu usually ally pho phosph sphoru orus, s, sulfur  sulfur  and/or selenium to improve machinability. Also used when minimum galling and seizing is desired. Corrosion resistance under certain conditions may be somewhat lower than Type 302. Special precautions are necessary in welding Type 303. Type 304.  Similar to Type 302 in chemical analysis except carbon is .8% max. The lower carbon decreases susceptibility to carbide precipitation in the 800°F. to 1550°F. temperature rang ra nge, e, ma makin king g it usefu usefull ov over er a wide widerr ran range ge of co corro rrosi sive ve conditions than Type 302. Type 304L.  An extra low carbon analysis similar to Type 304 except carbon is .3% max. Carbide precipitation does not occur if material is not held over two hours in the 800°F. to 1550°F. temperature range. Thus corrosion resistance is no nott affe affect cted ed by norm normal al weld weldin ing g an and d stre stress ss re reli liev evin ing g applications. Type 305.   modifi modified ed Type 304 304 grade of lower lower chromium, chromium, higher higher nickel nickel conten contentt to reduce reduce tenden tendency cy to work work harden harden when whe n sev severe erely ly cold worked worked.. Particu Particularl larly y wel welll suited suited for  di diff ffic icul ultt form formin ing, g, pe perf rfor orat atin ing, g, et etc. c.,, wher wheree ra rapi pid d wor ork  k  hardening harden ing makes fabrication difficult.

Ni. grade pro provid viding ing somew somewhat hat Type 308.   20% Cr. 10% Ni.  better corrosion resistance than the 18 18-- 8 grades. Because of  it itss hig highe herr all alloy oy cont conten ent, t, it is les lesss su susc scep epti tible ble to ca carbi rbide de  precipitation than T Type ype 304.

Type Type 314. 314.   Esse Essent ntia ially lly Ty Type pe 31 310 0 wi with th the the addi additi tion on of  ap appro proxi xima mate tely ly 2. 2.50% 50% silic silicon on to in incre creas asee resis resistan tance ce to oxidation and to retard carburization. Type 316.  A modified 18-8 grade containing approximately 2.50% molybdenum. molybdenum. It is more resist resistant ant to corrosive action of  most chemicals, especially sulfuric acid and fatty acids. Type 316 is less susceptible to pitting and pin hole corrosion by acetic ace tic acid acid vap vapors ors,, chlorid chloridee soluti solutions ons,, etc etc.. The ten tensil silee and creep strength at elevated temperatures are also su erior to the the ot othe herr CrCr-Ni type types. s. Type Type 31 316 6 is su subj bjec ectt to carb carbid idee  precipitation due to welding. Type 316L.  Similar to Type 316 in analysis except carbon is .3% max. max. It is immu immune ne to harmful harmful interg intergranu ranual al corr corrosio osion n  providing it is not held in the 800°F. - 1550°F. temperature range for over two hours. Type 317.  A modified 18-8 stainless containing approximately 3.50% 3.50 % molybd molybdenu enum. m. Res Resista istance nce to cor corrosi rosion on is som somewha ewhatt  better and susceptibility to carbide precipitation is slightly less than Type 316. Type 321. A modified 18-8 analysis with titanium (five times ca carbo rbon n co cont nten entt minim minimum um)) added added to make make it immu immune ne to harmful harm ful carb carbide ide precip precipitat itation ion.. The cor corros rosion ion resist resistanc ancee of  Type 321 is the same as Types 347 and 304. Type 347.   A mod Type modifie ified d 1818-8 8 formula formulation tion with columb columbium ium (two (tw o t mes mes carbo carbon n co cont nten entt minimu minimum) m) ad adde ded d to make make it immune immu ne to harmful harmful interg intergranu ranular lar cor corrosi rosion. on. The cor corrosi rosion on resistance of Type 347 is the same as Type 304.

For  m  JLK 318

 

ENGINEERING LETTER The New York Blower Company

●

15

 7660 Quincy Street, Willowbrook, Illinois 60521 -5530 

PRACTICAL L IMITS OF OF SPARK -RESI -RESISTANT STANT CONSTRUCT CONSTRUCTION ION INTRODUCTION

THE AMCA STANDARD

Fan applications with airstreams of explosive or flammable  particles or gases require spark-resistant system components for the safe handling of such airstreams. This includes components such as ductwork, dampers, filter devices, heating or cooling coils, and fans. This Engineering Letter presents practical considerations and methods of providing fans with varying types of Spark-Resistant Construction (SRC).

The Air Movement and Control Association (AMCA) established a standard set of Classifications for Spark-Resistant Construction. For reference, that Standard is shown here in its entirety.

ANSI/AMCA STANDARD 99-16 Classification for Spark-Resistant Construction Classification Fan and damper applications may involve the handling of potentially explosive or flammable particles, fumes, or vapors. Such applications require careful consideration of all system components to ensure the safe handling of such gas streams. This AMCA Standard deals only with the fan and/or unit installed in that system. The Standard contains guidelines which are to be used by  both the manufacturer and user as a means of establishing general methods of construction. The exact method of construction and choice of alloys is the responsibility of the manufacturer; however, the customer must accept both the type and design with full recognition of the potential hazard and the degree of protection required. Type

A

B

Construction

All parts of the fan or damper in contact with the air or gas being handled and subject to impact by particles in the airstream shall be made of nonferrous material. Ferrous shafts/axles and hardware exposed to the airstream shall be covered by nonferrous materials. Fans only: Steps must also be taken to assure that the impeller, bearings and shaft are adequately attached and/or restrained to prevent a lateral or axial shift in these components. Dampers only: Construction shall ensure that linkages, bearings and blades are adequately attached or restrained to prevent independent action. Ferrous containing bearings are acceptable if the bearings are located out of the airstream and shielded from particle impact. Fans only: The fan shall have a nonferrous impeller and nonferrous ring about the opening through which the shaft passes. Ferrous hubs, shafts and hardware are allowed, provided construction is such that a shift of impeller or shaft will not permit two ferrous parts of the fan to rub or strike. Steps must also be taken to assure that the impeller, bearings and shaft are adequately attached and/or restrained to prevent a lateral or axial shift in these components. Dampers only: Construction shall ensure that linkages, bearings and blades are adequately attached or restrained to prevent independent action. Damper blades shall be nonferrous. Fans Only: The fan shall be so constructed that a shift of the impeller or shaft will not

C

permit two ferrous parts of the fan to rub or strike. Dampers only: Construction shall ensure that linkages, bearings and blades are adequately attached or restrained to prevent independent action. Damper blades shall be nonferrous.

Note: 1. No bearings, drive components, motors or other electrical devices shall be placed in t he air or gas stream unless they are constructed or enclosed in such a manner that failure of that component cannot ignite the surrounding gas stream. 2. The user shall electrically ground all fan and/or damper parts. 3. For this standard, nonferrous material shall be any material with less than 5% iron or any other material with demonstrated ability to be spark resistant. 4. The use of aluminum or aluminum alloys in the  presence of steel that has been allowed to rust requires special consideration. Research by the U.S. Bureau of Mines and others has shown that aluminum impellers rubbing on rusty steel may cause high intensity sparking. 5. All structural components within the airstream, including non-metallic materials, must be suitable for conducting static charge safely to ground, thus  preventing buildup of electrical electrical potential. Dampers with non-metallic bearings must include means by manufacturer of transferring electrical charge from the blades to suitable ground.

The use of the above Standard in no way implies a guarantee of safety for any level of spark re sistance. “Spark -resistant -resistant construction also does not protect against ignition of explosive gases caused by catastrophic failure or from any airstream material that may be present in a system.”  system.”   This Standard applies to: Centrifugal Fans; Mixed Flow Fans, Axial and Propeller Fans; Power Roof Ventilators and Dampers. This Standard applies to ferrous and nonferrous metals. The potential questions which may be associated with fans constructed of FRP, PVC, or any other plastic compound were not addressed.

 

 

THE LIMITATIONS OF SRC The AMCA standard provides the system designer with a uniform way to specify the system requirements and provides fan manufacturers with general guidelines. The fan manufacturer must still develop unique designs to deal with the physical and  practical limitations of fan equipment when developing construction methods to comply with AMCA. A major limitation is the practical availability of truly “nonferrous” alloys that really can be used in fan construc tion. There are certain alloys or noble metals than are truly nonferrous, alloys that contain no iron, but for the most part they are extremely expensive and/or difficult to obtain in forms and strengths necessary for fan construction. For most purposes, the fan manufacturer uses more readily available alloys that are considered nominally nonferrous and which have strength and work properties suited to fan construction. The The New York Blower Company’s list of usable alloys is shown in Figure 1. Alloy Aluminum 5052* Aluminum 6061* Brass CDA 360 Bronze CDA 958 Co er CD CDA A 110 110 or 122 122 Monel 400 Shafting

% FE (iron) 0.45 0.70 0.00 4.75 0. 0.00 00 2.50

 Note: Alternate alloys may be substituted; not to exceed 5% iron content. Hardware, such as setscrews or keys, may have an iron content greater than 5% provided they are recessed and relatively inaccessible. * Iron content in most aluminum alloys is actually a random contamination and not a predicted element of the alloy. Figure 1 - Spark-Resistant Alloys used by nyb

fastening the wheel to the shaft and locking the shaft in the  bearings are sufficient. However, the degree of hazard in these situations dictates that extraordinary precautions to more securely prevent such shifting are in order, so further methods of attachment or restraint are required. The following types of SRC are furnished by The New York Blower Company. These types meet the AMCA Standard, but go a step further by explaining the specific construction methods used to achieve SRC. NEW YORK BLOWER SRC STANDARDS AIRSTREAM-TYPE SRC - (ANSI/AMCA Standard 99-16, Type A) to include all airstream parts constructed of a sparkresistant† alloy. Bearing stop blocks and/or an aluminum shaft sleeve shall be provided to prevent contact of the shaft with the housing at the shaft opening. Shaft set collars shall be provided to prevent axial movement of the shaft through the bearings. The fan wheel shall be secured to the shaft in such a manner that it cannot shift axially on the shaft. WHEEL-TYPE SRC - (AMCA Standard 99-16, Type B) to include the wheel constructed of a spark-resistant† spark- resistant† alloy, and a  buffer around the housing shaft opening. Bearing stop blocks and/or an aluminum shaft sleeve (in lieu of buffer) shall be  provided to prevent contact of the shaft with the housing at the shaft opening. Shaft set collars shall be provided to prevent axial movement of the shaft through the bearings. The fan wheel shall  be secured to the shaft in such a manner that it cannot shift axially on the shaft. BUFFER-TYPE SRC - (AMCA Standard 99-16, Type C) to include buffers constructed of a spark-resistant† spark- resistant† alloy attached to the housing interior adjacent to the wheel front and back. Fan designs which incorporate a conical inlet venturi within the confines of the housing shall utilize a spun-aluminum venturi in lieu of a separate buffer on the inlet side. A buffer will also be located at the housing shaft opening.

Aluminum is the most frequently used alloy due to its low cost. However, as pointed out in the AMCA Standard, when aluminum is in close proximity to steel, careful maintenance programs are necessary to prevent rust, because aluminum rubbing against rusty steel can cause high-intensity sparking. In applications where such maintenance is not possible, an SRC method that places steel in the airstream is not recommended.

† The term “spark -resistant alloy” may include, but is not limited to, those alloys shown in Figure 1.

Regardless of which classification is chosen, airborne foreign or “tramp” particles “tramp”  particles could either strike each other, or strike one of the components of the fan, causing a spark. Protection against such occurrence cannot be built into the fan itself.

Of these types, a fan furnished with AIRSTREAM-TYPE SRC should provide the greatest degree of spark resistance. In the event that two or more fan components in the airstream rub or strike together, a properly maintained fan should be able to continue in operation for some reasonable period of time, without producing a spark. However, the severity of a hazard that calls for AIRSTREAM-TYPE SRC dictates that the fan should be closely monitored and shut down immediately upon such an occurrence. If allowed to operate, the rubbing or striking of these fan components will generate frictional heat, quickly deteriorate, and eventually catastrophically fail. Good safety practice cannot be ignored!

SRC does not eliminate the potential for spark generation. Fans with any type of SRC are only intended to minimize the  potential that any two or more fan components might generate sparks within the airstream by rubbing or striking during operation. No type of SRC can be guaranteed to eliminate the  possibility of generating a spark, nor would any SRC type  preclude sparks resulting from any foreign influence such as airborne materials striking each other. The AMCA Standard requires construction that will not permit a wheel and/or shaft to shift due to some malfunction during operation. If two components are allowed to shift and rub against each other for any length of time, either sparks or frictional heat could become a hazard in an explosive or

WHAT THE NYB SRC TYPES OFFER AND HOW THEY ARE ACCOMPLISHED One or more of these SRC types are offered on most New York Blower fans as indicated in the specific literature describing those fans.

A fan furnished with WHEEL-TYPE SRC differs from AIRSTREAM-TYPE SRC in that only the wheel itself is constructed of a spark-resistant alloy. A spark-resistant buffer is added around the housing opening through which the shaft  passes as shown in Figure 2. The remainder of the fan components are furnished in their standard material, usually

flammable gas stream. Normally, standard procedures of

 

mild steel.

Page 2

 

Figure 3  –  Bearing  Bearing Stop Blocks/Shaft Set Collars

Figure 2  –  Spark  Spark Resistant Buffer

Fans furnished with WHEEL-TYPE SRC should not continue in operation for any length of time with the wheel rubbing any component or with the shaft striking the buffer. Practically speaking, it is not possible to predict a “safe” length of time, because there may be other ferrous components within the fan airstream which could be torn or  jarred loose by the rubbing or striking of the wheel or shaft, and such loose ferrous objects could create a spark. Also, the  buffer cannot support the weight or withstand the forces of the rotating shaft for any prolonged period of time. The AIRSTREAM-TYPE and WHEEL-TYPE SRC specifications go further to minimize the potential for sparking by taking extraordinary precautions to minimize the potential for abnormal movement or shift of the fan’s airstream components. While the standard bearing mounting bolts will resist vertical or axial movement, the addition of bearing stop blocks will resist horizontal movement and effectively secure the bearings in place. The addition of shaft set collars as shown in Figure 3 will further resist shaft movement through the bearings. These combined features virtually eliminate the possibility of any movement in the shaft and bearing assembly. There are many ways to secure the fan wheel to the shaft, but standard setscrews and keys are not enough for the more severe applications. Figure 4 details one alternative which includes a bolted aluminum wheel retaining plate on the end of the shaft. Other methods might include countersinking the shaft to accept a setscrew, sweat-fitting, or tapered bores to  prevent the wheel from slipping slippi ng on the shaft axially. axiall y. The  precise method wi will ll var vary y by fa fan n size and type. The BUFFER-TYPE SRC specifications utilize standard, usually mild steel, airstream component parts and employ spark-resistant plates or buffers to stop the wheel or shaft from coming into direct contact with other airstream components. A fan design which requires an inlet cone is usually furnished with an aluminum cone to act as the buffer on one side, as shown in Figure 5. Other designs might utilize a sparkresistant band or plate.

Figure 4 - Wheel Retaining Plate 

Figure 5 - Aluminum Inlet Cone (1), Steel Wheel (2)

The BUFFER-TYPE SRC is intended to provide a low cost alternative for non-critical applications. The user or specifier must exercise caution in selecting this type so that the safety of the installation is not compromised for the sake of initial cost. Generally, aluminum wheel construction is utilized for AIRSTREAM-TYPE AND WHEEL-TYPE SRC. Because the material strength characteristics of aluminum decrease sharply at elevated temperatures, it is not recommended for handling anything other than nonabrasive airstreams at less than 200°F. In cases beyond these limits, BUFFER-TYPE SRC may be the only readily available alternative. As with the WHEEL-TYPE SRC, fans furnished with BUFFER-TYPE SRC should not continue to operate for any length of time with the wheel or shaft rubbing the buffers. High speed fans will tend to wear away buffers more rapidly than slower speed fans, and thus BUFFER-TYPE SRC should be used with caution on high speed fans. The greater wheel tip speeds and shaft surface speeds, combined with their corresponding weights and forces, reduce the amount of time available to react. When a high speed fan application requires spark resistance  but AIRSTREAM- and WHEEL-TYPE SRC are not practical, The New York Blower Company will work with the system designer to provide special spark-resistant features on a case  by case basis. ba sis. Periodic inspection of the fan, and particularly the airstream, is recommended. The build-up of foreign material or rust, the  potential  potenti al deteri deterioration oration due to abrasion or corrosio corrosion, n, or the accidental shifting of any fan part could lead to further hazards of potential ignition or explosion.

 

Page 3

 

The centrifugal fan arrangements most compatible with the intended use of SRC are those in which the wheel is overhung on the shaft and the bearings are outside the airstream. Such arrangements include Arrangements 1, 8, 9, and 10 as described in ANSI/AMCA Standard 99-16 (pages ( pages 52-54). One item mentioned in the AMCA Standard for SRC is that the user must electrically ground all fan parts. This is necessary so that any electrical charge or static electricity that might  build up in operatio operation n can be safely conducted away. Though there is probably sufficient electrical conductivity through most bearings to transmit any static charge to the bearing  pedestal, brush type contacts on the pedestal may be a good added precaution. The pedestal can then be suitably grounded to the support structure. Steps should be taken by the user to ensure electrical conductivity to the connecting ductwork.

WHERE TO AVOID ATTEMPTING SRC The basic requirement that bearings should not be placed in hazardous airstreams eliminates several centrifugal fan arrangements from consideration. Single-width or doublewidth fans in either Arrangement 3 or Arrangement 7, where the fan bearings are located in the inlet, should not be furnished for such service. See Figure 7.

AXIAL FANS AND SRC Propeller Fans, Duct Fans, Vaneaxial Fans, and Tubular Centrifugal Fans have the common difficulty of placing the  bearings, and sometimes the drive dri ve components, either directly in the airstream or in an inner tube construction that is located within the airstream as shown in Figure 6.

Figure 7 - Arrangement 3 Double-Width Fan

CONCLUSION Moving explosive or flammable gas streams through fans requires the utmost care in system design and equipment selection. The system designer must weigh the total system from all angles to minimize risk, particularly when the system components and/or fans are in environments that are located in areas where people are likely to be working or passing.

Figure 6  –  Vaneaxial  Vaneaxial Fan

The New York Blower Company offers WHEEL- and BUFFER- TYPE SRC on its Duct, Tubeaxial, Vaneaxial, and Tubular AcoustaFoil fan lines. BUFFER-TYPE SRC on these fans requires bearings and drive components to be isolated from the airstream. To accomplish this, the fans are furnished with shaft seals and all airstream  junctions  junctio ns are continuously continuousl y welded and/or gasketed with suitable material. To prevent a shift of the impeller and/or shaft, a ceramic-felt shaft seal with retaining plates constructed of copper is used. For Tubeaxial and Vaneaxial fans, an aluminum wheel is also required. On the Duct Fan, a partial aluminum wheel is used. WHEEL-TYPE SRC utilizes all of the modifications of BUFFER-TYPE SRC. The addition of a wheel retainer, set collars, and bearing stop blocks help prevent a lateral or axial shift of the wheel, bearings, and shaft. FIBERGLASS-REINFORCED PLASTIC AND SRC Centrifugal fans made of FRP material present an excellent degree of spark resistance as FRP materials are nonsparking. However, FRP is also a nonconductor so the possibility of  building and retaining a stati staticc charge is greater and must be accounted for. Adding graphite to the final resin finish will  provide the necessary conducti conductivity vity to alleviate alleviat e this situation. situati on. The special construction features of FRP fans may also call for

The explosiveness of the gas mixture, the people factor, and the potential for foreign or “tramp” elements to enter e nter the system, are all necessary concerns in determining to what degree special-material construction should be used. Vibration detectors to warn of impending malfunction of bearings or rotating assemblies are a good preventive measure to forestall the actual rubbing or impact of two parts in any mechanical equipment, and should certainly be considered in “severe risk” situations. The extraordinary measures to pre-vent wheelSRC and shaft movement offered in nyb ’s   AIRSTREAM-TYPE nyb’s and WHEEL-TYPE SRC are features to help minimize the  potential  potenti al of allowing a llowing ttwo wo part partss to st strike. rike. The three classifications of spark-resistant construction in AMCA’s Standard and the specific construction methods offered by New York Blower provide only degrees of resistance to sparking. They have been used, and are continuing in use, as deterrents to possible sparking and ignition in hazardous systems. Care must be taken to recognize that there are no absolute guarantees. Therefore, in particularly hazardous applications, the location of the fan and perhaps the entire system should be a major consideration. In some cases, protective enclosures around the fan or other mechanical parts in the system may be another  protective  protect ive step to lessen the danger in the event that a spark might occur in spite of the precautions taken. The system designer is in the best position to weigh the alternatives and specify the required fan equipment. Form JLK 318

other considerations in dealing with hazardous fumes. See Engineering Letter 20.

 

 

ENGINEERING LETTER   1 6 The New York Blower Company

●

 7660 Quincy Street, Willowbrook, Illinois 60521-5530 

CORROSION-RESIS ION-RESISTANT TANT COATINGS FOR FA N EQUIPMENT CORROS INTRODUCTION A flow is combined with the binderthe to form thecontrol liquid agent, portionorofsolvent, the coating. The solvent prevents This Engineering Letter provides basic information regarding  binder from solidifying prematurely and ensures uniform the different types of corrosion-resistant coatings readily dispersion over the surface. This combination of binder and available for fan equipment. The coatings are described here solvent is called the vehicle portion of the coating. according to generic classifications having similar characteristics such as curing methods, adhesion qualities, chemical resistance, and temperature limitations. Coating manufacturers offer a The pigment is any substance, usually a powder, which gives variety of brand name coatings which can be categorized by color to the mixture. Most pigments are insoluble in solvents and are not affected by the vehicle portion of the coating. these generic classifications classifications..

The service life of air-moving equipment constructed of carbon steel may be significantly reduced when corrosives are allowed to attack the surface of the metal through chemical or electrochemical action. One method of inhibiting this corrosive action is  by applying a protective coating to the area in contact with the corrosives. Protective coatings act as a barrier between the corrosive and the parent material. A wide range of protective coating systems is available to provide protection from a variety of corrosives including acids, alkalis, solvents, salts, and oils. Although other materials of construction, such as special alloys (see Engineering Letter 14) and fiberglass-reinforced plastic FRP (see separate Engineering Letters) are available, protective coatings can offer a low-initial-cost solution to the corrosion  problem.

The generic coating classifications are differentiated by their chemical composition. While the chemical composition alone is not sufficient in determining which protective coating is selected selected for a specific application, it can be useful in determining the generic group of a particular brand name coating.

COATING INGREDIENTS

wide variety of concentrated acids at temperatures to 150°F. airdried or 400°F. baked.

COATING TYPES

The following descriptions of generic coatings present curing methods, adhesion qualities, chemical resistance, and temperature limitations. limitations. This information can be used as a guide to specifying and selecting corrosion-resistant coatings for fan equipment. For chemical resistance resistance to specific applications refer to the Corrosion-Resistance Table beginning on page 3.

Phenolic - resin systems include any of the several types of thermosetting resins obtained by the condensation of phenol or The selection of a protective coating is critical in determining substituted phenols with aldehydes, such as formaldehyde, the service life of the equipment. The selection process must acetaldehyde, or furfural. Phenolic resins can be cured by consider the actual chemical composition of the gas stream. To  baking, air-drying, or catalyzation. These curing processes evaluate the corrosive nature of the gas stream completely, the remove the solvents and oxidize the oils contained in the resin to concentrations and temperatures of the chemicals present must  produce coatings with an extremely hard finish. Phenolic also be considered. coatings possess excellent resistance to moisture, solvents, and a

Although protective coatings are differentiated by their specific Epoxy - coatings are derived from a thermosetting resin based chemical composition, the most common consist of three basic on the reactivity of the epoxide group. The most common form ingredients; a binder, a flow control agent, and a pigment or of this resin stems from a reaction between epichlorohydrin and filler. When these ingredients are combined, they can range in  bisphenol A. Another type is formed from the oxidation of consistency from thin liquids to semi-solid pastes in a variety of  polyolefins with peracetic acid. Epoxy resins can be cured by colors.  baking or catalyzing. When cured, these coatings have a supple The binder is the film-forming ingredient in the coating. It finish and superior adhesion qualities. Epoxy coatings are consists of either a drying oil o il or a polymeric substance. characterized by their excellent resistance to a variety of corrosive chemicals, including acids, alkalis, and salts with Drying oils form a hard film by reacting with oxygen in the air. temperature limitations between 200°F. and 300°F. Epoxy Coatings with this type of binder are usually cured by air drying coatings are not resistant to ultraviolet radiation and will “chalk”  but in some cases may be baked in order to cure more rapidly. when exposed to the sun. Coatings that utilize a polymeric substance as the binder require a “thermoset” cure. Thermosetting can be accomplished by Epoxy-Phenolic - coatings are modified phenolic coatings  baking the applied coating in some cases or by adding a catalyst created by blending phenolic resins with resins from the epoxide in other cases. The type of thermoset is dependent upon the group. Epoxy-phenolics can be cured by baking or by the utilization of a catalyst. Catalyzed epoxy-phenolic coatings characteristics of the polymeric substance itself. require a longer curing time and have lower chemical resistance than the baked epoxy-phenolic coatings. They can be applied in

 

 

greater thickness to attain virtually the same performance characteristics as the baked epoxy-phenolic coatings. These coatings are used mainly for alkali-resistance in moderate temperatures up to 400°F. Inorganic Zinc - coatings are formulated by adding zinc dust to inorganic binders. These binders give the zinc coatings their corrosion-resistant qualities, while the zinc adds cathodic  protection (alters the rate of electron flow which can produce corrosion) to metals below it in the galvanic series. (However, the zinc-rich coatings are not recommended for use over

aluminum substrates.) These coatings, which are cured by airdrying, are not subject to ultraviolet degradation and may be used without a top coat for severe weathering conditions. The inorganic zinc coatings have good solvent-resistant properties,  but may require an appropriate protective top coat for acid or alkali-resistant applications. Inorganic zinc coatings are suitable for temperatures to 750°F. Vinyl - coatings use resins from the vinyl-resin family as the major portion of the binder. These resins are formed by a reaction between acetylene and an acid. They consist largely of vinyl acetate, vinyl chloride, and vinyl copolymer. Vinyl coatings can be cured by baking or air-drying, and have excellent adhesion qualities to steel. As the vinyl dries, the film remains non-brittle and will easily follow the expansion and contraction of the underlying surface. Vinyl coatings are unique in that they possess superior corrosion-resistant performance over a  broad range of corrosive combinations. The vinyl coatings will give satisfactory results for most corrosive fume applications  below 200°F., but are not recommended for solvent-laden environments. Coal Tar Epoxy - coatings are formed by combining coal tar, a  black liquid obtained from the distillation of coal during the conversion of coke, and a resin from the epoxide group. These coatings, which are cured by air-drying or catalyzing, adhere well to metal surfaces. The blend of coal tar and the epoxy resin forms a coating which has good water-resistance characteristics and is resistant to acids and alkali fumes at temperatures to 250°F. Alkyds are fatty actually a type polyester modified addition- of acids or of drying oils.resin These resins by arethea  product of the thermosetting reaction between polyhydric alcohol and a poly-basic acid. Alkyd resins are cured by catalyzation or air-drying. They have the ability to harden at room temperatures in a very short time. These coatings are not generally selected or specified for corrosion-resistant applications, but are normally required for color-matching  purposes. Silicone - coatings are polymeric silicones formed by heating silicon in methyl chloride to yield methylchlorosilanes which are separated and purified by distillation. The desired compound is then mixed with water. Silicone coatings can be cured by baking or air-drying. Formulated for medium to high temperature service where temperatures seldom fall below 200°F. to 300°F., these coatings normally exhibit good to excellent fume resistance to acids, alkalis, solvents, salts, and water, but are not recommended for areas subjected to acid or alkali splash or spillage. Silicone coatings possess good 

weathering characteristics, but an inorganic zinc primer will greatly extend the coating’s service life when applied to steel, especially if service temperatures fall below 300°F. and moisture is present. The maximum temperature limitation for these coatings varies according to each specific manufacturer’s recommendation. Polyurethane - coatings are derived from prepolymers containing isocyanate groups and hydroxyl containing materials such as polyols and drying oils. Polyurethane coatings, which are cured by air-drying or catalyzing, are

frequently appliedan over zinc hard, and yet epoxy primers. coatings produce extremely flexible, high These gloss finish that is resistant to weathering, ultraviolet degradation, acids, and alkalis at temperatures to 200°F. Polyester - resins are thermosetting synthetic resins formed by the polycondensation of dicarboxilic acids and dihydroxy alcohols. Polyester resins are characterized by their ability to cure at room temperatures in a very short time after being catalyzed. They also have excellent adhesion qualities. The  polyester coatings are resistant to mild traces of acids, alkalis, and solvents. The maximum temperature limitation for these coatings varies according to each specific manufacturer’s recommendation. Vinyl Ester - resins are combined with a special curing system and inert flake pigment. Vinyl ester coatings, which are cured  by air-dryin air-drying g or catalyzing, catalyzing, provide provide exce excellent llent chemic chemical al resistan resistance ce to organic and inorganic acids, oxidizing agents, salts, and a wide range of solvents. Vinyl ester coatings are applied at 35 to 40 mils DFT.

