Patent ID: 8033126

Claim:
A flow controlling assembly configured to permit air flow between a first chamber and a second chamber, the flow controlling assembly comprising: a frame member including a damper contacting surface at least partially surrounding a frame opening configured to permit the air flow therethrough, and a bottom wall of the frame opening, the damper contacting surface being disposed at an interior angle of less than 90 degrees but greater than zero degrees relative to the bottom wall of the frame opening; and a damper plate including a frame contacting surface, the frame contacting surface being configured to contact the damper contacting surface when the damper plate is in a closed position, wherein one of the frame member and the damper plate has at least one void, and the other of the frame member and the damper plate has at least one protrusion received in the at least one void, the at least one void and the at least one protrusion being disposed above the frame opening; wherein the damper plate is configured to rotate about a rotational axis which translates relative to the frame when there is a predetermined positive air pressure difference between the first chamber and the second chamber.