NPSHR pressure value required by the manufacturer is required to allow the pump to operate properly. Serious damage may occur if a large pump has been sited incorrectly with an incorrect NPSHR value and this may result in a very expensive pump or installation repair. NPSH problems may be able to be solved by changing the NPSHR or by re-siting the pump. If an NPSHA is say 10 bar then the pump you are using will deliver exactly 10 bar more over the entire operational curve of a pump than its listed operational curve. Example: A pump with a max. pressure head of 8 bar (80 metres) will actually run at 18 bar if the NPSHA is 10 bar. i.e.: 8 bar (pump curve) plus 10 bar NPSHA = 18 bar. This phenomenon is what manufacturers use when they design multistage pumps, (Pumps with more than one impeller). Each multi stacked impeller boosts the succeeding impeller to raise the pressure head. Some pumps can have up to 150 stages or more, in order to boost heads up to hundreds of metres. References Hydraulics Fluid mechanics de:Pumpe#NPSH-Wert