BACKDRAFT DAMPER: Square air duct connector with check valve, made of durable and eco friendly material, resistant to oil and heat. The backdraft damper keeps odors and exhaust gases out of the house, preventing backflow. WORKING PRINCIPLE: 1. When the exhaust starts, the air pressure pushes the butterfly valve to open, and odor and exhaust gas is quickly discharged. 2. After the exhaust is completed, the pipeline butterfly valve will automatically close under the action of gravity. The check valve will always remain closed to prevent the exhaust gas, dust and odor from entering the room. VALVE OPENS AND CLOSES AUTOMATICALLY: The duct adaptor with butterfly Check valve design facilitates smooth opening of the valve when driven by airflow during exhaust. After exhaust, the butterfly valve will automatically close under the action of gravity. EASY TO INSTALL: Wall mount air duct check valve, with duct adapter rings, easy installation and maintenance. Can be perfectly match with 150mm, 160mm, 170mm, 180mm, 200mm diameter soft hard duct. Efficient exhaust air flow prevention tool can be installed in the flue port, pipe, range hood, etc. WITH SEALING STRIP: Backdraft damper for range hood with sealing strips reducing the gaps with the wall, can be closely attached to the wall, enhance the sealing performance, no leakage, and ensure good sealing performance. Specification: Material: PP Size: 21cmx21cmx18cm/8.27inchx8.27inchx7.09inch Applicable pipe diameter 150mm/160mm/170mm/180mm/200mm Package Includes: 1 Set Backdraft Damper Note: Please allow slightly errors due to manual measurement and different monitors.