Net Positive Suction Head (NPSH)

08/14/25

“What is the minimum pressure needed to avoid cavitation in pumps?”

If pumps don’t have enough pressure, then water vapor can form in the pumps and cause cavitation in the pump blades. Pumps can prevent this from occurring by maintaining pressure above the vapor pressure. The difference between these quantities is known as the Net Positive Suction Head (NPSH). The NPSH required (NPSH-R) is the pressure at the impeller entrance needed to avoid cavitation, equal to the difference between the stagnation pressure and the vapor pressure at the inlet. The Net Positive Suction Head Available (NPSH A) is the pressure available at the pump inlet above the vapor pressure and losses due to system friction. For functional system operation, NPSH A must be greater than NPSH R.