FLUID VISCOSITY SELECTION CRITERIA.pdf

FLUID VISCOSITY SELECTION CRITERIA FOR HYDRAULIC PUMPS AND MOTORS Steven N. Herzog, RohMax USA, Inc., Horsham, PA Thelma E. Marougy, Eaton Corporation, Southfield, MI Paul W. Michael, Benz Oil, Milwaukee, WI

Abstract Viscosity is one of the most important criteria in the selection of a hydraulic fluid. A hydraulic fluid that is too low in viscosity will cause low volumetric efficiency, fluid overheating, and increased pump wear. A hydraulic fluid that is too high in viscosity will cause poor mechanical efficiency, difficulty in starting, and wear due to insufficient fluid flow. Selecting the proper viscosity fluid requires an understanding of the low and high temperature requirements of different types of hydraulic components. The effects of mechanical shear on fluid viscosity must also be taken into consideration. This article aids users of hydraulic fluids in selecting the proper viscosity fluid by providing a compilation of minimum and maximum viscosity requirements specified by a number of manufacturers of hydraulic pumps and motors. Once the user determines the fluid operating temperature range, the user will be able to utilize the method described in this paper to select the proper viscosity hydraulic fluid. Selecting the proper viscosity hydraulic fluid will improve the efficiency and life of hydraulic equipment.

Nomenclature (1),(2),(3) ViscosityA fluid’s resistance to flow. Dynamic viscosityViscosity measured under force induced flow. The cgs unit for dynamic viscosity is cm⋅s/g which is commonly known as a centipoise, cP. Kinematic viscosityViscosity measured under gravity induced flow. The cgs unit for kinematic viscosity is mm2/s which is commonly known as a centistoke, cSt.

Newtonian fluidFluid whose viscosity is constant over all values of shear stress and/or shear rate such as a petroleum base oil. Non-newtonian fluidFluid whose viscosity is not constant over all values of shear stress and/or shear rate such as a polymer-containing petroleum oil at significantly high shear rates. Viscosity index-VI Dimensionless value indicating the effect of temperature change on the kinematic viscosity of an oil. Shear stabilityThe resistance of a fluid, especially a polymer-thickened fluid, to shear degradation. The higher the shear stability index, SSI, the more shear degradation of the fluid is likely to occur.

Effects of Viscosity on System Performance The performance of pumps and motors is a critical factor in overall hydraulic system reliability. Not only must these components transmit energy, they must do so in an efficient manner. There are two elements of hydraulic efficiency; volumetric efficiency and mechanical efficiency. Mechanical efficiency relates to the frictional losses within a hydraulic component and the amount of energy required to generate fluid flow. Volumetric efficiency relates to the flow losses within a hydraulic component and the degree to which internal leakage occurs. Both of these properties are to a large degree viscosity dependent.

E

As can be seen in figure 1 (4), mechanical efficiency varies inversely with fluid viscosity. Volumetric efficiency on the other hand increases with fluid viscosity. Consequently the range of optimum performance requires a compromise. The optimal overall efficiency corresponds to the maximum product of mechanical and volumetric efficiencies.

Viscosity → Figure 1.

Typical hydraulic pump efficiency curves

A hydraulic system that could operate at constant temperature, including start-up, would function at optimum efficiency at all times if the proper fluid viscosity had been selected. Unfortunately, such a hydraulic system is purely theoretical because a typical hydraulic system converts about 20% of its input horsepower into heat (5). Thus, the temperature of a fluid at start-up is nearly always lower than the fluid’s operating temperature.

Figure 2.

There are several prerequisites for cavitation to occur in a hydraulic pump. First, there must be dissolved gasses or a vaporizable liquid in the fluid. Second, there must be a flow restriction at the pump inlet that creates a low-pressure (vacuum) zone where these gasses form a cavity. Third, the resulting bubble must pass into a high-pressure zone where it energetically collapses.

