The return flap is used in round ventilation tubes to prevent the back flow of the air. The case is made of galvanised sheet steel. The damper blades are made of aluminum, the shaft and the spring are made of stainless steel. The internal rubber seal reduces noise. The outer foam strip provides a good seal and attachment of the check valve to the pipe. The non-return valve is designed for operation at ambient temperatures up to 60 ° C, for transporting clean air, free of coarse dust, grease, chemical vapor and other impurities.