It is used to switch on/off and change the speed of fans which are based on multi-speed motors.
BRF 125
The BRF 125 airtight backflow prevention damper is installed inside the ventilation duct. It effectively prevents undesirable backflow of air.
The BRF 125 air-tight backflow prevention damper is installed inside the ventilation duct. It effectively prevents undesirable backflow of ventilation air. Compared to metal blades, the damper’s rubber diaphragm ensures optimum system tightness with the possibly lowest noise level.

