Effects of balance holes diameter on cavitation characteristics of centrifugal pump under low flow rates

In order to investigate the cavitation characteristics of low specific speed centrifugal pumps under low flow rates, rotation rate reduction IS80-50-315 centrifugal pump is taken as the experimental object, and a device is especially designed so as to replace the balance holes of different diameters. Cavitation characteristics were measured and analyzed at 0.4Q_d, 0.5Q_d, 0.6Q_d, and 0.8Q_d when the balance hole diameter is equal to 4, 6, 8, and 11mm. The results show that with the increase of the balance hole diameter, the pump head and its efficiency reduce. Both the torque-drop and head-drop curves of impellers with different balance hole diameters have the same shape of dropping and the torque-drop has obvious creeping change, with the corresponding break-down points occurring asynchronously under the low flow rate condition. It is caused by the rotor-stator interaction between the volute and the impeller. When the balance hole diameter increases under the same cavitation number condition, the head coefficient increase, the axial forces acting on impellers decrease and the anti-cavitation characteristics of centrifugal pump are enhanced. The slower the flow with the same balance hole diameter is, the harder the cavitation of centrifugal pump becomes. But the descent speed of the fluid pressure in the pump chamber of the centrifugal pump increases first and then decreases, the axial forces acting on impellers tend to flat and then increase sharply with the development of cavitation. In order to suppress cavitation and decrease the axial thrust, it is proposed that the most appropriate balance hole diameter is in the range of 6mm to 8mm.