Mumbai University > Electronics and telecommunication > Sem 7 > Applied Hydraulics

Marks: 08

Years: DEC 2014

If a centrifugal pump consists of two or more impellers, the pump is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. A multistage pump is having the following two important functions :

(1) To produce a high head (2) To discharge a large quantity of liquid

If a high head is to be developed, the impellers are connected in series (or on the same shaft) while for discharging large quantity of liquid, the impeller are connected in parallel.

Multistage centrifugal pumps for high heads :

For developing a high head, a number of impellers are mounted in series or on the same shaft.

The water from suction pipe enters the 1st impeller at inlet and is discharged at outlet with increased pressure. The water with increased pressure from the outlet of the 1st impeller is taken to the inlet of the 2nd impeller, the pressure of water will be more than the pressure of water at the outlet of 1st impeller. Thus if more impellers are mounted on the same shaft, the pressure at the outlet will be increased further.

Let n= number of identical impellers mounted on the same shaft

$H_m =$ head developed by each impeller

Then total head developed $= n\times H_m$

The discharge passing through each impeller is same

Multistage centrifugal pumps for high discharge :

For obtaining high discharge, the pumps should be connected in parallel. Each of the pumps lift the water from a common pump and discharge water to a common pipe to which the delivery pipes of each pump is connected. Each of the pump is working against same head.

Let n= Number of identical pumps arranged in parallel

Q= Discharge from one pump

$\therefore $ Total discharge $=n\times Q$