Abstract: An underground valve box for encapsulating a service valve selected from a variety of valves having vertical or horizontal cylindrical bodies with horizontal inlet and outlet lines disposed linearly through the body consists of an upright with a horizontal member defining upper and lower portions therein, a plurality of concentric steps descending downwardly and inwardly from the horizontal member into the lower portion of the base, a pair of V-shaped seats diametrically disposed in the member, a pair of diametrically oposed topwardly accessible notches in the upper portion of the base aligned with the V-shaped seats and a horizontal external lip and a body with lower and upper vertical concentric barrels integrally connected by an inwardly and upwardly tapering intermediate segment.

Abstract: A structure having a metal body with a plurality of intersecting cavities and a consolidated corrosion resistant powdered metal lining and metallurgically engaging the walls of the intersecting cavities.

Abstract: A butterfly valve having a central cavity larger than the access ports. A disc is disposed within the central cavity to sealingly engage the interior of the valve. A molded elastomeric liner covers the interior of the valve and the disc. By utilizing a central cavity of larger cross sectional area than the access ports, internal valve and downstream pipe turbulence is reduced resulting in increased component lifetimes.

Abstract: A controlling valve, especially a valve ball, for a gaseous and liquid flow material, comprises a housing, two connector pipes, a flow-adjusting component and associated valve seat components. The flow-adjusting component and the valve seat components have corresponding flow ducts, which are provided in a special component made from sintered ceramic material. At least the flow duct of the flow-adjusting component is located in a sintered ceramic sleeve. This sleeve is inserted in a passage in the flow-adjusting component and pressure-relieved in regard to material flow. The sleeve is held under frictional forces or just fits in the passage.

Abstract: A flexible body member is constructed so as to be wrapped around a hose at connector portions thereof and has overlapping side portions. The body member has releasable securement on its overlapping areas and also has a widened portion intermediate the ends thereof for accommodating the interfitting coupling members and for holding the device on the coupling members. The releasable securement on the overlapping side areas is by continuous and full length fastening elements such as Velcro. The device also has padding to provide desired cushioning and insulation.

Abstract: A packingless gate valve comprises a housing having two opposed resilient sleeve units that compressibly engage end to end in the valve open condition and engage opposite sides of the gate in the valve closed condition. Each sleeve unit is a resilient annular body formed at one end with an axially projecting seal lip near the inner periphery and has a stiffener ring enclosed adjacent the outer periphery at the one end. An integral gasket forming flange is formed on the other end of the sleeve body.

Abstract: A letdown valve for slurries under pressure is provided with a throttle 13 inside a housing 15 with interposed lubricant sealer and grooves 16 to accommodate any excess lubricant sealer. The throttle body 13 is held in place by a retaining ring 17 which is welded in position.

Abstract: A hot fireplace includes an elongated main gas burner associated with a grate for supporting logs, there being a control operatively connected with the burner to control flow of combustible gas to the burner, the control located near the fireplace. In this environment there is a heat shield located proximate the control to intercept infra-red radiation toward said control, the shield having perforations sized for intercepting such radiation, and for passing convection air therethrough. Typically, the perforations have cross dimensions less than the wavelength of infra-red radiation.

Abstract: A plumbing fixture includes a tubular waterway and an enclosing cover. There is a space between the cover and waterway. In the method of manufacturing such plumbing fixture, a foam material consisting of a base and a catalyst therefor is positioned within the space between the cover and the waterway, with the foam material growing in the space until the space is completely filled and the waterway is secured to the cover. The foam material not only is the securing agent for the waterway and cover, but provides temperature, noise and vibration isolation therebetween.

Abstract: An improvement in a pipe flushing device is provided. The device includes a hollow, elastomeric tubular member expandible by water pressure and having open opposite ends. A hose connector is connected to the inlet end thereof and a valve connected to a transverse groove in the outlet end thereof. The valve includes a hollow cylindrical cage with open sides and front and a rear transverse closure plate sealing the rear end thereof. The plate may have a peripheral flange and in any event seats in the transverse groove. An elastomeric sheath which is both flexible and resilient forms the improvement. The sheath removably covers the exterior of the rear closure plate and helps seal the valve in the groove to prevent fluid by-pass except when the tubular member is expanded. The sheath may have a roughened slip-resistant exterior surface or striations in the exterior thereof to improve the seal and may enclose a portion of the sides of the cage.

