Backflow preventer

Drinking-water and service-water lines have to be separated reliably and permanently from each other in the backflow direction. Backflow preventors provided for this purpose must not have excessive pressure losses or produce disruptive flow noise. Known backflow preventers become inoperable owing to deposits of dirt or the formation of lime. As a result of their structural form, they have high pressure losses and produce disruptive flow noise. A flexible bellows (9) which can change in length and has an inflow connection stub (8) and a sealing disc (12) is installed in the housing (1) with an outflow connection stub (2) and a valve seat (5). In the rest position, the drawn-together bellows (9) forms, between the sealing disc (12) and the valve seat (5), a free air passage (14), via which only air can be sucked into the drinking-water line. In the event of water removal, the bellows (9) extends as a result of the flowing medium and presses the sealing disc (12) onto the valve seat (5). The backflow preventer is particularly suitable for use in washing machines and dishwashers.