Low temperatures can create high viscosity conditions that compromise the mechanical efficiency of the hydraulic system and cause sluggish system response, lubricant starvation and cavitation. Cavitation is defined as the dynamic process of gas cavity growth and collapse in a fluid (6). The characteristic appearance of cavitation wear is depicted in figure 2.

Cavitation is of significant concern in hydraulic applications because the resulting implosion of the gas bubble causes metal fatigue. Viscosity influences cavitation because high viscosity fluids can create excessive pressure drop at the pump inlet. Consequently, pump manufacturers specify a maximum fluid viscosity under start-up conditions in order to insure that cavitation conditions are avoided.

f

f

Cavitation damaged piston pump bearing plate (7)

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Another consequence of excessive viscosity under low temperature conditions is pump starvation. Starvation occurs when an insufficient amount of fluid is supplied to prime the pump. When this type of failure occurs it usually results in rupture of the lubricating film, high contact temperatures, wear and ultimate pump seizure.

contact takes place. This results in wear within the pump. While it is intuitive that wear is undesirable, what is less obvious is that it predominantly occurs in locations within a pump that are critical in terms of volumetric efficiency. Loss of volumetric efficiency causes the pump to work harder to produce the required flow to activate hydraulic actuators. At the same time, high temperatures compromise the volumetric efficiency of hydraulic pumps due to internal leakage as the result of low viscosity fluid bypassing critical pump clearances. Thus inadequate viscosity due to high temperatures creates a destructive cycle of rising temperatures and accelerated wear.

Multigrade Hydraulic Fluids

Figure 3.

Many types of lubricants are used in hydraulic systems - engine oils, automatic transmission fluids, anti-wear hydraulic fluids, gear oils, etc. Some of these lubricants known as multigrades or HV hydraulic fluids contain polymeric additives called viscosity index improvers (VI improvers). VI Improvers raise the viscosity of the base fluid to which they are added. Besides “thickening” the fluid, they also increase the viscosity index of the fluid and reduce viscosity fluctuation over a temperature range.

Rotor seizure due to lack of lubrication (8)

In the failure depicted in figure 3, the rotor and vanes are severely scored due to lack of lubrication. Starvation can also shorten the life of pump bearings. While pump starvation can result in a rapid and catastrophic hydraulic failure, and cavitation can accelerate fatigue failures, excessively high fluid viscosity also can produce sluggish hydraulic performance. Not only does this have a negative impact upon the productivity of hydraulic equipment, in applications such as electric company bucket trucks it can create safety hazards because sluggish hydraulic systems cause erratic actuator motion.

Multigrade hydraulic fluids are often recommended in equipment where temperature of operations can vary significantly. Multigrades allow the optimum viscosity of the fluid to be available over a wider temperature range than straight graded oils. Multigrades are also recommended as a way to eliminate seasonal oil changes since a properly formulated multigrade should perform in both winter and summer temperatures.

One of the functions of a hydraulic fluid is to provide a hydrodynamic lubricating film that reduces wear. The effectiveness of this film depends upon a balance between viscosity, sliding speeds and loads within a hydraulic pump. When the viscosity of a fluid is reduced due to high temperatures, it can create conditions where the hydrodynamic lubricating film ruptures and metal-to-metal

Multigrades are good for low temperature startup because at these startup temperatures, their viscosity is lower than a straight graded oil with the same high temperature viscosity. This allows the hydraulic fluid to flow more quickly for smoother operation, thus avoiding sluggish system response. Multigrades also reduce

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the likelihood of low temperature lubricant starvation, low mechanical efficiency and cavitation. These are the reasons that multigrades are often recommended for low temperature hydraulic operations.

VI improvers are available in various chemical compositions and molecular weights (Mw) ranging from about 20,000 to 900,000 Daltons. Previous studies of mechanical shearing have documented that different types of equipment impart different levels of shearing severity. Kopko and Stambaugh (10) demonstrated the relative severity of engines, automatic transmissions (AT), pumps and hypoid gear sets with polymethacrylate (PMA) VI improvers of differing molecular weights as shown in figure 5. The higher the Shear Stability Index, SSI, the greater the shearing of the polymer.