Although these coatings cover a broad range of generic types, they by no means cover them all. Types mentioned here are the most commonly specified and selected generic types offered for use on fan equipment. Selecting the proper coating system for the application is not enough to ensure its success. Proper surface preparation is essential to the effectiveness of any coating system. COATING SURFACE PREPARATION

Surface preparation not only ensures that the coating will adhere adequately but also removes contaminants which could  be detrimental to the service life of the equipment. The Steel Structures Painting Council further defines various types of surface preparation as shown in Engineering Letter 17. Coating manufacturers then suggest the recommended degree of surface  preparation for each of their brand br and name coatings. coatin gs. Based on the surface preparation necessary for each coating specification, nyb will either apply the coatings in its facilities or have them sent to an outside applicator. Most coatings applied by nyb receive a combination of phosphate wash and hand tool cleaning. This procedure removes all oil, dirt, grease, loose rust, and mill scale that hinders the effectiveness of the coating. This method of surface preparation is equivalent to a combination of Solvent Cleaning (SSPC-SP1) and Hand Tool Cleaning (SSPC-SP2). The application of a coating which requires any degree of sandblasting is handled by an outside applicator. Sandblasting is further defined in Engineering Letter 17.

Page 2

   

Airstream, exterior, and all surfaces are common area requirements for coatings. Airstream surfaces coated includes interior of housing, entire wheel, that portion of the shaft in contact with the airstream, airstream areas of collar, inlet ring and/or inlet plate, and all surfaces of the inlet cone. Exterior surfaces coated - includes all outside surfaces, except bearings, motor, and the shaft. All surfaces coated includes all surfaces inside and outside, except bearings, motor, and that portion of the shaft not in contact with the airstream APPLICATION AND SELECTION GUIDE

coating which will provide proper protection. nyb can only warrant that the coating will be applied according to the coating manufacturer’s instructions.

The table below provides a condensed guide to the corrosionresistant properties of generic coatings commonly available on fan equipment. Each coating should be chosen according to the specific corrosive chemical or chemicals involved in the application. The customer is responsible for selecting the

Protective coatings play an important role in corrosion-resistant construction. They often have the lowest first cost. Special alloy and fiberglass-reinforced plastic construction are also available for corrosive applications. Special alloy and FRP construction are able to handle a wider range of corrosives, are far superior when it comes to corrosion resistance, and many times result in the lowest life cycle cost.

Fume-and aerosol-contaminated air has been used as the basis for this guide. The fumes or aerosols of a substance are effectively diluted by air, reducing the chemical concentration to a level significantly lower than the liquid solution. Because this guide is based on dilute concentrations of fumes and aerosols, relatively few chemicals are listed as unsatisfactory for use with w ith these protective coating systems.

CORROSION-RESISTANCE CORROSION-RESIST ANCE GUIDE TO GENERIC COATINGS AND A SSORTED METALS COA TINGS

Corrosive  Agent  Ag ent  

  c    i    l   o   n   e    h    P    d   e    k   a    B

  c      i    l   y   x   c   d   o   c   d    d   i    i   e   n   y   o   e   l   e   z   e   z   p   l    i   x   o   r   y   h   y   o   E  o   n   l   n   l    d   -   e   t   a   P   a   p   d   e   t     r    i    h   a   E   e   h   a   y    A   P   C    k   P   C  x   o   a   p    E    B

  c   n    i    Z   c    i   n   a   g   r   o   n    I

   l   y   n    i    V    d   e    i   r    d     r    i

META L S

   d   y    k    l    A

   A

  y   x   o   p    E   r   a    T    l   a   o    C

   d   e   e   n    i   r   o    d   c   -   i   r   l    i    i    A   S

  e   n   a    h    t   e   r   u   y    l   o    P

  r   e    t   s   e   y    l   o    P

  r   e    t   s    E    l   y   n    i    V

   l   e   e    t    S   n   o    b   r   a    C

    m   u   n    i   m   u    l    A

   l    l   e   e   e   e    t    t      S    S           *    *   s            *   s    4   s   6   s    0   e   1   e    3   l    3   l   n   n    i    i   a   a    t    t    S

   S

 Acetic Acid Acid  Acetic Anhydride Anhydride  Acetone

E E E

N N N

N N S

T T S

N N S

N N E

E E N

N S N

N N N

S S S

N N E

E N N

E S N

N N E

S E E

S S E

E E E

 Acetylene  Aluminum Acetate Acetate  Aluminum Chloride (dry)  Ammonia (dry)  Ammonia (wet)  Ammonium Sulfite Sulfite  Aniline Barium Chloride Benzene Boric Acid Bromine Water Butane Calcium Chloride Carbon Tetrachloride (dry) Chlorine Gas (dry) Chlorobenzene Citric Acid Copper Sulfate Cyclohexanone Ethyl Acetate Ethyl Alcohol Ethylene Dichloride Ethylene Oxide Ferric Chloride Ferric Nitrate Fluorine Gas (dry) Formaldehyde

E E E E E E E E E E N E E E S S E E E E E E S S S N E

E E S S N S S S N E N S E E S N E S N N S N N S S N E

S N S N N S N S S S S N E N S N N S N S S N N E N N S

S S E E E S T E E E N E E E T E S E S S E S T E T T E

E N S S S S N E S E N S E S S S E E N S S S N E S N S

E S N N N N E S E N N S N S N S N S S S E S E S N N E

S S S N N N S E N E N S E N N S E E S S S N S E S S E

T T S S N S N S N S S T S S S N S S N S S N N S T T N

N N S N N N N N N N N S N N N N N N N N N N N N N N N

S S S S N S S S S S N S S S S S S S S S S S S E S S S

S S S S S S S S S S S S E S S S S S S S S N N S S N S

T S E S N S S S S S S T E S N S S S S N S S N S T T N

E E E E E E S E N E S E E S E S E E S E S N N E E E S

S T N S S N N N N N N E N S S S N N N S S S S N N N S

E S S E E N N N S S N S S N N S S N S S S S S N N E S

E E N E E S E E E E N E S S S S E E S E E E S N E E E

E E S E E E E E E E N E S E S S E E S E E E S N E E E

E = Excellent S = Satisfactory N = Not Recommended * 347 stainless steel has the same corrosion-resi corrosion-resistance stance characteristics characteristics as 304 stainless steel. ** Alloy 2205 has similar similar corrosion-re corrosion-resistance sistance cha characteristics racteristics as 316 stainless steel.

T = Test data not available

The suitability of the coatings found in this table has been based on fume concentration effectively diluted by air at 70°F. High 

chemical concentration and/or elevated temperatures and/or moisture may significantly reduce a coating s suitability. Page 3  

CORROSION-RESISTANCE N-RESISTANCE GUIDE TO GENERIC COATINGS AND ASSORTED METALS CORROSIO COA TINGS Corrosive  Ag ent  

  c    i    l   o   n   e    h    P    d   e    k   a    B

  c      i    l   y   o   x   c    d   c    d    d   i   e   n   e   y   o   i   e   l   z   e   p   l    i   o   z   r   o   y   x    E   y   h   n    l   n    l   o    d    P     a     a   p    d   e    t   e    t   r   h    i   a   E   e   h   a   y    k   P    C  x    A   P    C   o   a   p    B    E

META L S

  c   n    i    Z   c    i   n   a   g   r   o   n    I

   l   y   n    i    V    d   e    i   r    d     r    i    A

  y   x   o   p    E   r   a    T    l   a   o    C

  e   n    d   e   a   e   n    h    d    i   r   o    t   y    k   c   e   r    l    d      l   u   r   i    i    A    i   y    A   S    l   o    P

  r   e    t   s   e   y    l   o    P

  r   e    t   s    E    l   y   n    i    V

   l   e   e    t    S   n   o    b   r   a    C

    m   u   n    i   m   u    l    A

   l    l   e   e   e   e    t    t      S    S            *            *    *   s    6    4   s    1   s    0   e    3   s   e    3   l    l   n   n    i    i   a   a    t    t    S    S

Formic Acid

S

N

N

N

N

N

N

N

N

S

S

N

E

N

N

S

E

Gasoline Glycerine Hydrochloric Acid Hydrofluoric Acid Hydrogen Peroxide Hydrogen Sulfide (dry) Hydrogen Sulfide (wet) Iodine Lactic Acid Magnesium Carbonate Mercuric Chloride Methyl Alcohol Methyl Ethyl Ketone Mineral Oil Moisture Naptha

E E E N N E S E E E E E E E E E

S E S N N S N T S E E S N E E E

S E N N S S N N S E E N S E E S

E E S N N E S T S E E E S E E E

E S S N N S N N E E E S N E E S

E S N N N N N N N S S E E E E E

S S S S S E N N E E T E N E E N

N S N N N S S N S S S N N E E S

S N N N N N N N N S N N N S E S

S S S N S S N S S S S S S S S S

E S S N S S N T S S E E E E E S

S S N N S S N S S S S S N S E S

E E E S E E E E E E E S N E E S

E S N N N S N N N N N S S S S S

E E N N E S S E S S N S S S S E

E E N N E S N N S E N E E E E E

E E N N E E S N E E N E E E E E

Nitric OzoneAcid Perchloric Acid Phenol Phosphoric Acid Polyvinyl Acetate Potassium Chloride Potassium Cyanide Potassium Dichromate Potassium Hydroxide Pyridine Salt Spray Silver Nitrate Sodium Bicarbonate Sodium Chloride Sodium Cyanide Sodium Dichromate Sodium Hydroxide Sodium Hypochlorite Sodium Sulfate Steam Vapor Sulfamic Acid Sulfur Dioxide (dry) Sulfur Dioxide (wet) Sulfuric Acid Tannic Acid Toluene Trichloroethylene Xylene Zinc Chloride Zinc Sulfate

E N S E E E E E S N E E E E E N N N N E E E E E E E E E E E E

N N N N S N S S S N T S S E S S S N N S N S S S S E N N N S S

N N N S N E N N N S N E N S E S S S N S S S S S N S E N E S S

N N S S S T E E E N E E T E E S S S N E E T S S S T E E E E E

N N N N S N E S S S N S N E E S N N N E N S S N S E N N S E E

N S N S N N S N S S S E N N S N S S N N N N N N N N E S E N N

S S E S E N S S S E T E E E E S S E N E S S N N S E N N N E E

N N N N N T S S S S N E T E E S E S S S S S S S N E S N S S S

N N N N N N N N N N N S N S S N N N N N S N N N N N N N N S S

S S S S S S S S S S S E S S E S S N N S E S S N S S S S S E S

N N N S E T S T S S N E S S S S S E S S N S T T E S E N E S S

S T S S S N S S S S N S T S S S S S N S S S S N N T S N S S S

S S S S E E E E E E N E E E E E S E E E E S E S E E S N E E E

N N N S N N S S S S S N N N N S S S N S S N E N N N E S S N N

N S N E N T N N E N S S N S N N S N N E S N S N N N E S E N S

E S N E S E S E E E S S E E S E S E N E E T S N N S E S E N E

E S N E E E E E E E S S E E E E S E N E E S E S S E E S E S E

E = Excellent

S = Satisfactory

N = Not Recommended

T = Test data not available

* 347 stainless steel has the same corrosio corrosion-resistance n-resistance characteristics characteristics as 304 stainless ste steel. el. ** Alloy

2205 has similar similar corrosi corrosion-resistance on-resistance c characteristic haracteristics s as 316 stainless steel.

The suitability of the coatings found in this table has been based on fume concentration effectively diluted by air at 70°F. High

chemical concentration and/or elevated temperatures and/or moisture may significantly reduce a coating s suitability. Form

JL K   31 8 

 

ENGINEERING LETTER  

1 7 

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60521-5530 

SPECIFICATIONS COATING SURFACE PREPARA TION SPECIFICATIONS INTRODUCTION

This Engineering Letter is intended to be an aid for selecting the  proper surface preparation specifications for a given application. It also provides a better understanding of the Steel Structures Painting Council (SSPC) surface preparation specifications, which are the most commonly used. In addition, surface preparation standards published by the National Association of Corrosion Engineers (NACE) are crossreferenced where applicable. The life of a coating depends as much on surface preparation as on the subsequent coating system. Surface preparation, therefore, requires thorough consideration. The primary functions of surface preparation are:

  To remove surface contaminants and imperfections, such as oil, grease, dust, rust, weld spatter, etc., that will affect the performance of a coating.



  To provide an anchor pattern or surface profile which improves the mechanical bonding of a coating to the  prepared surface by increasing the surface area.



 Note that all coating systems will fail eventually. However, most premature coating failure can be attributed to inadequate surface preparation or lack of coating adhesion.

SUMMARY OF COMMON SURFACE PREPARATION SPECIFICATIONS SSPC STANDARD

DESCRIPTION

SP1 - SOLVENT CLEANING

Removal of oil, grease, dirt, soil, salts, and contaminants by cleaning with solvent, vapor, alkali, emulsion, or steam.

SP2 - HAND TOOL CLEANING

Removal of loose rust, loose mill scale, and loose paint by hand chipping, scraping, sanding, and wire brushing.

SP3 - POWER TOOL CLEANING

Removal of loose rust, loose mill scale, and loose paint by power tool chipping, descaling, sanding, wire brushing, and grinding.

SP5 - WHITE-METAL BLAST CLEANING

Removal of all visible rust, mill scale, paint, and foreign matter by blast cleaning. (For very corrosive atmospheres where the high cost of cleaning is warranted).

SP6 - COMMERCIAL BLAST CLEANING

Blast cleaning until at least two-thirds of the surface area is free of all visible residues. (For conditions where thoroughly cleaned surface is required).

SP7 - BRUSH-OFF BLAST CLEANING

Blast cleaning of all except tightly adhering residues of mill scale, rust, and coatings, exposing numerous evenly distributed flecks of underlying metal.

SP10 - NEAR-WHITE BLAST CLEANING

Blast cleaning until at least 95% of the surface area is free of all visible residues. (For high humidity, chemical atmosphere, marine, or other corrosive environments).

SP14 – INDUSTRIAL BLAST CLEANING

An industrial blast cleaned surface, when viewed without magnification, shall be free of all visible oil, grease, dust, and dirt. Traces of tightly adherent mill scale, rust, and coating residues are permitted to remain on 10% of each unit area of the surface if they are evenly distributed.

 

SSPC-SP1, “SOLVENT CLEANING”

SSPC-SP6, “COMMERCIAL BLAST CLEANING”

This specification includes simple solvent wiping, immersion in solvent, solvent spray, vapor degreasing, steam cleaning, emulsion cleaning, chemical paint stripping, and alkaline cleaners. Solvent Cleaning is used primarily to remove oil, grease, dirt, soil, drawing compounds, and other similar organic compounds.

The most common type of blast cleaning should be employed for all general purposes where a high, but not perfect, degree of  blast cleaning is required. It will remove all rust, mill scale, and other detrimental matter from at least two-thirds of the surface area. The advantage of Commercial Blast Cleaning lies in the lower cost for satisfactory surface preparation for the majority of cases where blast cleaning is believed to be necessary. If the cleaning done according to this specification is likely to result in a surface unsatisfactory for severe service, then Near-White

SSPC-SP2, “HAND TOOL CLEANING”

Hand Tool Cleaning is an acceptable method of surface  preparation for normal atmospheric exposures, for interiors, and for maintenance painting when using paints with good wetting ability. This specification includes hand chipping, scraping, sanding, and wire brushing. Hand Tool Cleaning is used primarily to remove loose rust, loose mill scale, and loose  paint after af ter all oil, gre grease, ase, and salts are removed aass specifi specified ed in SSPC-SP1, “Solvent Cleaning.”*

SSPC-SP3, “POWER TOOL CLEANING”

Power Tool Cleaning provides a better foundation for the  priming paint than Hand Tool Cleaning. This specification includes power tool chipping, descaling, sanding, wire brushing, and grinding. Power Tool Cleaning is used primarily to remove loose rust, loose mill scale, and loose paint after all oil, grease, and salts are removed as specified in SSPC-SP1 Solvent Cleaning.

SSPC-SP5, “WHITE-METAL BLAST CLEANING”

This blast cleaning method is generally used for exposures in very corrosive atmospheres and for immersion service where the highest degree of cleaning is required and a high surface  preparation cost is warranted. Blast cleaning by wheel or nozzle (dry or wet) using sand, grit, or shot to white metal will result in high performance of the paint systems due to the complete removal of all rust, mill scale, and foreign matter or contaminants from the surface. In ordinary atmospheres and general use, White-Metal Blast Cleaning is seldom warranted. Meets requirements of NACE Standard #1.

Blast Cleaning (SSPC-SP10) or White-Metal Blast Cleaning (SSPC-SP5) should be specified. Meets requirements of  NACE Standard #3.

SSPC-SP7, “BRUSH-OFF BLAST CLEANING”

This method of blast cleaning should be used when the environment is mild enough to permit tight mill scale, paint, and minor amounts of tight rust and other foreign matter to remain on the surface. The surface resulting from this method of surface preparation should be free of all loose mill scale and loose rust with the small amount of remaining rust serving as an integral part of the surface. Brush-off Blast Cleaning is not intended for very severe surroundings. It is generally intended to supplant Power Tool Cleaning where facilities are available for blast cleaning. Meets requirements of NACE Standard #4.

SSPC-SP10, “NEAR-WHITE BLAST CLEANING”

This type of blast cleaning is generally employed for all general-purpose applications where a high degree of blast cleaning is required to remove all rust, mill scale, and other detrimental matter from at least 95% of the surface area. Exposures include high humidity, chemical atmosphere, marine, or other corrosive environments. Blast cleaning to near-white metal was developed to fill the need for a grade of  blast cleaning cleanin g beyond that th at of Commercia Commerciall (SSPC-SP6) but less than White Metal (SSPC-SP5). The advantage of Near - White Blast Cleaning lies in the lower cost for surface preparation that is satisfactory for all but the most severe service conditions. Meets requirements of NACE Standard #2.

SSPC-SP14, “INDUSTRIAL BLAST CLEANING”

This type of industrial blast cleaning is used when the objective is to remove most of the coating, mill scale, and rust,  but when the extra ex tra effort required require d to remove every ever y trace of these is determined to be unwarranted. The industrial blast allows defined mill scale, coating, and rust to remain on less than 10% of the surface and allows defined stains to remain on all surfaces. Meets requirements of NACE Standard #8. * nyb’s standard surface preparation is a high-pressure chemical wash followed by SSPC-SP2 - Hand Tool Cleaning or SSPCSP3 - Power Tool Cleaning as required.

Form 213 MJN  

 

ENGINEERING LETTER

18

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60521-5530

CORROSION RESISTANCE OF FRP FANS INTRODUCTION

TYPES USED BY nyb TYPES OF RESIN USED

Process applications involve a wide variety of corrosive gas streams. Sele Select ctin ing g the the best best ma mate teria rials ls of co cons nstru truct ctio ion n for for air air handl handlin ing g equipm equ ipment ent can be diff difficu icult. lt. This Eng Engine ineeri ering ng Lette Letterr prov provide idess inform informati ation on abou aboutt the corr corrosio osion n resist resistanc ancee of the resins use used d to manufacture standard  nyb  nyb  FRP fans.

All vinyl esters are corrosion resistant to some degree. The resin used by nyb by  nyb is  is at the highly resistant end of the scale of corrosion resist resistanc ance. e. (The oppos opposite ite end from gen genera eral-pu l-purpos rposee resi resins, ns, sometimes called  “boat   “boat resins”.) resins”.)

GAS STREAM TYPES

Standard FRP construction   consists of Derakane® 510A40, a top-quality chemical-duty vinyl ester made by Ashland, Inc. (See separate Engineering Letter for a full description of  nyb resins.)  nyb  resins.)

vapors rs evol evolved ved from acid acids, s, sol solven vents, ts, etc. An Fumes   are the dry vapo example is the dry acid vapor scavenged from a process using acid. As a generalization, fumes are not as corrosive as aerosols.

SURFACE VEIL

 are suspensions of liquids or solids in a gas stream. For the Aerosols are Aerosols  purpose of this discussion, aerosols are considered as being wet. Water as fog is an example of an aerosol. Another example is the mist ofused acidaspresent air scavenged from a process where acid is  being a sprayinwash. As a generalization for the purpose of  estima estimatin ting g corr corrosi osiven veness ess,, aerosol aerosolss in fan-dri fan-driven ven sys system temss can be co cons nsid ider ered ed as bein being g dilu dilute te conce concent ntra rati tions ons of the the che chemi mica cals ls composing the aerosols. An example example of the disti distinct nction ion betwe between en fume fumess and aeroso aerosols ls is a syst system em wher wheree sulfur sulfuric ic ac acid id fu fume mess are are colle collect cted ed by hoo hoods ds an and  d  sc scrub rubbed bed.. Th Thee dry fum fumes es en ente teri ring ng the the scrub scrubber ber co coul uld d be qui quite te concentrated but have a relatively mild corrosive effect on the hood  and duct material. On the other hand, the wet gas down stream from the scrubber could be quite dilute but more corrosive because of the  converting the fumes to an aerosol. scrubber’s converting scrubber’s CORROSION-RESISTANCE GUIDE

The corrosion-resistance guide presented in this Engineering Letter  is adapted from the literature published by the manufacturers of the resins used in the standard construction of  nyb FRP  nyb  FRP fans. The guide  provides data for aerosols being handled in fan-system gas streams. Dataa for chemic Dat chemicals als that that are pote potenti ntiall ally y dam damagi aging ng as aerosol aerosolss are marked  “fumes   “fumes only”. only”. Where the user is unsure of the nature of the chemicals involved, or  of the corrosive effect of the combination of chemicals involved, it is advisabl advisablee to insert insert resin test coupon coupons, s, as wel welll as coupons of   possible alternate materials of construction, into the gas stream for  observation.

Deraka Derakane® ne® is a reg regist istere ered d tra tradem demark ark of Ashland Ashland,, Inc Inc.. Nexus Nexus ® is a regist registere ered d tradem trademark ark of Pre Precisi cision on Fab Fabric rics s Gro Group, up, Inc Inc..

Standard   nyb   constru Standard   constructi ction on does not include include the use of surfac surfacee veil. Years of service prove this construction to be cost-effective and functionally successful. Howeve How ever, r, the the gene genera rall ap appro proac ach h to the the desi design gn of mos mostt FRP FRP chemic chemicalal-proc process ess equ equipm ipment ent,, such such as storag storagee tanks, tanks, is to use surfacee veil. Therefore surfac Therefore,, the ASTM stan standard dard specif specificati ication on for FRP Fans and Blowers, D4167, calls for a layer of surface veil on the inner surface of the fan housing. If required, nyb required,  nyb  will construct a fan with synthetic veil on the housing airstream surfaces to meet ASTM D4167. Synthetic Synthe tic veil such as Nexus®, a polyester veil made by Precis Precision ion Fabrics Group, Inc. and used exclusively by  nyb advantageouss  nyb,, is advantageou in helping to build a relatively thick surface layer (approximately 10 mils) that protects the glass structure from attack by chemicals that that are part particu icular larly ly aggr aggress essive ive tow toward ard glass. glass. Whe Where re the use of  synthetic synthe tic veil is advisable, the corrosi corrosion-resi on-resistance stance guide is so noted. For more information on surface veil and its uses, refer to Engineering Letter 21. CUSTOMER RESPONSIBILITY

nyb will will prov provide ide qual quality ity FRP con constr struct uction ion usin using g eit either her of the above resin types as specified by the customer. This Engineering Letter and any discussions between   nyb  representatives and the cu cust stom omer er shoul should d not be con const strue rued d as a warra warranty nty of ma mate teri rial al suitability for a particular application. The system designer should  have sufficient knowledge of, or experience with, the application to select the appropriate resin or alternate material.

 

CORROSION-RESISTANCE GUIDE TO FUME AND AEROSOL CONTAMINATED AIR FOR nyb FRP CONSTRUCTION AND ASSORTED METALS Metals

FRP

F

t

oi

n a

ur

e

R

n

in br ul

o a C C

R*n R N R R R N R R T R R³ R R R R RVn R R R R RV R R R R R Rn N R R R R R R R R Rn R R* N R R R N R* R R R T R* Rn X R N R R R

N N N N N N N R N R* N R* T R* T N N N R* R* N N N N N N N R* N N T N N N N R* N N N N N N N N R* N N N N R N R* T T T T T N

ol o

in

l M

at at S S 3

R R* R R R R* R N N R R R T T T R R R*

a

ur

R* R* R R* R* R* R* R R* R* T R* T R* R R* R* R* R* R R* N R* N R* R* R R R* T T T T T T T RT R* R T R* T R T R R* R* T N R T T T T T R* R* R

R R R R R** R* R* R R R R* N R* T R* R R R* R R* R T T T T R* R R R R* T T T T N R* R* R* R* R R R R** R* R* T R* N R R R R* T R* T T T R R R

in ul

n n o S

m br a

C

† These compounds are normally solids; considered here as being water solutions. R* - Recommended for fumes only. Care must be taken to prevent formation of condensate on wheel or in housing

y n ol o

in

l M

at at S S

te s a

6 4 0 3

Calcium Hydroxide Calcium Hypochlorite Calcium Sulfate† Carbon Dioxide Carbon Disulfide Vapor Vapor Carbon Tetrachloride Cascade Solution Chlorine Dioxide Chlorine Gas, Dry Chlorine Gas, Wet Chloroacetic Acid Chlorobenzene Chlorofluorocarbon Chloroform Chlorosulfonic Acid Chlorotoluene Chrome-Plating Bath Chromic Acid Chromic Acid + Sulfuric Citric Acid Cooling Towers Copper Chloride Copper Cyanide Copper Nitrate Copper Oxychloride Copper Sulfate† Cyclohexane DDT, Insecticide Solution Dichlorobenzene Dichloroethylen Dichloroethylene e Dichlorophenox Dichlorophenoxyacetic yacetic Dichloropropane Dichlorotoluene Diesel Fuel Diethyl Ether Diethyl Glycol Diethyl Ketone Diethyl Maleate: W ater Diethylbenzene Diisobutyl Ketone Diisobutylene Dimethyl Sulfide Dimethyl Sulfoxide Dimethylformamide Dimethylamine Dipropylene Glycol Divinyl Benzene Dodecene Dodecylbenzenesulfonic  Acid: H2SO4: H2O: oil Esters, Fatty Acid Ethanol Chloride Ether Ethyl Acetate Ethyl Alcohol Ethyl Acrylate Ethyl Benzene Ethyl Chloride

e le

A C

C

s le

o

2l

s in

s

7 s

s

n t

6 S

u S

d

H 1

et

e

m

c at

l et S

te

dr

s

6

R R R N N N R R R R R R T R R R* N R R R R R R R R* R R R R T T N N N R R R R* R*

t

te

l e e

R

a

4 0

R* R R* R* R* R* N N N N N N R R* R R N R R R T R R* R T T R R R* R R* N R* N N R R R R R N R R* R N R R* R R* R* N R* R R R* R N R N T T T N N N N N N N R N R N R N R* R R R* R* R* R N R* R* R T R R* R N N R* R N N N N R* R T R R* R T T T T T T R* R T R R* R*

y n

in

3

 Acetaldehyde  Acetaldehyde  Acetic Acid  Acetic Acid, Glacial  Acetic: HCl: H2O  Acetic Acid: HCl  Acetic: H2O2  Acetic Anhydride Anhydride  Acetone  Acetyl Chloride  Acetylene  Acrylic Acid  Acrylonitrile ®  Aerosol , Wetting Agent  Almond Oil  Aluminum Acetate†  Aluminum Chloride (dry)† (dry)†  Aluminum Fluoride†  Aluminum Sulfate†  Ammonia  Ammonium Carbonate† Carbonate†  Ammonium Chloride†  Ammonium Hydroxide Hydroxide  Ammonium Nitrate†  Ammonium Persulfate  Ammonium Sulfate†  Ammonium Sulfite  Amyl Acetate  Amyl Alcohol  Aniline  Aniline Sulfate  Anthracene Oil Oil  Antimony Pentachloride Pentachloride  Antimony Trichloride† Trichloride†  Aqua Regia (HNO3 - HCl)  Arsenious Acid Barium Carbonate† Barium Chloride† Barium Hydroxide† Beer Benzaldehyde Benzene Benzene, Sulfonic Acid Benzoic Acid Benzoyl Chloride Benzyl Alcohol Benzyl Chloride Boric Acid Bromine, Dry Gas Bromine, Moist Gas Butane Butyl Acetate Butyl Alcohol Butyl Hypochlorite Butylene Glycol Butylene Oxide Butyric Acid Calcium Chlorate† Calcium Chloride†

e le

A

F

oi

n

Corrosive  Agen t C

s

m

n n

l

le

o s

d

2-

s s

S

Metals l

P 7

s u

t

6 S

m

c

S

et

e S

te

dr at

et

e l

P

Corrosive  Agen t

l

FRP

l

H 1 3

RV X R R R* R R R RV RV R* N R R* N R* R R R R R R R R R R R R N N Rn N Rn R N R N R R N R N R* R* R* R R R R

N N N R* R* R* R* N R* N N R* T N R* N N N N N T N N N N N R* T R* N T T N R R* R* T T N T T T T N T T T T T

N N R* R R N R* R* N N N R* T R* R* N N R* N R* T N N N N N R* T R* R* T T N R R* R* T T T T T T T R R T T T T

R* N R* R R* R* R N R* N R* R* T R N N R* R* R* N R T N R R N R R* T R* R* T T N R R* R T T N T T T T R* R T T T T

R R* R* R R* R R N R* N R R* T R N R* R* R R* R T N R R N R R* T R* R* T T T R R* R T T T T T T T R* R T T T T

R N R* R* R* R T T R N R* R* T R R* R* N R* R* R* T N N N N N R T R* R* T T T R* R* R* T T T T T T T R* T T T T T

R R R* R R* R R* R R R R R T R R N R R R R T R* R R R* R R* T R R* T T N R* R* R* T T T T T T T T T T T T T

R R R* R R N Rn R*

N T R* R* R* N N R*

R T R* R* R* R* R* R*

R* T R R R R* N R

R* T R R R R* R* R

R* T R* R* R* R* R* R*

R T R* R* R R R R*

R - Recommended

n

 - 120°F. maximum

N - Not recommended

T - Test data not available

V - Surface Veil required

D - Double layer of surface veil required

X - Consult New York Blower  

 Aerosol ® is a registered trademark of American Cyanamid Co.

