Check Valve Stainless Steel Silent Ventilation Fitting with Non-Return Damper Auto Hood and Hose Connector for Duct and Ventilation Duct Style and size: half opening 150 mm, 190 x 185mm, 150mm pipe installation hole can be 150-180mm. Function Pipe fitting with check valve prevents exhaust air return or inlet cold outside air. The flaps open when the fan pushes out the exhaust air and close automatically when the airflow stops. Blinds must be aligned horizontally for optimal closure. Universality applies to all air supply and exhaust systems such as air conditioning systems, dryers, hoods extractors and ventilation systems such as air fresheners, bathroom ventilation. The perfect choice for amateurs and professionals. Small fans can also open the flaps for smooth operation. Effectively prevent fumes from coming back, and fumes can only go out but not come in. The principle of operation of the non-return valve is that the fumes can only exit but not enter. Easily solve oil vapor problems The high temperature fuse device can be closed freely at 150C. In the event of a fire, the safety temperature exceeds 150C and the fuse is closed . The silicone gasket can enter seamlessly, the silicone gasket fills the closed space, and the cooking fumes from the public flue can enter seamlessly Thickened stainless steel is durable and not deformed, the real material is thickened stainless steel, waterproof and moisture-proof, not easy to oxidize and rust The opening and the large diameter closure can quickly discharge smoke, increase the volume of exhaust air, and do not affect the exhaust velocity Leakproof protection metal collars, multiple waterproof protections, seamless connection of smoke exhaust ducts Freehand installation without tools, made s-it yourself, three easy steps to install: Step 1: Press the loop and place it inside the flue duct Step 2: Install the flue Step 3: tighten the clamp