Automatic flue damper

TLDR: A relatively simple automatic mechanical flue damper is provided by a damper plate having a slot extending across a major portion of its diameter with a helically-shaped temperature responsive bimetal having one end attached to the damper at one end of the slot, and its other end attached with a bushing which in turn is fixed relative to the flue, with a shaft extending in rotatable relation through a bore in the bushing as mentioned in this paper.

Abstract: A relatively simple automatic mechanical flue damper is provided by a damper plate having a slot extending across a major portion of its diameter with a helically-shaped, temperature responsive bimetal having one end attached to the damper plate at one end of the slot, and its other end attached to a bushing which in turn is fixed relative to the flue in which the damper is situate, with a shaft extending in rotatable relation through a bore in the bushing and having its end opposite the bushing attached to the damper plate, the helical bimetal being responsive to changes in flue gas temperature to rotate the damper plate between predetermined open and closed positions with the shaft rotating to corresponding positions, and at least one of the shaft ends including indicia means to permit observation of shaft and damper rotative position. The arrangement adapts itself to the provision of electrical means responsive to the shaft rotation to shut down the furnace operation in response to failure of the damper plate to move the open position within a predetermined time after initiation of the furnace operation.