Page 2  

CORROSION-RESI ION-RESISTANCE STANCE GUIDE TO FUME A ND AEROSOL CONTAMINATED A IR CORROS FOR nyb FRP CONSTRUCTION CONSTRUCTION AND ASSORTED METALS Metals FRP FRP e

F

oi

te

e

a

rut

m n

ni

s

n o

M at S

S

a

rut

3

R* R Rn

R* R* T

R* R* T

R* R* T

R* R* T

R* R* T

R* R* T

R* N R N R R R R R R R RV RDn RV R R R R R

N R* R* R* N N N N N N N R* N N T R* N R* T

R* R* R R* R N N N N R* R* N R N T R* N R* T

R* R R* R* R* N R R* N R* T R* R N T R R* R T

R* R* R R R* R* R* R* R* R* N N R N R R* N N R* R* R* T R R* R R R* R T T R R R R* R R* T T

R* R* R R R R* R* R R* R* R* R R R* R* T R* R R T

T

T

T

m

te

e

n

ni

o C

e le M

at at S S 6 3

et s a

4 0

lol o

ni

A

y n

ni lu

a C

C

s

m rb

n

2l

le

o s

7 s

s

S

d

6 S

s u

c dr

S

l te S

te t

ta H

1

T

F n

s

6 0

e oi

et a

4 3

Ethyl Ether Ethylene Chlorohydrin Ethylenediamine Tetra  Acetic Acid Ethylene Dibromide Ethylene Dichloride Ethylene Glycol Ethylene Oxide Fatty Acids Ferric Chloride† Ferric Nitrate† Ferric Sulfate† Ferrous Chloride† Ferrous Sulfate† Flue Gas, (wet) Fluoboric Acid Fluorine Gas Fluosilicic Acid† Fluosulfonic Acid† Formaldehyde Formic Acid Fuel Oil Fungicides

lol o

at A

C

y n

ni

lu a

C

le ni

m rb

n

e

l e

n R

Corrosive  Agen t C

s le

o s

l

s

S

d

s

2-

Metals

l

P 7

S

u

c dr

6

S

te t

S

te

e

n R

ta

l

l

P

Corrosive  Agen t

l

H 1 3

Linseed Oil Lithium Carbonate Lithium Chloride† Lithium Hydroxide Lithium Hypochlorite Magnesium Carbonate† Magnesium Chloride† Magnesium Sulfate† Malathion Maleic Acid Mercapto Acetic Acid Mercuric Chloride† Mercurous Chloride† Mercury Methacrylic Acid Methyl Alcohol Methyl Bromide Methyl Chloride Methyl Ethyl Ketone Methylene Chloride Mineral Oil Monochloroacetic Acid Monochlorobenzene

R RV R RV X R R R R R N R R R R R* R* R N N R R* N

R* T R* N T N N R* T N T N N R* T R* R* N R* R* R* N R*

R* R R T T T N R R N R* R* T T T R* R R N N R* R* R* R* T T T R* R R** R* R* T T T N N N N N N N R R T R R R* R R N R* R* R* N R R R* R R R* R* R* R* R R N R R R* R* R*

N R R R R R R* R N R R R R R R R N R R R

R* R* R* N N N N N R* R T N R* T R* T R* R N T

R* R R R* R* R R R R* R* R R R R* R* N R* R R* R N R R R* R* N R* R* R* R* R R R N R* N R R N R R* R R** R* R* R* R* R* R* R R R R R T T T T T N R* R N T R R R R* R* R* T T T T T R R R R R T T T T T R* R* R* R* N R R R R R* R* R R* R R R* R* R* T T T T T

R* R R R R* R N N R R R T N R R

N N T R* N R* R* T N N R* N R* N R*

R* R* R* R* R* R T T T R* R R N N N R R R R R R T R R R* R R N R* R R* R R R* N N N R R R* R R** R R R R

Fungus, (95% Relativ e Humidity) Furfural Gasoline Gasoline, Aviation Glycerine Glycolic Acid Heptane Hexane Hexachlorocyclopentadiene Hexachloroethane Hexamethylenetetramine Hydrazine Hydrochloric Acid Fumes Hydrochloric Acid + Free Cl 2 Hydrocyanic Acid Hydrofluoric Acid Hydrogen Hydrogen Bromide Hydrogen Chloride

R

T

T

R*n R R R R R R R N R N RD RD R RDn R R R

R* R R R* N R* R* T T T T N N N N R N N

R R* R* R* R* R R R R R R R R R R R R R R R R* R* R* R* R* R R R R R** R R R R R* R T T T T T T T T T T T T T T T T R R T T N N N R* R N N N R* R* R R R* R R R N N N R R* R* R R R R R N N N N R* N N N R* R

Monoethanolamine Naphtha Naphthalene Nickel Chloride† Nickel Nitrate† Nickel Sulfate† Nitric, Red Fuming Nitric Acid Nitrobenzene Nitrogen p-Nitrotoluene Sulfonic Nitrous Acid Nut Oil, Ground Oakite Stripper SA® Oleic Acid Oleoparathion Oleum Oliv e Oil Oxalic Acid† Oxidizing Gases

Hydrogen Fluoride Hydrogen Peroxide Hydrogen Sulfide Hydroxyacetic Acid Hypochlorous Acid Insecticides Iodine Iron Perchloride† Isobutyl Alcohol Isopropyl Alcohol Isopropyl Amine Kerosene Lactic Acid Lead Acetate† Leather Dyeing & Finishing

RVn R R R R R R R R Rn R R R R R

N N R* N N T N T T R* T R* N N T

N N N R R* R R R R* R R* R* R R* R R* R* R* R* R* N N N N R* T T T T T R N N R* R T T T T T T T T T T R* R R R* R T T T T T R R R R* R* R* R* R N R* N R* R* R * R* R * R* R* R R R T R*

Ozone Palmitic Acid Parathion, W et Perchloroethylene Perchloric Acid Petroleum Ether Phenol Phenol, Sulfonic Acid Phosphate Salts† Phosphoric Acid Phosphorous Acid Phosphorous Oxychloride Phosphorous Trichloride Phthalic Acid Phthalic Anhydride

R* T R R* T R* R* R* R T R* R* T N N R* T R* T R* R* R* R T R*

R* T R R* T R* R* R R* T R* R* T R* R* R* R* R N R T R* R* R R R* R R*

R* T R* R* T T R R* N R* R R R R* T T R* R R* R R R R* R* T R* R* R* R* R R

† These compounds are normally solids; considered here as being water solutions. R - Recommended n - 120°F. maximum R* - R Rec ecom omme mend nded ed fo forr ffum umes es on only ly.. C Car are em mus ustt b be e ttak aken en to prev preven entt ffor orma mati tion on of cond conden ensa sate te on wh whee eell or or in in hou housi sing ng N - No Nott rrec ecom omme mend nded ed T - Test data not available V - Surface Veil required D - Double layer of surface veil required X - Consult New York Blower    Aerosol ® is a registered registered trademark of American Cyanamid Co.

Page 3  

CORROSION-RESISTANCE GUIDE TO FUME AND AEROSOL CONTAMINATED AIR FOR nyb FRP CONSTRUCTION AND ASSORTED METALS Metals

FRP

Corrosive  Agen t

   P  n    R   i   o    F   t   c    d   r   u   r   a   t    d   s   n   n   a   o    t    C    S

   l   e   e    t    S   n   o    b   r   a    C

  m   u   n    i   m   u    l    A

R T* R T T R* R* R* R R R* R* R R R** R T R T T

R T* R T T R* R* R R R R* R* R R* R* R R* R R* T

Metals

FRP

   l   e   e    t    S   s    l   s   e   e   n    l   n   o    i   a    M    t    S    6    1    3

   l   e   e    t    S   s   s   e    l   n    i   a    t    S    4    0    3

N T T T T R* R* R R* R* R R** R R R** N T R N T

   6    7    2      C   y   o    l    l   e    t   s   a    H

P chAlocrio dciyncA on le Pioclryic lolc ho eh xa Polyvinyl Acetate Emulsions Polyvinyl Alcohol Polyvinylidene Chloride Potassium Bicarbonate† Potassium Carbonate† Potassium Chloride† Potassium Cyanide Potassium Dichromate† Potassium Ferrocyanide† Potassium Hydroxide Potassium Nitrate† Potassium Permanganate† Potassium Persulfate† Potassium Sulfate† Propionic Acid Propionyl Chloride

R* R R R R RV RV R R*n R R RDn R R R R R T

N T N N T R* R* R* R* R* R* R* N R* T R* T T

N T T T T N N N N R R* N R* R T R* T T

R T* T T T R* R* R R* R* R* R* R* R R* R* R R R R T

Pro lene Gl col Pulp and Paper Mill Blow Down Gases Pyridine Rayon Spin Bath Selenious Acid Sewage Treatment Silver Nitrate† Sodium Acetate† Sodium Benzoate† Sodium Bicarbonate† Sodium Bisulfate† Sodium Bisulfite† Sodium Borate† Sodium Bromide† Sodium Carbonate† Sodium Chloride† Sodium Chloride (pH 10.5 Cl2 Sat.) Sodium Chlorite† Sodium Cyanide Sodium Dichromate Sodium Sod ium Fer Ferric ric ani anide† de† Sodium Hydroxide† Sodium Hypochlorite† Sodium Nitrate† Sodium Sulfate† Sodium Sulfide† Sodium Sulfite† Sodium Xylenesulfonate Stannic Chloride† Stannous Fluoride: Hydrofluoric Acid Stearic Acid Styrene

R RV

R* T

R* R* R* R* R* T T T T T

N R R R R R R RV R R R R RV R R

R* N N N N N T N N N N N R* N N

R* T N R* N R R R* N N R* N N N N

R R** N T R* R R* T R R* R* R* R* R R* N

R* R* R* T R* R R* T R R* R* R* R R** R R N

R R** T N T N R* R* R R R** R* R* R R** R* R N

R* R* R* T R* R* R R R** R R* R* R R* R* R R R

R R R R RV X R R R R R R RVn

N R* R* T R* N R* R* R* R* T N N

T N R* R N N R R N R* T N N

R R** R R* R* R* R N R R R* R T N N

R R R* R* R* R* R N R R R R T N N

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R* R* R* R R R* R* R R** R R* R* R* T R* T

R R*

N R*

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Corrosive  Agen t

S Aectie drgents Su ullffa am teidc D Sulfate Liquors Sulfite Liquors Sulfur, W ettable, Fungicide Sulfur Dichloride Sulfur Dioxide Sulfur Trioxide Sulfuric Acid Sulfuric Acid: Phosphoric Acid Sulfuric: Nitric Acids Sulfurous Acid Sulfuryl Chloride Sweet Oil Tannic Acid Tar Camphor Tartaric Acid Tetrachloroethane Tetrachloropyridine Tetrapotassium  Pyrophosphate† Thionyl Chloride Tin, Molten, Fumes Toluene Toluene Sulfonic Acid Tolyl Chloride Trichloroacetaldehyde Trichloroacetic Acid Trichloroethane Trichloroethylene Trichloromonofluoromethane Trichlorophenol Triethanolamine Trimethylene Chlorobromide Trisodium Phosphate† Turpentine Urea Urotropine Vinegar Vin l Chloride Vinyl Toluene Waste, Organic, H2O, HCl, Cl2 Vapors W ater, Deionized W ater, Demineralized W ater, Distilled W ater, Sea W ater, Steam Condensate Xylene Zinc Chloride† Zinc Hydrosulfite†

   P  n    R   i   o    F   t   c    d   r   u   r   a   t    d   s   n   n   a   o    t    C    S

   l   e   e    t    S   n   o    b   r   a    C

  m   u   n    i   m   u    l    A

   l   e   e    t    S   s   s   e    l   n    i   a    t    S    4    0    3

   l   e   e    t    S   s    l   s   e   e   n    l   n   o    i   a    M    t    S    6    1    3

   6    7    2      C   y   o    l    l   e    t   s   a    H

R R* R R R R R R R R

N N N N N N R* R* N N

N N N N R N R* R* N N

T T R* R* R N R* R R** N N

R T* R* R* R* R R* R* R R** R* R*

T T R* N R N R* R* R* R* R* R*

T T R* R R R* R* R R** R R** R*

R R* R R R R R

N N T R N R* N

N R* R* R N R R*

N N T R R* R R

R* R* T R R R R

N N R* R* R* R* R*

R* R* R R R* R* R R**

R* Rn R

R* T T

N T T

R* R T T T T

T T T

R T T

N R R R RV R R Rn R* R RV Vn T R N R R R R R N Rn RVn

N N R T T T N T R* T T R* T R* R* R* T N T T N

N N R T T T N N R* T T R* T N R* R* T R* R* T N

N N R T T T N R* R* T T R* T R* R R* T R R* R* T N

N N R T T T N R R** R* T T R* T R* R R* T R R R** T N

R* T R T T T R* T R T T R* T R* R R* T R* T T N

T R R T T T R R** R R T T R* T R R* R* T R R* T R

R R R R R R* R R

N N N N R* R* N N

R* R* N R* R* R N N

N R R* R* R R N R

R* R R R** R* R R R* R

T T N R* R* R* R R** T

R* R* R R R R R R** T

n - 120°F. maximum † These compounds are normally solids; considered here as being water solutions. R - Recommended R* - Rec Recom omme mend nded ed for for ffum umes es only only.. C Car are em mus ustt b be e ttak aken en to prev preven entt ffor orma mati tion on of cond conden ensa sate te on wh whee eell o orr in in hou housi sing ng N - No Nott rec recom omme mend nded ed T - Test data not available V - Surface Veil required D - Double layer of surface veil required X - Consult New York Blower  

 Aerosol ® is a registered trademark of American Cyanamid Co.

Form 318 JLK

 

ENGINEERING LETTER The New York Blower Company

●

19

 7660 Quincy Street, Willowbrook, Illinois 60521-5530

D E S I G N A N D C O N S T R UC T I O N O F n y b F R P F A N S INTRODUCTION Fiberglass-reinforced plastic (FRP) made from chemical-grade vinyl ester resin resists corrosion as well as, or in some cases  better than, high-priced materials such as titanium or highnickel alloys. In general, FRP (also known as RTP, or reinforced-thermoset plastic) is widely used in handling the fumes of acids and of many inorganic and organic chemicals where service temperatures do not exceed 250°F.

Coated fans, regardless of the inherent corrosion resistance of the coating, have the potential of coating failure and resultant rapid deterioration of the base metal. Failures occur when coatings are physically damaged, and when corrosive attack  permeatess the coating to attack  permeate at tack the metal metal.. Ref Refer er tto o Engineering Letter 16 for additional information on corrosion-resistant coatings for fan equipment.

COMMON USES FOR FRP FANS

Stainless steel is susceptible to attack by chlorides and resultant physical failure by stress cracking. Residential hotwater heaters are never made of stainless steel because the combination of small amounts of chlorine in the water, modest temperatures, and the stresses caused by changes in water  pressure results iin n rapi rapid d failur failuree of tthe he stainl stainless ess steel.

Potential applications for FRP fans include any process in which corrosive fumes must be captured, moved, cleaned, or vented. FRP fans are most often used in fume-scrubber systems where the scrubber itself may be constructed of FRP or an exotic alloy, but where FRP is the preferred fan material. Galvanizing and etching processes often have FRP exhaust hoods and ducts, and many of the fans used to convey fumes in such systems are also built of FRP. Wastewater-treatment  plants and laborato laboratory ry exhaust systems are other applicati applications ons for which FRP fans are being used with increasing frequency. When FRP is the selected material for an air-handling system, it is logical that the fan also be made of FRP. For example, the acids used in the pickling of stainless steel are necessarily those that attack stainless steel. In such a system, the acid-holding tanks, fume-control hoods, ducts, scubbers, and fans are often made of FRP because FRP resists acid corrosion and costs less than metal alloys having comparable resistance. In summary, FRP fans may be an economical alternative to stainless steeltemperature or other metal-alloy fans when corrosion concern and is below 250°F. In addition to is thea economic advantage, FRP fans often provide better performance than special alloys in handling airstreams that are particularly corrosive to metals.

As noted earlier, steelacids is alsothan muchismore susceptible to corrosive attackstainless by most FRP. Refer to Engineering Letter 14 for additional information on the use of stainless steel in fan construction. Costs for fans made of 3 16L stainless vary from about threefourths that of FRP fans for small Class I fans to almost twice the price of FRP fans for large Class III fans. Fans made of Monel ®, titanium, and the high-nickel alloys may be more or less corrosion resistant than FRP depending on the chemistry and temperature involved. Figure 1 shows the effect of simultaneously submerging a coupon of a high-nickel alloy (Hastelloy®  C-276), 316 stainless steel and FRP (Derakane® 510A40) in a bath of nitric and hydrochloric acid (aqua regia). While the 316 stainless was destroyed and the 276 alloy severely corroded, FRP was untouched. cost of fans made of such alloys isthe usually several times theThe cost of fans made of FRP.

COMPARISON OF FRP FANS TO FANS OF OTHER O THER MATERIALS A comparison of the corrosion resistance and economics of fans made of various materials leads to these generalizations: Coated steel fans vary greatly in the degree of corrosion  protect ion provided and cost. Coatings run the scale from  protection little-different-than-ordinary machinery enamel to baked-on  phenolics applied to sandblasted metal. Costs for coated fans run from about one-third that of FRP fans for the least-resistant coated-steel fans to about half the cost for the baked phenoliccoated fans. Monel ® is a registered trademark of Inco Alloys International, Inc. Hastelloy ® is a registered trademark of Haynes International, Inc.

Figure 1 - High-nickel, stainless, and FRP coupon in bath of nitric and hydrochloric acid.

Derakane ® is a registered trademark of Ashland, Inc

 

 

Fans made of rigid polyvinyl chloride (PVC) have good allaround corrosion resistance and generally cost less than fans made of FRP. However, PVC has two significant physical weaknesses that severely limit its use in fans: PVC becomes quite brittle at temperatures below freezing, and PVC loses its strength so rapidly with increasing temperatures that even ordinary summer rooftop operating conditions are marginal. Wheels sag and go out of balance and strike housings. PVC is a thermoplastic material that remembers ~ its original shape at about 150°F., and needs to reach only about 300°F. for it to have the zero strength needed for vacuum forming. ™

 Numerous users have disavowed the use of PVC fans because of their experiences with failures resulting from PVC's lowtemperature brittleness and high-temperature weakness. The use of PVC equipment involves some safety considerations as well. PVC does not burn, but because it is a low-temperature thermoplastic it collapses early in a fire and will drip molten PVC. Thus, rather than containing a potential fire within the duct system, as fire-retardant FRP will do, PVC tends to expand the fire into other areas, even though it is not inherently combustible. In addition, PVC releases highly toxic hydrochloric acid fumes when exposed to flame even though it is a self-extinguishing material. PVC, like FRP, is an insulating material and inherently sparkresistant. However, unlike FRP, it cannot be made electrically conductive to control static electricity. UNDERSTANDING FRP The term FRP describes a broad spectrum of fiber-reinforced  plastic material materials. s. For example, cabinets for office machines might be made of non-corrosion-resistant plastics reinforced with mica and loosely called FRP. However, the FRP used in making process vessels and equipment such as fans is composed of about 30% by weight of glass or other fibers that have been given a coating (sizing) to enhance their bonding with the resin, and about 70% by weight of corrosion-resistant  polyester or vin vinyl yl ester resin. The fibers provide physical strength, and the resin provides the corrosion resistance and rigidity that make FRP a workable solid. Sometimes, non-glass-fiber materials are used in FRP to impart special properties. For example, graphite fibers add tensile strength, and aramid fibers (Kevlar ®) add toughness. But FRP for process equipment usually has glass fibers  because they are more economical and easier to work with; graphite fibers, for example, are more difficult to handle and do not bond as well as glass. Glass fibers are available in a variety of forms, including continuous -strand roving, woven roving, continuous -strand mat, chopped-strand mat, chopped fibers, and milled fibers. nyb uses all of the above except woven roving and continuousstrand mat in the construction of its FRP products. Continuous-strand roving is used in the chopper guns for spray-molding of non-moving parts such as housings, inlet cones, inlet boxes, damper frames, and outlet transitions. Kevlar ® is a registered trademark of E.I. DuPont De Nemours & Company

Chopped-strand mat, consisting of Type E glass of 1 1/2 ounces  per square foot in weight, is used in hand lay-up lay- up of housings and Fume Exhauster wheel blades among other products. Castings such as FPB and RFE wheels and seal housings are made with chopped fibers. Milled fibers are primarily used to make putty for filling cracks, turning sharp angles into smooth radii, and encapsulating wheel hubs. The corrosion resistance of FRP depends on the resin. Resins used in FRP for process equipment are formulated for maximum corrosion resistance, and are consequently two or three times as costly as those used in everyday products such as boat hulls or auto body parts. FRP fan manufacturers normally use two types of resin in the construction of their products. Polyester is the resin of choice for non-moving components such as housings and inlet cones  because it provides excellent corrosi corrosion on resistance for most FRP applications at a relatively low cost. Unfortunately, this type of resin cannot withstand the dynamic stresses inherent in rotating parts such as wheels. Therefore, FRP wheel construction dictates the use of vinyl ester resins which are much stronger and more flexible than polyester resins. The strength and elasticity of vinyl ester resins enable FRP wheels to achieve maximum safe speeds comparable to similarsized steel wheels at 70°F. As with steel and other alloys, the strength and flexibility of vinyl ester is compromised at elevated temperatures, resulting in safe speed derate factors above 150°F. Refer to specific product bulletins for maximum safe speeds and applicable derate factors. FIRE RETARDANCE OF FRP RESINS Since many FRP applications involve a mixture of combustible chemicals and air, nyb FRP fans are made of fire-retardant resins. Fire retardance is measured by the ASTM E-84 test method, which determines flame spread ratings~ by comparing the rate at which flame spreads when material is fired in a long, narrow furnace with flowing air. (The test is also called the tunnel test~ and is recognized by Underwriters' Laboratory and the National Fire Protection Association.) ™

™

Completely incombustible materials, such as cement board, are rated zero flame spread. Red oak is used as the comparative value of a combustible material and is rated at 100. A flamespread rating of 25 or lower is considered non-combustible. (Resin systems rated at 25 or less are often referred to as Class I.) A flame-spread rating of 50 means that the material will gradually, but steadily, extinguish itself. (Resin systems rated at 26 to 50 are often referred to as Class II. Class III and IV denote less fire-resistant ratings.) Resins for chemical duty can be made fire retardant by formulating the resins to include adequate molecularly bound halogens, such as chlorine or bromine, or by the use of smaller amounts of halogens but with the addition of antimony trioxide. The first method is more costly but provides a clear resin that improves quality control of the product being manufactured since the workers and the inspectors can see into the finished 

  Page 2  

 product. Antimony trioxide is a white pigment which produces an opaque product that reduces the ability to visually check  product quality. Further, antimony additives additi ves can reduce the corrosion resistance and strength of the resin. nyb uses a resin that is fire retardant without the use of antimony trioxide. STANDARD nyb RESIN All nyb FRP components are made with Derakane 510A40, a  brominat ed epoxy vinyl ester resin manufacture  brominated manufactured d by Ashland Chemical Company. This resin offers the flexibility, low shrinkage, and excellent secondary bonding necessary to withstand the vibrational stress and fatigue of dynamic loading inherent in rotating wheels. Derakane 510A40 has an ASTM E-84 tunnel test rating of 25, offering Class I fire retardance without the use of additives which could could compromise its superior toughness and corrosion resistance. This satisfies the most stringent concern for the containment of ventilation-system fires. The clarity of Derakane 510A40 enables the fabricator and inspectors to locate and eliminate air inclusions in the laminate, thus maintaining high standards of quality control of a critical fan component. Since additives tend to adversely affect a resin's chemical resistance, nyb FRP products do not contain ultraviolet (UV) inhibitors. These additives have a tendency to inhibit resin cure and lose their effectiveness after long exposure to ultraviolet radiation. In order to prevent UV degradation, nyb applies a coating to the exterior surfaces of all FRP components. Years of successful outdoor service prove that this method of protection is superior to adding UV inhibitors to the resin. Corrosion resistance is the main concern when selecting a resin. nyb 's  standard resin has excellent corrosion resistance to nyb's a broad spectrum of corrosive environments.. The data on corrosion resistance to various chemicals, presented in Engineering Letter 18, were derived from tests of these resins.

