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Series-parallel centrifugal pumps realize series and parallel running conditions through unique inlet one-way valve and reversing valve structures. In the running process, changes in the openness of the inlet one-way valve cause changes in the running parameters of the two impellers and in the inner flow field, thereby inducing pressure fluctuation and intensifying unit vibration. In this study, the change law of internal flow of the series-parallel centrifugal pumps was disclosed under different openness degrees of the inlet one-way valve and its internal relationship with pressure fluctuation was clarified by combining numerical simulation and model experiment. The major causes of pressure fluctuation and hydraulic performance changes induced by changes of internal flow field were analyzed. Results show that when the openness of the one-way valve is smaller than 20°, the two impellers present different operational states under parallel connection, which deteriorate the hydraulic performance of pumps. Decreasing the openness of one-way valve can reduce the pressure around the inlet of the second-stage blade and induce eddies; however, it slightly influences the pressure at the inlet of the first-stage blade. With the changes in the openness of the inlet one-way valve, the fluctuation frequency at the occurrence of maximum fluctuation remains the same; however, the fluctuation amplitude changes considerably. The fluctuation amplitude under small openness is lower than that under large openness. Conclusions obtained in the study have important implications in reducing the vibration and noise of series-parallel centrifugal pumps.

Influence of the Openness of Inlet One-way Valve on the Flow Characteristics in Series-Parallel Centrifugal Pumps