CentriFugal
Pump
What is a Centrifugal Pump ?
If
Mechanical energy is converted into Pressure energy by means of a Centrifugal
force acting on the fluid then this type of hydraulic machine is called as
Centrifugal Pump.
Construction
& Various parts of the Centrifugal Pump :-
A
Centrifugal Pump essentially consists of the following main parts :-
1) Impeller :- It is the rotating part of the
centrifugal pump which consists of a number of blades,either open or shrouded
,mounted on a shaft that projects outside the casing.
2) Casings :- There are 3 general types of
casings ,but each consists of a chamber in which the impeller rotates,provided
with inlet and exit for the liquid being pumped.
a)
Circular casing
b)
Volute casing
c)
Diffuser-type / Guide vanes
3) Suction Pipe :- A pipe whose one end is
connected to the inlet of the pump and other end dips into the liquid in a sump
is known as suction pipe. A foot valve / Non-return valve is fitted at the
lower end of the suction pipe.
4) Delivery Pipe :- A pipe whose one end is
connected to the outlet of the pump and other end delivers the liquid at the
required height is known as delivery pipe.
Working
of a Centrifugal Pump :-
1)
In the operation of a centrifugal pump before the pump is started, PRIMING of
the pump is done.
2)
In the Priming operation ,the suction pipe,pump casing and the portion of the
delivery pipe up to delivery valve are completely filled with the liquid to be
pumped so that all the air,gas or vapours from this portion of the pump is
expelled and no air pocket is left.
3)
Without Priming if the impeller is made to rotate in the presence of air,
negligible pressure would be produced so that no liquid will be lifted in the
pump.
4)
After the pump is Primed properly ,the delivery valve is kept close and power
from outside source is applied to the shaft.
5)
The delivery valve is kept close in order to reduce the starting torque for the
motor.
7)
The rotation of the impeller produces a force which imparts a centrifugal head
to the liquid and thus results in an increase in the pressure thoughout the
liquid mass.
8)
As long as the delivery valve is closed and impeller is rotated there will be
just churning of liquid within the casing.
9)
When the delivery valve is opened,the liquid is made to flow outward thereby
leaving the impeller vanes with high velocity and pressure.
10)
Due to centrifugal action, a partial vaccum is created at the edge of the
impeller which causes the liquid from the reservoir to rush through the suction
pipe to the impeller.
Advantages
of a Centrifugal Pump :-
1)
It is Simple in construction.
2)
It operates at high speed and therefore,can be coupled directly to an electric
motor.
3)
It gives a steady delivery.
4)
Maintainance costs are lower than any other pump.
5)
No damage is done to the pump if the delivery line becomes blocked.
6)
It is much smaller than other pumps of equal capacity.
7)
Quiet in operation.
Disadvantages
of a Centrifugal Pump :-
1)
The single stage pump will not develop a high pressure.
2)
It is not usually self priming.
3)
If a non-return valve is not incorporated in the delivery or suction line ,the
liquid will run back into the suction tank as soon as the pump stops.
4)
Very viscous liquids cannot be handled efficiently.
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