In simple terms, what is NPSH?
NPSH is the acronym for Net Positive Suction Head. This term does NOT represent the height of liquid required on the suction side of a pump. NPSH is used to describe two values: NPSHa (Or NPSHavailable) describes the head that is available in the system at the pump inlet, taking into account the liquid pressure, the liquid vapor pressure, liquid static column and line losses. NPSHr (Or NPSHrequired) the suction head required by the pump above the vapor pressure of the pumped fluid. As the NPSHa takes the vapor pressure of the liquid into account, it is usually sufficient to only ensure that the NPSHa is greater than NPSHr for effective pump operation. As the liquid vapor pressure plays a large part in NPSH values, you must be familiar with the meaning of “Vapor Pressure” (VP) before you read further about NPSH. Any liquid will “boil”, or vaporize, at some pressure / temperature combination. Typically, liquids boil at lower temperatures when subjected to lower surface pressures and need
