Lab3E6_Series and Parallel Pump.pdf

​LabManual FACULTY OF ENGINEERING & BUILT ENVIRONMENT SUBJECT: EME3421 LABORATORY INVESTIGATIONS 3 EXPERIMENT 8: SERIES AND PARALLEL PUMP 1.0 OBJECTIVE i. To demonstrate the basic operation and characteristic of centrifugal pumps. ii. To differentiate the flow rate and pressure head of a single pump and of two

identical pumps that is run in series or parallel. 2.0 THEORY/INTRODUCTION

Pumps are used in almost all aspects of industry and engineering from feeds to reactors or distillation columns in chemical engineering to pumping storm water in civil and environmental. They are an integral part of engineering and an understanding of how they work is important for any type of engineer. Centrifugal pump is one of the most widely used pumps for transferring liquids. This is for a number of reasons. Centrifugal pumps are very quiet in comparison to other pumps. They have a relatively low operating and maintenance costs. Centrifugal pumps take up little floor space and create a uniform, non-pulsating flow. This equipment illustrates the basic operation and characteristics of centrifugal pumps. The equipment will explore flow rates and pressure head of a single pump and of two identical pumps that are run in series or in parallel. In this equipment, there are two pumps connected through a pipe work that allows for them to be operated individually, in series or in parallel. When identical pumps are in series the pressure head is doubled but the flow rate remains the same. This is useful when a high pressure is needed but the same flow rate as of a single pump is sufficient. When pumps are run in parallel the flow is increased and the pressure head produced is around the same as a single pump. Pumps are devices that transfer mechanical energy from a prime mover into fluid energy to produce the flow of liquids. There are two broad classifications of pumps: positive displacement and dynamic. In the experiments, students are able to operate Horizontal Single Stage Centrifugal Pump (PI) and (P2) in different arrangement-single, parallel and serial. 2.1 Dynamic Pumps Dynamic pumps add energy to the fluid by the action of rotating blade, which increases the velocity of the fluid. Figure 1 shows the construction features of a centrifugal pump, the most

commonly used type of dynamic pump.

Figure 1 Construction features of a centrifugal pump 2.2 Horizontal Single Stage Centrifugal Pump Centrifugal pumps have two major components: 1. The impeller consists of a number of curved blades (also called vanes) attached in a regular pattern to one side of a circular hub plate that is connected to the rotating driveshaft. 2. The .housing (also called casing) is a stationary shell that enclosed the impeller and supports the rotating drive shaft via a bearing. A centrifugal pump operates as follows. The prime mover rotates the driveshaft and hence the impeller fluid is drawn in axially through the centre opening (called the eye) of the housing. The fluid then makes a 90° turn and flows radially outward. As energy is added to the fluid by the rotating blades (centrifugal action and actual blade force), the pressure and velocity increase until the fluid reaches the outer tip of the impeller. The fluid then enters the volute-shaped housing whose increased flow area causes the velocity to decrease. This action results in decrease kinetic energy and an accompanying increase in pressure. The volute-shaped housing also provides a continuous increase in flow area in the direction of flow to produce a uniform velocity as the fluid travels around the outer portion of housing and discharge opening. Although centrifugal pumps provide smooth, continuous flow, their flow rate output (also called discharge) is reducing as the external resistance is increase. In fact, by closing a system valve (thereby creating theoretically infinite external system resistance) even while the pump is running at design speed, it is possible to stop pump output flow completely. In such a case, no harm occurs to the pump unless this no-flow condition occurs over extended period with resulting excessive fluid temperature build up. Thus pressure relief valves are not needed. The tips of the impeller blade merely shear to through the liquid, and the rotational speed maintains a fluid pressure corresponding to the centrifugal force established. Figure 2 shows the cutaway of a centrifugal pump

Figure 2 The Cutaway of a Centrifugal Pump 2.2.1 Pump Head versus Flow rate Curves for Centrifugal Pumps Figure 3 shows pump head versus flow rate curves for a centrifugal pump. The solid curve shows the rate for water, whereas the dashed curve is for a more viscous fluid such as oil. Most published performance curves for centrifugal pumps are for pumping water. Notice from Figure 3 that using a fluid having a higher viscosity than water results in a smaller flow rate at a given pump head. If the fluid has a viscosity greater than 300 times that of water, the performance of a centrifugal pump deteriorates enough that a positive displacement pump is usually recommended.

