What is an NPSH curve and what is its significance?

The NPSH curve displays the minimum required inlet pressure (expressed in m) allowing the pump to pump in accordance with the performance curve and in order to prevent evaporation of the pumped fluid so as to avoid cavitation inside the pump.

At a given flow rate, the NPSH value available at the pump's suction ports must always be at least 0.5 m greater than the required NPSH value:

NPSHA > NPSHR + 0.5 m safety margin