NPSH Net Positive Suction Head
Introduction of NPSH.
NPSH can be defined as the difference between the NPSH available (NPSHA) at the pump’s inlet and the NPSH required (NPSHR) by the pump to operate without cavitation.
NPSH Available (NPSHA): The absolute pressure at the suction port of the pump.
NPSH Required (NPSHR): The minimum pressure required at the suction port of the pump to keep the pump away from cavitation. (This is specified by vendor/manufacturer)
Introduction of Cavitation.
Cavitation is the formation of bubbles at the pump inlet, followed by their sudden collapse, which can cause permanent damage. The NPSH margin value must be positive to avoid cavitation.
NPSH = NPSHA NPSHR
NPSHA = Liquid pressure at pump suction – Vapor pressure of liquid.
NPSHA = Absolute pressure (at surface of reservoir) Liquid Vapor pressure – Loss in piping, valves +/ Static Head

Case1 If the pump is installed below the suction reservoir level.
Case2 If the pump is installed above the suction reservoir level.


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