Abstract: A pump discharge assembly for a submergible pump installation, for use in an oil well and the like, has inlet ports for receiving liquid from a pump discharge, which ports are regulated by a back-pressure compensating valve. The valve obturates the ports upon start-up of the pump and prevents liquid being pumped unless or until the pump discharge pressure has attained a suitable level. The arrangement prevents excessive flow rate on start-up of the pump if the back-pressure is too low.

Abstract: A fluid coupling component having a valve that functions in a conventional manner when the component is connected to a mating component, but functions as a pressure relief valve when the component is in a disconnected condition. The coupling component includes a poppet and a valve, both mounted for sliding movement within a housing, and urged into engagement by a valve spring, when in the disconnected condition. A shoulder inside the housing limits movement of the poppet in a direction out of the housing, and allows sufficient internal fluid pressure to move the valve out of engagement with the poppet.

Abstract: A check relief valve particularly suited for use with corrosive fluids includes a body having an input port and an output port connecting a fluid passageway therebetween. A ring spring is mounted to the body along the fluid passageway. An annular sleeve is attached to the ring spring. A rod, having a sealing member at one end adapted to engage an annular edge of the sleeve, is lightly biased against the sleeve so that forward flowing fluid flows relatively unhindered while reverse fluid flow is checked. When the pressure at the output port is sufficiently greater than the pressure at the input port, the rod and moveable sleeve cause the ring spring to flex. After the rod has travelled a predetermined distance, movement of the rod is halted so that further movement of the sleeve breaks the seal with the sealing member to allow reverse flow of fluid. Also disclosed is a governor, which includes the check relief valve and pilot valve, for use between a pump, a system and a reservoir.

Abstract: A combination hydraulic lock and pressure relief valve for use in an actuator system for operating a spoiler control surface is interposed between the retract side of the actuating piston and the servo valve controlling the piston. In this valve a poppet urged closed against a seat member by means of a light spring aided by the fluid pressure in the retract chamber of the piston holds the poppet closed whenever the system is shut down. A piston exposed to supply pressure carries a spring retainer which includes an elongated rod movable to dislodge the poppet from its seat to permit fluid to move toward and from the retract side of the piston during normal operation of the spoiler. A second retainer abuts against the seat and a heavy spring is interposed between the spring retainers. The seat member is loaded by the heavy spring to a predetermined level above normal system pressure.

Abstract: A "snap action" early warning bypass valve assembly (2), responsive to fluid pressure differentials and/or low pressure, functions as both an electrical switch to provide an indication of low pressure or an impending fluid bypass and as a mechanical valve to actually implement the fluid bypass. The valve assembly includes a sealing piston (24, 124) supported by a retaining surface (18, 106) having a central bore (22, 110) formed therein. The sealing piston (24, 124) contains a bypass aperture (36) and is shaped to present a differential sealing area (39) to fluid circulating within the central bore (22, 110). A spring-biased bypass disc (42, 134) covers the bypass aperture (36) to present a central sealing area (45) to fluid within the central bore (22,110). A first pressure differential acting simultaneously across the central (45) and differential (39) sealing areas forces piston (24) into contact with an electrical terminal pin (48,92,126) thus energizing an alarm circuit (48-64,90).

Abstract: The invention relates to a pressure limiting valve, mainly for hydraulic mine props, which has a working space with an inlet opening connected to a high-pressure space and an outlet opening connected to low-pressure space in the operative position of the valve, a displaceable first valve member engageable with a valve seat within this working space in the shut-off position of the valve, a spring pressing the first valve member to the valve seat and in a given case, a spring sustaining the valve seat, suitably a gas spring and in which according to the invention the first valve member has transfer passages ensuring communication between the inlet opening and the outlet opening in the open position of the valve, as well as second valve member provided with a frustoconical head facing the cover plate and having a stem loosely fitted in a guide bore formed in the first valve member which is formed with an annular axial flange surrounding the head of the second valve member which is concentrically arranged within

Abstract: A combined pressure regulator and jet pump includes a valve member and cooperating nozzle defining member which are coaxial and independently movable. Both members are responsive to the difference in upstream and downstream pressures and each member will move relative to the other in response to a predetermined pressure difference. The relative movement between the nozzle defining and valve members will not interrupt the pumping action resulting from fluid flow through the variable area nozzle formed by these members.

