When a centrifugal pump consists of two or more impellers, the pump is called as Multi stage centrifugal pump.
Important functions of a Multi stage centrifugal pump:
1] To produce high heads.
2] To discharge a large quantity of liquid.
Multi stage centrifugal pumps for high heads:
The fig show number of impellers mounted in series.
In this, 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 1st impeller is taken to the inlet of 2nd impeller with the help of a connecting pipe as shown in figure. At the outlet 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.
Total Head Developed = n x Hm.
Where, n = No. of identical impellers.
Hm = Head developed by each impeller.
Multi stage centrifugal pumps for high discharge:
For obtaining high discharge, the pumps should be connected in parallel. each pump lifts water from a common pump and discharges water to a common pipe to which the delivery pipes of each pump is connected, each pump is working against the same head.