The level switch will detect this change in water level and send a signal to the controller to activate the cleaning process. The device itself decides when the spray nozzles clean the screen depending on how dirty the screen is. The dirt is then rinsed into the drain. You decide whether the spray nozzles use tap water (min. pressure 2 bar, max. 4 bar) or clean pond water to rinse the screen. The filtered water flows through the sieve and is then taken to the main filter.