Not as often thought of, but just as important, is the multigrade’s effectiveness for maintaining pumping efficiency at high temperatures. As temperature in a hydraulic system rises, pumping efficiency drops since the increased temperature reduces the fluid viscosity leading to increased internal leakage. Multigraded fluids’ viscosity will decrease less with increasing temperature, thus maintaining optimum pumping efficiency to a higher temperature.

100

VI Improver Shear in Hydraulic Applications

90

80 70

As shown in figure 4 (9), when a sufficiently high shear stress is applied to a VI improved oil, the VI molecules will become stretched out in the direction of the fluid flow resulting in a temporary lowering of the fluid viscosity. This “temporary viscosity loss” reverses itself as the shear stress is reduced on the oil.

Gear Oil

SSI

60 50

40

ATF

30

Engine Oil

20 10

0 10

50

Shear stresses of sufficient magnitude to permanently shear VI improvers may exist in pumps, servos, directional valves and actuators. Once the VI improver molecule is ruptured, the two resulting smaller molecules provide less thickening than the original VI improver molecule. This “permanent shear loss” does not reverse itself when the shear stress is reduced or removed completely.

Figure 5.

1000

-3

SSI - Molecular weight relationship for various applications.

These data demonstrate a higher degree of shearing severity in a high pressure vane pump compared to automotive internal combustion engines and automatic transmissions, but less severity than in an automotive rear axle hypoid gear set. In general, multigrade hydraulic fluids tend to be formulated to be more shear stable than automatic transmission fluids (ATF’s) and engine oils but less shear stable than multigrade gear oils.

Shear Stress Higher Sheer Stress

Bond Breakage

Shear Stress

Figure 4.

500

100

Mw x 10

Removal of Shear Stress

Hydraulic Fluid

Example of Temporary and Permanent Viscosity Loss.

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These data also show that shear stability of a fluid varies with the molecular weight of the VI improver. The lower the molecular weight of the VI improver, the more shear stable the product. In fact, one can design an entirely shear stable hydraulic fluid by choosing the right molecular weight VI improver for the shear stress of the operation. For a more detailed discussion on multigraded hydraulic fluids, VI improvers and shear stability see reference # 11, chapter 5.

Table 1 - ISO 3448 ISO Viscosity Grades 2 Kinematic Viscosity, 40°C (mm /s) ISO VG

2 3 5 7 10 15 22 32 46 68 100 150 220 320 460 680 1000 1500

Hydraulic Fluid Viscosity Classification Systems Several viscosity classification systems are currently used. They were designed to provide lubricant suppliers, users and equipment manufacturers a common, meaningful basis for specifying and selecting lubricants for use. The classification systems range from the simple ISO system to the more recent ASTM D 6080-97.

Midpoint

Minimum

Maximum

2.20 3.20 4.60 6.80 10.0 15.0 22.0 32.0 46.0 68.0 100 150 220 320 460 680 1000 1500

1.98 2.88 4.14 6.12 9.00 13.5 19.8 28.8 41.4 61.2 90.0 135 198 288 414 612 900 1350

2.42 3.52 5.06 7.48 11.0 16.5 24.2 35.2 50.6 74.8 110 165 242 353 506 748 1100 1650

There are flaws in the ISO 3448 system. The ISO viscosity grades are not continuous. Each ISO VG is approximately 50% more viscous than the next lower grade. Since the ISO grades are only + or 10% around the midpoint viscosity, gaps exist between grades. A fluid with a viscosity that does not fall into a ISO VG range cannot be formally classified.

ISO Viscosity Grades In 1975, a co-operative effort between ASTM, ASLE, BSI, and DIN resulted in the ISO 3448 Viscosity Classification for Industrial Liquid Lubricants. This classification is commonly referred to as ISO viscosity grades. The ISO system classifies lubricants solely on kinematic viscosity measured at 40°C. The choice of 40°C as the reference temperature is a compromise between maximum operating and ambient temperatures.