Abstract: A restraint to enable temporary bracing and operation of a thermally cracked sparger nozzle mounted from a sparger manifold at the end of a pipe elbow is disclosed. The restraint includes a second and surrounding restraint elbow which is fitted over and captures the sparger elbow. The restraint elbow has a saddle surface baseplate communicated to the lower end which rest on the sparger manifold to form a substantially water tight base for the restraint. The nozzle end of the restraint elbow is fitted with a nozzle aperture plate for surrounding the outside of the sparger nozzle again in substantially water tight relation. The plate is mounted for movement on the end of the restraint elbow for conforming threading of the restraint at the plate over the sparger nozzle. The restraint can be rapidly mounted (in less than a minute), tack welded at the aperture and seat tensioning bold (in less than 4 minutes) and left in the reactor for a complete fuel cycle.

Abstract: An integral one-piece hopper tee is disclosed as providing a generally vertically directed hollow pipe section having a laterally outwardly direct flange at an upper end thereof for attachment to the bottom of a hopper truck. At the other end of the vertical pipe section, a generally transversely extending hollow pipe section is provided, with the opposite free ends thereof capable of being attached to pipeline tubing, through which pneumatic unloading of product obtained in the hopper truck may be routed first through the vertically and horizontally directed pipe sections and then into the pipeline tubing.

Abstract: The rotary fluid coupling decreases the possibility of microcontaminates entering the fluid flow line and is thus especially suitable for processing equipment in manufacturing of wafers and other components for the microcomputer industry. The rotary fluid coupling interconnects a fluid conveying passageway and a spindle element to a duct in a second element such that the two elements are rotatable with respect to each other. An axial channel is provided along the length of the spindle. A planar faced plate is mounted on the spindle. A bore in the spindle plate is in axial alignment with the spindle channel, generally forming a single continuous fluid conveying passageway. A second element has a generally planar distal faced plate. A fluid conducting duct extends from an aperture on the distal face of the second plate to a fluid source with the two faces generally aligned in parallel relationship to each other creating a fluid permeable gap.

Abstract: Disclosed are slide parts, comprising one part made of an aluminium alloy having an Alumite layer formed on the slide surface thereof and the other part made of an aluminium alloy having a Fe-series wet-plated layer formed on the slide surface thereof, which is to be in contact with and slide on the slide surface of the former alloy part; and a method of the manufacture of the slide parts. The slide parts are lightweight and are excellent in abrasion-resistance and baking-resistance. The clearance variation by temperature is little, and the slide parts are suitable for use as reciprocating slide parts.

Abstract: A plastics elbow cover (A) capable of being positively and securely mounted on an elbow section of piping. The elbow cover includes a tab (9, 10) extending from each of two sides of a cover section (8) which fits over the pipe. One of the tabs (9) includes: a tongue (9a) which engages a hole (10c) formed by a bridge (10d) on the other tab (10).

Abstract: A pipefitting cover specially designed to enclose an insulated Y-shaped joint is disclosed comprising two half sections, one adapted to the shape of a straight pipe segment and the other adapted to interlock with the other section while also accommodating an additional pipe segment protruding at an angle from the first straight pipe segment.

Abstract: A solenoid valve, especially an outlet valve for infusion water. A valve chamber (2) is accommodated in a valve housing (1) and communicates with a supply channel (Z) and with a drain channel (A) by way of a valve seat (3). The magnetic armature (6) of a magnetic system accommodated on valve housing (1) is connected to a valve plate (10) accommodated in the valve chamber (2) opposite the valve seat (3). The valve chamber (2) is sealed off from the interior (11) of the magnetic system by an isolating diaphragm (12). To prevent calcium deposits, the valve seat (3) has a sheet (13) of polytetrafluoroethylene accommodated coaxially along its inner circumference and projecting beyond the surface of the valve seat (3) on the side facing the valve plate (10). The upper edge of the sheet (13) facing the valve plate (10) is in sealing plane with respect to the valve plate.

