A Pressure Relief Damper (Sometimes called PRD), is a device used to help maintain a Pressure Cascade. These devices are typically mechanical with no power, simply a flap or blade with a tuneable weight to set the pressure required to rotate open.
Pressure Relief Dampers enable pressure cascades through their intrinsic feedback loop where low pressure difference closes the flap allowing a pressure to build and vice versa opening when overpressured.
PRDs are commonly placed near doors to support quick Pressure Cascade recovery after door open and close events.