CONSTRUCTION OF FRP FANS The fabrication of FRP is similar to the casting of metal. A  pattern is used to make a mold for the FRP part. In a fan, the airstream surfaces of the housing should be smooth to minimize resistance and prevent build-up of airborne contaminants. Thus, male molds are required rather than female ones. The smooth outside surface of the mold shapes the inside surface of the housing. Parts made with male molds must be removable, so FRP fan housings are usually made in two halves with matching flanges. In larger fans, these two halves are bonded together  by means of FRP filler between the flanges, as shown in Figure 2. A lamination laid over the joint on the inside of the housing provides a smooth surface. The joined flanges form a ridge that adds rigidity to the housing. The inlet subassembly is  bolted into pl place ace to allow a llow acce access ss for installa installation tion of the wheel. wheel . Smaller FRP fan housings are also molded in halves, but they are typically bolted together as shown in Figure 3. Removing the inlet side of the housing allows installation or removal of the fan wheel. Fan wheel construction is also different for large and small FRP fans. Small wheels, such as nyb 's   Fiberglass Pressure nyb's Blower, are made by casting or press-forming in fully enclosed molds; Figure 4 shows an example. Larger wheels, such as nyb 's   Fume Exhauster, are made by assembling and nyb's  bonding molded parts (wheel blades, frontp frontplates, lates, and back plates) with layers of laminat laminatee constructi construction on so as to make strong, smooth joints. See Figure 4. All FRP wheels are ovencured for several hours to improve physical strength and corrosion resistance of the FRP laminate.

r

Figure 2 - Fiberglass Fume Exhauster

Figure 3 - Fiberglass Pressure Blowe  

Figure 4 Fiberglass Pressure Blower wheel, upper left-   Fiberglass Fume Exhauster wheel, lower right

  Page 3  

Metal parts that are incorporated in the FRP parts, shafts, wheel hubs, and studs, are encapsulated in FRP so no metal is exposed to the gas stream. Shafts are encapsulated in an FRP sleeve that extends through a close-fitting opening in the side of the housing. (Shaft seals that can be lubricated are available as an option.) Bolts used to fasten smaller fan housing halves together are of 316 stainless steel.  Neoprene foam gasketing is used between bolted housing subassemblies and under access doors, inspection ports, and shaft seal assemblies. FRP fan wheels are permanently bonded to the fan shafts, the shafts encapsulated in FRP, and the assembly balanced as a unit. After the fan is assembled it is test run as a final check to guarantee smooth operation. Exterior surfaces of completed nyb FRP fans are coated with gray epoxy enamel. APPLICABLE STANDARDS FOR FRP FANS The purchaser of FRP fans should consider the importance of two published standards: one, ASTM D4167, covers the construction of FRP fans; the other, AMCA Standard 210, describes how fans are to be tested for air performance. The AMCA Certified Ratings Program is the method by which manufacturers certify their products' aerodynamic performance. The ASTM standard is concerned with the structural reliability of the fan. If the fan in a fume-control system fails, the entire  process may come to a halt. The importance of reliability has led to development of a standard for FRP fansAmerican Society for Testing and Materials (ASTM) D4167, Standard Specification for Fiber-Reinforced Plastic Fans and Blowers. This standard defines minimum specifications for construction of major fan elements. Here are six of the details: 1.  Fan housing construction must conform to the ASTM C582 specification which applies to all FRP process equipment. (nyb standard construction with optional veil complies with ASTM C582.) The same resin must be used throughout the housing unless the manufacturer and user agree to use different resins in different layers of the laminate. (nyb does not back up the corrosion barrier with less costly resin. nyb uses premium quality resin throughout.) The structural rigidity of the housing (or a  prototype) is tested by running the fan with the inlet closed and the outlet open. Inward flexing may be no greater than 0.5% of the fan-wheel diameter. 2.  Fasteners, hubs, and shafts exposed to corrosives must be either corrosion resistant or encapsulated in a material that is. 3.  The ASTM standard prohibits the use of additives in fan wheel resins that obscure visual inspection of wheel  parts, inc includin luding g the use of antimony antimony trioxide trioxide.. nyb standard construction provides fire retardance without the use of additives. 4.  Safe wheel operating speed is determined either by past experience or by destructive testing i.e., running the fan

Figure 5 - A graphite-impregnated FRP fan for spark resistance.

5.  Spark resistance. FRP is spark-resistant in the sense that contact of FRP parts does not generally produce sparks. However, FRP fans handling dry air can develop electrostatic charges on wheel and housing surfaces because FRP is a non-conductor. Still, an FRP fan can be made spark-resistant by incorporating graphite flakes in the wheel and housing airstream surfaces to make them conductive, and grounding the surface layers of the housing as shown in Figure 5. ASTM D4167 defines acceptable resistivity as no greater than 100 megohms  between all al l point pointss on the airstre airstream am surface surfacess and gr ground. ound. 6.

Dynamic balance is achieved either by balancing the wheel-shaft assembly as a separate unit or by balancing the wheel once it is installed in the fan (nyb does both). Unbalance is corrected by adding FRP weights.

The Air Movement and Control Association (AMCA) Certified Ratings Program is concerned with accurate performance ratings. The manufacturer submits published performance ratings to AMCA and fans for test in the AMCA Laboratory. Deviations are determined by plotting actual performance against the fan's cataloged performance . Manufacturers displaying the AMCA Certified Ratings Seal on their products, and in their literature, have agreed to a system of check testing in the AMCA Laboratory. If a product fails to perform within the tolerances specified by the program, the manufacturer must either republish the literature with correct ratings or republish without the seal.

wheel at increasing speeds until it fails, and applying a safety factor to the failure speed.

 

Fo rm 5 0 7 D J K

 

ENGINEERING LETTER The New York Blower Company

●

20  

 7660 Quincy Street, Willowbrook, Illinois 60527-5530

CCESS ESS OR ORIE IES S A ND CO CONS NSTR TRUC UCTI TION ON MOD MODIF IFIC ICA A TI TION ONS S  A CC FOR FRP FANS INTRODUCTION

The applicability of corrosion-resistant FRP fans to a wider range of applications is enhanced through the use of accessories and construction modifications. The purpose of this Engineering Letter is to provide supplemental information concerning accessories and modifications modifications that are unique to FRP fans. ACCESSORIES SHAFT SEALS are used where the standard close-clearance shaft opening is not deemed to be adequate. (Standard construction on nyb FRP fans have shaft openings fitted with Teflon® membranes that have shaft holes 1/32" larger than the FRP shaft sleeves.) nyb’s  standard shaft seal for FRP fans utilizes a pair of Viton ®  lip seal elements pressed into an FRP casing. As an option, Teflon shaft seal elements can be provided for more corrosive applications. The seal assembly is secured to the fan housing with 316 stainless steel studs. The heads of the studs are encapsulated in FRP to eliminate exposure to airstream corrosives. See Figure 1.

Seals are recommended wherever corrosive or toxic gases are  being handled, or when outside air is to be kept from entering the fan and contaminating a process. It is difficult to predict the conditions that increase leakage into or out of the fan around the shaft opening. However, as a general rule, higher  positive or negative pressure differentials will result in greater leakage. OUTLET DAMPERS are designed to bolt directly to the outlet flange on FRP fans. RFE and FPB dampers are round, with one blade. FE and GFE dampers are rectangular, with  parallel blades, and and are available available for MP fans fans only. See Figure Figure 2.

Casings and blades are constructed of Derakane ® 51 0A40. All damper parts are constructed of FRP except the 316 stainless steel control quadrant and hardware, and the corrosion-resistant, injection-molded bearings. Damper casing halves are bolted together to allow for easy replacement of damper vanes and bearings. All components can be disassembled except vanes from rods.

Because the seals must ride on a smooth, heat-conductive surface, the standard construction of the shaft encapsulated in FRP is not suitable. Therefore, the seal assembly includes the substitution of a 316 stainless steel sleeve for the standard FRP sleeve. As an option, Hastelloy ®  C-276 sleeves are available for those cases where the corrosive environment makes stainless steel unacceptable. ®

The seal assembly is lubricated with “Never -Seez -Seez ,” a graphite  compound.

Figure 1 - Photo of FRP shaft seal mounted and diagram illustrating lubricated lip seal elements.   Teflon® and Viton® are registered trademarks of E.I. DuPont de Nemours & Company. Hastelloy ® is a registered trademark of Haynes International, Inc.

Figure 2 - Three types of FRP outlet o utlet dampers as manufactured by nyb.  Never-Seez® is a registered trademark of Bostik. Derakane® is a registered trademark of Ashland, Inc.

 

 

INLET BOXES are used to accomplish a 90° turn at the fan inlet when space is limited. Fan applications typically involve less than ideal connections between the fan and the process. When the connections cause other than straight, uniform flow into the fan inlet, the fan suffers performance losses beyond those determined by ordinary duct-resistance calculations or  pressure drop measurements. (See Engineering Letter 5 for a description of the effects of inlet connections.) Therefore, it is advantageous to use nyb test-rated inlet boxes to reduce flow losses, and to make those losses predictable for inclusion in system design calculations. See Figure 3.

Inlet Boxes are available for Fume Exhausters and GeneralPurpose Fume Exhausters. See Figure 4. Construction of FRP inlet boxes is similar to that of FRP Fume Exhausters. Standard construction is with Derakane 510A40 vinyl ester resin. Inlet boxes are made in two sections bolted together with 316 stainless steel hardware. THREADED FRP DRAIN with PVC plug, 1" npt, is bonded to the lowest point in the housing scroll. COMPANION FLANGES are available with FPB and RFE fans for those applications where a flexible or slip connection to the fan inlet and/or outlet is required. Companion flanges are commonly used on fans furnished with vibration isolation.

 

INSPECTION PORTS are used for periodic maintenance checks on the wheel and the housing interior. They are available on all FRP fans, and are located on the drive side half of the housing (GFE and FE fans) or the inlet side half of the housing (FPB and RFE fans), at either the 2 o' clock or the 10 o’clock position, oppo site the fan discharge. High, unpredictable effect on fan selection and system performance.

RAISED BOLTED CLEANOUT DOORS are available on GFE and FE fans. They are located above the fan centerline at either the 2 o’clock or the 10 o’clock position, opposite the fan discharge.  OUTLET TRANSITIONS  provide for a rectangular -to-round transition on the outlets of various GFE and FE fan sizes. They are available on GFE and FE Sizes 18 through 36 and 48 (MP fans only). The I.D. of the round outlet is equal to that of the fan inlet, and also to the transition length. MODIFICATIONS

Minimum, calculable effect on fan selection and system performance. Figure 3 - Inlet Connections

ALL-VINYL ESTER AIRSTREAM  provides increased resistance to certain corrosives. Engineering Letter 18 provides data for the corrosion resistance of the standard construction and of the all-vinyl ester construction.

Standard construction uses vinyl ester resin for wheels. All other FRP parts are made of polyester resin. When an all -vinyl ester airstream is specified, parts normally made of polyester are made of vinyl ester. See Engineering Letter 19 for more details. SURFACE VEIL is used to reinforce the surface layer of resin for added resistance to specific corrosives or to meet the specification of ASTM D4167. Veil may be applied to just the wheel, or to just the housing, or to the entire airstream. nyb uses a synthetic surface veil that is described in detail in Engineering Letter 21. GRAPHITE IMPREGNATION of the final resin coat on airstream surfaces provides for static grounding. This important modification allows the fan to handle gas fumes that are not only corrosive but also potentially explosive.

FRP is inherently non-sparking and the electrical resistance of

Figure 4 - FRP Fume Exhauster with Inlet Box B ox

FRP may be considered infinitely high since it is essentially non-conductive or non-metallic material. Because FRP is non-a metallic, the physical contact of two FRP parts or a metallic

  Page 2  

 part with an FRP part will not produce a spark. However, FRP does have the tendency to hold a charge of static electricity. This charge can be generated by a dry gas or airstream passing over FRP. The fan can ultimately become a capacitor capable of discharging high-voltage, low-amperage sparks.

GROUNDING FEATURES - Surface resistivity of not more than 1 megohm from any point on the airstream to ground is generally considered adequate. ny nyb b ’s    process of static grounding by graphite impregnation provides surface resistivity well below the 1-megohm figure.

The static electricity or charge which builds up on the airstream surface of the FRP part must be eliminated in applications where the fumes are potentially explosive. This can  be accompli accomplished shed by making the surface electrically electrica lly

Tests of nyb FRP fans equipped for static grounding indicate that there is sufficient conductivity through the bearings to eliminate the need for supplemental brush-type contacts to ground the wheel and shaft assembly for most applications.

conductive, an electrical path to dissipate the relatively low-current providing static charge.

However, the burden of determining whether this isrests the with case for a particular installation and lubrication system the customer.

STATIC GROUNDING - FRP fans can be effectively grounded for the removal and control of static electricity by incorporating graphite in the airstream layer of resin. See Figure 5.

Static grounding by graphite impregnation does not interfere with the corrosion-resistant properties of the fan. Graphite is extremely corrosion resistant. However, the addition of the graphite makes the surface softer than normal and prevents the normal checking of the surface for Barcol-hardness readings. FRP fans are often the best alternative for those applications which require the handling of explosive, as well as corrosive gas fumes. However, care must be taken to realize that there can be no guarantees against possible sparking or ignition in such airstreams. All aspects of the application, the system components, and even the potential for sparks resulting from “tramp” or “foreign” elements in the airstream must be considered to ensure the safety of the installation. FLANGE-DRILLING PATTERNS for round inlet and round outlet flanges are in accordance with the National Bureau of Standards Voluntary Product Standard PS 15-69. This drilling pattern was developed by members of the FRP industry for FRP ductwork and specifies bolt hole diameters appropriate for bolting FRP ducts to FRP fans.

Figure 5  –  FRP  FRP Radial Fume Exhauster with graphite impregnation and copper grounding straps.

The proper application of the graphite-resin coat is critical if static grounding is to be achieved. Airstream and related surfaces are coated with a mixture of graphite flakes and resin to form a smooth, continuous graphite surface. FPB, RFE, and non-rotatable GFE and FE fans are furnished with contacts which are imbedded in the graphite layer to accommodate grounding straps made of twisted, bare copper wire. The straps are attached to the fan base on FPB and RFE fans and to inlet side angles on the large Fume Exhausters. Rotatable GFE and FE fans do not require grounding straps. These fans are completely grounded to the pedestal through the mounting studs on the housing. This design effectively grounds the airstream to the steel base of the fan. However, it is essential that the customer ground the fan base at the installation.

nyb FRP fans that have both round inlets and round outlets are also available with flanges drilled to ANSI 150. Because ANSI 150 is intended for bolting together heavy metal pipe, it uses  bolts that are unnecessarily large for FRP. Although nyb charges the same for drilling to PS 15-69 or ANSI 150, the cost to the user can be substantially different. Flanges are usually fastened together with corrosion-resistant alloy bolts, nuts, and washers. The cost difference between the sizes required for PS 15-69 and ANSI 150 can be significant. For example, a 12" inside-diameter PS 15-69 flange would have 7/16" diameter holes for twelve 3/8" bolts. An ANSI 150 flange would have 1" diameter holes for 7/8" bolts. The difference in cost can be $50 or more per flange for 316 stainless steel hardware and much more for higher-alloy hardware.

Since PS 15-69 and ANSI 150 drilling patterns only pertain to round flanges, they do not apply to FE and GFE outlet flanges. Therefore, nyb has developed a standard for drilling rectangular outlet flanges which provides holes drilled on 4" centers, straddling the flange centerlines.

Form

318  J L K 

Page 3  

NGINEERING LETTER   21 The New York Blower Company   ● 7660 Quincy Street, Willowbrook, Illinois 60521 -5530

S U R F AC E V E I L F O R F R P F A N S INTRODUCTION

ASTM STANDARD D4167

This Engineering Letter has several functions: to describe   nyb surface veil characteristics, define the purposes of surface veil, explai exp lain n the rel relati ations onship hip betw between een sur surfac facee veil veil and ASTM ASTM D4167, D41 67, det detail ail the specif specific ic cor corros rosive ive agents agents that that requ require ire a double dou ble layer layer of ve veil, il, and describ describee the spe specia ciall constr construct uction ion requirements involving hypochlorite applications.

The American Society Society for Testing Testing and Materials Materials (ASTM) D41 67, Stan Standard dard Speci Specificati fication on for Fibe Fiber-R r-Reinfo einforced rced Plast Plastic ic Fans and Blowers defines the basic guidelines for the construction of FRP FRP fan fans ha han ndl dlin ing g co corr rros osiv ivee fum umes es.. On Onee of the specifications within D4167 is that the laminate construction be in ac acco cord rdan ance ce wi with th anot anothe herr ASTM ASTM stan standa dard rd,, C5 C582 82.. Th That at standard specifies that the working surface (the surface to be in contact with corrosives) of the laminate consist of one layer of  surface surf ace veil bac backed ked by two lay layers ers of cho choppe pped-st d-stran rand d mat or  equiva equ ivalen lentt from a cho choppe pperr gun, gun, fol follow lowed ed by the struct structura urall layers. Therefore, in order to comply with ASTM D4167, all FRP fans must be furnished with at least one layer of surface veil on all housing surfaces.

SURFACE VEIL CHARACTERISTICS

The synthetic surface veil used exclusively by  nyb  is Nexus®. It ® is a non-w non-wove oven n formed formed fab fabric ric produc produced ed from Dacron 106 homopolymer. This binder-free polyester fiber has an apertured (perforated) design that provides the necessary flexibility for  the fabrication of fans. Each layer of surface veil contains about 90% resin and 10% veil material and is applied at a minimum of  10 mils.

CORRO CORROSI SIVE VES S RE REQU QUIR IRIN ING G A DO DOUBL UBLE E LA LAYE YER R OF SURFACE VEIL

There The re are some some ch chemi emical cal age agents nts that that are aggres aggressiv sivee tow toward ard gla glass. ss. For these these spe specif cific ic corr corrosi osive ves, s,   nyb ’s resin resin sup suppli pliers ers recommend the addition of a layer of surface veil for increased corrosion resistance. resistance. Additi Additionally onally,, in those application applicationss where the corrosive agent is extremely aggressive, a second layer of  vei veill is req requir uired. ed. The cor corros rosionion-res resist istan ance ce gu guide ide fou found nd in Engine Eng ineeri ering ng Le Letter tter 18, Corros Corrosion ion Resist Resistanc ancee of FRP Fans, Fans, indica ind icates tes where one or two layer layerss of veil veil are requi required red.. The corrosi corr osives ves listed as req requir uiring ing a dou double ble layer layer of surfa surface ce veil veil include  fluorine gas, hydrochloric acid, hydrofluoric acid, hydrog hyd rogen en flu fluori oride, de, potass potassium ium hyd hydrox roxide ide,,   and   various hypochlorite compounds.

Nexus Synthetic Surface Veil

ADDITIONAL REQUIREMENTS FOR HYPOCHLORITE APPLICATIONS

PURPOSES OF SURFACE VEIL

One purpose of surface veil, also referred to as surfacing mat or tissue, is to prevent protrusion of the chopped-strand mat glass fibers to the surface which could allow chemical wicking to occur. A se seco cond nd,, but but eq equa uall lly y imp import ortan ant, t, pu purp rpos osee is to pr prov ovid idee reinforcement to the surface layer of resin to prevent cracking and crazing. Finally, the addition of surface veil allows  nyb  fans to meet the requirements of ASTM Standard D4167.

Applicati Applic ations ons inv involv olving ing   buty butyll hy hypo poch chlor lorit ite, e, calc calcium ium hypochlorite hypoch lorite,, lithium hypochlorite hypochlorite,,   or  sodium hypochlorite hypochlorite require special FRP construction considerations. In addition to the aforementioned double layer of surface veil, resin suppliers recomme reco mmend nd a su subst bstitut itution ion for   nyb’s stan standa dard rd cata cataly lyst st and  promoter.  promot er. nyb’s standard polyester and vinyl ester resins both use cobalt napthanat napth anatee (CoNap (CoNap)) as a prom promoter oter and Lupe Lupersol rsol®, a methyl ethyl ethyl ketone ketone peroxi peroxide de (ME (MEKP) KP),, as a cataly catalyst. st. Gas stream streamss containing conta ining hypochl hypochlorites orites attack CoNap whenev whenever er MEKP is us used ed as a cata cataly lyst st.. Th Ther eref efore ore,, a be benz nzoy oyll pe perox roxid idee (B (BPO PO))

cat cataly alyst st is recomm recommen ended ded for these these app applic licati ations ons becau because se it Dacron® is a registered trademark of E.I. DuPont de Nemours & Company, Inc.  Nexus ® is a registered trademark of Precision Fabrics Group, Inc.

Lupersol ® is a registered trademark of Elf Atochem North America, Inc.

 

does not use CoNap as its promoter. The BPO catalyst requires dimethyll anilin dimethy anilinee (DMA), which is unaffe unaffected cted by hypochlorites, hypochlorites, as its accelerator in lieu of the CoNap. Special BPO/DMA construction is limited in that it cannot be used for FRP wheel construction. It can only be used to apply surface veil to the wheel. All other FRP components can be constructed using this special catalyst/accelerator system. In addition, note that due to reactivity between BPO catalysts and graphite, which reduces the graphite’s conductivity, static

grounding by graphite impregnation is not an available option when used in conjunction with a BPO catalyzed resin. CUSTOMER RESPONSIBILITY

This Eng Engine ineerin ering g Let Letter ter and any discus discussion sionss betw between een   nyb representatives and the customer should not be construed as a warranty of material suitability for a particular application. The syst sy stem em de desi sign gner er sh shou ould ld ha have ve suffi suffici cien entt kn know owle ledg dgee of, or  experience with, the application to select the appropriate resin or  alternate material.

Form 607 GAW

 

ENGINEERING LETTER   22 The New York Blower Company ● 7660 Qu Quincy incy Street, Willowbrook, Illinois 60527 60527-5530 -5530

I N T E G R AL M O T O RS F O R C E N T R I F U G AL F A N S INTRODUCTION

The most common power source for fans is the electric motor. A moto motor’ r’ss se serv rvic icee li life fe is larg largel ely y de depe pend nden entt upon upon pr prop oper  er  select selection ion an and d instal installati lation. on. Since Since the mo motor tor an and d its control control circuitry represent a substantial portion of the cost of many fan system sys tems, s, the they y deserv deservee car carefu efull consid considera eratio tion. n. This Let Letter  ter  introduces some of the more important matters for consideration. SELECTION CRITERIA

The selection of the proper motor is based on numerous criteria. Included Inclu ded are horsepowe horsepower, r, serv service ice factor, factor, enclosure, enclosure, ambient temperature, phase and voltage, speed, and efficiency.

The The major major di diff ffer eren ence ce in the the BH BHP P cu curv rvee fo forr ba back ckwa wardl rdly yinclined fans is its “non-overloading” characteristic. Figure 2 illustrates a BHP curve that reaches a peak and then drops off  as the volume continues to increase. This makes it possible to select a motor for the maximum BHP at a given speed without fear of overload despite any variance in the volume/pressure relationsh relati onship ip of the installed installed sys system. tem. Since BHP varie variess with changes in fan speed, the non-overloading characteristic only applies to a given fixed speed.

Horsepower.   If all air-handling systems had exactly the same

volum vol ume/p e/pres ressu sure re rel relati ations onship hip the design designer er antici anticipat pated ed,, all motors could be selected merely to cover the fan brake horse power (BHP) calculate calculated. d. However, system design usuall usually y involves some estimating, and systems are not always installed exactly as intended by their designers. With all centrifugal fans, the fan speed must be increased to handle the desired volume when the system resistance is higher  tha than n antici anticipat pated, ed, creati creating ng a sub substa stanti ntially ally highe higherr fan BHP requirement. For radial and forward-curved wheels, if the system res resist istanc ancee is lower lower than than antici anticipat pated ed,, fan BHP will will inc increa rease se with the greater volume of air being handled. Refer to Figure 1.

The fan capacity table (Figure 3) shows the fan BHP for a given volume/pressure relationship. However, it is not uncommon to size the motor for a static pressure 5% to 10% higher than design des ign to allow allow for varian variances ces in the insta installe lled d sys system tem.. The system designer should also be prepared to reduce fan speed if  resistance is lower than anticipated. Motors should be selected so that the fan BHP rating for the requir req uired ed vol volume ume and pre press ssure ure is less less than than the rated mot motor  or  horsepowe horse power. r. The rated motor horse horsepowe powerr is the mechanical mechanical  power available availabl e at the motor shaft at full-load speed without exceeding the motor’s maximum temperature rise.

 

4 ” SP RPM BHP

41/ 2” SP RPM BHP

5 ” SP RPM BHP

5 1/ 2” SP RPM BHP

2100 2200 2300

1140 1154 1167

9 .2 9 9 .7 9 1 0 .2

1194 1205 1218

10.4 10.9 11.4

1248 1257 1269

1300 1308 1318

12607 12924

2400 2500

1183 1200

1 0 .8 1 1 .4

1232 1248

12.0 12.6

1282 13.3 1330 14.6 1296   13.9   1342   15.2

13441

2600

1217

1 2 .0

1263

13.3

1310

CFM

OV

10856 11373 11890

1 1 .6 1 2 .1 1 2 .7

1 4 .5

1355

1 2 .8 1 3 .3 1 3 .9

1 5 .9

Figure 3 - At 12,924 CFM and 5" SP, the BHP required is(5 13.9. With an additional 10% system resistance margin 1 / 2 "  SP), the BHP required is 15.2.

Service Factor.  Integral open-dripproof and totally enclosed motors usually have a service factor of 1.15, while explosion proof motors usually have a 1.0 service factor. When the motor nameplate voltage and frequency frequency are maintaine maintained, d, the motor can be run up to the capacity obtained by multiplying the rated horsepower by the safety factor shown on the motor  nameplate.

For example, a fan in a given system might require 5.0 BHP according accor ding to origin original al estimates, estimates, but minor system changes could increase the demand to 5.25 BHP. In this case, a 5 HP open motor rated with a 1.15 service factor could still be used (5 HP x 1.15 = 5.75 HP) without detrimental overheating. Enclosure. The selection of a motor enclosure depends upon ambient conditions. Electric motors are air-cooled machines and their their servic servicee lif lifee depend dependss gre greatl atly y upon upon protec protectin ting g the motor from contaminated surroundings. Basically, all motor  enclos enc losure uress can be div divide ided d into into two cat catego egories ries:: open open and totally enclosed. OPEN MOTORS - This type is recommended for relatively clean clean envir environm onment entss since since the ventil ventilati ating ng ope openin nings gs permit permit  passage of external cooling air over and around the motor  windings. Open motors are usually less expensive than other  enclosures. DRIPPRO DRI PPROOF OF MOTOR MOTORS S - Thes Thesee ar aree op open en moto motors rs wi with th ventila ven tilatin ting g openin openings gs so con constr struct ucted ed and pos positi itione oned d tha thatt op oper erat atio ion n is no nott hamp hamper ered ed wh when en dr drop opss of liq liqui uid d or soli solid d  parti cles strike the enclosure at any angle from 0° to 15°  particles downward from the vertical axis. The standard insulation is Class B with a 1.15 service factor rating. WPI AND AND WPII WPII MOTO MOTORS RS - Th Thes esee ar aree es esse sent ntia iall lly y open open motors with vacuum vacuum-pressure -pressure impre impregnat gnation ion (VPI) windi winding ng treatment for moisture resistance and weather protection. WPI motors are equipped with space heaters. WPII motors have ventilating openings arranged so that high-velocity air and/or  airborne contaminants blown into the motor during storms or  high winds can be discharge discharged d without without entering the internal internal electrical parts of the motor. Generally, the weather protected motors are only available in frame sizes larger than NEMA sta standa ndard rd and they they are less less exp expens ensive ive tha than n totally totally enclos enclosed ed motors in those cases. TOTALLY ENCLOSED - This type is recommended for any installation where dirt or contaminants can collect in or around the motor. They are constructed in a manner that prevents the

TOTALLY ENCLO TOTALLY ENCLOSED SED FAN FAN-COOLED -COOLED MOTORS - These are totall totally y enc enclos losed ed mo motors tors equip equipped ped with a coo coolin ling g fan, fan, or  fans, fan s, integr integral al wit with h the mot motor or assem assembly bly but extern external al to the enclosed parts. These motors should be installed so that the inta intake ke of the the cool coolin ing g fan fan is not not bl bloc ocke ked d or im impe pede ded. d. Th Thee standard insulation is Class F with a 1.15 service factor rating. TOTALL TOTA LLY Y EN ENCL CLOS OSED ED AI AIRR-OV OVER ER MO MOTOR TORS S - Th Thes esee special-purpose totally enclosed motors are intended for use in fan applic applicati ations ons wh where ere the fan provide providess su suffi fficie cient nt coo coolin ling g airflow over the surface of the motor. However, they are not self self-cool -cooling ing,, so th they ey shoul should d only only be us used ed wh when en air airflow flow is  present at or above the velocities velocit ies necessary for continuous operation within the rated motor temperature rise. TEFC SEV TEFC SEVERE ERE DU DUTY TY MOTORS MOTORS - The These se spe specia ciall pu purpos rposee TEFC motors are intended for use in contaminated environments such as in the paper, metal, or chemical industries. Special features includ includee cas castt-iron iron frame, frame, end bracke brackets, ts, co condu nduit it box and fan cover, cove r, plated plated hard hardware ware,, and stainless steel name nameplates plates.. They are also rated with 1.15 service factors and Class F insulation. Some trade names include “Mill and Chemical,” “Dirty Duty,” “Extra Tough,” and “Chemical Duty.” TOTALLY TOTALL Y ENC ENCLOS LOSED ED NON NON-VENTI -VENTILA LATED TED MOT MOTORS ORS These are basically totally totally enclosed motors with larger frames to dissip dissipate ate hea heat, t, but no coo coolin ling g fan. fan. Typica Typically lly off offere ered d in the smaller fractional horsepowers, these motors should only be used in open, well-ventilated areas. EXPLOSION EXPLOS ION-P -PROO ROOF F MOTO MOTORS RS - These These spe specia ciall-pur purpos posee totall totally y enclos enclosed ed mo motors tors are des design igned ed to wit withst hstand and intern internal al explosions of gases or vapors, and to prevent the ignition of  gases or vapors surrounding the motor. Refer to Engineering Letter 23, Electric Motor Codes and Standards, for details. Various motor insulatio insulation n syst systems ems are avail available. able. Insulation.   Various The rated temperature for a given insulation classification is the maxim maximum um tem temper peratu ature re for susta sustaine ined d ope operati ration. on. Thre Threee common insulation classes are shown in Figure 4. INSULATION NEMA Class B F H

Ambient Temperature* 4 0 °C . 41° - 65°C. 66° - 90°C.