Figure 3 Pump Head versus Flow rate Curves for Centrifugal Pump for water and for a more viscous liquid The maximum head produced by a centrifugal pump is called pump shutoff head because an external system valve is closed and there is no flow. Notice from Figure 4 that as the external system resistance decrease (which occurs when a system valve is opened more fully), the flow rate increases at the expense of reduced pump head. Because the output Flow rate changes significantly with external system resistance, centrifugal pumps are rarely used in fluid power systems. Zero pump head exists if the pump discharge port were opened to the atmosphere, such as whenfillingnearby open tank with water. The open tank represents essentially zero resistance to flow for the pump. Figure 4 shows why centrifugal pumps are desirable for pumping stations used for delivery water to homes and factories. The demand for water may go to near zero during the evening and reach a peak during the daytime, but a centrifugal pump can readily handle these large changes in water demand. Since there is a great deal of clearance between the impeller and housing, centrifugal pumps are not self-priming, unlike positive displacement pumps. Thus if a liquid being pumped from a reservoir located below a centrifugal pump, priming is required. Priming is the prefilling of the pump housing and

inlet pipe with the liquid so that the pump can initially draw the liquid and pump efficiency. Priming is required because there is too much clearance between the pump inlet and outlet ports to seal against atmospheric pressure. Thus the displacement of a centrifugal Pump is not positive where the same volume of liquid would be delivered per revolution of the driveshaft. The lack of positive internal seal against leakage means that the centrifugal pump is not forced to produce flow when there is a very large system resistance to flow. As system resistance decrease, less of the fluid at the discharge port slips back into the clearance spaces between the impeller and housing, resulting in an increase in flow. Slippage occurs because the fluid follows the path of least resistance. 2.2.2 Performance Characteristic Curves for Centrifugal Pumps When Centrifugal Pump manufacturers test their pumps, they typically produce (for a given geometry and speed) performance curves of head, overall efficiency, and input shaft power versus flow rate of the specified fluid. Figure 5 shows these three curves plotted on the same graph. Note that as the flow rate increases from zero, the efficiency increases from zero until it reaches maximum, and then it decreases as the maximum flow rate is approached. The point where the maximum efficiency occurs is the best efficiency point (BEP), and the corresponding flow rate is the design flow rate. When selecting a pump for a given application, it is usually desirable to use a pump that will operate near its efficient point. Maximum efficiency values for centrifugal pumps typically range from 60% to 80%. 2.3 Centrifugal pump connected in Parallel If a single pump does not provide enough flow rate for a given application, connecting two pumps in parallel as shown in Figure 4, can rectify the problem. The effective two-pump performance curve is obtained by adding the flow rates of each pump at the same head. As shown, when two pumps are connected in parallel, the operating points shift from A to B, providing not only increased flow rate as required but also greater head. Figure 6 shows identical pumps, but the pumps do not have to be the same.

Figure 4 Two centrifugal pumps connected in parallel

2.4 Centrifugal pump connected in series On the other hand, if a single pump does not provide enough head for a given application, two pumps connected in series, as shown in Figure 5, can be a remedy. The effective two-pump performance curve is obtained by adding the head of each pump at the same flow rate. As, shown, the operating point shifts from A to B, thereby providing not only increased head as required but also greater flow. Figure 5 shows identical pumps, but the pumps do not have to be the same.

