US Patent 7422519 Chimney damper

A chimney damper that includes a rigid first peripheral frame surrounding an open window area, a cap moveable toward and away from the open window to selectively close and open the same and springs interconnecting the cap and frame resiliently urging the cap to an open position. The springs are connected at the upper ends thereof to second rigid frame. The cap is mounted on the second frame and the latter is allowed to pivot relative to the cap. The springs and the arrangement thereof are such as to cause the second frame to rotate relative to the first frame during opening and closing of the damper with the rotation being about one quarter turn. An articulated link interconnects the first frame and coupling between the second frame and the cap so as to prevent pivoting of the cap when moving the cap from one to the other of an open and a closed position.