Hot-Spot Temperature 130°C (266°F.) 155 °C. (311°F.) 180 °C. (356°F.)

*Note that these ratings apply to 1.0 service factor only. Figure 4

 Not all parts of the motor windings operate at the same temperature. The temperature at the center of the coil is the hottest, and is commonly referred to as “hot-spot temperature.” This hot-spot temperature is used to establish the rating of an insulation class. The actual temperature is the sum of all the heat-pro heat -producin ducing g facto factors rs inclu including ding the ambient ambient tempe temperature rature,, motor induced temperature rise, and the hot-spot allowance. Ambient temperatures.  Whenever possible it is best to select a motor with the appropriate insulation for the specific ambient conditions. For example, a TEFC motor with Class F insulation is su suita itable ble for ambie ambient nt tem tempera peratur tures es of 40° 40°C. C. (104°F (104°F.) .) wit with h 1.15 service factor or 65°C. (149°F.) with 1.0 service factor. If 

free exchange of air between the inside and outside of the motor case, but they are not airtight.

this this same same moto motorr is used used in an ambi ambien entt of 75 75°C °C.. (1 (167 67°F °F.) .)

Page Page 2  

continuously, the life of the motor will be greatly reduced. Phase and voltage.  Although these are limited to the power  supply sup ply availa available ble at the installa installation tion site, the gener general al rule rule of  thumb is to use polyphase (three phase) motors of the highest availa ava ilable ble voltag voltagee in order order to achiev achievee the most most econom economica icall equipment equipm ent and installation installation costs. Single phase motors typically cost more than polyphase because of the need for capacitors, centrifuga centri fugall switches, switches, etc. Highe Higherr voltage voltage rating ratingss can reduce installation costs by reducing the required electrical line size.

In most U.S. and Canadian industrial sites, the power supply typically found for the average polyphase motor is 230 or 460 volts (U.S.) and 575 volts (Canada) at 60 Hertz (cycles per  second) generation. In many large cities where 120/208 volt networks are employed, commercial and small industrial loads require motors rated for 200 volts. Motors for 2300 volts can be furnished in motor frames 445T and larger. Because of the cost of starting equipment for this higher voltage, 2300 volt motors are not generally available  below 200 HP. Single phase motors are available for service on 115/230 volts for 3 HP and smaller. Motors up to 10 HP are available for  230 volt service in single phase. The standard motor frequencies are 60 and 50 cycles per second, or “Hertz.” The prevailing frequency in the United States and Canada is 60 Hertz. Most of Europe, the Middle East, and the Pacific Rim have 50 Hertz service. Many motors specified for  50 Hertz will require 380 volts, 440 volts, or 220/380 volts . . . all of which are considered standard by motor manufacturers. Although motors built for 50 Hertz are becoming more readily available in this country, consideration should be given to the accepted practice of derating 60 Hertz motor speed and horse power. Ratings can be derated by a factor of .833 (50/60) to determine the operating characteristics in 50 Hertz service. For example: 60 Hertz - 10 HP, 1800 RPM, 3/60/230/460 50 Hertz* - 8.3 HP, 1500 RPM, 3/50/190-380 * Note: This does not apply to single phase or explosion-proof  motors. RPM and Voltage rounded to standard nomenclature.  NEMA stand standards ards state that motors must be capable capable of delive delivering ring their rated horsepower at a variance of nameplate voltage of ± 10% voltage, although not necessarily at the standard rated temper tem peratu ature re rise. rise. One excep exception tion is a mot motor or na namep meplat lated ed as 208-230/460 volts. The ± 10% voltage only applies to 230 or  460, and thus requires very good voltage regulation for operation in a 208 volt network. Another exception is 60 Hertz motors derated for 50 Hertz operation. A 208 volt network requires a 200 or 200/208 volt motor.  Note that the 200/208 does not mean dual voltage, (as with a standard 23 0/460 rating), but is simply a 200 volt motor rated and recommended for 208 volt service. The NEM NEMA A standa standard rd 230 230/46 /460 0 volt volt rat rating ing is not genera generally lly recommended for 208 volt service unless authorized by the motor mot or man manufa ufactu cturer. rer. Motors for us usee in a 208 volt network  network  should be ordered with a 200 volt rating, with windings and nameplate so designed and stamped.

However, Howeve r, belt belt-driv -drivee fan app applic licati ations ons are usual usually ly lim limited ited to 1800 180 0 RPM mot motors ors when when the hor horsep sepowe owerr requir requireme ements nts are 25 and up. Generally, TS (short shaft) frames are used on larger  3600 RPM motors, and these are not well-suited to belt-drive arrangements. Although T frame motors are available for larger  horsepower 3600 RPM motors, they are not standard, so long  procurement  procure ment lead times and cost can be prohib prohibitive. itive. The majority of electric motors used in fan applications are single single spe speed. ed. How Howeve ever, r, mul multis tispee peed d mot motors ors are av avail ailabl ablee in either single phase or three phase. The motor synchronous speed is expressed as: 120 x F Synchronous RPM = P where: F = supply frequency in Hertz P = numb number er of poles in motor winding winding The actual full load RPM (nominal speed) will be somewhat  below the synchrono synchronous us speed. The percenta percentage ge in speed is known as the  percent slip.  Thus, an 1800 RPM (4 pole) motor  with a 2.8% slip will have a full load nominal speed of 1750 RPM (1800 - 50 = 1750). The exact slip percentage will vary from one motor size and type to another. Slip is also somewhat dependent upon load. A  partially  partia lly loaded motor will run slightly slightl y faster than a fully loaded motor. Since calculating the precise nominal speed for  each application would be impractical, the Air Movement and Control Association (AMCA) has established nominal speeds to  be used uniformly to determine fan performance. See Figure 5. NOMINAL SPEEDS FOR 60 HERTZ MOTORS NOMINAL Number Synchronous Nominal of Poles Speed (RPM) Speed (RPM) 2-po le: 3600 th ru 1 H P 345 0 11/ 2thru 25 HP 3 5 00 30 HP and up 3 5 50 4-po le: 1800 thru  3 /4  HP 1 7 25 1 thru 20 HP 1 7 50 25 HP and up 1 7 70

6-po le: th ru 3 H P 5 HPand up 8-po le: thru  1 /8  HP 1/ 2 HP and up

1200 1 1 50 1 1 75 900 850 875

 Note: 50 Hz motor speeds can be determined by multiplying the above ratings by .833 (50/60). Figure 5

Motor Efficiency.  The continued increase in energy costs and emerg emergenc encee of ene energy rgy savin savings gs progra programs ms hav havee he heigh ighten tened ed concer con cern n for electr electrica icall us usage age an and d mo motor tor eff effici icienc ency. y. Goo Good d system design necessitates necessitates the selec selection tion of the most efficient motor for a given application. Motor manufacturers are able to improve motor efficiency by altering any number of design factors. The use of thinner steel laminations in the stator and rotor core, using better grades of 

Speed.   The The gene genera rall rule rule of th thum umb b is to se sele lect ct th thee hi high ghes estt  practical motor speed to reduce the size, weight, and cost of the  practical motor.

steel, more copper in the stator, and more efficient, smaller  cooling fans are just a few examples.

Page Page 3  

In an eff effort ort to distin distingu guish ish one manuf manufact acture urer’s r’s mo motor tor from another, motor manufacturers use a number of names, such as standard, high, premium, etc., to qualify published efficiency va valu lues es.. Th Thee ge gene nera rally lly ac acce cepte pted d ba basi siss fo forr co comp mpari ariso son n of  efficiency effic iency values is the “gua “guarantee ranteed d minim minimum um efficiency” efficiency”  based on NEMA recommend recommendations. ations. Motor efficie efficiency ncy can be calculated by the following formula: Motor Efficiency =

746 x HP output Watts Input

When comparin g d. motor efficiencies, the power powe r facto factor must also also becomparing con consid sidere ered. At aefficien given given cies, eff effici icienc ency, y, a higher hig her rpower  pow er  factor results in a lower current demand. The power factor is the ratio of real current (current required to run the motor) to the total current (real current plus the reactive current that creates the the magn magnet etic ic fi fiel eld). d). Th Thee po powe werr fa fact ctor or fo forr a give given n moto motor  r  should be obtained from the specific motor manufacturer, manufacturer, but it it can be calculated by the following formula: Pow Power Fact Factor or =

Wa Watt ttss In Inpu putt Volts x Amps x 1.73* * For 3-phase motors only.

SPECIAL CONSIDERATIONS

In addition to the previous selection criteria, there are several other special considerations that affect proper motor selection. These include high or low voltage, starting times, minimum sheave diameters, heavy cycling, and excessive loading. High or low voltag voltage. e.   Motor Motor servic servicee lif lifee can be sh short orten ened ed cons conside idera rabl bly y if the the moto motorr is oper operat ated ed ou outs tsid idee the the ± 10% 10% voltage variance range.

With low voltage, motor torque decreases. The motor is therefore forced forc ed to slow slow dow down n to dev develo elop p the required required tor torque que.. Thi Thiss causes increased current draw which creates additional heat in the motor winding. In addition, at the slower speed ventilation is reduced and heat will not be dissipated as rapidly. High voltage will cause an increase in magnetizing current in the motor. This causes additional heating in the motor windings. Particu Part icularl larly y with olde olderr mot motors, ors, increa increased sed voltag voltagee can bre break  ak  down the motor insulation by breachin b reaching g its insulating insulating capability. Starting times. an electric motor is used to drive centrifugal fan,  Whenever both the fan’s maximum power demand anda the motor starting torque characteristics must be considered. Where larger centrifugal fans are to be driven by relatively small motors, motors, it is possible that the motor will not be capable capable of  overco ove rcomin ming g the fan’s inert inertia ia to bring bring it up to the required required speed in a reasonable time. Excessive starting time, generally greater than 10 to 15 seconds, will raise the temperature of the motor windings to a point where circuit breakers can trip out, or the motor itself can be damaged. The user must be aware of this problem when selecting the fan and motor combination.

The two main factors to be considered are the fan wheel inertia (WR   2   or WK   2)  and the starting torque characteristics of the motor. Exact curves of the motor starting torque, as a percentage of full load torque at a given speed, are available from the motor manufacturer. Many fan applications require a fan speed other than a nominal motor speed, so a belt-drive configuration is used. In these cases, the WR 2  must be corrected to include the effects of the

It is best to consult the fan manufacturer for confirmation of  questionable fan/motor combinations, i.e. large fans with small motors. motor s. If the combinat combination ion has an unac unaccepta ceptable ble starting time, the solution could be to use a larger motor, damper the fan for  reduced reduc ed load start starting, ing, or in some some case casess cons consider ider clu clutch tching ing systems so the fan can be brought up to speed without tripping electrical breakers or damaging the motor. Minimum Sheave Diameters. Special consideration should be given to the diameter of drive sheaves used on motors. As belt tens tension ion must must increa increase se to avo avoid id slipp slippag agee with with small small diame diameter  ter 

sh shea eave ves, s, the the radi radial al load load im impo pose sed d on the the moto motorr be bear arin ing g  becomes signifi significant. cant. The motor manufact manufacturer urer can provide specif spe cific ic recomm recommend endati ations ons for minimum minimum she sheave ave diam diameter eters. s. Somee ge Som gener neral al recomm recommen endati dations ons are shown shown in Engine Engineerin ering g Letterr 23 - Electric Motor Codes and Stand Lette Standards. ards. Heavy Cycling. When a motor is started and stopped frequently, heat heat bu build ild-up -up from from the the he heav avy y star starti ting ng cu curre rrent nt cann cannot ot be adequately adequ ately dissipa dissipated. ted. Heat will build up on successive successive starts and the temperature will rise even after the motor is stopped  because air movement is not present for heat dissipation. This type of operation poses unusual problems in the selection of   proper protect protective ive devices. Thermal prote protectors ctors located in the motor starter will cool more rapidly than the motor windings, so  protection  protect ion is compromised. Interna Internall tempera temperature ture sensors, known as thermal overload detectors, can be embedded in the motor motor win windin dings gs to provide provide the best form of protec protectio tion n for  motors subjected to heavy cycling.

Generally, standard integral motors are designed for continuous oper operat atio ion. n. Cy Cycl clic ic serv servic icee of any any fan/ fan/mo moto torr co comb mbin inat atio ion n demand dem andss spe specia ciall con consid sidera eratio tion. n. Such Such situat situation ionss sho should uld be explai exp laine ned d an and d carefu carefully lly rev review iewed ed with with the fan and mot motor  or  manufacturers. Excessive Loading. When too much is demanded of a motor, it willl attem wil attempt pt to com compen pensat satee by draw drawing ing more more cur curren rent. t. Hea Heatt  build-up  buildup is proportional to the square of the increase in current. Properr overload Prope overload prote protection ction will guard against excessiv excessivee heat  build-up; however, it is unwise to use overcurr overcurrent ent protect protectors ors with with au autom tomat atic ic rese resets ts be beca caus usee the the moto motorr can can cycl cyclee un until til enough heat builds up to damage the windings.

The potential problems problems of exce excessiv ssivee loadin loading g are often dealt with by using using backwa backwardly rdly incline inclined d fan design designs. s. As exp explain lained ed  previously,  previou sly, it is possibl possiblee to select a motor for a backwardly inclined fan that will not overload at a fixed speed, regardless of  any changes in system resistance. CONCLUSION

The New York Blower Company frequently supplies the entire fan, drive, and motor package. However, because motor selection is dependent upon the actual location, environment, and intended service, and since only the system designer or end us user er can be fully fully aware aware of these these var variab iables les,,   nyb   cannot cannot be expected to select or recommend motor specifications. The informa information tion contain contained ed in this Let Lettter prov provide idess the sys system tem designer or user with fundamental information to aid in the selection and application of motors. Further information can  be obtained by contacting contact ing motor manufactur manufacturers ers direct directly. ly.

fan shaft and fan sheave. Form 507 DJK 

Page Page 4  

ENGINEERING LETTER

23

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60527 -5530 

E L E C T R I C M O T OR C O D E S A N D S T A N D A R D S INTRODUCTION Electric motors are often required to meet various industry NEC - Nationa Electricc Code is an ANSI standard sponsored -  Nationall Electri standards and national codes in addition to specific application  by the National Fire Protection Association for the purpose of requirements. The more common of these standards and codes safeguarding persons and property from electrical hazards. The are explained in this Engineering Letter. Also included are some code covers wiring methods and materials, protection of general motor dimensions and weights for reference purposes.  branch circuit circuits, s, motors and controls, control s, ground grounding, ing, hazardo hazardous us locations, and recommendations. See Figure 1. In the early days of electric motors, motors were built to the specifications and standards of individual manufacturers. Each Electrical cal Manufactur Manufacturers ers Associati Association on is a NEMA -  National Electri  brand usually had its own unique nomenclature, nomenclatur e, dimensio dimensions, ns, trade association organized and supported by manufacturers of ratings, etc., thus interchangeability was seldom possible. electrical equipment and supplies. Voluntary standards define  products,, processes, and procedur  products procedures es with refere reference nce to Currently, a number of independent groups and several special nomenclature, construction, dimensions, tolerances, operating interest organizations provide uniform specifications to which characteristics, performance, testing, and rating. The standards motor manufacturers can comply on a selective or voluntary cover such matters as motor-frame sizes and designations,  basis. Some of the t he more common of these are li listed sted bel below. ow. circuit connections, lead markings, torque classifications, and a  basis for ratings. Some of the more important import ant items MOTOR STANDARDS ORGANIZATIONS standardized by NEMA are: AIM - Automotive Industrial Motors include specific brands manufactured on a selective basis to meet the specifications Speeds - see Figure 3. established by the automotive industry. Examples include Horsepower Ratings - see Figure 3. GMC - 7EQ, Ford EM-1, and Chrysler NPEM-100. Frame Sizes and Dimensions - see Figure 4. Conduit Box Locations - see Figure 5. ANSI - American National Standards Institute represents Standard Voltages and Frequencies* manufacturers, distributors, and consumers. A wide variety of Service Factors* subjects are covered, such as dimensions, material specifications, Enclosures* test methods, and performance. Standards frequently reference Starting Current those adopted by NEMA and IEEE. Torques CSA - Canadian Standards Association provides material standardization services for Canada. It develops or adopts standards for safety, quality, and performance. IEC - International Electrotechnical Commission defines metric equivalancies to some NEMA standards, such as enclosures, frame sizes, conduit box locations, and mounting arrangements. IEEE - Institute of Electrical and Electronics Engineers covers such fundamentals as basic standards for temperature rise, classification of insulating materials, and the appropriate test codes and rating methods. ISO - International Standards Organization establishes uniform terminology, units, and equivalancies in international metric terms.

* Note: refer to Engineering Letter 22 - Integral I ntegral Motors for Centrifugal Fans. UL - Underwriters Laboratories, Inc. is an independent testing organization specializing in testing products, systems, and materials with particular reference to life, fire, and casualty hazards. Standards have been developed for motors and controls in cooperation with the manufacturers. The variety of standards for motors compliance include: 1.  Motors for use where explosive vapors, combustible dusts, or easily ignitible flyings exist… exist …as adopted by  NEC. 2.  Motor-operated appliances. 3.  Motor overload protection devices.

 

 

NEC EXPLOSION-PROOF MOTOR DESIGNATIONS The National Electrical Code categorizes common hazardous atmospheres and locations. Classification of hazards might be defined by the plant safety engineer or by the insurance company. Since the type and degree of hazard varies widely according to the materials encountered and their probable presence in hazardous quantities, the following methods of identification are used: Class - materials are “classed” as flammable vapors or gases (Class I); or as combustible dusts (Class II).   Group - materials are “grouped” according to their relative degree of hazard with Groups C and D applicable to vapors or gases, and Groups E through G applicable to combustible dusts. Division - the containment aspects are defined by “divisions” according to the likely concentration of the hazard. Division 1 is applicable to routine or periodic exposure, while Division 2 refers to a hazard that is normally confined within a system or container and which would only escape in the event of some abnormal circumstance or equipment failure. NEC requires the use of explosion-proof motors for all Division 1 locations. Class I Group C - Atmospheres containing ethyl vapors, ethylene, or cyclopropane. Class I Group D - Atmospheres containing gasoline, hexane, naptha, benzine, bu butane, tane, alcohol, acetone, benzol, lacquer-solvent vapors, or natural gas. Class II Group E - Atmospheres containing metal dust. Class II Group F - Atmospheres containing carbon black, coal, or coke dust. Class II Group G - Atmospheres ccontaining ontaining flour, starch, or grain dust. The specific motor Class and Group must be determined for the particular hazard involved. Motors designed and rated for one type of hazard or location are not necessarily suitable for use in another situation . . . consult the motor manufacturer for specific application information. The explosion-proof motor ratings normally stocked by motor manufacturers or distributors are Class I, Group D and Class II, Groups F and G, Division 1. Other ratings, such as Class I, Group C or Class II, Group E, Division 1 are non-standard but are available on special order. Figure 1

COMMON MOTOR WEIGHTS AND SHEAVE LIMITS Motor Weights (lbs.)1  Sheave Limitations (Inches) 2  Frame  ODP TE Maximum Width Min. Min./Max. Min./Max. Pitch Dia. Narrow Conven. 143T 145T 182T 184T 213T 215T 254T 256T 284T 284TS 286T 286TS 324T 324TS 326T 326TS 364T 364TS 365T 365TS 404T 404TS 405T 405TS 444T 444TS

26/41 33/55 50/105 60/120 90/137 100/160 145/275 160/3 10 228/374 225/372 275/409 250/380 366/495 333/478 415/600 406/565 580/792 519/777 620/835 600/821 845/1110 750/1108 816/1163 800/1150 1122/1528 1100/1515

28/65 35/70 55/111 70/125 99/197 121/224 23 1/384 265/415 359/495 356/425 390/499 380/475 490/700 458/671 526/766 490/73 8 748/948 730/916 804/1040 777/1004 1100/1220 1000/1211 1049/1368 907/1312 1400/1820 1365/1799

2.2 2.4 2.6 3.0 3.0 3 .8 4.4 4.6 5.0 * 5.4 * 6.0 * 6.8 * 7.4 * 9.0 * 9.0 * 11.5 * 11.0 *

21/4 21/4 23/4 23/4 33/8 33/8 4 4 45/8 * 45/8 * 51/4 * 51/4 * 57/8 * 57/8 * 71/4 * 71/4 * 81/2 *

41/4 41/4 51/4 51/4 61/2 61/2 73/4 73/4 9 * 9 * 101/4 * 101/4 * 111/2 * 111/2 * 141/4 * 141/4 * 163/4 *

445T 445TS

1250/1750 1200/1600

1500/2458 1481/2300

13.2 *

81/2 *

163/4 *

* Not recommended for b elt drive Figure 2

NEMA STANDARD FRAME SIZES Rating (HP)  3/4 1 11/2 2 3 5 71/2 10 15 20 25 30 40 50 60 70 100 125 150 200

Synchronous Speed (RPM)  3  3600 1800 1200 ODP TEFC ODP TEFC ODP ODP TEFC --143T 145T 145T 182T 184T 213T 215T 254T 256T 284TS 286TS 324TS 326TS 364TS 365TS 404TS 405TS 444TS

--143T 145T 182T 184T 213T 215T 254T 256T 284TS 286TS 324TS 326TS 364TS 365TS 405TS 444TS 445TS 447TS

-143T 145T 145T 182T 184T 213T 215T 254T 256T 284T 286T 324T 326T 364T 365T 404T 405T 444T 445T

-143T 145T 145T 182T 184T 213T 215T 254T 256T 284T 286T 324T 326T 364T 365T 405T 444T 445T 445T

143T 145T 182T 184T 213T 215T 254T 256T 284T 286T 324T 32 6T 36 4T 36 5T 40 4T 40 5T 444T 445T 445T 445T

143T 145T 182T 184T 213T 215T 254T 256T 284T 286T 324T 326T 364T 365T 404T 405T 444T 445T 445T 447T

Figure 3

1. Motor weights are not standardized and vary with manufacturer, enclosure, frame, etc. The minimum and maximum weights shown are representative of the range available from several major manufacturers as of March, 2018. Where exact weights are required, consult the specific manufacturer. 2. The sheave limitations shown represent the most restricted  parameters from several major manufacturer manufacturers. s. It may be possible to exceed these parameters for a given situation by consulting the specific manufacturer. 3. Motor frame sizes may vary with special features or characteristics. Refer to Engineering Letter 22 - Integral Motors for Centrifugal

Refer to Engineering Letter 22 Fans for nominal speeds.

Integral Motors for Centrifugal

Page 2  

NEMA STANDARD DIMENSIONS (Inches)

C-ODP1 

Frame

BA

D*

E

F

143T 145T 182T 184T 213T 215T 254T

2.25 2.25 2.75 2.75 3.50 3.50 4.25

3.50 3.50 4.50 4.50 5.25 5.25 6.25

2.75 2.75 3.75 3.75 4.25 4.25 5.00

2.00 2.50 2.25 2.75 2.75 3.50 4.12

.875 .875 1.125 1.125 1.375 1.375 1.625

2.00 2.00 2.50 2.50 3.13 3.13 3.75

Min. 10.99 11.12 12.36 13.56 15.50 16.31 20.00

Max. 12.82 12.99 14.72 16.50 18.19 18.19 22.32

C-TE1  Min. Max. 10.45 13.35 11.45 14.35 13.55 17.15 13.55 17.15 17.18 20.28 17.18 20.28 21.50 25.60

256T 284T 284TS 286T 286TS 324T 324TS 326T 326TS 364T 364TS 365T 365TS 404T

4.25 4.75 4.75 4.75 4.75 5.25 5.25 5.25 5.25 5.88 5.88 5.88 5.88 6.63

6.25 7.00 7.00 7.00 7.00 8.00 8.00 8.00 8.00 9.00 9.00 9.00 9.00 10.00

5.00 5.50 5.50 5.50 5.50 6.25 6.25 6.25 6.25 7.00 7.00 7.00 7.00 8.00

5.00 4.75 4.75 5.50 5.50 5.25 5.25 6.00 6.00 5.62 5.62 6.12 6.12 6.12

1.625 1.875 1.625 1.875 1.625 2.125 1.875 2.125 1.875 2.375 1.875 2.375 1.875 2.875

3.75 4.38 3.00 4.38 3.00 5.00 3.50 5.00 3.50 5.63 3.50 5.63 3.50 7.00

21.69 23.19 21.82 23.81 22.44 21.38 21.38 26.69 25.19 28.62 26.50 26.57 27.50 32.38

23.19 25.94 22.44 25.06 23.69 27.25 25.75 28.50 27.00 29.69 29.70 29.69 29.81 34.19

23.20 25.33 23.95 26.83 25.45 28.15 26.65 29.65 28.15 31.28 29.15 31.28 29.15 33.88

25.60 28.93 27.55 28.93 27.55 32.25 30.75 32.25 30.75 34.28 32.15 34.28 32.15 39.91

404TS 405T 405TS 444T 444TS 445T 445TS

6.63 6.63 6.63 7.50 7.50 7.50 7.50

10.00 10.00 10.00 11.00 11.00 11.00 11.00

8.00 8.00 8.00 9.00 9.00 9.00 9.00

6.12 6.87 6.87 7.25 7.25 8.25 8.25

2.125 2.875 2.125 3.375 2.375 3.375 2.375

4.00 7.00 4.00 8.25 4.50 8.25 4.50

29.38 33.88 30.88 37.56 33.81 38.62 35.87

31.19 34.19 31.19 39.94 36.18 39.94 36.18

30.89 36.85 33.85 39.56 35.31 39.56 35.31

36.91 41.95 38.95 46.68 42.93 48.68 44.93

U

 

V † 

*Tolerance: 8" or less, + .000, - .03 1, Over 8", +.000, - .062.  Tolerance: 11 / 2 " dia. or less +.0000, - .0005; Over 11 / 2 " dia. + .000, - .001. † V is usable shaft length.  length.   Figure 4

1. The overall motor length is uniformly designated as  NEMA “C,” “C,”   but the dimension itself varies between manufacturers. The “C” dimensions shown are

2. The distance from the center of the motor shaft to the outside edge of the conduit box is known as NEMA “AB.” Since this dimension varies with manufacturer,

representative of the range available from several manufacturers as of March, 2018. Where exact dimensions are required, consult the specific motor manufacturer.

enclosure, frame, etc., consult the specific motor manufacturer.

Page 3  

Conduit-box locations . . . the standard location for floor mounted motors is designated as F-1, where the conduit box is on the right when viewing the end opposite the shaft. Although other arrangements are available as indicated, theyand are extended non-standard and require special production delivery schedules in most cases. Thus, the F-1 is used for the majority of fan applications regardless of fan arrangement. arrangem ent. See Figure 6. Assembly F-1, W-2, W-3, W-6, W-8 and C-2 = Standard Lead Location. Assembly F-2, W-1, W-4, W-5, W-7, and C-1 = Lead Location Opposite Standard.