Abstract: An improvement in a pipe flushing device is provided. The device includes a hollow, elastomeric tubular member expandible by water pressure and having open opposite ends. A hose connector is connected to the inlet end thereof and a valve connected to a transverse groove in the outlet end thereof. The valve includes a hollow cylindrical cage with open sides and front and a rear transverse closure plate sealing the rear end thereof. The plate may have a peripheral flange and in any event seats in the transverse groove. An elastomeric sheath which is both flexible and resilient forms the improvement. The sheath removably covers the exterior of the rear closure plate and helps seal the valve in the groove to prevent fluid by-pass except when the tubular member is expanded. The sheath may have a roughened slip-resistant exterior surface or striations in the exterior thereof to improve the seal and may enclose a portion of the sides of the cage.

Abstract: A removable reusable insulating unit for insulating an exposed section of an insulated pipe system is disclosed. The insulating unit has a hollow body portion with insulating walls for enveloping the exposed section of the pipe system. The body portion has a parting line along its length to permit opening thereof so that the unit may be wrapped around the exposed section of the pipe system. The body portion is made of a sufficiently flexible insulating material to permitt such spreading apart of the body portion at its parting line. Fasteners are provided for securing the unit closed with the insulating walls abutting one another along the parting line. Each opening of the unit, through which a pipe or the like of the system may extend, has a substantially more rigid insulating material which snugly envelopes the system to form an insulative blanket for the exposed portion.

Abstract: In the valve casing according to the invention, a cylindrical elastic member is fitted to solidly coat a whole inner surface of the valve casing to form a passage, while performing a function as a seal ring for pipe lines and a function as a seat ring for a valve disc.

Abstract: A throttling gasket insert (34) for attaching a knife gate valve (10) into a pipe string is constructed of a single piece of resilient gasket material having a washer-shaped flange portion (36), to be clamped between a facing surface (52) of a knifegate-valve face plate (26) and a pipe flange (60), and a tubular portion (42), extending through a knife-gate valve flow passage (22) to a knife-gate blade (12) thereof, having a V-shaped passage therethrough.

Abstract: The regulator and shut off valve for a corrosive media, particularly for a wet chlorine-containing gas and a chloride ion containing fluid, comprises a pressure resistant housing and a shut-off member held between at least two seat rings. The housing has a passage for the corrosive media. The seat rings are supported in the housing and contact the shut off member under tension. To protect against abrasion and erosion the housing is made of titanium or a titanium alloy, at least one sintered ceramic wear sleeve is provided on the circumference of the passage in the housing and the wear sleeves are inserted in the housing with radial play an with axial play so that a space is formed between the outer circumference of the wear sleeve and the housing, which is connected with the passage cross section of the wear sleeve by a compensating gap.

Abstract: A control valve assembly to be assembled with a discharge nozzle of a sandblasting abrasive cleaning system or the like, comprising a valve housing to be connected at an inlet end to a supply conduit having a lower valve chamber and a well formation providing a lateral compartment communicating with the valve chamber, a circular valve seat at the discharge end of the valve chamber providing a beveled seating surface, and a pivot valve member supported for movement into and from the valve chamber having a generally cylindrical valve head and beveled surface to conform to and seat tightly against the seating surface and having an elongated stem portion extending in inclined relation from the valve head.

Abstract: A butterfly valve housing which is to be interposed between two sections of as conduit includes a metallic core body and a covering body of a high-rigidity synthetic plastic material which is molded around the core body to substantially completely encase the same and to form a substantially self-supporting shell around the core body. The core body has and annular portion that bounds an internal opening and two projections which extend radially outwardly from the annular portion. The projections and the annular portion bound transverse passages that are centered on a common axis extending across the internal opening and in use accommodate respective trunnions that support a disc-shaped valve member of the butterfly valve. The covering body has regions which penetrated into these transverse openings to cover the core body within the latter.

Abstract: A pressure relief valve having an external valve body substantially cylindrical, with a bore therethrough positioned atop the exterior of the pipe, an internal stem portion movable within the bore within the valve body, including a tip for extruding in through a bore in the wall of the pipe, a piston member housed within the internal movable valve body movable from a first position locking fluid flow up through the internal body and a second position allowing fluid to enter the internal body and enter a drain port, a spring member intermediate the upper portion of the valve head and the internal body for biasing the piston member in a normally closed fluid bloding position, means on the valve body for imparting force on the upper portion of the internal member for driving the lower tip portion through the wall of a particular type of fluid flow pipe, and insulation means for housing the external valve and for insulating the valve from direct contact with the fluid flow line.