Another flaw is that this is a simple viscosity classification system that addresses only the fluid’s kinematic viscosity at one temperature. Because it only deals with 40°C viscosity, ISO 3448 does not deal with viscosities at higher or lower temperatures that equipment might experience such as cold start ups or high temperature operations.

The ISO classification system is made up of 18 ISO viscosity grades, usually written as ISO VG. The grades start with ISO VG 2 and go up to ISO VG 1500. Each grade is named by the whole number which is the rounded, midpoint viscosity of its associated range of viscosity. Each range is + or - 10% of the midpoint viscosity. The viscosity ranges for all the ISO grades are shown in table 1.

A third flaw with the ISO 3448 system is that it does not deal with high or low VI hydraulic fluids. Based on this system, a user cannot tell if he has a 30 VI or a 200 VI fluid. The fourth deficiency of this system is that it only deals with fresh oil viscosity. It does not take into consideration the hydraulic fluids used oil viscosity.

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ASTM D 6080 ASTM D 6080 (Standard Practice for defining the Viscosity Characteristics of Hydraulic Fluids) builds upon the ISO VG system because of its wide recognition. It addresses the above issues by including a second tier of information that indicates the following: • Cold temperature grade • 40°C viscosity after shearing • VI after shearing

Table 2 Low Temperature Viscosity Grades for Hydraulic Fluid Classification ASTM D 6080 ISO Temperature, °C for Brookfield VG Viscosity of 750 cP L5 -50 or below L7 -42 to -49 L10 -33 to -41 L15 -23 to -32 L22 -15 to -22 L32 -8 to -14 L46 -2 to -7 L68 4 to -1 L100 10 to 5 L150 16 to 11

The second classification tier does not require viscosity to fall within the standard ISO ranges. This system is limited to ISO VG 5 through ISO VG 150 since these grades represent the vast majority of hydraulic fluids. A fluid description under ASTM D 6080 would look like the following:

To address the issue of shear stability of VI improved oils (zz), ASTM D 6080 includes a kinematic viscosity at 40°C after a 40 minute sonic shear test. Previous work has indicated a strong correlation between this sonic shear test and mechanical shearing of multigraded fluids in pump service.10

ISO VG xx Lyy-zz (VI) Where • xx is the fresh 40°C viscosity grade of the hydraulic fluid (as per ISO 3448) • Lyy is the low temperature viscosity grade (based on the temperature at which the fluid’s viscosity reaches 750 cP, measured by ASTM D 2983, Brookfield viscometer) • zz is the used oil viscosity at 40°C after shearing (in the 40 minute sonic shear test, ASTM D 5621) • VI is the viscosity index after shearing (in the same 40 minute sonic shear test)

The viscosity index (VI) of the fluid after the above shear test is also included in this classification system in order to provide a means of calculating the viscosity of the fluid at any temperature from 40°C to 100°C. This gives a much better understanding of a fluid’s viscosity at the pump’s operating temperature.

Viscosity Selection Criteria A number of hydraulic component manufacturers were surveyed regarding the fluid viscosity requirements of their pumps and motors. Table 3 shows the minimum, maximum and optimum viscosity recommendations provided by these manufactures. There are two ways in which this data may be used to select the proper viscosity fluid. The first method is based on a Temperature Operating Window or TOW. The second method, which we call the ALTOW method (ALternate TOW), is based upon a modification of the conventional viscosity-temperature technique for selecting fluid viscosity.

The 750 cP low temperature limit was chosen because it represents a relatively severe case for allowable viscosity at pump startup. The “L” viscosity grades and the ranges associated with each were established by extrapolating the 40°C viscosity ranges of each ISO VG , using 100 VI, down to the 750 cP limit. For example, an ISO L32 has a temperature range of -8 to -14.9°C. All the low temperature grades are shown in table 2.

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The TOW and ALTOW methods are discussed in more detail below. An overview of the procedure for viscosity selection is depicted in the flow chart, figure 8, that appears at the end of this document.

