Flush cleaning experiments were conducted in a combined sewer in the city of Hannover using two existing gate valves. The aim of the investigation was to find a practicable cleaning recipe for a particular sewer section, where frequent cleaning actions are necessary due to massive sedimentation. Flush cleaning could be shown to be a powerful method to move sediments, however, the distance between the gate valves and the sewer section to be cleaned was to large, as to successfully clean the particular sewer section. The flush height, its velocity and duration, the frequency of flush events and perhaps the time of arrival of a flush are important qualities in oder to achieve good cleaning results. Modern flush cleaning tools like the Biogest system and the Hydrass Valve are powerful devices with excellent performances and without the shortcomings of other typs of valves. Flush cleaning should be considered when choosing a cleaning method for a particular sewer. It is a method which is economic and ecologic.

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