Cavitation is the formation and abrupt collapse of vapour-filled bubbles. This process takes place at points inside the pump where the pressure falls below the vapour pressure of the pumped medium. The vapour pressure of a liquid is the pressure at which the liquid begins to boil or evaporate. Cavitation, which may damage the pump, occurs when the net positive suction head (NPSHR) needed by the pump is not available.
In order to avoid cavitation, a minimum pressure referred to as the net positive suction head available (NPSHA) must be present at the suction port so that the liquid does not boil or evaporate. It must be ensured that the pressure applied at the suction port is always greater than the vapour pressure of the liquid at a given temperature of the medium.
Note: If a pump cavitates, the control valve on the pressure side should be throttled in order to reduce the flow rate and thus the NPSH value required by the pump. However, it must be ensured that the flow rate remaining is large enough to sufficiently cool and lubricate the pump.