Calculation of the net positive suction head available for pump installation

NPSHa~effective net positive suction head is the amount of energy that remains, in excess of the vaporization pressure head, after the liquid flow reaches the pump inlet via the suction pipeline from the suction tank; it is denoted by the symbol NPSHa. The value of the effective net positive suction head is determined by the operating conditions of the pump system (such as the pressure in the suction tank or the atmospheric pressure at the liquid level in the suction tank, the geometric installation height of the suction pipeline, the resistance losses, the properties and temperature of the liquid, etc.), as well as the flow rate in the pipeline. It is not related to the structural dimensions of the pump itself; hence it is also referred to as the net positive suction head of the system. It can be seen that when Hg remains constant, an increase in flow rate leads to greater resistance losses in the suction pipeline, and as a result, the effective net positive suction head NPSHa becomes smaller, increasing the likelihood of cavitation occurring.