Figure 5 Two centrifugal pumps connected in series 3.0 APPARATUS

Figure 6 Equipment Assembly 3.1Specifications Before operating the unit, students must familiarize themselves with the unit. Please refer toFigure 7to understand the process. The unit consists of the followings: a) Pumps v 2 units of Horizontal Single Stage Centrifugal Pump (PI) and (P2) Flow rate : 20-90 LPM Head : 20.7-15 m Max. Head: 22 m b) Circulation Tank Transparent acrylic water tank is provided to supply water to PI and P2. c) Flow rate and pump head All gauges and meters are provided in a way for easy viewing and data collection. d) Process piping The process piping is made of industrial PVC pipes. Valves used are non-ferrous to minimize rust and corrosion. Overall Dimensions Height: 700 mm Width: 650 mm Depth: 1100 mm General Requirements Electrical: 240 VAC, 1-phase, 50Hz Water tap water.

​: Clean

P1 Figure 7 Process Diagram for Serial / Parallel Pump Test Unit 3.2

​Installation Procedures 2. Unpack the unit and place it on a table close to the single phase electrical supply. 3. Place the equipment on top of a table and level the equipment with the adjustable feet. 4. Inspect the all parts and instruments on the unit and make sure that it is in proper condition. 5. Connect the equipment to the nearest power supply.

3.3

​Commissioning Procedures 1. Install the equipment according to Section 3.1. 2. Make sure that all valves are initially closed. 3. Fill up the sump tank with clean water until the water level is sufficient to cover the return flow pipe. 4. Then test the pumps according to Section 5.1. 5. Check that pumps, flow meter and the gauges are working properly. Identify any leakage on the pipe line. Fix the leakage if there is any. 6. Turn off the pumps after the commissioning. 7. The unit is now ready for use.

4.0 PROCEDURES 4.1 General Start-up Procedures Before conducting any experiment, it is necessary to do the following checking to avoid any

misused and malfunction of equipment.

1. Make sure that the circulation tank is filled with water up to at least the end of the pipe output is submerge with water.

2. Make sure that the V5 is in partial open position. 3. Switch on the main power supply. 4. Refer to Table 1, select the appropriate pump and check for following valve position. Pump Operation Single Serial Parallel

5.

Table 1 Valve Position for General Start-up Running Pump Open Valve Close Valve Pump 1, PI 1,4 2,3 Both Pump, PI &P2 1,3 2,4 Both Pump, PI &P2 1,2,4 3

Turn on pump and slowly open V5 until maximum flow rate is achieved as shown in Table 2.

Table 2 Flow Rates of Pump Orientation Minimum Flow Rate(LPM) Maximum Flow Rate(LPM) Single 20 90 Series 20 90 Parallel 40 180

Eto

4.2 General Shut-down Procedures 1. Turn off the pump. 2. Make sure valve V5 is in fully close position. 3. Switch off the main power supply. 4.3 Experiment 1: Single Pump Operation Objective:Single pump operation with variable flow rate Table 3 Equipment Set Up of Experiment 1 Fully Close valve Fully Open Valve Variable parameter 2&3

1& 4

Valve 5

Pump ON Pump 1

Procedures: 1. Follow the basic procedure as written in section 3.2. 2. Ensure that all setting follows the equipment set up. 3. Slowly open valve V5 until the flow rate reaches 20 LPM. 4. Observe the pressure reading on the pressure indicator. Record flow rate and pressure value when stable condition is achieved. 5. Repeat observation by increasing the flow rate with increment by 10 LPM until the flow rate reaches 90 LPM

4.4 Experiment 2: Series Pump Operation Objective: Series pump operation with variable flow rate Table 4Equipment Set Up of Experiment 2 Fully Close valve Fully Open Valve Variable parameter X4

1,3

Valve 5

Pump ON Both Pump

Procedures: 1. Follow the basic procedure as written in section 3.2. 2. Ensure that all setting follows the equipment set up. 3. Slowly open valve V5 until the flow rate reaches 20 LPM. 4. Observe the pressure reading on the pressure indicator. Record flow rate and pressure value when stable condition is achieved.

