Cavitation in Single‐Vane Sewage Pumps

Abstract

Chair fluidsystemdynamics at TU Berlin investigated the cavitation behavior of a full‐size single‐vane sewage pump. Single‐vane pumps are used for raw sewage with high content of dirt and sediments in larger sewage pumping stations. Cavitation measurement was done by using standard NPSH 3% and the more sensitive incipient cavitation NPSH IC . Also, vibration and noise where observed. Contrary to very low NPSH 3% values, very high NPSH IC values were measured. In a second step, the impeller was modified with special cavitation bores to reduce the cavitation effects. The NPSH 3% values increased with cavitation bores, which underlines that this value is not a sufficient criteria describing cavitation. Using the much more sensitive NPSH IC , a significant reduction was obtained. Moreover, the cavitation formation was changed from a relative concentrated cloud to a distributed bubble form, which is much less aggressive in view of noise and erosion. Operational behavior improved with cavitation bores, noise and vibration levels especially came down to acceptable level. Practical experience demonstrates also avoidance of cavitation erosion.