ANSI/HI 9.6.1-2012

This guideline covers rotodynamic, general purpose pumps with power levels as high as 5300 hp and impeller tip speeds less than 130 feet per second and describes the benefits to pump longevity of maintaining suitable NPSH Margin. Pump users should be aware that -the full published pump head will not be achieved when the NPSH Available equals the NPSH3 of the pump. If the NPSH Available matches the NPSH3, the first-stage head will be 3% less than the fully developed value. Todays higher speed, higher energy density pumps might not achieve acceptable service life under suction conditions without an adequate NPSH Margin.

The document serves as a tutorial on the subject of NPSH as well as providing guidance for determining NPSH Margin. The following considerations are discussed relative to the sensitivity of a pump to NPSH-related problems:Impeller inlet tip speedLarger vs. smaller impeller eye diameterSuction specific speedCharacteristics of the pumpageOperating range of the pump and proximity to POR and AORMaterials of construction and cavitation resistanceImpeller vane overlapPump size and relationship of size to cavitation damageDuty cycle - time of operation under cavitating conditionReduction of NPSHA with time

This excellent NPSH reference helps pump users understand why it is essential to specify an appropriate NSPH Margin and learn about the negative aspects of specifying an excessive NPSH Margin.



Keywords: A118

This product replaces:ANSI/HI 9.6.1 (M118) - Centrifugal and Vertical Pumps - NPSH Margin