Damper assembly for gas duct

A damper assembly for use with a rectangular cross section gas duct having upstream and downstream duct sections with opposed open ends of equal height and equal width spaced apart to define a transverse slot therebetween, comprising, in combination, a rectangular frame having vertical side members and horizontal cross members attached thereto to provide a planar surface adapted to be flexibly secured to flanges on said duct members, said vertical side members extending both above and below the duct a distance at least equal to the height of the duct and said horizontal cross members comprising frame cross members substantially coextensive with the upper and lower edges of said flanges and a top frame cross member spaced from the upper edge of the duct a distance substantially equal to the height of the duct, a damper plate having a length at least twice the height of the duct and a width substantially equal to the width of the frame, said plate comprising a lower portion having an opening formed therein at one end thereof substantially equal to the duct opening and an upper baffle portion, said damper plate slidably supported within said frame for vertical reciprocal travel whereby the opening in the damper plate and said baffle portion can be moved into and out of alignment with the duct, a pair of upper and lower cross-bars pivotally secured to upper and lower ends of said plate respectively mounted in said frame for reciprocal vertical travel therein, piston-cylinder means engaging each end of the upper and lower cross-bars for raising and lowering the cross-bars and damper plate whereby the opening formed in said damper plate can be aligned with the duct, and sealing means to prevent egress of gas from said assembly when said damper plate is in an opened, closed or transitional position and to prevent movement of gas between said upstream and downstream sections of the duct when said damper plate is in a closed position.