Abstract: A damper controls fluid flow and includes a frame with an opening through which the fluid is intended to flow when the damper is open, and a closure cap movable between a first position in which it blocks the opening and a second position in which the opening is unblocked. In the second position, the closure cap is rotated with respect to its first position, so as to minimize interference with fluid flow through the opening. A mechanism controls the movement of the closure cap, and includes a first and second bracket fixed with respect to the frame and the closure cap, respectively. An elongate guideway is defined in one bracket and a pin on the other bracket is captive within the elongate guideway.