With an accumulation of wastewater, our backwater valve exerts pressure on the Stop Silent SL13 Membrane. The membrane opens its sealing lip upwards and releases the flow for the waste water. When the wastewater flow is stopped, the sealing lip is closed and the wastewater valve closes. In order to prevent sewage gases from escaping from the cellar, for example, the rubber membrane is filled and pressed against the pipe wall during the backflow.