Abstract: A buffer valve or compensator for use in a margarine mold system to permit continuous operation of a positive discharge pump in the system, such valve including a valve housing connected to a conduit section for a flow line on the discharge side of the pump, a central discharge tube in the housing, a blind bore in the discharge tube terminating at the inward end of the tube, lateral discharge ports in the discharge tube into the bore at the inward end thereof, an annular piston in the housing around the discharge tube movable between a first inward end position covering the discharge ports and a second outward end position uncovering the discharge ports, a stop member limiting the outward movement of the annular piston, and ports in the closed outward end of the housing for introducing air under pressure to bias the piston toward the inward end position. The buffer valve is connected between the positive displacement pump, a chiller, and the mold machine.

Abstract: A pressure relief valve includes a two-piece housing having therein a generally circular diaphragm backed by a spring biased plate. The outer edge of the diaphragm is captured between the two pieces of the housing and to provide a first sealing area. The central portion of the diaphragm has a circular opening therein with an annular sealing lip formed thereabout. The sealing lip provides a seal when the spring biased plate moves the diaphragm against a flat circular seat. When pressure at the inlet of the housing overcomes the spring biasing force, the diaphragm is moved away from the seat and the gas is relieved through an outlet in the housing.

Abstract: A "snap action" early warning bypass valve assembly (2) responsive to fluid pressure differentials functions as both an electrical switch to provide an indication at impending fluid bypass and as a mechanical valve to actually implement the fluid bypass. The valve assembly includes a piston (24) supported by a retaining surface (18,106) having a central bore (22,110) formed therein. The piston (24) contains a bypass aperture (36) and is shaped to present a differential sealing area (39) to fluid circulating within the central bore (22,110). A spring-biased bypass disc (42) covers the bypass aperture (36) to present a central sealing area (45) to fluid within the central bore (22,110). A first pressure differential acting simultaneously across the central (45) and differential (39) sealing areas forces piston (24) into contact with an electrical terminal pin (48,92), thus energizing an alarm circuit (48-64,90).

Abstract: A capping assembly for use in a fuel storage tank provided for a motor vehicle and the like includes a diaphragm positioned inside the assembly so as to divide an internal space into two spaces. One space communicates with the inside of the tank and is separated from the other space which communicates with the outside of the tank. The assembly further includes a valve arrangement, comprising a needle valve and a valve seat, which cooperates with the diaphragm so that the two spaces can be selectively communicated with each other in response to a relative change of pressure inside the tank with respect to a predetermined pressure.

Abstract: A control valve that can be used as a pilot-assisted pressure relief valve or as a sequence valve, which is substantially insensitive to system back pressure. The valve comprises a valve body 10 defining a multistep bore 36, and a valve member 44 engageable with a coaxial valve seat 46, both supported for reciprocating motion within the bore 36 and cooperating to control the fluid communication between first and second ports 30, 32 defined in the valve body 10. A primary biasing spring 48 enclosed within a vented spring chamber 52 urges the valve member 44 into engagement with the valve seat 46. Fluid pressure at the first port 30 exerts fluid forces on the valve member 44 that opposes the primary spring force. The valve member 44 is a unitary element including first and second annuli 44a, 44b joined by a reduced diameter shank portion 44c. A radial surface on the first annuli 44a defines a net effective pressure area against which fluid pressure at the port 30 is applied.

Abstract: There is disclosed a two-way valve which includes a single valve seat for controlling the flow of fluid in opposed directions through the valve responsive to differential fluid pressures across the valve. The valve includes first and second ports and a valve chamber. Across the valve chamber there is disposed a resilient diaphragm having an opening defining the valve seat. A ball valve element is supported in aligned relation to the valve seat and biasing means urge the ball element and valve seat into sealing engagement. When the pressure at the first port is greater than the pressure at the second port by a predetermined amount, the ball element moves away from the valve seat permitting fluid flow from the first port to the second port. When the pressure at the second port is greater than the pressure at the first port by a predetermined amount, the valve seat moves away from the ball element permitting fluid flow from the second port to the first port.