Abstract: A butterfly valve housing which is to be interposed between two sections of as conduit includes a metallic core body and a covering body of a high-rigidity synthetic plastic material which is molded around the core body to substantially completely encase the same and to form a substantially self-supporting shell around the core body. The core body has and annular portion that bounds an internal opening and two projections which extend radially outwardly from the annular portion. The projections and the annular portion bound transverse passages that are centered on a common axis extending across the internal opening and in use accommodate respective trunnions that support a disc-shaped valve member of the butterfly valve. The covering body has regions which penetrated into these transverse openings to cover the core body within the latter.

Abstract: A ball cock having sinter ceramic valve ball and seat rings, also has wear-resistant bushings between the pipe connectors joined to the ends of the housing sleeve and the seat rings. Compressible seals bearing upon the bushings and clamped between the bushings and the pipe connectors press the bushings against the seat rings and the seat rings against the valve ball.

Abstract: A gate valve formed with spaced parallel housing plates having axially aligned apertures which constitute a housing therebetween. Elastomeric sleeves line the apertures of the housing plates to provide an annular space between the sleeves. An elongated gate plate, having an apertured section and an imperforate section, is positioned in sliding contact with the sleeves. Actuator means reciprocate the gate plate between an open and closed position.

Abstract: A container intended for transporting and discharging aggressive liquids, such as silicon tetrachloride, is closed with a container lid which carries a valve head. The inner surfaces of the container and of the container lid are lined with fluorinated hydrocarbon. The valve head has a valve block which, in valve block drilled holes accommodates valve inserts and is enclosed by a steel jacket which is bolted to the container lid. All the parts which come into contact with the aggressive liquid consist of fluorinated hydrocarbon, so that contact between the aggressive liquid and metal is avoided.

Abstract: A wear monitoring device for use in a choke valve. The device includes a wear liner which fits in the flow annulus of the valve. The liner is sealed at either end from the fluid inlet valve and defines an annular void space in fluid communication with a port to the exterior of the valve. Leakage caused by flow cutting through the liner can be observed as fluid discharge from the port.

Abstract: A heated, insulated cover for a portion of a pipeline with valve and backflow preventer components exposed to the atmosphere, the cover being sectionalized so as to be assemblable around the valve components, with hand manipulated clamps to hold the cover together, an electric heating element inside the cover to keep it above freezing temperature, drain openings in the cover at ground level to let any water drain out of the cover, doors in the cover to permit inspection and testing of the components when the cover is in place.

Abstract: A housing for heat insulated armatures and/or flange connections with two box like housing parts, wherein different dimensions of pipelines or and actuating device for an armature, for example, a control gate, is compensated by at least one adapter piece, whereby the adapter piece as well as the housing parts are designed in a heat insulating manner.

Abstract: An electromagnetic valve comprising a housing having fluid containing region and first and second ports in communication therewith, an electromagnet carried by the housing located external to the region, and a thin fluid impermeable diaphragm barrier hermetically isolating the electromagnet from the region. An armature in the housing is movable within a body of magnetically permeable material and has a pole portion located for magnetic attraction by the electromagnet and has a valve portion located for opening and closing one of the ports to place the ports in fluid communication through the region in one state of the valve and to block fluid communication between the ports in another state of the valve. The armature is moved from a rest position through a forward stroke when attracted by the electromagnet and is returned by a biasing spring to the rest position.

Abstract: In a fluid flow line from a well in the earth, a choke means is employed to restrict the flow of fluids through that line. The choke has a body with apertures therein for passing fluid therethrough and an insert means in one of the apertures of the body which mates with a movable means for creating the choking restriction. The insert means extends to the fluid outlet end of the body of the choke and for a finite distance beyond and outside the body of the choke so that any blast effect that may occur due to pressure change inside the insert means is transferred by the insert means outside of the body of the choke before being released.

Abstract: A tapered plug valve containing a tapered plug surrounded by a sleeve of elastomeric material which deflects upon high fluid pressure applied through the valve inlet port, leakage which might otherwise occur due to such deflection being absorbed by `O` ring seals. The plug may also be urged into the valve body by hydraulic pressure from the inlet port, and this maintains a sealing contact between the elastomeric material and the valve body surrounding the ports.

Abstract: A butterfly valve for controlling high-temperature fluid including a ceramic valve is disclosed. The butterfly valve exhibits excellent high-temperature sealing and heat insulating characteristics and strength sufficient to rigid support the valve disc therein. The valve comprises a valve stem and a valve disc integrally formed of ceramics and is housed in a casing through a valve guide opening and the valve guide opening is closed with a plug through which the valve stem is inserted.

