A centrifugal pump pressure head is created by
centrifugal action of liquid. This is imparted to the liquid by the rotating
impeller.
Before starting the pump, air is driven out by a method
called priming. After removing air, the pump is started to rotate the impeller.
This imparts centrifugal head to the liquid and liquid leaves the vanes of the
impeller from the outer circumference with high velocity and pressure and
enters the casing. The design of the casing is such that during the flow of
liquid through the casing, it’s velocity head is converted into pressure head. Thus
the outlet of the casing, the pressure head of the liquid becomes very high.
When the liquid leaves the impeller, vacuum is created it’s centre. As a
result, the liquid which is under atmospheric pressure in the pump, sucks
through the suction pipe to the centre of the impeller and the operation is
then repeated.
A centrifugal pump is one of the simplest pieces of
equipment in any process plant. It's purpose is to convert energy of a prime
mover(a electric motor or turbine) first into velocity or kinetic energy and
then into pressure energy of a fluid that is being pumped. The energy changes
occur by virtue of two main parts of the pump, the impeller and the volute of
diffuser. The impeller is the rotating part that converts driver energy into
the kinetic energy. The volute or diffuser is the stationary part that convert
the kinetic energy into pressure energy. We know all of the forms of energy
involved in a liquid flow system are expressed in terms of feet of liquid i.e.,
head generation of centrifugal force, the process liquid enter the suction
nozzle and then into eye (centre) of a revolving device known as an impeller.
When the impeller rotates, it spins the liquid sitting in the cavities between
the vanes outward and provides centrifugal acceleration.
As liquid leaves the
eye of the impeller a low-pressure area is created causing more liquid to flow
toward the inlet because the impeller blades are curved, the fluid is paused in
a tangential and radial direction by the centrifugal force. This force acting
inside the pump is the same one that keep water inside a bucket that is
rotating at the end of string.
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