The effect of balancing holes on performance of a centrifugal pump: numerical and experimental investigations

In the present work, the effect of balancing hole's diameter on the performance of a centrifugal pump is experimentally and numerically investigated. Normally, in centrifugal pumps, design of impeller and volute is carried out in such a way that pressure distribution on both sides of the impeller becomes similar, thus minimizing the axial force exerted on the pump impeller and bearings. However, in reality this goal is not totally fulfilled and due to design and manufacturing circumstances and limitations, significant axial forces are generated. As a result excessive load on bearings, noise, vibration and damage to pump performance are experienced. In order to reduce the axial force, several methods are proposed. The simplest method is drilling balancing holes on the impeller eye. In this study, numerical and experimental investigations have been conducted to study the effect of balancing holes on a centrifugal pump performance and axial force reduction. A test rig is designed and equipped with measuring instruments. Experimental data for pump performance including flow, head, power and efficiency were obtained. Next, numerical results were validated against experimental data and a good agreement was observed. It was found that increasing balancing holes diameter up to 5 mm can lead to 5.6% reduction in head at design point. Furthermore, it was found that the diameter of balancing hole affects the pump efficiency and can reduce it by 2.6%. Numerical investigation showed that the diameter of balancing hole can play a prominent role on the axial force reducing it significantly. Extreme care must be taken in selecting the diameter of balancing holes since increasing holes diameter beyond a specific value does not reduce the axial force significantly, but, still aggravates the pump performance undesirably. Therefore, an optimum diameter of 3.5 mm was selected whereby the axial force is reduced up 56% at design point while reduction in performance characteristics are acceptable.