BACKDRAFT DAMPER: Square air duct connector with check valve, made of durable and eco-friendly 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 gas to be discharged efficiently. 2. After the exhaust cycle ends, the butterfly valve automatically closes due to gravity. The check valve remains closed to help block exhaust gases, dust, and odors from re-entering the room. VALVE OPENS AND CLOSES AUTOMATICALLY: The duct adapter features a butterfly check valve design that opens smoothly when activated by airflow during exhaust operation. Once airflow stops, the valve closes automatically under gravity. EASY TO INSTALL: Wall-mounted air duct check valve with adapter rings for simple installation and maintenance. Compatible with 150mm, 160mm, 170mm, 180mm, and 200mm diameter ducts, both flexible and rigid. Suitable for installation in flue outlets, ventilation pipes, range hoods, and other exhaust systems. WITH SEALING STRIP: Backdraft damper includes sealing strips that minimize gaps between the unit and the wall, ensuring a tight fit, improved sealing performance, and no air leakage. Specification: Material: PP Size: 21cm x 21cm x 18cm / 8.27inch x 8.27inch x 7.09inch Applicable pipe diameter: 150mm / 160mm / 170mm / 180mm / 200mm Package Includes: 1 Set Backdraft Damper Note: Please allow slight variations due to manual measurement and differences in display monitors.