Abstract: A fluid pressure actuated by-pass valve and relief valve are positioned between a source of fluid under pressure and the hollow interior of a rotor in a fluid pressure actuated downhole drilling motor. The valve includes a hollow mandrel with an inlet opening at one end and an outlet opening at the other end connected to the rotor interior and slidably received in a movable sleeve. Fluid pressure at a first predetermined value moves the mandrel into the sleeve to block the inlet opening such that the fluid by-passes the valve and flows between the stator and the rotor to rotate a bit. Fluid pressure at a higher second predetermined value moves the sleeve relative to the mandrel to expose the inlet opening and relieve the fluid pressure on the rotor and the stator. The movement of the sleeve exposes a greater surface area thereof to the fluid pressure such that a spring moves the sleeve back to block the inlet opening only at an intermediate third predetermined fluid pressure value.

Abstract: A self sealing fluid coupling utilizing separable interconnectable fittings wherein valve structure within one of the fittings simultaneously functions as the associated self sealing valve and as a pressure relief valve adapted to open and relieve excessive internal fluid pressure when the fitting is uncoupled. The combination self sealing and relief valve comprises an axially slidable sleeve including a radial surface exposed to internal fluid pressures for producing axial forces on the sleeve which are counteracted by a spring.

Abstract: A fluid pressure actuated by-pass and relief valve are utilized in a fluid pressure actuated downhole drilling apparatus. The valve is normally closed such that fluid under pressure is directed between a rotor and a stator to rotate a drill bit. When the fluid pressure reaches a predetermined value, the valve is actuated to direct the flow to the hollow interior of the rotor to protect the rotor and the stator from damage due to excessive torque loading. The relief valve is of the sleeve type which can become stuck in the open position due to contaminents in the fluid. In the open position, the pressure drop across the valve will be insufficient to close the valve and the drill bit will not be rotated. A screen is positioned between the outlet of the valve and the interior of the rotor. The screen is then plugged by dropping pieces of plugging material, such as small chips of rubber, down the drill pipe to collect in the screen.

Abstract: An excess pressure valve particularly for props having telescopic parts which are extensible or retractable by fluid under pressure used in underground mining operations, comprises a valve housing having a bore therethrough with a connection end connectable to the fluid under pressure and an opposite opened end. A tubular sleeve is slidable in the bore and has a passage therethrough for the fluid under pressure and it has an annular inlet end face facing the connection end and an opposite annular pressure end face which opposes a piston which is also slidable in the bore between the sleeve and the opened end. The fluid under pressure maintains the sleeve and the piston in slightly spaced relationship so that there is a small space therebetween which is sealed by an annular pressure seal.

Abstract: A temperature or pressure sensor that produces a hydraulic pressure signal proportional to temperature or pressure. The sensor or transducer utilizes a plurality of bellows acting on a valve nozzle plate so that the temperature signal which is a gas pressure moves the nozzle plate to control the flow through the nozzle as a function of temperature thus producing a metered pressure proportional to temperature. The bellows are arranged to minimize temperature error in the transducer. Where the temperature sensed is engine inlet temperature the metered pressure may be used to control the fuel through the turbine engine as a function of the engine inlet temperature. This same device is equally utilized in measuring a pressure, such as compressor discharge pressure.

Abstract: A valve assembly for preventing a column of drilling fluid from spilling out of the lower end of a kelly includes an elongated body which has an axial opening and is threaded at both ends. A cam is rigidly mounted in the bore and a hollow piston in the opening is mounted for axial movement relative to the cam, the piston being shaped so that fluid pressure in the body will exert a downward force on the piston. A valve element is pivotally mounted in the piston (the piston inner surface defining a valve seat) and movable between a lower-closed position when the valve element is above the cam and engages the seat to an upper-open position where the cam engages the valve element and holds it away from the seat. A spring urges the valve element toward the closed position and the piston is urged upwardly in the bore so that the valve element is normally in its closed position.

Abstract: A relief valve, particularly adapted for use on racing car tires, which pops open to relieve at a set pressure and then reseats at a pressure slightly lower than the opening pressure. The valve includes a diaphragm (28) a diaphragm retaining plate (36) which has a resilient sealing element (39) molded or otherwise attached to it, a valve seat attached to the center of the diaphragm, and a compression spring (26) acting on the diaphragm to bias the valve seat against the resilient sealing element. When the valve pops open against the spring force, the area above the diaphragm is exposed to a venting pressure, via a port formed through the valve seat and through the diaphragm, which is higher than atmospheric and thus adds to the spring force, resulting in a resealing pressure which is slightly less than the opening pressure.

Abstract: A check valve assembly which when opening has a valve closure which is lifted from its seat before fluid flows past the unseated closure, and which when closing terminates flow in advance of the closure reengaging its seat.

