ABSTRACT
A change in NPSH in the inlet pipe of a centrifugal pump is directly relatable to the difference in pressure driving the growth and collapse of cavities within the liquid flowing through its impeller. A datum value based on NPSH, which is demonstrable by an industrial grade test, provides a commercially acceptable basis for the quantitative assessment of the total NPSH necessary to suppress unacceptable levels of cavitation. Cavitation surging that arises from impeller design is dependent upon NPSH and the impeller inlet pipework configuration. Greater values of NPSH head-drop, up to and including the NPSH at which the generated head collapse becomes independent of flowrate, the so-called “breakdown” value NPSH, have scientific validity but these put the machine on test at risk from cavitation erosion attack and vapour locking. The practical difficulties of observing pump inlet conditions where high inlet pressure, high temperature, or opaque/chemically aggressive liquids are present mean direct measurement using transparent components is seldom possible.