When selecting a hydraulic fluid using TOW criteria, determine the lowest ambient temperature at start-up and the highest fluid temperature in use. This defines the temperature operating range. Any fluid that has a Temperature Operating Window, that encompasses the temperature operating range may be selected for the application. For example, consider a plastic injection molding press with a Denison Vane pump. This pump is highlighted in bold on table 3. Assume the lowest temperature at start-up is 15°C and the maximum for this system is 65°C. This operating temperature range falls within the TOW of ISO VG 46, 68 and 100 fluids. Thus any of these viscosity grades may be selected, assuming they are 100 VI or higher.

The TOW Method The temperature ranges for the viscosity grades that appear in the TOW chart, figure 6, are based upon the calculated temperatures for which a mid-range ISO VG, 100 VI hydraulic fluid has a viscosity between 13 and 860 cSt. Based upon the data in table 3, the majority of pumps and motors provide satisfactory performance with a fluid that has a minimum viscosity of 13 cSt under operating conditions and a maximum start-up viscosity of 860 cSt (approximately 750 cP). Components listed in bold in the Equipment Builders’ Viscosity Guidelines, table 3, meet this criteria. Thus for the components listed in bold, the appropriate viscosity grade may be determined from the TOW Chart.

ALTOW Method Many hydraulic applications do not fall within the TOW system because of wide operating temperature ranges or the pump manufacturer recommends a viscosity range of less than the 13 to 860 cSt range developed for the TOW system. In these applications the optimum fluid viscosity may be determined by using a variation on the ASTM D 341 viscosity-temperature chart. A viscosity-temperature chart is routinely used to generate a graphical depiction of the relationship between viscosity and temperature. Normally viscosity selections based upon a viscosity-temperature chart involve the determination of actual fluid viscosity at 40°C and 100°C. In the ALTOW chart attached, figure 7, normal ranges for the standard ISO viscosity grades are identified at low and high temperatures. The low temperature ranges are based upon the standard ranges established by ASTM D 6080. The high temperature ranges are based upon a similar extrapolation. The 40°C viscosities for the various ISO grades were extrapolated to 100°C assuming a minimum VI of 100. These ranges are provided to simplify interpretation of the viscositytemperature chart.

Temperature, °C

Temperature Operating Window For 13 to 860 cSt Straight Grade, 100 VI Hydraulic Fluid

ISO Viscosity Grade

Figure 6.

TOW Chart

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The procedure for using the attached ALTOW chart, figure 7, is describe below: 1)

2) 3)

4)

5)

6)

7)

8)

9)

points on the ALTOW chart. An ISO 22 oil meets the low temperature requirement and an ISO 32 oil meets the high temperature requirement for this application. Since the high temperature viscosity grade is greater than the low temperature viscosity grade, a multigrade fluid is required. In this instance one would select a fluid that meets the L2232 specification per ASTM D 6080. In applications where the high temperature grade is 2 or more ISO viscosity grades higher than the low temperature ISO grade, it is usually necessary to employ seasonal oil changes or use reservoir heaters/coolers.

Look up the minimum and maximum viscosity requirements for system pumps and motors. Determine the lowest and highest fluid temperature. Plot the highest recommended viscosity at the lowest fluid temperature on the ALTOW chart. Plot the lowest recommended viscosity at the highest fluid temperature on the ALTOW chart. Draw a line through these values that connects the low temperature and high temperature areas of the chart. Where the line intersects the horizontal boxes is the low temperature viscosity grade requirement. Where the line intersects the vertical boxes is the high temperature viscosity grade requirement. If the low temperature viscosity grade is ≥ the high temperature viscosity grade requirement, a straight grade hydraulic fluid that meets either grade may be used. If the low temperature viscosity grade is < the high temperature viscosity grade requirement, a multigrade hydraulic fluid that meets both viscosity grades should be used.

