Abstract: A guillotine damper for a duct is provided with a thrust frame upstream of the path of a blade that is movable into and out of an operative position in sealing engagement with a seat downstream of the blade path when the flow path is not obstructed by the blade and in sealing engagement with and seating the blade against the seat when the blade is positioned to block the duct. Devices are provided with each utilizing resilient components to thrust the frame into its sealing positions and a hydraulic component to retract the frame when the blade is to be moved into or out of its duct blocking position. Each device exerts the force of either component to the frame through a series of mechanical elements spaced a substantial distance apart along the sides of the frames and connected thereto.