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Multi stage centrifugal pumps.

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 $1^{st}$ impeller at inlet and is discharged at outlet with increased pressure. The water with increased pressure from the outlet of $1^{st}$ impeller is taken to the inlet of $2^{nd}$ impeller with the help of a connecting pipe as shown in figure. At the outlet of the $2^{nd}$ impeller, the pressure of water will be more than the pressure of water at the outlet of $1^{st}$ 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 $H_m$.

Where, n = No. of identical impellers.

$H_m$ = 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.

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