Abstract: A fan damper includes a frame and a plurality of hollow airfoil blades, each having a leading edge, a trailing edge, a seal on the trailing edge, and a pivot mechanism on either end of each blade, including an extension having a weight. A secondary seal is positioned between the pivot mechanisms and the sides of the frame. A ladder bar connects the pivot mechanisms. During significant air pressure changes, the blades move against the weights from a first, closed, overlapping position, whereupon the seal on the trailing edge of a relatively upper blade seals against the leading edge of an adjacent relatively lower blade, and the secondary side frame seal seals against the pivot mechanisms, to a second, open position. When the air pressure decreases sufficiently, the blades return to the closed, overlapping position.

Abstract: A fan damper includes a frame and a plurality of hollow airfoil blades, each having a leading edge, a trailing edge, a seal formed on the trailing edge, and a pivot mechanism on either end of each blade, each of which pivot mechanisms includes an extension that includes a weight. A secondary seal is positioned between the pivot mechanisms and the sides of the frame. A ladder bar connects the pivot mechanisms. During significant air pressure changes, such as when a fan is turned on, the airfoil blades are caused to move, against the weights from a first, closed, overlapping position relative to the frame, whereupon the seal on the trailing edge of a relatively upper blade seals against the leading edge of an adjacent relatively lower blade, and the secondary side frame seal seals against the pivot mechanisms, to a second, open position. The airfoil blades will stay in the open position as long as the air pressure is enough to overcome the effect of the weights.