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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
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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.
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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
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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)
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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.
.
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Result Sample
Rotameter (FI1)
LPM
Suction Pressure (P1) Delivery Pressure (P2)
kgf/cm2cmHg kgf/cm2
90
80
70
60
50
40
30
0