Net Positive Suction Head (NPSH)
Net positive suction head is the margin of pressure available at a pump's suction above the liquid's vapour pressure, ensuring the liquid stays liquid. The available NPSH must exceed the pump's required NPSH or cavitation occurs.
NPSH comes in two forms: NPSH available, set by the system (suction tank pressure, liquid level, friction losses, fluid temperature), and NPSH required, a property of the pump that rises with flow. To run a pump safely the available value must comfortably exceed the required value, leaving a margin. Engineers raise NPSH available by lifting the supply tank, reducing suction-line losses, or cooling the liquid, and watch it closely with hot or volatile fluids.
Related terms
Cavitation · Pressure Transmitter · Deaerator