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NPSH Value 

The NPSH value (Net Positive Suction Head) or holding pressure head of a pump refers to the difference between the inlet pressure and the lowest pressure level inside the pump. It is a measurement that captures the internal pressure loss on the suction side of the pump housing up to the inlet. 

On the suction side of the pump, the pressure drops before it rises again on the discharge side to a level above the inlet pressure. Usually, the pressures at the inlet and outlet are measured and the difference between these pressures gives the head of the pump, which is given in metres and is independent of the liquid density. The NPSH value depends on the product type and volume flow, and it increases with increasing volume flow. This ratio is crucial to ensure that cavitation (vapour formation) does not occur in the flowing liquid inside the pump, as this can lead to noise generation and damage to the pump. To prevent this, the inlet pressure of the unit must always be higher than the respective vapour pressure of the transported medium. The standard unit for the NPSH value is metres (m).