Abstract: A solenoid valve comprising a housing having opposed inlet and outlet ports which communicate via a passage containing a poppet member movable in response to energization of a coil is disclosed. A flexible wall is further provided in said passage to define inlet and outlet chambers communicating respectively with said inlet and outlet ports. A second passage in said flexible wall connects said chambers, and a resilient spring urges a valve seat defined in said second passage into fluid tight engagement with the poppet member, whatever the position of the latter. The poppet member is movable between a first position in which it urges the wall against an abutment, thereby preventing any communication between the inlet and outlet ports, and a second position in which the wall is movable relative thereto, whereby said wall acts as a non-return valve between the inlet and outlet ports.

Abstract: An air valve for the demand or second stage of a scuba regulator disposed between the intermediate pressure region and the low or breathing pressure region which includes, a stationary valve seat and a tubular, movable valve element whose sealing edge is sealingly biased against the valve seat. The interior of the tubular element is in communication with the low pressure chamber and the forward portion of the exterior of the tubular element is in communication with the intermediate pressure chamber. And a flexible sealing means forming a wall between the low and the intermediate pressure regions and supporting the valve element for limited movement between a closed and an open position.

Abstract: A pressure relief valve for fluid systems which accommodates partial to complete bypass of fluid while maintaining working pressure in the system, the valve comprising a housing enclosing a chamber, with a portion of the chamber being moveable, and with an inlet and an outlet communicating with the chamber. A plunger assembly is mounted within the housing and adapted for reciprocatory motion between normal and bypass operational modes, the plunger assembly comprising a plunger body slidably received within the valve housing and having seal means about the periphery thereof for sealing engagement with the inner periphery of the housing. A first spring normally biases the moveable portion of the plunger body in a direction toward the valve inlet in opposition to inlet pressure.

Abstract: A relief valve is provided with slots across the end of the valve stem where contact is made with the valve body to eliminate gas pressurization in the annular area bounded by circumferential contact between the valve stem and the body and a smaller diameter circumferential contact between valve seat/seal members. This construction prevents any leakage gas from becoming trapped between the valve stem and the container which would lower the design cracking pressure thereby adversely affecting the operation of the relief valve.

Abstract: An oxygen regulator for supplying a recipient with breathable fluid in response to an inhalation demand. A diaphragm which is responsive to the inhalation demand operates a balanced oxygen valve to allow pressurized oxygen flow into a mixing chamber. The flow of pressurized oxygen into the mixing chamber draws air into the mixing chamber through an altitude responsive valve. The pressurized oxygen and air are combined in the mixing chamber to create a volume of breathable fluid sufficient to meet the inhalation demand of the recipient.

Abstract: The housing of a pressure-relief valve has an inlet port forming an inlet valve seat, an outlet port, a valve chamber between the ports, and an abutment in the valve chamber. A valve body in this chamber has an inlet end engageable in the inlet valve seat and an outlet end, and is displaceable in the housing between a closed position with its inlet end seated in and blocking the inlet valve seat and an open position engaging the abutment and with its inlet end spaced from the inlet valve seat. A pilot piston in the valve chamber has a throughgoing passage opening at one end at the outlet port and forming at its opposite end an outlet valve seat engageable with the outlet end of the valve body. This piston is itself displaceable in the housing between an open position with its outlet valve seat spaced from the outlet end of the valve body in either position thereof and a closed position with its outlet valve seat engaging and blocked by the outlet end. A spring urges this piston into the closed position.

Abstract: For use in helium or other gas reclamation, a diver gas safety valve adapted for attachment to a diver's helmet and to an exhaust gas recovery system, the safety valve including a collapsible tube for expanding to transfer exhaust gas having a pressure greater than ambient water pressure surrounding the diver and for collapsing to prevent such exhaust gas transfer at exhaust gas pressure below the ambient water pressure in order to prevent dangerous, sudden outflows of the exhaust gas from the diver's helmet.

Abstract: A pressure regulating valve for use in a high-pressure fluid flow line, comprises a cylindrical needle-housing structure that is slidable within a bore in a valve body. An external spring urges the needle-housing structure toward a valve seat at a selectable pressure. Contact between the needle-housing structure and the valve seat is prevented by an annular protrusion in the bore. Conduit means through the valve body, connectable to the flow line, permits passage of the flow-line fluid into the needle-housing structure. A cylindrical needle is disposed coaxially within the needle-housing structure, and is urged toward the valve seat by a spring located in the needle-housing structure. When the pressure of the flow-line fluid entering the needle-housing structure exceeds the selected pressure urging the needle-housing structure toward the valve seat, the needle-housing structure assumes a position at which the needle remains spaced apart from the valve seat.

