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Centrifugal Pump Operation without NPSH Problems

Centrifugal Value with Centrifugal Pumps General

There are many detailed publications on the subject of the NPSH value. In practice, however, mistakes are made repeatedly, with pump damage or even complete system failure as a result.

This guideline is therefore intended to indicate where and how the system NPSH value can be rendered more favorable using various parameters, and the criteria which are important for pump selection.

NPSH means "Net Positive Suction Head." A system from which, for instance, cold water flows to a pump from a height of 1 m without a pressure drop has an NPSH value of aprox 11 m (not 1m).

NPSH = 11 m

A = available

Here, only one pump with an NPSHR value of 10.5 m or less can normally be used, in order that a safety margin of at least 0.5 m is available.

NPSHR = 10.5 m

R = required

NPSHA Value of the System

Here, a customary formula which is fully adequate for practice is provided. The latest symbols in accordance with DIN 24 260 Part 1, September 1986 edition, are used here.
sec j5 fig1 calc 
sec j5 fig2 calc 2 

This data is referred directly to the center point of the suction nozzle. For the sake of simplicity, gravitational acceleration has been assumed not at 9.81 m/s2 but instead at 10.0 m/s2.

sec j5 fig3 calc diagram