Summary and Conclusions This paper provides a compilation of the viscosity requirements for hydraulic pumps and motors. It has been shown that the TOW and ALTOW methods can be a simple and useful means of selecting the appropriate viscosity fluid. By selecting a hydraulic fluid with the proper viscosity, designers and users of hydraulic equipment are able to maximize the efficiency, reliability and durability of hydraulic equipment.

References (1) Godfrey, D. and Peeler, R. “Explanation of Viscosity Units” Lubrication Engineering, Vol 38, No. 10, Oct 1981, pp 613-614. (2) Exxon Encyclopedia for the User of Petroleum Products, Lubetext DG-400, 1993. (3) ASTM D 6080-97, Annual Book of ASTM Standards, Volume 5.03, Petroleum Products and Lubricants, 1999, ASTM, Philadelphia. (4) Totten, G.E., Handbook of Hydraulic Fluid Technology, Marcel Dekker, New York, 2000, p 27. (5) Schneider, R.T., Hydraulics & Pneumatics, Vol. 52, No. 11, Nov 1999, p 47. (6) Totten, G.E., Handbook of Hydraulic Fluid Technology, Marcel Dekker, New York, 2000, p 257. (7) Photograph courtesy of Benz Oil.

For example, consider a compactor operating outdoors in Chicago with a EatonVickers mobile piston pump. The low temperature at start-up could be as low as –20°C. The highest temperature in the application can reach 65°C. This operating temperature range does not fall within any of the Temperature Operating Windows for straight grade oils given in the TOW Chart, figure 6. Since the TOW method cannot be used in this application, the ALTOW method should be used. From table 3 it is evident that the minimum viscosity allowed is 10 cSt and the maximum viscosity allowed is 860 cSt. On the ALTOW chart, plot 10 cSt , the minimum viscosity allowed, at 65°C, the maximum fluid temperature expected. Plot 860 cSt, the maximum viscosity allowed, at -20°C, the minimum fluid temperature expected. Draw a line through these 2

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(8) Pump Failure Analysis, Vickers publication 513-K91JJ, 1991, p 9. (9) Hyndman, C.W., Kinker, B.G., Placek, D.G., ”Shear Stability of Multigraded Hydraulic Fluids,” Hydraulic Failure Analysis: Fluids, Components, and Systems Effects, ASTM STP 1339, 2000 (10) Kopko, R.J. and Stambaugh, R.L. “Effect of VI Improvers on the InService Viscosity of Hydraulic Fluids,” 1975 SAE Paper 750683. (11) Kinker, B.G., “Fluid Viscosity and Viscosity Classification,” in Handbook of Hydraulic Fluid Technology, G.E. Totten ed., Marcel Dekker, New York, 2000, pp 305-338. (12) Stambaugh, R.L., Kopko, R.J., Roland, T.F., “Hydraulic Pump Performance - A basis for Fluid Viscosity Classification,” 1990, SAE Paper 901633.

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Appendix Table 3 EQUIPMENT BUILDERS’ VISCOSITY GUIDELINES FOR HYDRAULIC FLUIDS

Manufacturer

Bosch Form No S/106 US

Commercial Intertech Danfoss Denison Bulletin 440

Dynex/Rivett axial piston pumps

Eaton

Eaton - Vickers

Eaton - Char-Lynn

Haldex Barnes Kawasaki P-969-0026 P-969-0190

Equipment

Minimum cSt 15

Maximum cSt 216

Start-up (Under Load) Maximum cSt 864

21

216

864

32-54

32 10 14

216 65 450

864 162 647

43-64 21-54 32-65

10 10 13 10

--107

20 21-39 24-31 30

PF4200 Series PF2006/8, PF/PV4000, and PF/PV6000 series. PF 1000,PF2000 and PF3000 series. Heavy Duty Piston Pumps & Motors, Medium Duty Piston Pumps & Motors Charged Systems, Light Duty Pumps. Medium Duty Piston Pumps & Motors - Non-charged Systems. Gear Pumps, Motors, & Cylinders. Mobile Piston Pumps Industrial Piston Pumps Mobile Vane Pumps Industrial Vane Pumps. J, R, and S Series Motors, and Disc Valve Motors. A Series and H Series Motors. W Series Gear Pumps

