Blade dampers deliver less sounds and come in two types: parallel and opposed dampers. Parallel blade dampers: Their blades move in a similar direction and sustain the airflow. Opposed blade dampers: As being the identify reveals, they shift in reverse directions and support in directing the airflow in opposite directions. https://aircontroldampersforengin89901.bloggazza.com/35545734/air-control-dampers-for-engine-sheds-fundamentals-explained