Question

Determine the number of impellers required for a multistage pump to lift 3840 litres per minute against a total head of 80m at a speed of 700rpm given that the limiting specific speed for each impeller is 700units

Answer 1

There are total 5 impellers are required to deliver a total head of 80m.

The specific speed of centrifugal pump is given by the formula

Ns=$\frac{\sqrt{Q}N}{H^{3/4}}$

Here, Q is the discharge, h is the manometric head of the pump.

Plugging the values in the above equation

700=$\frac{700sqrt{(3840/60)}}{h^{3/4}}$

h=16 m

Now the number of impellers required to supply the total head of 80 m is calculated as

H=n*h

80=n*16

n=5

Therefore total 5 impellers are required.

Answer 2

Answer:

1 impeller is enough. From given questions u will get 245.2 m head for single impeller. so number of stages will be 0.326 ~1 Stage. make sure to write correct unit in equations.