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 exhaust operation ends, the butterfly valve automatically closes by gravity. The check valve remains closed to help block exhaust gas, 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. Once airflow stops, the valve closes automatically due to 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 soft and rigid). Suitable for installation in flue outlets, ventilation pipes, range hoods, and similar applications. 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 reduced air leakage. SPECIFICATIONS: Material: PP Dimensions: 21cm x 21cm x 18cm (8.27in x 8.27in x 7.09in) Compatible Pipe Diameter: 150mm / 160mm / 170mm / 180mm / 200mm PACKAGE INCLUDES: 1 x Backdraft Damper Set NOTE: Slight measurement variations may occur due to manual measurement and display differences.