Automatic flue damper

Claim 1

A flue damper arrangement for furnace exhaust gas flue comprising: a shaft extending diametrically through said flue with its opposite ends projecting beyond said flue; a bushing; a damper plate having an open slot extending across the major part of its diameter and including means formed in said damper plate at one end of the slot receiving and securing in non-rotatable relation an end portion of said shaft, and means formed in said damper plate at the other end of said slot receiving said bushing in rotatable relation therein; said bushing having a bore receiving said shaft therein in rotatable relation; a helically-shaped bimetal strip situate in said slot and extending from end to end thereof, said bimetal having one end secured relative to said damper plate adjacent the location of securement of said plate to said shaft, and having its other end secured to said bushing; means securing said bushing to said flue in fixed relation; damper stop means comprising interacting means on said damper plate and said bushing to limit movement of said damper plate between predetermined open and closed positions; said bimetal being responsive to changes in flue gas temperature to rotate said damper plate between said predetermined open and closed positions with said shaft rotating to corresponding positions; and at least one of said shaft ends including indicia means to permit observation of shaft and damper rotative position.