What is "npsh"

In a hydraulic circuit, net positive suction head (NPSH) may refer to one of two quantities in the analysis of cavitation:

1. The Available NPSH (NPSH): a measure of how close the fluid at a given point is to flashing, and so to cavitation.
2. The Required NPSH (NPSH): the head value at a specific point (e.g. the inlet of a pump) required to keep the fluid from cavitating.

NPSH is particularly relevant inside centrifugal pumps and turbines, which are parts of a hydraulic system that are most vulnerable to cavitation. If cavitation occurs, the drag coefficient of the impeller vanes will increase drastically - possibly stopping flow altogether - and prolonged exposure will damage the impeller.