NPSH is an acronym for Net Positive Suction Head. NPSH measures the absolute pressure present in a fluid. There are two main ways that NPSH is expressed in a pump system NPSHa - This is the amount of Net Positive Suction Head available at the pump inlet. NPSHa demonstrates the amount of pressure acting on a fluid as it enters the pump. This measures the amount of pressure between the liquid staying in its current state and forming vapour bubbles (beginning to boil). NPSHr - This is the amount of Net Positive Suction Head that the pump requires to operate without experiencing the damaging effect of cavitation, thus causing a dramatic reduction in pump performance. It is very important to pay attention to these values when making a pump selection. Selecting a pump that requires more NPSH than is available in your system will cause fast and long-lasting damage to the pump and thus you will incur large repair costs and downtime.