Abstract: A unitary removable and reuseable jacket for the thermal insulation of pipe accouterments is disclosed. The fully-formed generally-rectangular jacket is composed of three layers: a heat and water resistant outer fabric layer, a hardened rigid-cell polyurethane middle layer, and a thin flexible heat-shrinkable plastic inner layer. The inner and outer layers are joined together by perimeter seams and a transverse center seam which form two pockets adapted to contain the polyurethane foam middle layer. Said inner and outer layers are formed at time of manufacture while the middle layer is formed during the application process. During the application process, an exothermic chemical reaction is generated by the combination of the chemicals polyol and isocyanate which are inserted between the inner and outer layers through holes contained in the outer layer, to form a rapidly expanding and hardening rigid cell polyurethane foam middle layer.

Abstract: Disclosed is a plastic lined rotatable valve. The valve includes a valve body that is formed by at least two connected together body parts or halves. Each body half is lined with an inert plastic material. The seal between the body halves or parts is provided by sealing flanges on the plastic lining. The sealing flanges are resiliently urged together, thereby to compensate for cold flow and to isolate the sealing flanges from stresses on the valve body due to uneven piping loads. The valve body halves or parts include rims about the junction where the halves or parts are joined together which form a rigid shell for the valve body, which further isolates the sealing flanges from mechanical stresses. The valve includes a plastic encapsulated valve member that is rotatable by a plastic encapsulated stem. A packing is provided for sealing between the stem and valve body.

Abstract: A packingless gate valve is disclosed which includes a housing having opposed similar housing halves with resilient sleeve units which compressibly engage each other in the valve open condition and engage opposite sides of the gate in the valve closed condition. Each sleeve unit has a flange on the inner and outer axial ends, with the flanges extending radially outwardly from the sleeve body. An encircling thin stiffening ring of harder material is bonded to the axially outer surface of the flange on the inner end of each sleeve, each stiffening ring being shaped with a right angle bend so as to provide both axially and radially facing surfaces for each sleeve body. The particular configuration and position of the stiffener rings has been found to function advantageously in preventing the pliable sleeve material from following the gate as it penetrates between the opposed sleeve units.

Abstract: A float valve assembly comprises a valve body defining an internal chamber having upper and lower openings and a vertically movable ball or poppet in the chamber for moving upwardly to close the upper opening to prevent upward flow of fluid and for moving downwardly away from the upper opening to permit downward flow of fluid. A resilient, deformable seal positioned adjacent the upper opening has three separate seal elements to provide primary, secondary and tertiary sealing phases. The interior of the valve chamber is lined with a continuous liner to minimize abrasion of the valve. The liner and the resilient seal are formed simultaneously as a single unit by in-situ molding and curing of a thermosetting elastomer material.

Abstract: A trunnion type ball valve arranged so that biasing means is not needed to establish a seal between the valve seats and the ball when the valve is in the closed position. There is no load on the valve seats in the open position and a sufficient load in the closed position to effect a fluid seal in the closed position. The valve seats are movably mounted in the valve body so that they are displaced during opening and closing movement, but center themselves in the open and closed positions.

Abstract: A plastic gate valve including a plastic valve casing having a passage and a valve chamber therein; a spindle extending in the valve chamber and rotatably supported by the valve casing; a handle connected with the spindle and rotating it; and a plastic valve body engaged with the spindle and moving along an inner wall of the valve chamber in response to the rotation of the spindle whereby the valve body opens and shuts the passage. The valve body is made of heat-resistant rigid vinyl chloride resin and covered with rubber-like elastic material by means of vulcanization adhesion so as to be integral with the valve body.

Abstract: A butterfly valve includes a body having pipe connecting parts forming two opposite ends thereof and a cylindrical flow path interconnecting the pipe connecting parts, a stem attached rotatably at the central part of the body diametrically across the cylindrical flow path, a lever handle connected non-rotatably to the external leading end of the stem, and a disc formed by joining two substantially circular metallic plates in a mutually opposed manner, coating the entire outer surfaces of the metallic plates with a corrosionproof, resilient material, and boring a stem-insertion hole between the two joined metallic plates in the central diametric position thereof and disposed inside the cylindrical flow path of the body for accommodating the stem non-rotatably within the stem-insertion hole thereof. An externally open groove having a substantially U-shaped cross section is formed in the joint periphery of the two joined metallic plates of the disc.

