BACKDRAFT DAMPER: Square air duct connector with check valve, made of durable material, resistant to oil and heat. The backdraft damper helps prevent odors and exhaust gases from entering the house by stopping backflow. WORKING PRINCIPLE: 1. When the exhaust system operates, air pressure pushes the butterfly valve open, allowing odor and exhaust to be quickly discharged. 2. After exhaust operation ends, the butterfly valve automatically closes by gravity. The check valve remains closed to help block exhaust, dust, and odors from re-entering the room. VALVE OPENS AND CLOSES AUTOMATICALLY: Duct adapter with butterfly check valve design allows smooth opening during exhaust. After exhaust, the butterfly valve automatically closes by gravity. EASY TO INSTALL: Wall-mounted air duct check valve with adapter rings, compatible with both soft and hard ducts. WITH SEALING STRIP: Backdraft damper for range hood includes sealing strips that help create a tight seal against the wall, improving sealing performance and reducing air leakage. Size Chart: S Size: Fits 150–180 mm diameter ducting hose. L Size: Fits 150–200 mm diameter ducting hose. Package Includes: 1 x Backdraft Damper Note: Please allow slight variations due to manual measurement and differences in display screens.