Abstract: Disclosed is a valve especially adapted for the control of gases in large cross sectional ducts, flues, chimneys and the like. The valve comprises a plurality of elongated, vane-like closures which, when in closed position not only substantially stop the flow of gas in the duct, etc., with which it is associated, but also form a closed chamber extending across the duct. Outside gas such as atmospheric air under pressure greater than the pressure of the gas being controlled is introduced into the closed chamber formed by the closures, thereby precluding leakage of the controlled gas past the valve. Further, when open, and due to their construction, the controlled gas flows through portions of the closures, thus reducing flow losses in the duct.

Abstract: A guillotine-type valve in which the plate thereof is sealed around all edges relative to the housing in which it operates, said seals being pressure assisted. Adjacent the periphery of the plate, including its upper and lower edges, are curved, flexible strips of sealing material which contact the opposite face surfaces of the plate near the edges to form the seal. Surrounding such seals is a chamber and means is provided to maintain such chamber under pressure greater than the pressure of the fluid being controlled by the valve.