Patent ID: 8672734

Claim:
A damper flap assembly for mounting on a fan construction having a fan housing and a fan mounted in the housing; the damper flap assembly comprising: a mounting member having an opening through which the air passes and a flange surrounding the opening; a pivotally mounted damper flap arranged to extend in a closed position across the opening when the fan is not running, with an outer peripheral portion of the damper flap engaging the flange around the opening; the damper flap being movable from the closed position through an intermediate position to a fully open position under forward air flow from the fan by pivoting on a hinge away from the flange; and a biasing arrangement for applying force to the damper flap, the biasing arrangement being arranged on one side of the intermediate position adjacent the closed position to bias the damper flap into the closed position and on an opposed side of the intermediate position adjacent the fully open position to bias the damper flap into the fully open position; wherein the biasing arrangement includes a spring for providing a spring force; and wherein the biasing arrangement includes a cam surface engaging a cam follower with the spring applying spring force between the cam follower and the cam surface.