MOTOR ROTATION DESIGNATIONS

Motor rotation . . . the direction of the motor rotation can be significant, particularly in large fan-cooled motors. The increasing demand for energy-efficient and quiet-operating motors has forced motor manufacturers to use uni-directional cooling fans in many cases. Thus, the motor manufacturer will need to know the required rotation in many cases. Most motor manufacturers specify CW or CCW when viewing the end opposite the shaft. Therefore, the motor rotation will be the same as the fan rotation in Arrangements 4, 7, 8, and 1 or 3 with motor  positions  posit ions X and Y. The moto motorr rota tion will be opposite the fan’s in Arrangements 9, 10, and 1 or 3   with motor positions W and Z. This may differ with some manufacturers, since there is no formal standard.

Figure 6 Form 318 JLK

   

ENGINEERING LETTER   24 The New York Blower Company   ●  7660 Quincy Street, Willowbrook, Willowbrook, Illinois 60521-5530

F U N D A M E N T AL S O F S T E A M INTRODUCTION

A good knowledge of steam heating, for process work and air  handling/ventilation systems, is important to design engineers,  building  buildi ng owners, and maintenance mainte nance personnel personne l who may encounter steam systems. This Engineering Letter was written as a basic reference tool, primarily for those who have not been regula regularly rly involv involved ed in des designi igning ng and operati operating ng steamsteam-heati heating ng systems. LATENT HEAT

One of the fac factor torss import important ant in hol holdin ding g the ear earth’ th’ss su surfac rfacee temper tem peratu ature re withi within n its rather rather narrow narrow bounds bounds is the fac factt tha thatt wh while ile it take takess abou aboutt 1 Btu to ch chan ange ge the the tempe temperat ratur uree of a  pound of liquid water by 1 °F., it takes 144 Btu to freeze one  pound of water (latent heat of fusion) and about 1000 Btu to conver con vertt one pound pound of water water to ste steam am (laten (latentt heat heat of ev evap apooration). The relatively large amount of heat change required to convert water into either ice or steam acts to keep the earth’s temperature moderate. Heating water from 32°F. to its boiling point, 2 12°F. at sea level, requires about 180 Btu per pound (one Btu per degree). This is referred to as sensible heat. Converting the water at 212°F. to steam at the same temperature requires about 1000 Btu per pound. This is the heat applied in a steam boiler. Conversely, when the latent heat is extracted from the steam,  perhaps by condensing it in a section of STEELfin coil, the 1000 100 0 Btu per pound pound is given given up by the ste steam am witho without ut any change in temperature. Figure 1 shows how the temperature of one pound of water  would vary if subjected to a constant rate of Btu input. Notice that it would stay at 32°F. and 2 12°F. (at sea level) until, in each case the latent heat conversions had taken place for the entire pound of water.

BTU to raise the temperature of one pound of water. Figure 1

SATURATION

If a contai containe nerr of wa water ter is hea heated ted sufficie sufficientl ntly y at a con consta stant nt  pressure, the water temperature will rise until the boiling point is reached. While boiling, the temperature will remain constant un until til all the wa wate terr has has be been en co conv nver erte ted d to steam. steam. Th Then en th thee temperature will rise again as the steam is further heated, as shown in Figure 1. Steam at the temperature at which it co-exists with water is called  saturated steam.  The temperature is called the   saturation temperature.  The saturation temperature varies with with the the pre press ssur ure. e. An incr increa ease se in pr pres essu sure re incr increa ease sess the the temperature at which the latent heat transfer takes place. The  pressure at which the latent heat transfer takes place (at a gi give ven n tem tempe pera ratu ture re)) is call called ed the the   satura saturation tion press pressure. ure.

 

For example, at sea level normal atmospheric pressure is 14.7 The increase in temperature above the saturation temperature  psia (absolute pressure). The saturation temperature is 212°F. At is called   superheat.  Steam that has a small amount of super2 12°F. the saturation pressure is also 14.7 psia (which is also 0 heat is called   dry steam.   If heated more than a few degrees abov ovee the the satur aturat atio ion n tem tempe perratu ature it is ref referre erred d to as  psig see Pressur Pressures, es, below). Almost all useful steam-h steam-heat eat ab Obviously, neithe neitherr dry nor supe superheat rheated ed tran transf sfer er work work take takess pl plac acee at the the late latent nt heat heat--sa satu tura rati tion on  su pe rh eated ea ted st ea m.   Obviously, temp temper erat atur uree and and pr pres essu sure re po poin int. t. Satu Satura rati tion on pr pres essu sure res, s, steam can co-exist with liquid water. Since steam is a gas it tends tends to expand expand with a dire direct ct relati relation on to tem temper peratu ature. re. The temperatures, and latent heat values are shown in Figure 2. increased volume and small amount of extra heat value makes superheat a relatively worthless factor in steam heating. Its only real value is to ensu ensure re that there will be dry steam at the Gauge Pressure

Temp. °F.

Latent Heat

Gauge Pressure

Temp. °F.

Latent Heat

2 5 10 15 20 25 30 40 50 60 70

219 227 239 250 259 267 274 286 298 307 316

966 960 953 945 939 933 929 920 912 905 898

80 90 100 110 120 130 140 150 175 200

324 331 338 344 350 356 361 366 377 388

891 886 880 875 871 866 861 857 847 837

Steam gauge pressures, saturation temperatures, and latent heat values at sea level, standard barometric pressure of  29.92" Hg = 14.7 psia. Figure 2

 point where the steam is to be used. In other condensation words, a few degrees of superheat at the boiler will minimize in the supply lines to the steam coils. CONDENSATION

When steam gives up its latent heat and changes from saturated ste steam am to wa water ter at the same same tempera temperatur ture, e, it con conden denses ses.. The water is referred to as  condensate. HEAT TRANSFER 

Figure 3 shows the cross section of a typical steam coil. The he heat at pr prod oduc uced ed by the the cond conden ensa sati tion on of the the stea steam m trave travels ls th thro roug ugh h th thee bo bou unda dary ry lay layer of steam team,, th thro roug ugh h th thee condensat conde nsation ion that forms on the insid insidee of the tube, throug through h the tube itself, out into the fins, and through the boundary layer of  air on the fins’ surfaces and into the passing stream of air.

PRESSURES

In the the En Engl glis ish h syst system em of meas measur ure, e, stea steam m press pressur ures es ar aree measu mea sured red in pounds pounds per sq squar uaree inch. inch. In intern internati ationa onall un units its,, steam pressures are measured in pascals or kilopascals where 1  psi is equal to 6894.7 pascals. For the sake of simplicity, simpli city, English units are used in this Engineering Letter. There The re are are,, necess necessari arily, ly, two ref refere erence nce levels levels for me measu asurin ring g  pressur e. One is the pressure above atmospheric.  pressure. atmospher ic. This is the  boiler pressure pressure,, commonly called   g a ug ug e p r eess su su r e   and abbreviated either psi or psig. Because of the variable nature of  atmosp atm ospher heric ic pressu pressure, re, ste steam am pres pressu sures res are more more acc accura urately tely described in terms of their absolute pressure. This is the total amount amo unt of pressu pressure re abo above ve a per perfec fectt vacuum vacuum.. At se seaa level, level, atmospheric pressure is 14.7 psia. Hence gauge pressure (psig) + 14.7 = absolute pressure (psia). SUPERHEAT

Steam is a gas. As in the case of any gas, it can be heated ab abov ovee th thee bo boil ilin ing g po poin int. t. On Once ce it is past past the the sa satu tura rati tion on temperature it requires only about .5 Btu per pound to increase its temperature 1°F.

Steam coil cross-section showing the temperature gradient with 5 psig steam (227°F. saturation temperature) heating air to 90°F. Figure 3

All steam coils are 100% efficient in the sense that the heat released by condensing steam within the coil has nowhere to go but into the air surrounding the coil. Tube-and-fin material, fin spacing, air velocity, and some other factors affect the  rate at which which the heat transfe transferr (and therefor thereforee the condens condensation ation)) takes place but they cannot alter the fact the steam’s latent heat has only one place to go: into the airstream.

Form 607 GAW

 

ENGINEERING LETTER   25 The New York Blower Company   ● 7660 Quincy Street, Willowbrook, Illinois 60527-55 60527-5530 30

INDUSTRIAL STEAM HEATING SYSTEMS INTRODUCTION

Reduced to its barest elements, a steam heating system consists of a boiler to convert water to steam, piping to conduct the st stea eam m to wher wheree it is to be use used, d, a co coil il or ot othe herr su surf rfac acee fo for  r  condensing the steam and transferring the latent heat from the st stea eam m to the the ai air, r, a trap trap to pr prev even entt the the stea steam m fro from m pass passin ing g through the coil before it is condensed, and return piping to  bring the condensat condensatee back to the boiler boiler.. The purpose of this Engineering Letter is to provide a basic overview of the major  elements found in typical industrial steam heating systems.

1. The meta metall or metals of which a stea steam m coil is manufacture manufactured d are relati relativel vely y un unimp importa ortant nt insofa insofarr as hea heatin ting g capaci capacitie tiess are concerned but may be extremely important in determining the life of the coil. Coils have been successfully made from almost every conceivable conceivable metal. Copper tubes have have long been a favorite  because of copper’s supposed corrosio corrosion n resistance resista nce and ease of  so solde lderin ring, g, br braz azin ing, g, and and fo form rmin ing. g. Howev However er,, oth other er tube tubes, s,  particularly steel, are quite adaptable to the manufacture of  steam coils. Conventional copper or steel tube coils are usually adequate for commercial heating installations.

SYSTEM COMPONENTS Boilers

While the boiler and its attachments are major factors in the

2. Ind Indust ustria riall hea heatin ting g and proc process ess app applic licati ations ons demand demand the most rugged possible coil construction. The most practical coil is one us using ing he heavy-g avy-gaug auge, e, wel welded ded-s -stee teell tub tubes es wit with h an ova ovall-

steam heating system, it isboilers noters theare intent of this Letteredtointo doo shap shaped cross-s cross-sectio ection. n. The resu resultant ltanttubing. strength severa several l times moree tha mor than n point poin t out that boil gen genera erally lly divided divid int that ed of light-gauge copper or steel A is round tube will “Low Pressure” Pressure” and “High Press Pressure” ure” designs. designs. Low pressure split when filled with water and frozen, as so often happens  boilers,  boiler s, running up to 15 psig, are generally generall y used for space when when the con conden densat satee return return syste system m fails fails for one reason reason or  heatin hea ting g with uni unitt hea heater ters, s, makemake-up up air un units its,, heatin heating g and another. An oval tube deforms slightly, increasing its crossventilating units, etc. There is no benefit in raising the steam sectional area, but rupture normally will not occur if the oval  pressure or temperature much beyond the minimum needed to tube is made of heavy-gauge, high-strength steel.  boil water and to provide the pressur pressuree necessary to drive the steam through through the piping system. system. Higher pressures pressures not only 3. Cond Condensa ensate te is water and it runs down downhill. hill. The conde condensat nsatee require requ ire mor moree exp expens ensive ive pi pipin ping g and fitting fittingss but the added added drains from the coil’s tubes by gravity. Good coil installation danger involved in higher pressures and temperatures has given  produces an almost unifor uniform m pressur pressuree through the coil. The rise to municipal and insurance codes requiring additional safety stea steam m pre press ssur uree cann cannot ot an and d does does no nott forc forcee the the cond conden ensa sate te features, licensed operators, etc. through the tubes. For high heating capacities, the tubes should  be vertical. vertica l. This allows quick drainage drainag e and clearing of the High Hig h pr pres essu sure re boil boiler erss ge gene nera rate te more more than than 15 ps psig ig.. Hi High gh-- tubes. In addition to reducing the possibility of freezing, the wash shin ing g acti action on broug brought ht ab abou outt by the the quic quick k dra drain inage age also also  pressure systems are used either to provide provid e adequate pressure wa for long runs of steam piping or to develop higher temperatures reduces the boundary layer of water in the tubes and improves for process systems. The air passing across a steam coil cannot heat transfer.  be heated any higher than the steam temperature. temper ature. At 5 psig the steam temperature is 227°F. At 200 psig it is 388°F. There is little difference between the amount of total heat at 5 psig and at An advantage of vertical-tube coils, often overlooked, is their  lack of suscep susceptib tibilit ility y to wat water er ham hamme mer. r. Wat Water er is virtua virtually lly 20 200 0 psig psig bu butt the the fact fact that that the the he heat at is re rele leas ased ed at a hi hig ghe her  r  lack incompress pressible. ible. When driven through a pipe or coil tube at the temperature gives the capability of producing substantially higher  incom velocity of steam, it “hammers” the turns in the pipe or the end final air temperatures. of the coil tube. Vertical drainage eliminates water hammer in vertic ver tical-tub al-tubee coi coils. ls. Hor Horizo izonta ntall-tube coi coils ls are destro destroye yed d by Piping repeated water hammer. Typically, water hammer results in a Piping is addressed on page 3. fairly uniform bulge, or rounding, at the end of the steam coil tube. When the bulge finally ruptures it is frequently mistaken Steam Coils for failure due to freezing. The visual distinction between the The steam coil is the part of the system designed to condense results of the two kinds of failures is that water hammer gives a the steam and transfer the latent heat to the airstream. If all coils are 100% efficient, then what differentiates a good steam coil from a poor one? Here are some important factors:

symmetrical bulge at the end of the tube, where freezing gives a non-symmetrical distortion.

 

4. Lack of maintenance maintenance,, particularly in industrial industrial plants, can cause deterioration of the coil and of its capacity. Coils with thin thin co copp pper er tube tubess an and d thin thin alum alumin inum um or co copp pper er fins fins ar aree  physically  physical ly weak. Normal industr industrial ial cleaning methods can be too rough. Cleaning Cleaning aluminum or copper fins with an air hose is almost certain to deform the fins and result in a loss of heating capacity. Welded-steel tubes with steel fins bonded to them and reinfor rein forced ced with with hothot-dip dipped ped galvan galvanizi izing ng off offer er the physic physical al str streng ength th to withs withstan tand d scrubb scrubbing ing or high high-p -pres ressure sure air-h air-hose ose cleaning.

For systems systems with mod modula ulating ting types types of steam steam con control trol,, the trap should be at least twelve inches below the coil to ensure the trap of a water head when the modulating valve has throttled down to 0 psig at the coil. Therefore, for modulating systems, the trap should be sized to handle the maximum condensate load load at the the pre press ssur uree avai availa labl blee in the the wate waterr leg leg only only.. For a twelve-inch leg, this would be .43 psi.

Although not precisely related to the subject of this Engineering Letter, it seems worth recording the “Steam Formula”, the equation used to predict coil performance at one steam pressure and entering air temperature from the performance of the same coil at the same standard air velocity but at a different steam  pressuree and/or enteri  pressur entering ng air temperat temperature: ure:

The Float and Thermostatic Trap   shown in Figure 1 is the closest close st thing to a gene general-purp ral-purpose ose trap for industria industriall heati heating ng and process process work. F and T traps traps fun functi ction on well well ove overr broad broad ranges ran ges of pre press ssure ure and steam steam vol volume ume.. The They y are esp especi eciall ally y suita su itable ble for low to mediu medium m press pressure uress up to abo about ut 20 psig. psig. However, they should not be used on systems involving steam that is superheated more than a few degrees. In operation, air is vented through the thermostatic element on systems with under  20 psi steam pressur pressuree at the coil. Conde Condensa nsate te rais raises es the float, opening the lower port.

TR 1   ST 1  - EAT 1 TR 2   ST 2  - EAT 2

, where

TR is air temperature rise through the coil, ST is steam saturation temperature, EAT is entering air temperature. Traps

All steam traps serve the same basic purposes:

The two types of traps of most interest for industrial heating and process work are described below:

The Inverted Bucket Trap  of Figure 2 should, generally, take the place of the F and T trap for both high pressure steam and for superheated steam systems. There are other types of traps,  but they should not be used as condensate traps on heating and

ventilating systems.

1. The trap prevents prevents the higher steam supply pre pressure ssure from  passing direc directly tly to the return line. If the supply pressure had ready access to the return piping, the whole system would be at the same pressure and there would be reduced steam flow. 2. The steam steam must not be allo allowed wed to pas passs thr throug ough h the trap until it has condensed in the coil. The whole purpose of the steam heating system is to condense the steam in the coil, and nowhere else. 3. When a steam heating heating sys system tem is started up, the system system is fill filled ed wit with h air air.. The wa water ter use used d to produc producee ste steam am contain containss dissolved air, which is released when the water is heated. It may also contain nascent oxygen and noncondensable gases which can form CO2  and which, if not released immediately from the coil, will inhibit heat transfer and may attack the tube walls. The air and gases must be allowed to pass through the coil and out of the trap. On high-pressure steam systems, the trap may not have enough air-venting capacity. Refer to note 3 on condensate piping later on in this Letter.

Float and Thermostatic Trap (Courtesy of Sarco Co.) Figure 1

All traps are rated on the basis of constant steam and condensate flow at a differential in pressure across the trap. In practice, consta con stant nt flow flow rates rates are se seldom ldom enc encoun ounter tered. ed. Tempera Temperatur turee control variations are the principal cause of uneven flow rates. All steam traps should should be sized to handle handle three times the anticipated antic ipated maximum conde condensate nsate rate to ensu ensure re conde condensat nsatee removal under surge-load conditions and cold startups. Condensate will not flow from one side of a trap’s orifice to the other without a pressure differential. For systems with non-modulating types of steam control, the trap must at least be below the coil to ensure that the water 

Inverted Bucket Trap (Courtesy of Sarco Co.)

level in the trap is below the coil.

Figure 2

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PIPING

The key to successful steam piping requires that these two  princi ples be kept in mind:  principles A. Steam is a gas and and can flow flow in any direction, direction, but but condensate, a liquid, flows downhill. C. Bot Both h st stea eam m and and co cond nden ensa sate te ca caus usee fr fric ictio tion n wh when en they they flow. As with air flowing in ducts, consideration must be given to velocity, pipe size, and pressure drop. Bringing the steam to the coil is not nearly so difficult nor  troublesome as getting the condensate from the coil back to the boiler. boiler. Bec Becaus ausee “s “steam team”” is the workin working g eleme element nt in the system and condensate is, after all, only ordinary water, we ten tend d to concen concentrat tratee our attent attention ion on the steam steam piping piping and ignore the condensate piping. We should do just the opposite. Although Althou gh the follow following ing discussi discussion on treats steam piping first, it is the return piping that demands most careful attention. Referring to Figures 3 (Low Pressure) and 4 (High Pressure) the elements of a good steam-piping system are: A. Ste a m m a i ns  must be sized based on the steam pressure, how much of the pressure may be used to overcome friction drop, dro p, and the lengt length h of the long longest run. (Syste (System m design designers ers accustomed to air-duct design will recognize the basic similarity.) A nomograph for sizing steam pipes is contained on page 8.

Pipe expands when heated. The increase is .00008 in./ft.°F. A 10 100 0-foot -foot lo long ng main ain fo forr 50 psig psig stea steam m would ould ex expa pand nd .00008(100) (298-70) = 1.82". Piping must be installed so the expansion may take place without placing stress on the pipe or  the equipment to which it is connected. Some of the methods employ employed ed to acc accomm ommoda odate te expans expansion ion are me metal tal bellow bellowss expansion joints, expansion loops (Figure 5), swing connections (Figure 6), and pipe-support brackets employing rollers.

Page Page 3  

Some steam condenses in the steam mains. The amount may  be minimized minimiz ed by insulati insulating ng the pipes and by using superheat superheat,,  but all steam supply piping should provide provid e for condensate drainage. Vertical-steam pipes cause no particular problem if the steam if fl flow owin ing g dow down, n, but but long long upup-flow flowin ing g st stea eam m lin lines es ca can n be trouble trou blesom some. e. Water Water ham hamme merr can be avoide avoided d by instal installing ling a short horizontal swing connection and drip leg every 20 to 40 feet. The condensate that forms in the steam pipe is passed through a trap to the return (condensate) line. (Sometimes the connection and trap are called the  drip leg  and  and  drip trap.)  See Figure 7.

Steam or Condensate Strainers (Courtesy of Sarco Co.) Figure 8

C. Condensate (return) piping  should include:

1. A stub pipe or ““dirt dirt pock pocket”, et”, at least least 8" long, dir directly ectly b below elow the coil. This is simply a settling spot for dirt and scale, and should be periodically emptied.

Figure 7 -Drip Leg and Trap Systems Use Swing Connection Connectionss

The purpose of good drainage and drip lines is to avoid water  hammer. Steam traveling at high velocity has the capability of  scooping up condensate and driving it, in slugs, against a pipe tur turn, n, va valve lve,, coil, coil, etc etc.. The ha hamme mmering ring effect effect can be violen violentt enough to burst pipes. The only prevention of water hammer is to keep the steam lines “dry”, i.e., clear them of condensate at frequent intervals. B. Stea Steam m supp supply ly to the the coil coilss   shoul should d co cons nsis istt of thes thesee components:

2. The The stra strain iner er,, Figu Figure re 8, with with the the di dirt rt pock pocket et,, keep keepss ext extran raneou eouss matte matterr from the mecha mechanis nism m of the trap. trap. Boi Boilers lers,,  pipes, and coils are apt to contain small particles of scale, weldspatter or thread-turnings. The strainer in the condensate line is intended primarily to pick up dirt, pipe dope, etc., that find their  way into the system during installation. The element should be remove rem oved d from the conden condensat satee str strain ainer er assem assembly bly afte afterr the system is fully in operation. It should not be replaced. The strainer on the supply side of the coil is adequate for the entire system. Since “high pressure” steam implies high velocity and rapid scouring of dirt from pipes, especially when the system is ne new, w, it may may be bes bestt to us usee strai straine ners rs th that at are are av avai aila lable ble with accessory blow-down valves for frequent and quick cleaning.

3. On highhigh-pre press ssure ure sys system tems, s, over 15 psig, it is desir desirabl ablee to 1. A drip line and trap shoul should d par parall allel el the coils coils unless unless the  provide more air- venting capacit capacity y than is incor incorporated porated in the coils are located quite close to a drip line on the main. The trap. This may be done in one of two ways: steam supply should rise above the drip line, as it approaches the coil, for best drainage. a. With an air eliminator, which is a thermostatic vent. This type should should be used only if it can be guarantee guaranteed d to operate operate 2. Swing Swing connec connections tions,, see Figures 3, 4, and 6, from the main at the elevat elevated ed tem temper peratu ature re cor corres respon pondin ding g to the ste steam am to the branch and from the branch to the coils. temperature. 3. A strainer strainer to keep foreign foreign matter out of the val valves, ves, coil coils, s, and traps. See Figure 8. 4. A shutoff valve valve for possible m mainten aintenance ance use. use. 5. A pressur pressure-control e-control v valve alve.. 6. A un union ion.. By putti putting ng unions unions and shutoff shutoff valves valves on both si side dess of co coils ils and tra traps ps,, an indiv individ idua uall co coil il or trap trap may may be removed without shutting down the entire system.

 b. By means of a petcock left continuo continuously usly open. The lost steam is far less costly than the damage done to coils by inadequate venting. Improper venting of high pressure systems is a major cause of  coi coill pro proble blems ms.. The hig high-temp h-tempera eratur turee gas gases es entrai entrained ned in the steam, if not eliminated, may combine with the condensate to form acids.

Page Page 4  

6. Where Where ove overhe rhead ad return returnss are una unavoi voidab dable, le, the onl only y goo good d sol soluti ution on is to dro drop p firs firstt into into a ven vented ted reserv reservoir oir (so (somet metime imess called receiver) and use a motor-driven condensate pump to lift the water into the overhead line. This relieves the trap and coil of the dangers of waterlogging. Despite all of the reasons for not using overhead returns without condensate pumps, such installations are found. In fact, they are so common that they will be discussed here. This is best do done ne by diffe differe rent ntia iati ting ng betw betwee een n thos thosee sy syst stem emss that that us usee modulating steam control and those that use non-modulating control. a.

4. The traps, described in a previous section, must be installed  below the coils. Water flows downhill. downhill . Overhead return lines (Figure 9) are perhaps the biggest single cause of freezing, water  hammer, coil corrosion, and trap failure. While it is theoretically possible for the steam pressure in the coil to push (lift) water into an overhead return line there are  just too many reasons why the pressur pressuree may not be available availab le whe when n mos most t needed needed. Consid er,through for ex examp ample, le, a the 25 remaining psi boiler  boiler  system. Assuming a. 5Con psi sider, drop the lines, 20 psi should be able to raise water 46 feet. (One sea level atmosphere atmos phere is equal to 14.7 psi. This is, in turn, equiv equivalent alent to a “hea “head” d” of 34 feet feet of wa water ter.. Stat Stated ed di diff ffer eren entl tly, y, stan standa dard rd  barometric pressure at sea level is 34 feet of water. Since 14.7  psi will “lift” 34 feet of water then 1 psi will lift 2.3 feet and the 20 psi in the example will lift 46 feet.) On this basis a 15foot “lift” into an overhead line would seem reasonable.

settles out across a coil and is allowed to sit there for any length of time, the coil is apt to corrode at the water  surface.  b.

But,, on the first cold Monday But Monday morning morning of winter winter,, when when the  plant heating and process systems were shut down over the we week eken end, d, ever every y term termin inal al on the the stea steam m sy syst stem em wi will ll be at maximum demand. The boiler may develop only 20 psi. The steam will travel at higher-than-ordinary speeds, and the  pressur  pressure may become 10pressure psi. The steam normall normally y thoughteofdrop as having negligible drop, willcoils, be temporarily starved for steam. The steam will condense so rapidly in the cold coils that the 10 psi at the coil inlets might drop to 5 psi in the coils. Five psi will lift water 11 1/ 2  feet, but cannot buck the 15-foot rise. The trap and coil will become waterlogged. Water  hammer may be severe in horizontal tube coils. If the coil is handling air below 32°F. the coil will freeze. Or, consider shutting down the same system at the end of the heating season. As the steam pressure drops, a point is reached where the coil is again waterlogged. A stagnant water level in a coil is an invitation to corrosion. 5. Not shown in Figures 3 or 4, but often advantageous, is an “aquastat” strapped to the return line just beyond the trap. It is

Non-mo Non-modul dulati ating ng control control syste systems ms may be calcu calculat lated ed as the steam pressure is always great enough to overcome the rise in the return line. It can be argued that there are stea steam m syst system emss that that do no nott invo involv lvee hand handli ling ng low lowtemper tem peratu ature re air and theref therefore ore pre presen sentt no proble problem ms of  fr free eezi zing ng.. Su Such ch a sy syst stem em mig might ht be a pro proce cess ss sy syst stem em comple com pletely tely enc enclos losed ed within within a manuf manufact acturi uring ng plant. plant. Howev How ever, er, even in such such a sys system tem there come comess a tim timee when the steam valve is shut off. The condensate that is, at the moment, on the supply side of the trap cannot be discharged disch arged from the syst system em (unle (unless ss fitted with ano anothe ther  r  small sma ll tra trap p line line that that can drain this trapped trapped wa water ter into a sewer) and if the water level happens to be such that it

Modulat Modulating ing systems present a unique situation situat ion in that under   most   conditions the only pressure available at the trap is the water leg between the coil and the trap. For  example, a coil that will heat from -10°F. to 60°F. with 5  psig (227°F.) steam will heat from -4°F. to 60°F. with 0  psig (212°F (212°F.) .) steam. This not only makes contro controll difficult but aggravates the condensate removal problem. Therefore, a modulating system must be provided with a vacuum-breaker on the   r e tur n  side of the coil to ensure th that at th thee trap trap wi will ll at leas leastt ha have ve eq equa uall pr pres essu sure re on the up upst stre ream am an and d downs downstre tream am sid sides es - plu pluss the maxi maximum mum water head over twelve inches that space will allow. (A vacuum-breaker is just a swing check valve installed so it opens ope ns into into the syste system.) m.) Obviou Obviously sly ove overhe rhead ad return returnss cannot be tolerated on this type system without the use of  a vented reservoir and condensate pump.

c.

Du Duee to the di diff ffer eren ence ce in volu volume me betw betwee een n wa wate terr an and d steam, steam, conde condens nsate ate pipes may be sized sized at 60% of the diameter of the steam pipe, for gravity-return systems. Pumped systems may be sized at 40% of the steam pipe diameter.

