Backdraft dampers are used in ventilation systems to allow airflow in one direction and prevent airflow in the opposite direction. A pressure relief damper is developed with an elevated and adjustable start-open pressure while providing the backdraft function. When selecting the correct damper for your application, you need to know: • System velocity and back pressure requirements • Mounting orientation and airflow direction • Mounting configuration (inserted into duct/opening or flange mounted) • Damper operation (gravity or motorized) • Start-open pressure