Effect of back clearance and balance hole upon centrifugal pump performance

Abstract

A study was performed to investigate the performance of a centrifugal pump with a semi open impeller. Four volumetric flow rates for the maximum attainable speed with the pump test facility were identified as the operating conditions for the pump after generating performance curves. The static pressure distribution inside the pump was measured through pressure taps drilled around the pump housing. Instantaneous pressures at key locations on the pump were also measured with flush mounted high frequency pressure transducers. These pressure measurements were obtained for distinct geometric configurations comprising of varying positions of the impeller with respect to the back housing and different sizes of balance holes. Pressure contour plots were generated for all the operating conditions and a non-uniform pressure distribution was observed inside the pump. Higher pressures were witnessed near the exit of the pump. Hydraulic loads acting on the impeller were calculated by integrating the average pressure acting on it as measured by the pressure taps. A net axial thrust on the impeller, trying to push it towards the suction side, was observed, which decreased in magnitude with increasing back clearance and balance hole size. Moments acting on the impeller were found to approach to a minimum value for flow rates close to the B.E.P. A geometric configuration was identified for better overall performance of the pump.