CONT ROL ME T HODS

Control,, when Control when referri referring ng to steam, steam, means means contro controll of the air  temperatu tem perature re leavin leaving g the coi coil. l. Pro Propon ponen ents ts of other other heatin heating g method thodss poi point nt out that that tem temper peratu ature re co contr ntrol ol is dif diffic ficult ult with with set so cold temperature, indicating no condensate flow, shuts me off the fan and thereby prevents freezing air from passing over a steam. This is a fair criticism. Compare a steam coil to a gas waterwat er-fil filled led coi coil. l. It doe doess not pre preven ventt the occurrence occurrence of water  water   burner, for example. The heat released by the gas burner is a hammer in horizontal tube coils.

more or less direct function of the amount of gas burned.

Page Page 5  

Co Cont ntra rast st th this is to a 5 ps psig ig stea steam m sy syst stem em.. The The maxi maximu mum m temperature of the coil, at 5 psig, is 227°F. By throttling the steam pressure down to 0 psig the temperature can be reduced only to 212°F. This difference doesn’t doesn’t allow good control. control. Attempting to go to a lower temperature necessitates operating at a les lesss than than atmosph atmospheric eric pressu pressure re and introduci introducing ng more more air  into the coil through the vacuum-breaker. This raises the very sort of condensate drainage problems that were discussed in the previous section.

However, there are methods of obtaining satisfactory control. A.   On-Off. Two-position control is relatively trouble-free but gives the least desirable type of temperature control. In Unit Heaters it is accomplished by leaving the steam “on” all the time and turning the fan on or off as required by a thermostat. In Make-Up Air and most process and ventilation systems, where constant airflow is desired, the steam is turned full-on or full-off. Before dismissing such systems as too primitive, recognize that most residential heating is done by basically onoff systems. On-off steam systems have one great advantage full steam pressure is available at all times to operate traps and (despite warnings) overhead return lines, and to minimize the danger of freezing.

assume that summer operation will be with the steam off and air flowing through the face. Most customers seem to prefer  low unit height to full bypass capability. 3. The two dif differ ferent ent tem tempera peratur turee air airstr stream eamss force force the fan (gener (ge nerall ally y dow downs nstrea tream m of the coils) coils) to ope operate rate wit with h inlet inlet stratification. This damages fan performance. One importa important nt factor factor often often ove overlo rlooke oked d in the select selectio ion n or  design of face-and-bypass systems is that the damper blades should shoul d have their axis of rotation perpendic perpendicular ular to the axis of the coil tubes. tubes. Imag Imagine ine horizontal horizontal dampers and horiz horizontal ontal tubes and you can see that in a partly throttled condition, air would  be directed towards some tubes and away from others. Using vertical tubes and horizontal dampers gives the best possible combination. C.   Modulating Valves. Since the heat comes from the steam, it seems reasonable to control the heat by throttling the incoming stea steam. m. By now now the the reade readerr ha hass be been en thro throug ugh h the the pr prev evio ious us discussion discu ssion of the difficulti difficulties es invol involved ved in opera operating ting with this sort of control that results in poor drainage. In addition to the danger of freezing, there is the possibility that horizontal coils and long tubes can set up water hammer that will ruin the coil.

B.   Face and Bypa Bypass ss..   By allowing allowing some air to bypass bypass the coils, and thereby remain unheated, and by blending the “face” and “bypass” airstreams it is possible to obtain good temperature control and still maintain full steam pressure on the coils. This is the system best-suited for steam Make-Up Air (See Figure 10). Face and bypass systems may be built-up (plenum) or   packaged. Both may have the disadvantages disadvant ages listed below but, generally speaking, built-up systems can be designed to avoid them. 1. The presence presence of steam in the coils gen generally erally preclude precludess the  possibility of handling 100% bypass air without a temperature rise of a few degrees. 2. Most Most pac packag kaged ed un units its are design designed ed with with less less by bypas passs are areaa than is desirable for 100% bypass flow. Most manufacturers

D.   Preheat-Reheat.   Two coils in series can be used to give good tempera good temperature ture con control trol and a reas reasona onable ble measu measure re of freeze freeze  protection  protect ion (See Figure 11). The coils must be accurate accurately ly sized. The The firs firstt “preh “prehea eat” t” co coil il is sele select cted ed to rais raisee th thee en ente terin ring g air  temperature to about 40°F. to 50°F. The second “reheat” coil raises the air to the desired final temperature. The preheat coil is supplied with a snap action on-off steam valve. The reheat coil has a modu modulating lating steam valve valve.. Under maximum con conditi ditions ons,, with the coldest (design) entering air temperature, temperature, both coils will  be under maximum maxi mum pr pressure. essure. The ther thermostatic mostatic controls are set to throttle the reheat coil until it is fully closed. The preheat coil is sized so that it will not overheat at full pressure.

Page 6  

E.   Combinations   can be made of preheatpreheat-rehea reheatt with face and bypass. Fresh air and recirculating dampers may be used to exercise some control by closing down on fresh air in cold weather. weath er. Caution Caution shoul should d be used in desig designing ning combination combination system sys tems. s. Comple Complex x con control trol sy syste stems ms are often often ma maint inten enanc ancee headaches. Keep it simple. F.   High-pressure steam  presents the special problems of  superheat and “flashing”.

The high temperature of high pressure steam can aggravate thea  problems of control. One solution iiss to pass tthe he steam through  pressure-r  pressu re-reducin educing g valve before it gets to the coil or temperature temperature control valve. Reducing Reducing the pressure reduces the temperature temperature at which whi ch the laten latentt hea heatt wil willl be re relea lease sed d an and d makes makes control control easier eas ier.. How Howeve ever, r, red reduci ucing ng the pre press ssure ure does does not not,, in itself itself,, ext extrac ractt any any heat heat from the steam steam - so the reduced reduced press pressure ure steam is super superheate heated. d. Reducing Reducing satura saturated ted 150 psi steam, at 366°F., to 25 psi steam, at 266°F., gives steam with up to 52° of superheat. superheat. Since superh superheated eated steam is just anoth another er gas until it has been coo cooled led to sat satura uration tion tempe temperatu rature, re, it is nec necess essary ary to incr increa ease se the the si size ze of the the co coil il.. The The ad adde ded d co coil il fa face ce may may be thought of as room for the superheated steam to sit and cool to the saturation temperature. Dry superheated steam has a lower  film coefficient than does the wet saturated steam. This also

adversely affect adversely affectss the overall coefficie coefficient nt of heat transfe transfer. r. A good rule of thumb is to increase the coil area by 10% for each 100° of superheat. When high pressure steam is used, without pressure reduction, the condensate temperature may be high enough to cause some of the condensate to flash back into steam as it enters the low pressuree condensat  pressur condensatee line, downstre downstream am of the trap. Not all the condensate flashes - just a small part of it, enough to absorb the amount of heat needed to produce a stable mixture of steam and water. The mixture is therefore at a lower temperature than the high-pressure condensate. G.   Vacuum-steam Vacuum-steam systems. systems.   One-pipe One-pipe steam steam sys system temss and some other variations were, and sometimes still are, used for  small sma ll spa space ce he heati ating ng instal installati lations ons.. The They y are seldom seldom of much much interest in industrial heating or process work. CONCLUSION

A kn knowl owledg edgee of the fundam fundament entals als of steam steam he heatin ating g is stil stilll a necessity nece ssity in some process applic application ationss and buildi building ng heating heating systems. The purpose of this Engineering Letter was to provide a basic overview. overview. Engin Engineers eers and desig designers ners of steam steam-heati -heating ng system sys temss are enc encour ourage aged d to see seek k out additio additional nal trainin training g and resources to build their knowledge base.

Page Page 7  

Page 8

 

ENGINEERING LETTER

E

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60521 - 5530  

MISCELLANEOUS ENGINEERING DATA The purpose of this Engineering Letter is to pr ovide reference data commonly required in routine fan system computations.

BASIC FAN LAWS Variable

When Speed Changes

( ) RPM   Pressure P  = P ( RPM  ) RPM Horsepower BHP  = BHP ( RP RPM M  ) Volume

2

1 

2

When Density Changes

RP RPM M2  RP RPM M1 

CF CFM M 2  = CFM 1  

FAN EFFICIENCY

Does Not Change

2

1

2

1 

2  1

3

BHP2

D2  D1 

( ) D     = B H P  ( ) D  

P2 = P1 

1

2

1

Air Horsepower out 

Mechanical Efficiency

= Shaft Horsepower   x 100% in

Mechanical Efficiency

TP x CFM = 6343.3 x BHP x 100%

Static Efficiency

SP x CFM = 6343.3 x BHP x 100%

UNITS COMMONLY USED IN FAN APPLICATIONS Pressure In. WG 1 .00403 27.761 13.635 .03937 .53681

Pascals 248.36 1 6894.7 3386.4 9.7779 133.32

Psi .03602 .00015 1 .49116 .00142 .01934

In. HG .07334 .00030 2.0360 1 .00289 .03937

mm WG 25.400 .10227 705.13 346.33 1 13.635

mm HG 1.8628 .00750 51.715 25.400 .07334 1

Atm .00245 .00001 .06805 .03342 .00010 .00132

407.98

101325

14.696

29.921

10363

760.00

1

CFM

m3 /s

1 2118.9 35.314 .58858 2.1189 .03531

.000472 1 .01667 .00028 .00100 .00002

Volume Flow m3 /min. m3 /hr.

.02832 60.000 1 .01667 .06000 .00100

1.6990 3600.0 60.000 1 3.6000 .06000

l/s

l/min.

.47195 1000.0 16.667 .27778 1 .01667

28.317 60000 1000 16.667 60.000 1

Velocity ft./min.

m/s

m/min.

m/hr.

mph

Knots

1 196.85 3.2808

.00508 1 .01667

.30480 60.000 1

18.288 3600.0 60.000

.01136 2.2369 .03728

.00987 1.9425 .03238

.05468 88.000 101.34

.00028 .44704 .51479

.01667 26.822 30.887

1 1609.4 1853.2

.00062 1 1.1516

.00054 .86839 1

Rotating Speed RPM rps

1 60.000

.01667 1

Density lbs./ft.3  

Kg/m3  

1 .06243

16.018 1

Power HP 1 1.341

Watts .7457 1

   

VELOCITY PRESSURES (At Standard Density .075 lbs./ft.3 )

PRESSURE EQUIVALENTS Inches Water

Inches Mercury

Ounces Per Sq. In.

Pounds Per Sq. In.

Millimeters Water

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

.0733 .1467 .2200 .2934 .3667 .4400 .5134 .5867 .6601 .7334 .8067 .8801 .9534 1.027 1.100 1.173 1.247 1.320 1.393 1.467 1.540 1.613 1.687

.5763 1.153 1.729 2.305 2.882 3.458 4.034 4.611 5.187 5.763 6.340 6.916 7.493 8.069 8.645 9.222 9.798 10.374 10.951 11.527 12.103 12.680 13.256

.0360 .0720 .1081 .1441 .1801 .2161 .2522 .2882 .3242 .3602 .3962 .4323 .4683 .5043 .5403 .5763 .6124 .6484 .6844 .7204 .7565 .7925 .8285

25.4 50.8 76.2 101.6 127.0 152.4 177.8 203.2 228.6 254.0 279.4 304.8 330.2 355.6 381.0 406.4 431.8 457.2 482.6 508.0 533.4 558.8 584.2

24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

1.760 1.834 1.907 1.980 2.054 2.127 2.200 2.274 2.347 2.420 2.494 2.567 2.640 2.714 2.787 2.860

13.832 14.409 14.985 15.561 16.238 16.714 17.290 17.867 18.443 19.019 19.596 20.172 20.748 21.325 21.901 22.478

.8645 .9005 .9366 .9726 1.009 1.045 1.081 1.117 1.153 1.189 1.225 1.261 1.297 1.333 1.369 1.405

609.6 635.0 660.4 685.8 711.2 736.6 762.0 787.4 812.8 838.2 863.6 889.0 914.4 939.8 965.2 990.6

40 41 42 43 44 45

2.934 3.007 3.080 3.154 3.227 3.300

23.054 23.630 24.207 24.783 25.359 25.936

1.441 1.477 1.513 1.549 1.585 1.621

1016.0 1041.4 1066.8 1092.2 1117.6 1143.0

DENSITIES OF SATURATED AIR Temp. (°F.)

Density (lbs./ft.3 )

Temp. (°F.)

Density (lbs./ft.3 )

-20 -10 0 10 20

.09027 .08824 .08632 .08445 .08264

100 110 120 130 140

.06917 .06741 .06552 .06349 .06132

30 40 50 60

.08090 .07921 .07753 .07589

150 160 170 180

.05895 .05634 .05346 .05036

Velocity (FPM)

VP (In. Water)

Velocity (FPM)

VP (In. Water)

500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 2000 2200 2400 2600 2800

.016 .022 .031 .040 .050 .062 .075 .090 .105 .122 .140 .160 .180 .202 .249 .302 .359 .421 .489

3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 5200 5400 5600 5800 6000 6200 6400 6600 6800

.561 .638 .721 .808 .900 .998 1.10 1.21 1.32 1.44 1.56 1.69 1.82 1.96 2.10 2.24 2.40 2.55 2.72 2.88

FAN SYSTEM EFFECT FACTORS Pressure Drop, Inches Water Gauge Round, Mitred Elbow Air Velocity Two(FPM)  piece

3000 4000 5000

Multi-piece 

Square-Duct Elbow W/Out Turning With Turning Vanes Vanes

R R =1 =2 D D

1.8 3.2 5.0

R R =1 =2 D D

Elbow On The Inlet  0.7 0.6 0.7 0.5 1.3 1.0 1.3 0.8 1.8 1.5 1.8 1.3

R R =1 =2 D D

0.3 0.6 0.8

0.1 0.3 0.4

Elbow (2) Duct Diameters From The Inlet 

3000

1.2

0.4

0.3

0.4

0.3

0.2

4000 5000

2.0 3.0

0.7 1.0

0.6 0.8

0.7 1.1

0.5 0.7

0.4 0.5

0.1 0.2 0.3

Elbow (5) Duct Diameters From The Inlet 

3000 4000 5000

0.6 1.0 1.5

0.2 0.3 0.5

0.2 0.3 0.5

0.2 0.4 0.5

0.1 0.3 0.4

FAN PRESSURES

TP = SP + VP TP fan = TP outlet - TP inlet SP fan = SP outlet - SP inlet - VP inlet  VP = Velocity Pressure

0.1 0.2 0.3

0.0 0.1 0.2

70 80 90

 

.07425 .07262 .07094

190 200 212

TP = Total Pressure

.04667 .04270 .03730

SP = Static Pressure

Page 2  

ALTITUDE AND TEMPERATURE CORRECTION FACTORS (Multiply Factor by SP at Conditions) Air Temp. (°F.)

0

0 50 70 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000

Altitude (feet) 1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

.87 .96 1.00 1.07 1.15 1.25 1.34 1.43 1.53 1.62 1.72 1.81 1.91 2.00 2.10 2.19 2.28 2.38 2.47 2.56 2.66

.91 1.00 1.04 1.10 1.20 1.29 1.39 1.49 1.59 1.69 1.79 1.88 1.98 2.08 2.18 2.27 2.37 2.48 2.57 2.66 2.77

.94 1.04 1.08 1.14 1.24 1.34 1.45 1.55 1.62 1.75 1.86 1.96 2.06 2.16 2.26 2.36 2.47 2.57 2.67 2.76 2.87

.98 1.08 1.12 1.19 1.29 1.40 1.50 1.61 1.72 1.82 1.93 2.03 2.14 2.24 2.35 2.46 2.56 2.66 2.77 2.87 2.98

1.01 1.11 1.16 1.23 1.33 1.45 1.56 1.67 1.78 1.89 2.00 2.11 2.22 2.33 2.44 2.55 2.66 2.76 2.87 2.97 3.09

1.05 1.15 1.20 1.28 1.38 1.51 1.62 1.74 1.85 1.96 2.08 2.19 2.30 2.42 2.54 2.65 2.76 2.86 2.96 3.07 3.19

1.09 1.20 1.25 1.33 1.44 1.56 1.68 1.79 1.91 2.03 2.15 2.26 2.39 2.50 2.62 2.74 2.81 2.98 3.09 3.20 3.33

1.13 1.25 1.30 1.38 1.50 1.63 1.74 1.86 1.99 2.11 2.24 2.35 2.48 2.60 2.73 2.85 2.96 3.09 3.21 3.33 3.46

1.17 1.30 1.35 1.43 1.55 1.69 1.81 1.93 2.07 2.19 2.32 2.44 2.58 2.70 2.84 2.94 3.08 3.21 3.33 3.46 3.59

1.22 1.34 1.40 1.48 1.61 1.75 1.88 2.00 2.14 2.27 2.41 2.53 2.67 2.80 2.94 3.01 3.19 3.33 3.46 3.58 3.72

1.26 1.39 1.45 1.54 1.67 1.81 1.94 2.07 2.22 2.35 2.49 2.62 2.77 2.90 3.05 3.18 3.31 3.45 3.58 3.71 3.86

2.76

2.87

2.98

3.09

3.20

3.31

3.45

3.59

3.73

3.86

4.00

WEIGHTS OF MATERIALS, MEAN VALUES  Density lbs./ft.3  Air .0749 Aluminum 165 Alum Alumin inum um ch chii s 48 Antimon Antim on 414 Asbestos 153 Asbestos Asbe stos loose 64 Ashes, coal, dry 40 As Ashes hes,, woo wood, d, dr 47 Bakelite, Laminated 86 wood filler 85 asbestos asbes tos fill filler er 118 crushed 43 Bakin Bakin owd owder er 56 Bauxite, dry, crushed 43 Borax 109 Borax,, dr , crushe Borax crushed d 75 Brasss Bras 530 Brass chips 163 Brick, masonr 118 Bronze 509 Bronze Bro nze hos hor 554 Calcium, carbonate 177 Calcium Calc ium chlori chloride de 134 Calcium sulphate 185 Carbide Carbi de dr crushe crushed d 50 Carborundum 195 Carborundum Carbo rundum,, loose 140 Caustic soda 88 Celluloid 90 Cellulose 94 Cement, loose 94 Cereals, bulk barley, corn 37

Density lbs./ft.3  Cinders 43 Clay, loose, dry 63 mo mois istt 110 Coal, anthr anthracit acitee 98 anthracite, piled 54 bituminous bituminous 85 bituminous, piled 47 Cof Coffee fee 48 Coke 75 Coke, piled 28 Coke, dr , crushe crushed d 15 Concrete, cinder 97 sto stone ne 142 Copper 556 Co er ore, crus crushed hed 190 Co er oxide 190 Cork 15 Corn meal 40 Corundum, alundum 247 Cotton, baled 93 loose loose 30 Dolomite 181 Dural Duralumin umin 175 Earth, dry and loose 76 Eart Earth h mois moistt & loose 78 Emery 250 Felds ar 160 Feldspar, crushed 88 Ferrous, rind dust 125 Flour, com ressed barreled 47 loose 28 Fullers earth, dry 30

Density lbs./ft.3  Gravel, loose, piled 120 Grit blast dust 160 G sum sum,, co com m re ress ssed ed 152 loose 70 Iron, gray cast 442 Iron ore loose 150 Lead 710 Lead Lead oxi oxide de red 567 Leather 56 Lime 53-64 Lime Limestone stone 163 Lucite 74 Ma nesia nesia 214 Magnesium 109 Man anese ore, crushed crushed 259 Marbl Marble, e, crushe crushed d 95 Mica 183 Monel metal 556 Natural as 0.04475 Nickel 547 N lon 70 Paper 58 Straw Strawboard board or newspaper 33-44 Paraf Paraffin fin 56 Peat, dry 30 Phos hate, round 75 Porcelain 150 Potash 60 Quartz 165 Quartz, round 84 Resin 67

oats wheat rye, Chalk Charcoal, hardwood

Glass, flint crown Glass, pyrex ground

Rubber, India compound hard hard sponge

Material

26 48 142 34

Material

160 215 140 90

Material

58 115 75 30

Material  

Salt, gran, and piled Saltpeter Sa Sand, nd, dr , loose loose Sand, wet Sandstone Sandst Sandstone one crushe crushed d Sawdust Sha Shale le,, ri ra Shavin s, laner Slag, Iron Sla , ranulated Slate Soda ash Soda ash, granulated Sodium carbona carbonate te Sodium nitrat nitratee Sodium sul hate Starch ranulated Steel Sucros Sucrosee Sugar, bulk Sul hur Sulphur, crushed Talc Talc Tar, bituminous Tile Tin Tobacco Water Zinc Zinc oxide

Density lbs./ft.3  48 80 99 110 144 82 7-15 105 7-15 172 60 172 74 30 91 141 167 95 35 487 100 55 126 50 170 69 113 457 16 62.4 443 350

softwood  broken

23 12

Granite loose, piled Graphite

165 96 132

tire reclaim, solid tire reclaim reclaim,, shred

74 27

  Page 3  

U. S. INCH

MISCELLANEOUS CONVERSION FACTORS Fraction

Decimal

MM

1/16

0.06250

1.588

1/8

0.12500

3.175

3/16

0.18750

4.763

Volume

1/4

0.25000

6.3 50

1 in.3 = 16.3871 cm3  

5/16

0.31250

7.938

3/8

0.37500

9.525

7/16

0.4375

11.113

1/2

0.5000

12.700

9/16

0.56250

14.288

5/8

0.62500

15.875

Metric Prefixes

11/16

0.68750

17.463

deci = x 0.1 centi = x 0.01 mili = x 0.001 micro = x 0.000001 deca = x 10.0 hecto = x 100.00 kilo = x 1000.00

3/4

0.75000

19.050

13/16

0.81250

20.638

7/8

0.87500

22.225

15/16

0.93750

23.813

1

1.00000

25.400

Pressure 1 Pa = 1 N/m2  1 Pa = 10 dy/cm2  1 psi. = 0.0703 kg/cm2  1 lb./ft.2 = 4.884 kg/m2 

Area 2 1 in.  = 6.4516 cm2   1 ft.2 = 0.0929 m2   1 yd.2 = 0.8361 m2   1 mi.2 = 2.5899 km2  

Length 1 mil. = 0.0254 mm

3

1 ft.  = 0.0283 m3   1 ft.3 = 7.48 gal. 1 ft.3 = 28.316 l. 1 yd.3 = 0.7646 m3   1 oz. = 29.57 ml. 1 gal. = 3.785 l. 1 gal. U.S. = 0.833 Imp. gal.

1 in. = 2.54 cm 1 ft. = 0.3048 m 1 mi. = 1.6093 km 1 nau. mi. = 1.1516 mi. Energy 

1 Btu = 777.97 ft.-lb. 1 HP = 2545 Btu/Hr. 1 HP = 1.014 metric HP 1 HP = 0.0761 boiler HP 1 KW = 3414 Btu/Hr. 1 Ton = 12000 Btu/Hr. Mass 

1 lb. = 453.5924 g.

SHAFTING DATA (Mild Steel, Stainless)

METAL SHEET AND PLATE DATA Mild Steel, Stainless T-1, INX

Aluminum

Gauge 

Thickness 

Weight (lbs./ft.2 )

Gauge 

1" 3/4" 5/8" 1/2" 3/8" 1/4"

1.0 1. 0 .75 .625 .50 .375 .250

40.8 30.6 25.5 20.4 15.3 10.2

.250 .190 .160 .125 .100 .080

.1875 .1345 .1046 .0747 .0598 .0478

7.5 5.625 4.375 3.125 2.50 2.0

7 (3/16") 10 12 14 16 18

ELECTRICAL FORMULAS

Weight (lbs./ft.2 )

3.50 2.65 2.24 1.75 1.40 1.12

Diameter (in.)

5/8 1 1 3/16 1 7/16 1 11/16 1 15/16 2 3/16 2 7/16 2 11/16 2 15/16 3 3/16 3 7/16 3 15/16 4 7/16 4 15/16 5 7/16 6

Weight (lbs./ft.)

1.04 2.67 3.77 5.52 7.60 10.02 12.78 15.87 19.29 23.04 27.13 31.55 41.40 52.58 65.10 78.95 96.13

Volts (E) = Amps (I) x Ohms (R) BHP (3 phase) = Volts x Amps x 1.732 x Eff. x Power Factor 746 BHP (1 phase) = Volts x Amps x Eff. x Power Factor 746 Torque (lb.-ft.)= Horsepower x 5250

TEMPERATURE CONVERSION

°C = (°F - 32) ÷ 1.8 °K = °C + 273.15 °F = (°C x 1.8) + 32 °R = °F + 459.67

RPM Form 219 JLK

   

ENGINEERING LETTER

G

The New York Blower Company ● 7660 Quincy Street, Willowbrook, Illinois 60527-5530

GLOSSARY The following terms are common to the fields of air movement, general ventilation, industrial process, and pollution control. The definitions contained in this glossary provide brief descriptions of the terms as generally used in these fields. In many cases, a more thorough discussion of these terms can be found in the text of the appropriate Engineering Letter.

ABSOLUTE TEMPERATURE degrees Rankine, where absolute 0°R. = -459.7°F.; density corrections for temperature are based on the percentage rate of change in degrees Rankine: degrees Kelvin where absolute 0°K = -273.1°C.

Density corrections for altitude are made using the following formula where Z is the feet above sea level. Density (Alt) = Density (Std) x [1 - (6.73 x 10

 Density (temp.) =  Density (std.) x

ALTITUDE the height above sea level of a given location.  

(

460°F. +70°F. 460°F. + °F. (non-standard)

)

ABSORPTION the process of one substance entering into the inner structure of another.

ACCELERATION LOSS the energy required to induce air to

-6

) Z] 5.258 

AMBIENT immediate surroundings or vicinity. AMCA Air  Movement and Control Association. ANEMOMETER a device which reads air velocity such as a  wind vane. In fan applications, it is usually a spinning-vanetype instrument used to read low velocities at registers or grills.

move at the entry to a system.

ANNEAL the process of relieving stress and brittleness in  

ACCESS DOOR a door mounted on the housing of fan to

metals by heating.

allow access to interior of fan for inspection.

ANODIZE an electrolytic action of affixing a protective 

ACFM actual cubic feet per minute; the quantity or volume coating or film, usually applied to aluminum. of a gas flowing at any point in a system. Fans are rated and ANSI American National Standards Institute.

selected on the basis of ACFM, as a fan handles the same volume of airregardless of density.  ACFM =

.075  x SCFM  actual density

ACTUATOR mechanical device attached to a damper to move

API American Petroleum Institute. APPURTENANCES accessories added to a fan for the purposes  of control, isolation, safety, static pressure regain, wear, etc.

its blades. May be manual, electric, pneumatic, or hydraulic.

ARI Air Conditioning and Refrigeration Institute.

adhesion of a thin film of liquid or gases to the ADSORPTION surface of a solid substance.

ASHRAE American Society of Heating, Refrigeration, and  Air Conditioning Engineers.

AIRFOIL fan wheel design with airfoil-shaped blades.

ASME American Society of Mechanical Engineers.

AIR CONDITIONING treating air to meet the requirements of a ASPECT RATIO the ratio of the width to the length. conditioned space by controlling its temperature, humidity, cleanliness, and distribution.

ASTM American Society for Testing and Materials

AIR CURTAIN mechanical air-moving device designed to

ATMOSPHERIC PRESSURE one atmosphere is approximately

limit the influx of unwanted air at a building opening.

AIR-HANDLING UNIT factory-made encased assembly consisting of a fan or fans and other equipment to circulate, clean, heat, cool, humidify, dehumidify, or mix air. IR ELOCITY rate of speed of an airstream, expressed in A FPM.V

14.7 PSI; 408" water gauge. Airflow is the result of a difference in pressure (above or below atmospheric) between two points.

ATTENUATION absorption of sound pressure. Attenuation reduces the amplitude only of a sound wave while leaving the frequency unchanged.

AXIAL FAN fan where the airflow through the impeller is  predominant ly parallel to the axis of rotation. The impeller is  predominantly contained in a cylindrical housing.

AXIAL FLOW in-line air movement parallel to the fan or  motor shaft.

 

BABBITT METAL an alloy containing tin, copper, and   BTU British Thermal Unit; heat required to raise the antimony; commonly used for lining bearings. aerodynamic, single surface blade  shape offers alternative selection points to the Airfoil.

Backward Incline

BACKDRAFT DAMPER damper used in a system to relieve  

temperature of 1 pound of water by 1 °F. The Btu/hr. required to raise the temperature of a volume of standard air a specific number of degrees is calculated by the formula:  Btu/hr = Temp. R Rise ise x CF CFM M x 1.085

air pressure in one direction and to prevent airflow in the opposite direction.

