NPSH
From Wikipedia, the free encyclopedia
NPSH is an acronym for Net Positive Suction Head. It shows the difference, in any crosssection of a generic hydraulic circuit, between the pressure and the liquid vapor pressure in that section.
NPSH is an important parameter, to be taken into account when designing a circuit : whenever the liquid pressure drops below the vapor pressure, liquid boiling occurs, and the final effect will be cavitation : vapor bubbles may reduce or stop liquid flow.
Considering the circuit shown in the picture, in 1-1 NPSH is :
NPSH = P0 + H − Y − Vt
(to be solved with coherent measuring units), where Y is the friction loss between 0-0 and 1-1, and Vt the liquid vapour pressure at the actual temperature in section 1-1.
In pump operation, two aspects of this parameter are called respectively NPSH (a) Net Positive Suction Head (available) and NPSH (r) Net Positive Suction Head (required), where NPSH(a) is computed at pump inlet port, and NPSH(r) is the NPSH limit the pump can withstand without cavitating.