Abstract: A pneumatic conveying system includes a conveying conduit, a gas conduit which communicates with it at least at one juncture, and a release valve at the juncture. The release valve includes a housing connected with the conveying conduit and the gas conduit, a flexible diaphragm secured to the housing and subdividing the same into one chamber communicating with the gas conduit and another chamber connected with the conveying conduit, the diaphragm having a substantially central opening, a valve-seat member connected to and movable with the diaphragm in response to flexing of the same and forming a valve seat surrounding the opening, a valve member carried by the housing and located in the one chamber, means guiding the valve seat member for movement relative to the valve member between a valve-opening and a valve-closing position, and valve-closing spring means located in the one chamber and permanently tending to urge the valve-seat member to the valve-closing position thereof.

Abstract: A device is provided for monitoring and controlling the above-ambient pressure in a system by comparing a net pressure force, produced by the system pressure on a pair of diaphragms having unequal areas, with a net spring force produced by a pair of opposed springs which clamp together a valve member and a valve seat in a pressure-relief member. The valve seat is connected by a passage to a port which is connected to the system pressure. While thus clamped together, the valve member and the pressure-relief member travel together through most of the total stroke created by movement of the pair of diaphragms and activate a microswitch for admitting additional fluid to the system when the system pressure is insufficient. If the net pressure force is sufficiently greater than the net spring force because of excessive system pressure, a port is opened when the valve strikes a stop and the pressure-relief member continues to move.

Abstract: The invention is a fluid discharge valve wherein the force necessary to mtain the valve in a closed position in the absence of fluid pressure is kept at a very nominal pressure. The fluid discharge valve further provides for the force on the valve body to increase proportional to the pressure up to a pre-determined value. At this pre-determined value, means are provided to open the valve and thereby allow fluid to pass. The invention provides for a discharge valve which maintains its initial calibration, as well as avoids the valve body and valve member to be exposed to a high closing force in the absence of fluid pressure. Further, means are provided to allow for selecting the pre-determined value.

Abstract: A valve adapted for insertion in a radially enlarged portion of the kelly saver sub to retain mud in the kelly when the drill pipe is disconnected therefrom, including a tubular body with a downwardly extending closure member supported thereby, and a piston having an axial passage for the flow of drilling mud therethrough, axially movble within the body. The plug may be removed from the bore by the application of an upwardly directed tension force thereto, so that wire line tools may be run through the bore and the passage.

Abstract: A unidirectional tubular energy-conserving axial flow control vave is provided, capable when open of accommodating the full flow of fluid through a fluid line at uniform velocity and a high flow rate with a negligible pressure drop comprising, in combination, a valve housing; a valve fluid flow passage therethrough substantially free from sharp bends and abrupt changes in direction and having an enlarged intermediate portion; a valve seat disposed in the enlarged portion of the fluid flow passage, defining the passage as an annulus about the outer periphery of the valve seat; a tubular valve element reciprocably disposed in a portion of the flow passage and movable between open and closed positions, into and away from engagement with the valve seat; having an open center through which must pass fluid flowing through the valve flow passage in the valve housing; the tubular valve element when in sealing engagement with the valve seat extending across the line of flow between its central portion and the annular

Abstract: A valve intended to open in response to a pressure difference between the interior of the valve and the exterior thereof comprises a diaphragm which in its closing position is conical. The diaphragm has an opening which is normally closed by means of a valve stem. Arrangements are made to prevent communication between the interior of the valve and the exterior thereof until said diaphragm has been deformed to a substantially planar shape.

Abstract: A pressure regulating valve is provided having a balance diaphragm for positioning a slide valve in flow controlling relation to maintain a fluid outlet in pressure balanced relation despite pressure variations at the inlet. The valve arrangement includes in combination with the inlet a pre-sensing chamber to apply a biassing force component on the valve member in a closing direction, responsive to inlet pressure. In a further embodiment utilizing a pair of such valves in opposed mutually balancing relation as a pressure balancing valve, in addition to modifying the characteristic valve response time, the arrangement has the particular benefit of being able to virtually close off the flow from one of the two sources of line pressure in the event that pressure at the respective other inlet falls to an ineffective value. While useful with many fluids, particular utility is found in mixing hot and cold liquids.