CAPACITOR START MOTOR type of single-phase induction

BI fan wheel design with backwardly-inclined blades.

CFM cubic feet per minute; the volume of flow for a given  

motor with a capacitor connected in series with the starting winding. High-starting and breakdown torque, medium starting BALANCING the process of adding (or removing) weight on a   current. Used in hard-starting applications; compressors, rotor in order to move the center of gravity toward the axis of  pumps, etc. rotation. CAPTURE VELOCITY air velocity necessary to overcome BARCOL NUMBER a standard measure of FRP surface hardness. opposing air currents or natural flow and cause contaminated air, fumes, or material to flow in a desired direction. BAROMETRIC PRESSURE a measurement of the pressure of   CARBON  STEEL  steel with the main alloying element being the atmosphere; standard is 29.92" Hg. carbon, and whose properties are dependent on the percentage BEARING LOSSES the power losses resulting from friction in   of carbon present (also referred to as Mild Steel) the main bearings. CATALYST the final ingredient that triggers the chemical BERNOULLI’S THEOREM the principle that the total energy   reaction known as curing, which converts liquid resin to a solid.  per unit of mass in the streamline flow of a moving fluid is constant, being the sum of the potential energy, the kinetic CELSIUS a thermometric scale in which water boils at 100° energy, and the energy due to pressure. In terms of air and freezes at 0°, same as centigrade: movement, the theorem states that the static pressure plus °C = .5556 x [°F. - 32°] velocity pressure as measured at a point upstream in the direction of airflow is equal to the static pressure plus velocity pressure as measured at a point downstream in the direction of airflow CENTRIFUGAL FAN a fan design in which air is discharged   perpendicular  perpendicul ar to the wheel’s rotational ro tational axis.  plus the friction and dynamic lo losses sses between the points.

BILLET a section of semi-finished metal or non-ferrous alloy. BLADE the flow element of a wheel. BLADE LINERS  pieces of material added over the wheel   blades to reduce redu ce abrasion of the th e blades.

BLADE-PASS FREQUENCY the tone generated by the blades   passing a fixed object.

fan or system.

COATINGS specialty coverings, typically referred to as paints,   with varying degrees of resistance to atmospheric or chemical corrosion.

CLEAN OUT DOOR see Access Door  COEFFICIENT OF CONDUCTIVITY the rate of heat transfer   through a material, expressed in Btu transmitted per hour through one square foot of surface per degree difference in

BLAST AREA the fan outlet area less the projected area of the   temperature across the material. Figures are usually expressed cut-off.

for basic materials, such as wood or insulation; per inch of thickness, and called by the symbol “K”.

BOILER HORSEPOWER the capability to evaporate 34.5   COMPRESSIBILITY a factor used by fan manufacturers to 

 pounds of water per hour into dry steam at 2 12°F. at sea level; 33,500 BTU/Hr.

correct performance ratings in higher pressure ranges to account for the fact that air is a compressible gas that does not BRAKE HORSEPOWER [BHP] mechanical energy consumed  follow the perfect gas laws. at a rate of 33,000 ft. lbs. per minute; a consumption rating, as COMPANION  FLANGES  flange designed to fit flush with fan  compared to the production rating of horsepower itself. inlet or outlet flanges, provided with a matching hole pattern

BREAKDOWN TORQUE maximum torque a motor will  COMPRESSION a phenomenon related to positive pressure.    produce without a sudden s udden decrease in speed. Often referred to When air is forced into a system it is compressed and becomes as pull-out torque or maximum torque. more dense. Depending on the volume or weight of air BRINELL NUMBER a standard measure of metal surface   required down stream in the positive pressure portion of the hardness; metals with Brinell hardness ratings of 250 or more system, the volume of air at the inlet of a fan may have to be adjusted by the ratio of absolute pressure at the entrance of the are generally considered abrasion-resistant.

fan

versus

the

design

requirements

in

the

system.

Page 2

 

CONVEYING VELOCITY the air velocity required in a duct DUST COLLECTOR an air-cleaning device used to remove system to maintain entrainment of a specific material.

CORROSION the deterioration of a material by chemical or  electrochemical reaction resulting from exposure to weathering, moisture, chemical, or other agents in the environment in which it is placed.

heavy-particulate loadings from exhaust systems prior to discharge.

DWDI double-width, double-inlet fans, Arrangement 3. DYNAMIC BALANCE the mechanical balancing of a rotating  part or assembly in motion.

CRP Certified Ratings Program.

DYNAMIC INSERTION LOSS a reduction of airborne noise Standards Association. Sets safety standards for  levels affected by the installation of an acoustical silencer. CSA Canadian motors and other electrical equipment used in Canada. CURVE, FAN PERFORMANCE a graphic representation of  DYNE a unit of force equal to that which would accelerate one static or total pressure and fan BHP requirements over an gram by one centimeter per second. airflow volume range at a stated inlet density and fan speed.

EFFICIENCY, MECHANICAL TOTAL the ratio of fan output

CURVE, SYSTEM a graphic representation of the pressure to the power applied to the fan. Can be helpful in selecting fan versus flow characteristics of a given system and density.

DAMPER an accessory to be installed at the fan inlet or outlet for air-volume modulation.

size, type, or manufacturer for the same application:  ME =

TP x CFM  6356 x BHP

EFFICIENCY, STATIC the ratio of fan output less the kinetic

dbA sound-pressure level corrected to the “A” weighing energy [outlet-velocity pressure] leaving the fan to the power applied to the fan:

network.

DECIBEL the logarithmic ratio between some known reference SE =

and some quantity of electric or acoustic signal power.

DENSITY the measure of unit mass equal to its weight divided 3

 by its volume (lbs./ft. (lb s./ft.3); standard air is .075 lbs./ft. .

SP x CFM 6356 X BHP

ELEVATION the distance of the subject site above or below sea level.

DEW POINT the temperature at which condensation begins to END REFLECTION a known value of sound radiated back  form as air is cooled.

into a duct or opening.

DFT dry-film thickness usually expressed in thousandths of  ENTHALPY the heat content per unit mass of a substance. an inch (mils).

ENTRY LOSS the loss in pressure caused by air flowing into a

DIFFERENTIAL PRESSURE the difference of static pressures system; normally expressed in fractions of velocity pressure. at the fan outlet and inlet; also see FAN CAPACITY. EQUIVALENT DUCT DIAMETER for rectangular duct with DILUTION VENTILATING the mixing of contaminated air  sides a and b is: with uncontaminated supply air for the purpose of attaining acceptable working or living conditions.

 D = (4ab/ π )0.5 

DIRECT DRIVE wheel fitted to or connected to a motor without EVASE a diffuser at the fan outlet which gradually increases in a drive mechanism, a housing, or a means of variable speed drive.

DIRECTIVITY FACTOR the number representative of the radiation characteristics of a sound source.

DRAIN  welded tank flange located at the lowest point in the housing scroll.

area to decrease velocity and to convert kinetic energy to static  pressure [regain.] [rega in.]

FAHRENHEIT a thermometric scale in which water boils at 212° and freezes at 32°. °F = (1.8 x °C) + 32°

DRY- BULB TEMPERATURE the combined temperature of a FAN a power-driven machine which moves a continuous water vapor and air mixture.

DUST air suspension of particles [aerosol] of any solid material, usually with a particle size smaller than 100 micrometers.

volume of air by converting rotational mechanical energy to an increase in the total pressure of the moving air.

FAN CAPACITY  performance requirement for which a fan is selected to meet specific system calculations given in terms of ACFM at the fan inlet.

FAN CLASS operating limits at which a fan must be physically capable of operating safely.

Page 3  

GALVANIZING the process of coating or plating with a zincFAN LAWS theoretical constant relationships between CFM, rich solution; can be a hot-dip process, cold spray, or brush RPM, SP, and BHP for a given fan used in a given fixed system: CFM varies as RPM SP varies as (RPM)2   BHP varies varies as ((RPM) RPM)3 

FC fan wheel design using forward-curved blades.

application.

GAS STREAM the specific airstream composition within any fan or system.

GASES formless fluids which tend to occupy an entire space uniformly at ordinary temperatures and pressures.

GAUGE (GAGE) metal manufacturers’ standard measure of  FINITE ELEMENT ANALYSIS (FEA) computerized analytical thickness for sheet stock; some examples for steel are: technique used to divide a rotating body into many segments to determine the stress of each segment and therefore the complete body.

Gauge

Thickness (Inches)

Weight of Steel (Lbs./Ft. 2) 

7 10 12 14 16 

.1793 .1345 .1046 .0747 .0598

7.50 5.625 4.375 3.125 2.50

FLANGED  INLET /OUTLET enables bolted attachment of duct work to the fan’s inlet or outlet.

FLASHING sheet-metal strip placed at the junction of intersecting exterior building surfaces to make the joint water-tight.

FOOT- POUND

(Ft. - Lb.) torque rating or requirement;

equivalent to the force required to move a one-pound weight one foot in distance, equal to 12 in.-lb.

GAUGE PRESSURE the pressure differential between atmospheric and that measured in the system.

GEL COAT a special resin system, sometimes including FORCED DRAFT how air is provided in a process, such as a  pigment, but without glass-reinforc glass-reinforcing, ing, that is applied to the combustion process; when air is blown or forced into a process, it is known as a “forced draft” system. Also see induced draft.

FPM feet per minute; commonly defines air velocity (to determine velocity pressure or suitability for materialconveying), shaft/bearing speeds (used to determine lubrication requirements) and wheel tip speeds.

FRAME SIZE a set of physical dimensions of motors as established by National Electrical Manufacturers Association (NEMA) for interchangeability between manufacturers. Dimensions include; shaft diameter, shaft height, and motor mounting foot print.

FREE FIELD the surroundings of a specific equipment location in which no obstructions or reverberant surfaces exist to distort or amplify sound waves.

FREQUENCY any cyclic event whether vibration, alternating current, or rotational speed. Usually expressed in cycles per second (cps) or just “cycles.”

mold before applying the FRP.

GROUND MOTOR a short circuit between any point in the motor’s electrical circuit and its connection to the ground.

HEAT EXCHANGER a device such as a coil or radiator which is used to transfer heat between two physically separated fluids.

HEPA FILTER high-efficiency particulate air filters commonly called absolute filters.

HERTZ frequency measured in cycles per second. Hg symbol for mercury. Pressure is often measured in inches of mercury: (1" Hg. = 13.64" WG)

HORSEPOWER (as applied to motors) is an index of the amount of the work the machine can perform in a period of time. 1 HP equals 33,000 ft. lbs. of work per minute, also equal to 0.746 kilowatts. Horsepower can be calculated by:

FRICTION LOSS resistance to air flow through any duct or  fitting, given in terms of static pressure.

HP =

Torque (ft. lbs.) x RPM 5250

FRP abbreviation for fiberglass-reinforced-plastic.

HOUSING the casing or shroud of a centrifugal fan.

FULL-LOAD SPEED the speed at which the rated horsepower  is developed. This speed is less than synchronous speed and varies with motor type and manufacturer.

HVAC heating, ventilating, and air conditioning. IMPELLER another term for fan “wheel.” The rotating portion of the fan designed to increase the energy level of the gas

FULL-LOAD TORQUE the torque required to produce the stream. r aated ted horsepower at full-load speed.

IMPELLER DIAMETER the maximum diameter measured FUMES airborne particles, usually less than 1 micrometer in over the impeller blades.

size, formed by condensation of vapors, sublimation, distillation, or chemical reaction.

Page 4  

LITHIUM a soft element in the alkali metal group commonly IMPINGEMENT striking or impacting; such as material used as a lubricant base.

impingement on a fan wheel.

INCH

OF

LOGARITHM a mathematical term used as a basis of the WATER unit of pressure equal to the pressure decimal system. A logarithm is the exponent of 10 which

exerted by a column of water one inch high at a standard  produces a given number. For instance, instance, the log of 100 is 2 since: density (27.73" water = 1 PSI).

INCH-POUND torque equal to one-twelfth foot pound. INCLINED MANOMETER a metering device used to obtain accurate pressure measurements.

INDUCED DRAFT how air is provided in a process, such as a combustion process; where air is drawn or pulled through a  process. Also see se e forced draft.

INDUCTION the production of an electric current in a conductor  in a changing magnetic field.

INERTIA tendency of an object to remain in the state it is in;

l o g 10  1 0 0 = 2

1 0 2= 100  

LOUVER a device comprised of multiple blades which, when mounted in an opening, permits the flow of air but inhibits the entrance of undesirable elements.

LOWER EXPLOSIVE LIMIT the lowest percentage of an element in otherwise standard air that will explode when exposed to a spark.

LS WHEEL flat radial-blade design. Best for materialconveying applications with airstreams containing coarse material or heavy dust and particulate matter.

see WR 2.

MACH NUMBER a fraction of the speed of sound; used in fan

INLET  BOX  device which minimizes entry losses normally

engineering where air moving at a Mach number of 0.9, or 9/10 the speed of sound, begins to deviate from the fan laws.

associated with 90  turns at or near fan inlet  ᵒ

MAKE-UP AIR a ventilating term which refers to the

INLET  CONE  a streamlining device used to reduce entrance replacement of air lost because of exhaust air requirements. losses at the inlet of a fan. MANOMETER instrument for measuring pressure, u-shaped, INLET SCREEN screen on inlet of fan. Allows passage of air, but  prevents  prev ents object object from ent enteri ering ng ffan an h housi ousing. ng.

and partially filled with liquid, either water, light oil, or mercury.

MAXIMUM CONTINUOUS RATING the point at which the

INLET-VANE DAMPER round multiblade damper mounted fan is expected to operate. to the inlet of a fan to vary the airflow.

INSTABILITY the point of operation at which a fan or system will “hunt” or pulse; common in FC fans and some other fan types where the point of operation is left of the peak of the static-pressure curve.

INTERFERENCE FIT specified interference between mating  parts requiring either a press ffit it or a shrink fit. f it. KELVIN see Absolute Temperature.

KILOPASCAL Kpa; metric pressure unit; one-inch water gauge is 0.24836 Kpa.

KILOWATT Kw; measure of power equal to 1.34 horsepower.

MICROBAR a unit of pressure equal to one-millionth of an atmospheric pressure; 0.0000 146 PSI.

MICRON a unit of measure equal to one-millionth of a meter, commonly used in dust collection and material-handling applications to designate particle size. a unit of measure equal to 25 microns or one-thousandth MIL of an inch.

MILD  S TEEL see Carbon Steel  MIXED- FLOW FAN a fan where the airflow is primarily axial and is changed by the blade shape to induce a small radial flow at the discharge.

L-10 BEARING LIFE the theoretical number of hours after  MOLECULAR WEIGHT the weight of a molecule expressed on a scale in which the carbon isotope weighs exactly 12.0; represents the sum of the weights of all the atoms in a molecule. As air is a gas mixture, it does not have a true molecular LAMINAR FLOW gas or fluid in parallel layers with some weight but an apparent molecular weight determined by the sliding motion between the layers.  percentages of the molecular weights of each gas in a composition. which 90% of the bearings subjected to a given set of conditions will still be in operation; also known as B-10.

AMINATE the total structure of the FRP part. For ny b MOTOR B ASE structure that the motor is mounted to. L corrosion-resistant products it consists of a resin-rich surface

and a thickness of glass-reinforced resin as required for

NACE  National Association Assoc iation of Corrosion Engineers.

structural strength.

LIFTING  EYES attachments to allow for easy lifting of the fan.

NATURAL FREQUENCY the frequency at which a component or system resonates.

Page 5  

NEC  National Electrical Electric al Code.

PLENUM a chamber or enclosure within an air-handling

NEMA the National Electrical Manufacturers Association;

system in which two or more branches converge or where system components such as fans, coils, filters, or dampers are located.

the trade association establishing standards of dimensions, ratings, enclosures, insulation, and other design criteria for electric motors.

NOISE CRITERIA a way for an architect to specify the maximum permissible sound-power level in each of the eight octave bands. NC curves give, in a graphical form, maximum  permissible intensity inte nsity per octave octav e band.

PLR WHEEL flat, single-thickness, backwardly inclined  blades. Includes Include s a non-overloading non-overlo ading power curve. cur ve.

PLUG F AN fan having an unhoused wheel arranged such that the system into which it is inserted acts as a housing, allowing air to be drawn into the wheel inlet.

OCTAVE BANDS ranges of frequencies. These octave bands POINT

OF OPERATION the intersection of a fan’s static  pressure curve and the system curve to which the fan is being are identified by their center frequencies (63, 125, 250, etc.). applied; may be designated as velocity pressure divided by OHM a measure of electrical resistance. A wire in which one static pressure or by a given CFM and SP. volt produces a current of one ampere has a resistance of one POLES the number of magnetic poles established inside an Ohm. electric motor by the placement and connection of the OPPOSED-BLADE DAMPER a type of damper where windings. adjacent blades rotate in the opposite direction. POLYESTER a large group of thermosetting plastics which OSHA Occupational Safety and Health Administration. exhibit a high degree of corrosion-resistance over a wide spectrum of corrosive agents. OSI ounces per square inch; a unit of pressure equal to onePSI  pounds per square inch measured in gauge pressure, not sixteenth PSI or 1.733 inches of water.

PARALLEL- BLADE DAMPER a type of damper where the

including atmospheric.

 blades rotate in the same direction. direct ion.

PSIG  pounds per square inch measured in gauge pressure, not

PARALLEL FANS two or more fans which draw air from a common source and exhaust into a common duct or plenum. A  parallel fan arrangement is generally used to meet volume requirements beyond that of single fans. Two identical fans in  parallel will effectively deliver twice the rated flow of any one of the fans at the same static pressure.

PERMANENT SPLIT CAPACITOR MOTOR very low starting torque. Performance and applications similar to shaded pole  but more efficient, with lower line current and higher horse power capabilities. capabilitie s.

including atmospheric.

PSYCHROMETRIC CHART a graphic depiction of the relationship between pressure, density, humidity, temperature, and enthalpy for any gas-vapor mixture, used extensively in comfort ventilation.

PULL-OUT TORQUE breakdown torque. torq ue. PURE TONE a sound that is characterized by a very uniform wave pattern. Such a sound might be created by a tuning fork.

PVC polyvinyl chloride; a synthetic therm thermoplastic oplastic polymer polymer.. a symbol as partonofa ascale logarithmic designation to taken indicate pH acidity or alkalinity from 0 to 14; pH7 is as neutral, 6 to 0 increasingly acid, 8 to 14 increasingly alkaline.

QUADRANT commonly the damper control plate.

PHENOLIC a thermosetting resin system used for coatings and

RADIAL BLADE fan wheel design with blades positioned in

adhesives.

straight radial direction from the hub.

PIEZOMETER RING a device consisting of a number of  pressure taps connected to a common manifold to measure  pressure.

RADIAL  TIP  blade design to be curved forward at entry and

PITCH DIAMETER the mean diameter or point at which V-belts

constantly changing frequency.

ride within a sheave. This dimension is necessary for accurate drive calculations.

radial at the tip of the leaving end.

RANDOM NOISE a sound that has an average amplitude and RANKINE see Absolute Temperature. RAREFICATION a phenomenon related to negative pressure.

PITOT TUBE a metering device consisting of a double-walled When air is drawn through resistance into a fan inlet, the air is

tube with a short right-angle bend; the periphery of the tube has several holes through which static pressure is measured; the  bent end of the tube has a hole through which total pressure is measured when pointed upstream in a moving gas stream.

stretched out,system. or rarefied, andnegligible becomes less dense than at and the entry to the While at low pressures volumes, high pressure fan selection must be based on rarefied

inlet density.

Page 6  

RELATIVE HUMIDITY the ratio of existing water vapor to

SI UNITS Systeme International d’Unites, International

that of saturated air at the same dry-bulb temperature.

System of Units; any one of the units of measure in the international meter-kilogram-second system.

RESIN an organic polymer in liquid form which, when reacted

SLIP the percentage difference between synchronous and

with the proper catalyst, becomes solid.

operating speeds.

REYNOLDS NUMBER a mathematical factor used to express

SOUND  produced by the vibration of matter. The vibration

the relation between velocity, viscosity, density, and dimensions in a system of flow; used to define fan proportionality.

causes sound waves to spread through the surrounding medium.

RIM  WHEEL  flat radial-blade design best for materialconveying application with rim plate on either side of wheel. 

SOUND-POWER LEVEL acoustic power radiating from a

ROCKWELL HARDNESS a standard measure of a metal’s

SOUND-PRESSURE LEVEL the acoustic pressure at a point

surface hardness. Also see Brinell Number.

in space where the microphone or listener’s ear is situated. Expressed in units of pressure or in decibels.

ROTOR the rotating part of most AC motors. RPM revolutions per minute. RT fan wheel design with radial-tip blades. RTP reinforced thermoset plastic. Also see FRP. SATURATED AIR air containing the maximum amount of water vapor for a given temperature and pressure.

SCFM standard cubic feet per minute; a volume of air at 0.075 lbs./ft.3 density; used as an equivalent weight.

SCROLL the general shape of a centrifugal fan housing; the

sound source. Expressed in watts or in decibels.

SP static pressure; pressure as measured in all directions within an air-handling system, not including the force or  pressure of air a ir movement.

SPECIFIC GRAVITY the ratio of the weight or mass of a given volume of any substance to that of an equal volume of some other substance taken as a standard. The ratio of the density of any gas to the density of dry air at the same temperature and pressure is the specific gravity of the gas.

SPECIFIC HEAT the ratio of the quantity of heat required to raise a certain volume one degree to that required to raise an equal volume of water one degree.

formed piece to which housing sides are welded.

SPI Society of the Plastics Industry.

SENSIBLE HEAT any portion of heat which effects a change in a substance’s temperature but does not alter that substance’s state.

SPLIT  HOUSING   housing of a fan is divided into spate

outlet of one fan exhausts into the inlet of another. Fans connected in this manner are capable of higher pressures than a single fan and are used to meet pressure requirements greater than single fans.

current, high breakdown torque. Used on easy-starting equipment, such as belt-drive fans.

sections to allow for access of interior housing.

SPLIT-PHASE MOTOR the most common type of singleSERIES FANS a combination of fans connected such that the  phase induction motor. Moderate starting torque, high starting

SERVICE FACTOR the number by which the horsepower rating is multiplied to determine the maximum safe load that a motor may be expected to carry continuously.

SPRING ISOLATORS  springs used to reduce vibration, usually mounted on a unitary base.

SQUIRREL-CAGE WINDING a permanently short-circuited

winding, usually uninsulated and chiefly used in induction motors, having its conductors uniformly distributed around the SHADED-POLE MOTOR a special type of single-phase  periphery of the machine and joined jo ined by contin continuous uous end rings. ring s. induction motor. Low starting torque, low cost. Usually used on direct-drive fans. SRC Spark-Resistant Construction; AMCA standard of  SHAFT COOLER   used to absorb and dissipate heat from the guidelines for general methods of fan construction when handling potentially explosive or flammable particles, fumes, shaft while circulating air over the inboard bearing.  SHAFT SEAL a device to limit gas leakage between the shaft or vapors. and fan housing. SSPC Steel Structures Painting Council.

SHUNT-WOUND MOTOR a DC motor in which the field circuit and armature circuit are connected in parallel.

STANDARD AIR DENSITY 0.0750 lbs./ft.3, corresponds approximately to dry air at 70°F. and 29.92 in. Hg.

STARTING TORQUE the torque produced by a motor as it  begins to turn from a standstill and accelerate. Sometimes

called locked rotor torque.

Page 7  

STATIC BALANCE the mechanical balance of a rotating part or  TORQUE a force which produces, or tends to produce, rotation; assembly by adding weights to counter-balance gravitational commonly measured in ft.-lbs. or in.-lbs. A force of one pound rotating of the part without power driving it. applied to the handle of a crank, the center of which is displaced one foot from the center of the shaft, produces a torque of one STATIC PRESSURE the static pressure for which a fan is to be ft.-lb. on the shaft if the force is provided perpendicular to, not selected based on system calculations; along, the crank. Torque can be calculated by:  fan SP = SP out let - SP inl et - VP inl et

Torque (ft. lbs.) =

STATOR the stationary parts of a magnetic circuit with associated windings.

HP x 5250 RPM

TP total pressure; the sum of velocity pressure plus static  pressure. SURGE LIMIT that point near the peak of the pressure curve which corresponds to the minimum flow at which the fan can TUBEAXIAL FAN axial fan without guide vanes.  be operated without with out instability. TUBULAR CENTRIFUGAL FAN fan with a centrifugal SWSI Single-Width Single-Inlet Centrifugal Fans. impeller within a cylindrical housing discharging the gas in an axial direction. SYNCHRONOUS SPEED rated motor speed expressed in RPM. Synchronous speed = 120 x frequency divided by TURBULENT FLOW airflow in which true velocities at a number of poles. given point vary erratically in speed and direction. SYSTEM a series of ducts, conduits, elbows, filters, diffusers, UNBALANCE the condition of a rotor in which its rotation etc., designed to guide the flow of air, gas, or vapor to and from one or more locations. A fan provides the energy necessary to overcome the system’s resistance to flow and causes air or gas

results in centrifugal force being applied to the rotors supporting bearings.

to flow through the system.

NIFORM FLOW airflow in which velocities between any U two given points remain fairly constant.

SYSTEM CURVE graphic presentation of the pressure versus volume flow rate characteristics of a particular system. SYSTEM EFFECT the effect on the performance of a fan resulting from the difference between the fan inlet and outlet connections to the actual system, and the standardized connections used in laboratory tests to obtain fan-performance ratings.

TACHOMETER an instrument which measures the speed of  rotation; usually in RPM.

TENSILE STRENGTH the maximum stress a material can withstand before it breaks; expressed in pounds per square inch.

TEST BLOCK an operating point above and beyond the maximum specified continuous rating demonstrating the fan margin to the customer.

UNIT HEATER factory-assembled unit designed to heat and circulate air. Types include steam, hot water, or gas fired.

UNITARY  BASE  base which provides common support for fan and motor.

UTILITY SET centrifugal fan designed as a packaged unit, ready to run.

VANEAXIAL FAN axial fan with either inlet or discharge guide vanes or both. Includes fixed-pitch, adjustable-pitch, and variable-pitch impellers. VENA CONTRACTA the smallest flow area for flow through a sharp-edged orifice.

VENTILATION supplying and removing air by natural or  mechanical means to and from any space.

THRESHOLD LIMIT VALUES TLV; the values for airborne VIBRATION alternating mechanical motion of an elastic

toxic materials which are to be used as guides in the control of system, components of which are amplitude, frequency, and health hazards and represent time weighted concentrations to  phase. which nearly all workers may be exposed 8 hours per day over VIBRATION   ISOLATOR   rubber-in-shear or spring-type isolation mounted to unitary base reduces the transmission of extended periods of time without adverse effects (OSHA). vibration to the mounting structure. TIP SPEED fan wheel velocity at a point corresponding to the VINYL ESTER a significant variation of polyester providing outside diameter of the wheel blades; normally expressed in in increased creased corrosion-resistance, strength, and flexibility, hence feet per minute (circumference times RPM). its suitability to the fabrication of FRP fan wheels.

VISCOSITY the characteristic of all fluids to resist flow. VOLT a unit of electrical potential or pressure. 110 or 220

volts

are

normally

found

in

the

U.S.

Form 507 DJK 

Page 8  

VP velocity pressure; the pressure or force of air in motion. The common equation based on standard air is: VP =

(

Velocity 4005

)

2

VP/SP velocity pressure divided by static pressure; a single number reference used to define a fan’s point of operation. Each system curve has a unique VP/SP value.

WET- BULB DEPRESSION the difference between the dry bulb and wet-bulb wet-b ulb temperatures at the same location. loc ation. WET- BULB TEMPERATURE temperature at which air is  brought to saturation by evaporating a liquid into the air at the same temperature. WG water gauge; see Inch of Water. WHEEL the rotating portion of the fan designed to increase the

WATT a unit of power. In electrical terms, the product of  voltage and amperage. 746 watts are equal to one horsepower.

WEATHER C OVER completely encloses the motor and drive assembly for protection. can be easily removed for inspection and maintenance.

energy level of the gas steam.

WR2 the unit designation of fan wheel rotational inertia in lb.ft.2, also known as WK 2.

YIELD STRENGTH maximum stress to which a ductile material can be subjected before it physically distorts.