Method for Controlling Air Flow of an Extraction Fan

摘要

An extraction fan has a housing mounted in a wall with an outlet duct extending through the wall to an outlet opening outside the wall. A damper flap is mounted on the fan suspended by a hinge at an upper edge so as to extend in a closed position across the opening and is movable to an open position under forward air flow from the fan, and tightly closes against a resilient deformable seal when the fan is shut off. A spring biasing cam applies inwards force to the damper flap to bias the damper flap into the closed position, and an outwards force also to bias the damper flap into the fully open position. The mounting plate includes a hood having a top wall extending over the top of the damper flap and a down-turned front flange extending parallel to the damper flap to a bottom edge.

主权项

1. A method for controlling air flow of a fan in a fan housing comprising;
the fan housing having the fan in the housing arranged to direct air through an opening of the fan housing; mounting the housing in a location where it is exposed to exterior wind forces; providing a damper flap on the fan housing at the opening; when the fan is not running, causing the damper flap to move to a closed position to close the opening to prevent a backdraft through the housing; when the fan is running at high speed causing the damper flap to move from the closed position to a fully open position to allow full air flow from the fan to pass through the opening; when the fan is running at a low speed, preventing opposing winds from causing a backdraft through the opening thus halting the air from the fan by holding the damper flap in a partially open position extending across the opening.