Performance of Low Specific Speed Pumps

An efficiency of very low specific speed pump is very low. In order to reveal the reason and to improve efficiency, two kinds of experiments are performed together with the Q3D analysis. One is the pump performance test using 12 combinations of 6 impellers and 2 volutes, and the optimum combination and the matching performance of an impeller and a volute are determined. The other is the free impeller test using three impellers of different specific speed, and the reason of low efficiency is determined. It is mainly due to the disk friction and the formation of a reverse flow at the BBP in an impeller channel, which increases slip velocity and hydraulic losses