The total head (or pressure) at the suction nozzle side of a centrifugal pump that is required to avoid the potentially destructive phenomenon of cavitation. To avoid vapour bubble formation at the eye of the impeller, the pressure head must be greater than the head corresponding to the vapour pressure of the liquid. The available net positive suction head is a function of the particular system and layout of pipework, whereas the required net positive suction head is a function of the pump. The available net positive suction head is required to exceed the required net positive suction head for cavitation to be avoided. Details of the required NPSH for a particular pump are supplied by the pump manufacturer.