What is Net Positive Suction Head (NPSH)?
Simply stated, NPSH is an analysis of the energy conditions on the suction side of the pump to determine if the liquid will vapourise at the lowest pressure point of the pump. The pressure that a liquid exerts on its surrounding is dependent on its temperature. this pressure is called its vapour pressure. It is a unique characteristic of every fluid and it increases with temperature. When the vapour pressure of a fluid equals the pressure of its surroundings, the fluid begins to vapourise, or boil. If we wish to pump a fluid effectively we must keep it in liquid form. NPSH is simply a measure of the amount of suction head present to prevent this vapourisation at the lowest pressure point in the pump. NPSH required is a function of the pump design and varies with speed and capacity. NPSH available is a function of the system the pump is operating in. It is the excess pressure of the liquid, in metres absolute, over its vapour pressure as it arrives at the pump suction.
