Vapour Pressure

Vapour pressure is the absolute pressure (also saturated steam pressure).

Defined as that absolute pressure at which the vapour contained in a substance is at equilibrium with its liquid or solid phase. Significant for centrifugal pump technology is only the actual transition between gaseous and liquid phases.

The vapour pressure of the pumped fluid greatly influences Cavitation Behaviour and thus the System NPSHavailable.

Also see:
System NPSH_available