1.5

372

1600 1618 860 (low speed & pressure) 372

2.3

413

413

20-70

3.5

342

342

20-70

6

--

2158

10-39

6

--

432

10-39

6 10 13 9 13

-200 54 54 54

2158 860 220 860 860

10-43 16-40 16-40 16-40 16-40

13

--

2158

20-43

20 11

---

2158 750

20-43 21

Staffa Radial Piston Motors K3V/G Axial Piston Pumps

25 10

150 200

2000 (no load) 1000

50

FA;RA;K. Q;Q-6;SV-10, 15, 20, 25, VPV 16, 25, 32. SV-40; 80 &100 VPV 45, 63. Radial Piston (SECO) Axial & RKP Piston Roller and Sleeve Bearing Gear Pumps. All Piston Pumps Vane Pumps

Operating

Optimum cSt 26-45

20-70

Table 3 (continued) EQUIPMENT BUILDERS’ VISCOSITY GUIDELINES FOR HYDRAULIC FLUIDS

Manufacturer

Linde Mannesmann Rexroth

Parker Hannifin

Equipment

Operating

All V3 , V4, V5, V7 Pumps V2 Pumps R4 Radial Piston pumps G2, G3,G4 pumps & motors G8, G9, G10 pumps. Gerotor Motors. Gear Pumps PGH Series. Gear Pumps D/H/M Series.

Poclain Hydraulics Sauer-Sundstrand, USA Sauer-Sundstrand, GmbH

Hydraulic Steering. PFVH / PFVI vane pumps. Series T1. VCR2 Series. Low Speed High Torque Motors. Variable Vol Piston Pumps. PVP & PVAC. Axial Fixed Piston Pumps. Variable Vol Vane - PVV. H and S series motors All Series 10 and 20, RMF(hydrostatic motor). Series 15 open circuit. Series 40, 42, 51,& 90 CW S-8 hydrostatic motor. Series 45. Series 60, LPM(hydrostatic motor). Gear Pumps + Motors.

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Minimum cSt 10 25 16 10

Maximum cSt 80 -160 200

Start-up (Under Load) Maximum cSt 1000 800 800 --

Optimum

10 8 --8 -10 13

300 --------

1000 -1000 1000 -1000 1000 1000

25-160 12 – 60 17 – 180 17 – 180 12 – 60 17 – 180 10 – 400 --

10 ----9 6.4

--------

-1000 1000 850 440 1500 1600

-17 – 180 17 – 180 12 – 100 16 – 110 20-100 13

7 12

---

1000 860

12-60 12-60

7 9

---

1600 1000

12-60 12-60

9 10

---

1600 1000

12-60 12-60

cSt 15-30 25-160 25-160 25-160

Figure 7

ALTOW Chart Viscosity-Temperature Chart 100 VI Hydraulic Fluid

Figure 8 Viscosity Selection Process

Determine the min. and max. viscosity requirements from Table 3

Locate pump and hydraulic motor in Table 3

Are components highlighted in bold?

Plot the intersection of viscosity requirements with operating temperatures on ALTOW Chart (Figure 7)

NO

YES

Identify the viscosity grades that encompass the operating range in the TOW chart (Figure 6)

Is there a TOW that covers operating conditions?

NO

NO

YES

Select the fluid with the appropriate ISO viscosity grade based upon the TOW

Draw a line connecting high and low temperature regions in the ALTOW chart (Figure 7)

Use the ALTOW method

Is the low temp vis grade below that of the high temp grade?

YES* Select a straight-grade or multigrade fluid for the application that corresponds to the vis grades identified in the ALTOW chart

Select the appropriate multigrade fluid based upon the ASTM D6080

* If the high temp. ISO grade is two or more ISO grades higher than the low temp. ISO grade, it may be necessary to employ seasonal oil changes or use reservoir heaters/coolers.

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