Abstract: An automatic pressure regulator of the rolling diaphragm type requiring but one single rolling diaphragm. The diaphragm is of the deep convolution type. The rolling wall of the diaphragm controls the effective cross-sectional area of an orifice means which, in turn, effects the regulation of pressure. The force created by the high pressure acts against a spring tending to move the rolling wall of the rolling diaphragm to the orifice closing position thereof. The effective area of the rolling wall of the rolling diaphragm is variable to compensate for variations of the force of the spring resulting from changes of its length.

Abstract: A pressure relief valve including a housing, first and second bores in axial alignment in the housing, first and second plungers in the first and second bores, respectively, a third bore in the first plunger, a seal between the first and second plungers with the end of the second plunger being located in communication with the third bore, a first conduit for placing the housing in communication with a source of fluid pressure to expose the first plunger thereto and also expose a portion of the second plunger thereto through the third bore, a shear pin for holding the second plunger in position whereby the fluid pressure on the first and second plungers is exerted on the shear pin, a plurality of radial bores in the housing proximate the seal between the first and second plungers, and a second conduit in communication with the radial bores for conducting high pressure fluid from the housing upon shearing of the shear pin and after movement of the second plunger away from the first plunger.

Abstract: A safety valve cap providing an elongated inner chamber with an internally screw-threaded open lower end for threaded engagement on the extended end of a conventional valve stem associated with a vehicle tire, for example. A check valve is movably positioned in the inner chamber between a compression spring and a depressor plate. When the safety valve cap is threaded onto the valve stem, the depressor plate actuates the valve stem check valve releasing compressed air into a first portion of the inner chamber until the air pressure therein is balanced with the tire pressure.

Abstract: A pressure-relief valve device has a housing with bores for admitting and discharging pressure fluid. The fluid admitted to the housing passes via a hollow member or sleeve to a valve inlet. The sleeve has at its upper end a chamfered seating surface for engaging with a sealing surface of a valve member and these surfaces form the valve. The valve member has a head with the sealing surface at its periphery and a stem which is guided within the sleeve. The stem is axially and circumferentially grooved to allow pressure fluid to pass through the housing to flush dirt away from the valve inlet even while the valve is closed. Opposed spring forces bias the surfaces of the valve together and a stop member limits the movement of the sleeve. The spring or springs acting on the valve member engage on a support member and this support member engages via a punctiform contact with a thrust piece.

Abstract: A valve intended to open in response to a pressure difference between the interior of the valve and the exterior thereof comprises a diaphragm which in its closing position is conical. The diaphragm has an opening which is normally closed by means of a valve stem. Arrangements are made to prevent communication between the interior of the valve and the exterior thereof until said diaphragm has been deformed to a substantially planar shape.

Abstract: A relief valve having a main passage normally closed with a main valve member and a vent passage normally closed with a vent valve member, the vent valve member being constructed to open the vent passage upon application of a predetermined pressure into the main valve passage to thereby prevent application of greater than said predetermined pressure to the outlet of the valve is disclosed.

Abstract: A pressure protection valve includes a housing having first and second ends. A passageway is formed in the housing for interconnecting the ends to permit fluid to flow from the first to the second end. Also, the housing includes a first portion of the passageway adjacent the first end and a second portion of the passageway adjacent the second end. A pressure responsive element is provided in the first portion to respond to preselected pressure conditions for permitting and limiting the flow of fluid from the first to the second end. In addition, a check valve is provided in the second portion for permitting the flow of fluid from the first to the second end and for limiting the flow of fluid from the second to the first end.

Abstract: A fluid valve assembly suitable for a number of different uses, including use as a fluid pressure regulator for a pump whose output pressure is to be kept uniform for changing load conditions. The assembly includes a housing, a pair of relatively shiftable valve members in the housing, and means biasing the valve members together. Each valve member has a face which is contiguous to the corresponding face of the other members. One of the valve members has a central orifice therethrough and its face surrounds the orifice to present a land having a length from the orifice to the outer periphery of its corresponding face greater than the diameter of the orifice. The face of a first of the valve members is preferably tapered to present a transversely wedge-shaped space between said faces to facilitate separation of the valve member to open the valve formed thereby. The housing has a fluid inlet in communication with the region surrounding the valve members and a fluid outlet communicating with said orifice.