Abstract: This invention is concerned with a check valve made up of two housings or castings, each of which has a corrosion resistant liner which provides improved support and operation of the ball or check member and increased resistance to liner collapse when operating under vacuum conditions.

Abstract: This invention is intended to solve the problem that a valve casing for use in a butterfly valve formed by press working, which is advantageous from the standpoint of productivity, thickness and weight, has such as a serious disadvantage of breakage or deformation and lowering in the sealing performance due to release on aging or the seal ring when the valve is mounted on pipe line and clamped from both sides. From this point of view, a valve casing according to this invention is formed into a double structure composed of an inner shell and an outer shell, the inner shell comprising a cylindrical part defining a bore and seal ring receiving portions formed on both ends with their diameters enlarged larger than the cylindrical part substantially forming an S-shape in cross section, the outer shell defining a space by surrounding a whole outer periphery of the inner shell, and the inner shell and the outer shell being superposed to each other at both end of the valve casing.

Abstract: An improved valve well-suited for controlling the flow of particulate solids comprises a valve body having a flow passageway comprising inlet and outlet passages extending transversely to a slide chamber. A plug member having a flow orifice, which is preferably of extended length extending transversely through it is mounted for sliding movement within the slide chamber to seal the flow passageway when the flow orifice is out of register therewith and to connect the inlet and outlet passages in flow communication when registered therewith. The flow orifice is preferably of ovoid cross-section and provides, at all operating positions of the valve, a cross-sectional flow area from the flow orifice to the outlet passage which is at least as great as the smallest cross-sectional flow area of the flow orifice. The flow orifice in its wide open position does not restrict the cross-sectional area available for flow between the inlet and outlet passages of the valve body.

Abstract: A portable collapsible tank for storing and insulating hot water or other liquid is contained by an elongate flexible and foldable outer sleeve which defines the outer perimeter of the tank and is formed with sufficient tensile strength to support the tank and stored water. A side wall of insulating material is contained within the sleeve extending around the inside circumference of the sleeve from the top to the bottom of the tank. The outer sleeve and side wall layer overlap and frictionally engage the edge of a floor or base disk of rigid insulating foam material for stability of the tank without tilting and to prevent ballooning of an inner liner from the bottom of the tank. An inner liner of impervious flexible material suitable for contacting hot water, for example, for consumptive use is removeably seated within the side wall and base and extends over the top of the tank.

Abstract: Apparatus and method for depositing a corrosion resistant weld clad material upon a cylindrical surface of a workpiece such as the internal cylindrical conduit of a valve body (10). The apparatus includes a turntable (12) having a rotating platform (24) which is adapted for supporting the valve body for rotation about the cylindrical axis of its internal conduit (14). The platform (24) can be tilted from a horizontal position through to a vertical position such that the central axis of the valve body conduit connected thereto can be angled between 30 and 60 degrees. A wire-fed, gas-shielded welding torch (16) is supported adjacent to the cylindrical surface of the conduit (14) to be coated such that as the valve body (10) is rotated by the turntable (12), weld material (82) is deposited circumferentially about the surface of the conduit.

Abstract: In a solenoid valve with ON/OFF switch arranged by a valve member and the associated valve seat defined in an electrically conductive body, the solenoid valve has a stopper connected to the valve member for setting the stroke of the valve member and comes in contact with the body when an actuator for driving the valve member is in its de-energized state and an electrically insulating sheet provided between the stopper and the body so as to prevent the valve member for coming in contact with the body through the stopper.

Abstract: A butterfly damper with a plurality of blades which can be locked in the open position, and which, when released, rotate about a hinge to the closed position. A pawl member, attached to one blade, extends away from the blade and through an opening in a second blade when the blades are in the open position. A mounting member attached to the second blade restrains the pawl member thereby holding the blades in the open position. A bimetallic link attached to the mounting member causes the pawl member to be released when the temperature of the air passing through the duct increases beyond a preselected level. A closure spring attached to the blades acts on the blades tending to force them apart against the action of the mounting member and the pawl member when the blades are restrained in the open position. The damper blades can be insulated to prevent the heat from a fire on one side of the damper from being conducted by the damper to the other side when the blades are in the closed position.