LabManual

FACULTY OF ENGINEERING & BUILT ENVIRONMENT

SUBJECT:EME3421 LABORATORY INVESTIGATIONS 3

EXPERIMENT 7: CENTRIFUGAL PUMP

1.0 OBJECTIVE

To study the characteristics of a centrifugal pump.

2.0 THEORY/INTRODUCTION

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.

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 1Construction features of a centrifugal pump

LabManual

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.

LabManual

Figure 2The Cutaway of a Centrifugal Pump

3.0 APPARATUS

The unit is constructed on a stable stainless steel base plate, comprises of a fixed speed

centrifugal pump, a water sump tank and all required pipe works. It is installed with pressure

gauges and flow meter for pump characteristic studies. The pump casing is made of transparent

material; therefore the pump mechanism can be clearly visualized.

Figure 3 Equipment Assembly

LabManual

4.0 PROCEDURES

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 suction valve is open.

3. Switch on the power supply to the pump.

4. Regulate the delivery valve to achieve the desired operating condition.

5. Slowly regulate the delivery valve until the flow rate reaches 90 LPM.

6. Observe the pressure reading on the pressure gauges. Record flow rate and pressure

values when stable condition is achieved.

7. Repeat observation by decreasing the flow rate as follows.

5.0 RESULTS

Table 1 Flow Rate and Pressure Value

Rotameter (FI1)

LPM

Suction Pressure (P1) Delivery Pressure (P2)

kgf/cm2cmHg kgf/cm2

90

80

70

60

50

40

30

0

i. Calculate the hydraulic power, Pi =ρgHQ (W)

Where,H = Total Head (mH20)

Q = Water Flow rate (m3/s)

ii. Calculate the pump efficiency, η=Pi

Px 100 %

Where,Pi = Hydraulic power (watt)

LabManual

P = Motor power (watt) = 180 watt

iii. Plot pressure difference versus flow rate

iv. Plot the pump efficiency versus flow rate

6.0 DISCUSSION

i. Discuss relationship between pressure and flow rate

ii. Discuss relationship between pump efficiency and flow rate

iii. Discuss on flow rate effect on pressure and pump efficiency.

iv. Comment on the accuracy of the experiment and ways of improving it.

7.0 REFERENCES

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

Laxmi Publications (P) Ltd, India.

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

International (P) Ltd, India.

.

LabManual

Result Sample

Rotameter (FI1)

LPM

Suction Pressure (P1) Delivery Pressure (P2)

kgf/cm2cmHg kgf/cm2

90

80

70

60

50

40

30

0