Centrifugal Pumps

NPSH - Net Positive Suction Head.

A pump displaces (throw outward) the water in its suction side and thereby attempt to create a vacuum.

The atmospheric pressure then have to be capable of pushing the water up the pipe to fill the void. The NPSH required are therefore the required atmospheric pressure available to get the water there (overcoming static + friction.}

Cavitation or a vapour lock will occur when the pressure in the eye drops to a negative.

What I have seen in practise (with water) is that the system may work some days and wont on another (due to atmospheric changes).

It is always advisable not to have the pump at the highest level or selecting too small suction piping.

You need to configure the pump so that the NPSH is adequate to handle worse case condition. However, during lesser conditions, you will incur costs resulting from the conservative design. But this is true in aspects of engineering.

If you fail to do so, the pump will cavitate and the impeller will be ruined (as Hendrick has stated).

Dear All,

My question is Simple what is the meaning of NPSH (3pc) and R3 (pc) how it is related to NPSHR and NPSHA. I know the meaning of NPSHR and NPSHA.

rangacharya

NPSH is the required Head to avoid vapour generation, due to negative pressure in side the pipe. As the fluid temp.increases the tendency for vapour lock increases as the vapour generation is more due to disturbance in the SATURATION POINT.

DHAYANANDHAN.S