NPSH in Centrifugal Pumps

NPSH stands for Net Positive Suction Head and is a measure of the pressure experienced by a liquid on the suction side of a centrifugal pump.

It is expressed in suction head (in feet or meters) rather than actual pressure (lb/in2, psi, or Pa), because “suction head” is a fluid-independent property: a pump will lift different fluids to the same height regardless of their density.

Understanding NPSH

Insufficient NPSH leads to a serious problem called cavitation, which is why it is important to understand NPSH.

Understanding NPSH is crucial because it directly affects the reliability and efficiency of the pump.

A pump operating at the correct NPSH value will run smoothly, quietly, and last longer.
A pump that has trouble with a low NPSH value makes noises that sound like it's pumping bricks and will wear out quickly.

What is a Centrifugal Pump?

NPSH⁃A and NPSH⁃R

Two important NPSH values are used for pump operation and system design.

NPSH⁃A is a system property. Net Positive Suction Head Available is calculated based on the configuration of the system on the suction side. It is essentially the pressure on the suction side minus the vapor pressure of the pumped liquid at that point. NPSH-A must be higher than the NPSH-R value of the pump for the selected operating conditions to prevent cavitation.

NPSH⁃R is a pump characteristic. Net Positive Suction Head Required is the minimum head required to operate a specific pump without excessive cavitation. This value is a characteristic of the pump design itself and is determined by the manufacturer through testing.

Reference.. www.michael-smith-engineers.co.uk

Summary.. NPSH (Net Positive Suction Head) is a measure of the pressure experienced by a liquid on the suction side of a centrifugal pump. It is used to prevent a pump from operating under conditions that promote cavitation. NPSH-R (NPSH Required) and NPSH-A (NPSH Available) are two important values.