Net Positive Suction Head
To avoid cavitation in centrifugal pumps, the pressure of the fluid at all points within the pump
must remain above saturation pressure. The quantity used to determine if the pressure of the
liquid being pumped is adequate to avoid cavitation is the net positive suction head (NPSH).
The net positive suction head available (NPSHA) is the difference between the pressure at the
suction of the pump and the saturation pressure for the liquid being pumped. The net positive
suction head required (NPSHR) is the minimum net positive suction head necessary to avoid
cavitation.
The condition that must exist to avoid cavitation is that the net positive suction head available
must be greater than or equal to the net positive suction head required. This requirement can be
stated mathematically as shown below.
