Cavitation in Single-Vane Sewage Pumps

Chair fluidsystemdynamics at TU Berlin investigated the cavitationbehavior of a full-size single-vane sewage pump. Single-vane pumpsare used for raw sewage with high content of dirt and sediments inlarger sewage pumping stations. Cavitation measurement was done byusing standard NPSH3% and the more sensitiveincipient cavitation NPSHIC. Also, vibrationand noise where observed. Contrary to very lowNPSH3% values, very highNPSHIC values were measured. In a secondstep, the impeller was modified with special cavitation bores toreduce the cavitation effects. The NPSH3% valuesincreased with cavitation bores, which underlines that this valueis not a sufficient criteria describing cavitation. Using the muchmore sensitive NPSHIC, a significantreduction was obtained. Moreover, the cavitation formation waschanged from a relative concentrated cloud to a distributed bubbleform, 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. Practicalexperience demonstrates also avoidance of cavitation erosion