Abstract: An exhaust gas stack includes an elongate, tubular stack member having inlet and outlet ends and a central longitudinal axis. An end section is mounted on the outlet end and has open first and second ends, the first end connected to the outlet end of the stack member and a frustoconical passage extending between these ends. An inner duct section has a central axis co-axial with the axis of the stack member and is mounted centrally in the end section. An annular gas passage is formed between the duct section and the end section. An air plug is movable between an open position at which exhaust gases can flow through the inner duct section and another position at which the plug restricts or prevents passage of exhaust gases through this duct section. An actuator is connected to the plug in order to move it between an open and other positions.

Abstract: Provided is a damper for controlling air flow through an air duct. The damper includes a mounting fame secured to the interior of the duct which has a circular opening for air flow therethrough when the damper is open. A circular damper plate is provided which is dimensioned to block the circular opening in the closed position while in the fully open position the plate is rotated approximately 90 degrees where it is parallel to the flow direction through the duct. The movement of the damper plate is controlled by an actuator mechanism having a pair of spaced guide plates each of which is provided with two diverging arcuate guide slots. Corresponding guide slots in the two plates are aligned at the same vertical height. A movable support bracket is disposed between the two plates and supports two guide pins which extend horizontally through the aligned slots.