ABSTRACT

The work of Stepanoff in establishing that specific speed truly represents centrifugal pumps generically has been a cornerstone in the forecasting of their performance characteristics. The fact that it also characterises the internal hydraulic shapes — impeller, volute, etc., for a particular design method has also proved invaluable to pump designers. Performance evaluation based upon a pump internal geometry that gives the highest possible pump efficiency for a given pump speed and flowrate is sound where a progressive and consistent design methodology is maintained. Whilst the shape of the outlet flow passage controls the hydraulic performance of an impeller, it has almost no effect upon flows and pressure drops at the pump inlet. Non-cavitating centrifugal pump performance characteristics provide a base from which deviations caused by cavitation can be measured. The validity of relationships derived is limited to conditions where Q, H, n and D are the only significant variables to describe pump performance.