5. Repeat observation by increasing the flow rate with increment by 10 LPM until the flow rate reaches 90 LPM 4.5 Experiment 3: Parallel Pump Operation Objective: Parallel pump operation with variable flow rate Table 5Equipment Set Up of Experiment 2 Fully Close valve Fully Open Valve Variable parameter 3

1,2 & 4

Pump ON

Valve 5

Both Pump

Procedures: 1. Follow the basic procedure as written in section 3.2. 2. Ensure that all setting follows the equipment set up. 3. Slowly open valve V5 until the flow rate reaches 40 LPM. 4. Observe the pressure reading on the pressure indicator. Record flow rate and pressure value when stable condition is achieved. 5. Repeat observation by increasing the flow rate with increment by 20 LPM until the flow rate reaches 180 LPM

5.0 RESULTS

Rotameter Pressure Gauge 1 (FI1) LPM (PI1) kgf/cm2 20 30 40 50 60 70 80 90

Table 6Result of Experiment 1 Pressure Gauge 2 (PI2) kgf/cm2

•

2.92

1.05bar

1.04 1.03

bar

2.85

bar

1.02

02

1 .

1

.

2.79 2.70

01

2.60

2.50

sppgh DP

Fg

.

-

h

mm

"

/ line

best

LPM flow

of

fit

graph

rate

M3/g

:

Rotamete r Pressure Gauge 1 (FI1) LPM (HI) kgf/cm2 20 30 40 50 60 70 80 90

Table 7Result of Experiment 2 Pressure Gauge 3 Pressure Gauge 4 (PI3) kgf/cm2 (PI4) kgf/cm2

4.75

2.92

4

1.03

4.63

2.85

1.03

4.50

2.79

4.33

2.69

1.02

4.16

2.60

1.01

2.48

1.00

3.97

Table 8Result of Experiment 3 Rotamete r (FI1) LPM 40 60 80 100 120 140 160 180

Pressure Gauge 1 (PI1)kgf/cm2

1.04

Pressure Gauge 2 (PI2) kgf/cm2 3.04

Pressure Gauge 4 (PI4) kgf/cm2 2.99

04

2.98

2.93

1.04

2.93

2.88

1.03 1.02 1.01

1.00 1.00

= 2.85 2.78

2.70

2.60

2.50

2.73

2.65 2.80 2.56

2.45

i. Plot pressure different vs. flow rate for three experiments 6.0 DISCUSSION

i. A ii. B C

7.0 CONCLUSION

i. Conclude the experiment process and results. ii. Comment on the accuracy of the experiment and ways of improving it. 8.0 REFERENCES

i. R.K. Bansal 1983, A Textbook of Fluid Mechanics and Hydraulic Machines, 1

st

Laxmi Publications (P) Ltd, India.

Edition,

ii.

st

Rama Durgaiah, 2002, Fluid Mechanics and Machinery, 1 International (P) Ltd, India.

. Result Sample

Rotameter Pressure Gauge 1 (FI1) LPM (PI1) kgf/cm2

Table 6 Result of Experiment 1 Pressure Gauge 2 (PI2) kgf/cm2

20 30 40 50 60 70 80 90

Rotamete r Pressure Gauge 1 (FI1) LPM (HI) kgf/cm2

Table 7 Result of Experiment 2 Pressure Gauge 3 Pressure Gauge 4 (PI3) kgf/cm2 (PI4) kgf/cm2

20 30 40 50 60 70 80 90 Table 8 Result of Experiment 3 Rotamete r Pressure Gauge 1 (PI1) Pressure Gauge 2 (FI1) LPM kgf/cm2 (PI2) kgf/cm2 40 60 80

Pressure Gauge 4 (PI4) kgf/cm2

Edition, New Age

100 120 140 160 180