NPSH

Pump NPSH Requirement (NPSHR)
This figure is the necessary amount of energy required (measured in metres) in the liquid at the pump inlet to overcome the internal losses/resistances within the pump and provide sufficient internal pressure to avoid cavitation. These losses are caused by the flow of liquid through the pump suction passage and the shock loss which occurs at the impeller blade. The NPSHR is calculated by the pump manufacturer and will vary depending on the size and speed of the pump.

Available NPSH (NPSHA)
The available NPSH (NPSHA) is the amount of energy (measured in m) available to the fluid at the pump inlet after the factors from section 1 have been taken into account. For a pump to run the NPSHA value must be greater than the NPSHR value. The NPSHA value will govern the amount of suction lift which may be attained with a given pump or the amount of static suction head which is required above pump suction to ensure correct operation.