Backdraft dampers: Mounted to allow 1-way airflow, these forms incorporate shafts on 1 end of every blade to circumvent air from flowing back in the opposite direction. If required, a counterbalance can assist. They are typically installed while in the ductwork of your method and will be manual or computerized. https://cruzgyncp.laowaiblog.com/35498922/about-air-control-dampers-for-engine-sheds