These simple “butterfly” type backdraught dampers have lightweight hinged blades which will only open in one direction, preventing airflow in the opposite direction. A small spring helps to keep them in the closed position without causing significant back pressure when the fan is running.
Backdraught dampers are normally used on ducted extract systems to prevent cold outside air from being blown back into the building when the fan is turned off. They can also be used with wall fans if the wall fan does not have it’s own BDS.
The galvanised steel casing is designed to slip inside spirally wound steel ducting or flexible ducting.
|2nd Duct dia (mm)
Low cost solution for preventing backflow through a duct
Galvanised casing and blades
Spring assisted closing
Metal hinge pin