The NPSHrequired is the lowest NPSH value at which definite cavitation criteria (i.e. wear due to cavitation, vapour formation, vibration, noise, head loss) can be contained.
As a function of the volume flow Q, NPSHreq is a characteristic of the centrifugal pump and is specified for many types as pump characteristic curve NPSH(Q). At low volume flow rates, the NPSH value is almost constant, whereas it rises steeply at high volume flows.
The NPSH value of the pump changes with the speed as well as the impeller diameter.
For some pump types, the NPSH value can optionally be reduced by an additional construction. A typical example of this is the inducer, in which an axial impeller with a small number of blades is arranged directly in front of the actual impeller of the centrifugal pump.