During rain, the pipes of a combined sewer network are exposed to many times the amount of water of the dry weather discharge. Since the sewage treatment plant connected to the sewer network cannot absorb such a volume of water, the water volumes are temporarily stored in sewer back-up areas and rainwater basins. After rainfall, the water is fed to the treatment plant at a constant rate over a longer period of time.
In order to be able to achieve this, one needs a discharge throttle at the outlet of the rainwater storage tanks.
The discharge throttling devices available on the market can initially be roughly divided into electromechanically driven and externally powered systems. However, the mode of operation of all systems is the same. Depending directly or indirectly on the water level, the volume flow of the throttle discharge is subjected to a flow resistance which changes with the water level.