BAS-CVS Backdraft Dampers (also called Non-Return Dampers) allow airflow in one direction and prevent reverse airflow for use in exhaust or intake HVAC systems. Backdraft dampers are generally operated by gravity, where pressure or velocity opens the blades while gravitational force closes the blades. BAS-CVS backdraft dampers are suitable for installation in round ductwork and comply with the requirements of SMACNA, DW144 and AMCA relating to these dampers. Available in various materials including Galvanized Steel, and Stainless-Steel construction. BAS- CVS control dampers are AMCA certified for Air Performance & Leakage.