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 quickly. 2. After exhaust operation ends, the butterfly valve automatically closes under gravity. The check valve remains closed to help block exhaust gases, dust, and odors from entering the room. VALVE OPENS AND CLOSES AUTOMATICALLY: The duct adapter features a butterfly check valve design that allows smooth opening when activated by airflow during exhaust. Once airflow stops, the butterfly valve automatically closes due to gravity. EASY TO INSTALL: Wall-mounted air duct check valve with adapter rings for easy installation and maintenance. Compatible with 150mm, 160mm, 170mm, 180mm, and 200mm diameter ducts (both flexible and rigid). Suitable for installation in flue outlets, pipes, range hoods, and similar applications. WITH SEALING STRIP: Backdraft damper includes sealing strips that reduce gaps between the unit and the wall, ensuring close contact with the surface. Enhances sealing performance, prevents leakage, and maintains effective closure. SPECIFICATIONS: Material: PP Dimensions: 21cm x 21cm x 18cm (8.27in x 8.27in x 7.09in) Applicable pipe diameter: 150mm / 160mm / 170mm / 180mm / 200mm PACKAGE INCLUDES: 1 x Backdraft Damper Set NOTE: Please allow slight variations due to manual measurement and differences in display monitors.