Lab3E6_Series and Parallel Pump.pdf

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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 supportsthe 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. Thetips 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 pointwhere 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 : Clean

tap water.



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.

Table 1 Valve Position for General Start-up

Pump Operation Running Pump Open Valve Close Valve

Single Pump 1, PI 1,4 2,3

Serial Both Pump, PI &P2 1,3 2,4

Parallel Both Pump, PI &P2 1,2,4 3

5. Turn on pump and slowly open V5 until maximum flow rate is achieved as shown inTable 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





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 Pump ON

3 1,2 & 4 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

Table 6Result of Experiment 1

Rotameter

(FI1) LPM

Pressure Gauge 1

(PI1) kgf/cm2

Pressure Gauge 2

(PI2) kgf/cm2

20

30

40

50

60

70

80

90

•

1.05bar

2.92

1.04

bar

2.85

1.03

bar

2.79

1.02

2.70

1

.

02

2 60

.

01

2.50



sppgh

mm

LPM

M3 g

P

.

-

h

flow

rate

line

of

best

fit

graph




Rotamete r

(FI1) LPM

Pressure Gauge 1

(HI) kgf/cm2

Pressure Gauge 3

(PI3) kgf/cm2

Pressure Gauge 4

(PI4) kgf/cm2

20

30

40

50

60

70

80

90


Rotamete r

(FI1) LPM

Pressure Gauge 1

(PI1)kgf/cm2

Pressure Gauge 2

(PI2) kgf/cm2

Pressure Gauge 4

(PI4) kgf/cm2

40

60

80

100

120

140

160

180

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

6.0 DISCUSSION

i. A

ii. B

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, 1st Edition,

Laxmi Publications (P) Ltd, India.

:

4

2.92

4.75

1.03

2.85

4.63

1.03

2.79

4.50

1.02

2.69

4.33

1.01

2.60

4.16

1.00

2.48

3.97

1.04

3.04

2.99

=

04

2.98

2.93

1.04

2.93

2.88

1.03

2.85

2 80

1.02

2.78

2.73

1.01

2.70

2.65

1.00

2.60

2.56

1.00

2.50

2.45

C



ii. Rama Durgaiah, 2002, Fluid Mechanics and Machinery, 1st Edition, New Age

International (P) Ltd, India.

.

Result Sample

Table 6 Result of Experiment 1

Rotameter

(FI1) LPM

Pressure Gauge 1

(PI1) kgf/cm2

Pressure Gauge 2

(PI2) kgf/cm2

20

30

40

50

60

70

80

90


Rotamete r

(FI1) LPM

Pressure Gauge 1

(HI) kgf/cm2

Pressure Gauge 3

(PI3) kgf/cm2

Pressure Gauge 4

(PI4) kgf/cm2

20

30

40

50

60

70

80

90


Rotamete r (FI1) LPM

Pressure Gauge 1 (PI1)kgf/cm2

Pressure Gauge 2(PI2) kgf/cm2

Pressure Gauge 4(PI4) kgf/cm2

40

60

80



100

120

140

160

180

Lab3E6_Series and Parallel Pump.pdf

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