Prediction of the Effect of Impeller Trimming on the Hydraulic Performance of Low Specific-Speed Centrifugal Pumps

Abstract

The effect of trimming of radial impellers on the hydraulic performance of low specific-speed centrifugal pumps is studied. Prediction methods from literature, together with a new prediction method that is based on the simplified description of the flow field in the impeller, are used to quantify the effect of trimming on the hydraulic performance. The predictions by these methods are compared to measured effects of trimming on the hydraulic performance for an extensive set of pumps for flow rates in the range of 80% to 110% of the best efficiency point. Of the considered methods, the new prediction method is more accurate (even for a large impeller trim of 12%) than the considered methods from literature. The new method generally overestimates the reduction in the pump head after trimming, and hence results less often in impeller trims that are too large when the method is used to determine the amount of trimming that is necessary in order to attain a specified head.