Abstract: A fluidic device for supplying working fluid includes: a fluid line for the flow of the working fluid; a pressure regulator adapted to reduce the pressure of the working fluid from the upstream pressure to a downstream pressure; a valve adapted to be pressure-controlled for opening or closing, depending on whether a pressure exerted on its valve head is substantially equal to the upstream pressure or to the downstream pressure; a distributor including a first opening connected to an upstream side of the pressure regulator, a second opening downstream of the pressure regulator, and a control opening connected to the valve head. The distributor is adapted to cause the opening or closing of the valve, depending on whether the control opening is connected to the first opening or to the second opening.

Abstract: A frac manifold isolation tool configured to connect to a zipper spool, and comprising a mandrel that is axially movable and a hydraulic setting tool configured to move the mandrel from an open position, in which fracturing fluid is allowed to flow from a zipper spool to a connected frac tree, to a closed position, in which the mandrel and its associated cup tool prevent fracturing fluid from flowing to the connected frac tree.

Abstract: A technique facilitates control over fluid flow via controlled operation of a flow control valve. The flow control valve comprises a first component with a hydraulic flow configuration and a second component with a corresponding hydraulic flow configuration. The first component and the second component are mounted in a body such that the second component is shiftable between operational positions with respect to the first component. Shifting of the second component relative to the first component causes the hydraulic flow configuration and the corresponding hydraulic flow configuration to move into different cooperating flow configurations which provide different flow paths through the flow control valve. Additionally, the first and second components are biased toward sealing engagement with each other.

Abstract: The invention relates to a device for providing pressurized fluid. The device includes a first functional assembly including a pressurized fluid bottle having an opening having attached therein a first tap including an inner fluid circuit including an insulating valve. The device includes a second functional assembly forming a physical entity separate from the first assembly. The second assembly includes a second tap having an inner fluid circuit. The first tap and the second tap include respective coupling members forming a removable rapid connection system. The device includes in the first assembly at least one electronic data storage communication unit that is removably, wirelessly queryable via electromagnetic waves and in that the second assembly includes at least one electronic communication unit for removably, wirelessly reading, via electromagnetic waves, data from the electronic member of the first assembly.

Abstract: A valve assembly capable of converting a small leak of a device into a measurable, relatively larger or “burst” flow event is described. In certain embodiments, the valve assembly includes a compliant chamber and, following pressurization of the device, permits flow when the pressure in the compliant chamber drops to a configured fill pressure and restricts (or prevents) flow when the pressure in the compliant chamber increases to a shut-off pressure. The disclosed valve assemblies may be incorporated into a leak detection assembly capable of transmitting usage and/or alarm data to a central service.

Abstract: An overpressure safety system for use with a distribution of pressurized fluid associated with hydrocarbon production operations includes a safety valve in fluid communication with a main bore of a fluid control manifold assembly. The safety valve has a blocking condition where the safety valve blocks a flow of pressurized fluid through the safety valve, and a venting condition where the safety valve provides a fluid flow path for the pressurized fluid at a set overpressure to pass through the safety valve. A valve member is moveable within the safety valve between a first position where a pressure side of the valve member blocks the flow of the pressurized fluid at a pressure below the set overpressure from passing through the safety valve, and a second position where the valve member provides a fluid flow path for the pressurized fluid at any pressure to pass through the safety valve.

Abstract: An improved punch tool and a method for relocating a section of pipeline using the improved tool are presented. The improvement includes an interior channel running through the center of the shaft of the punch tool and a connector that is attached to one end of the shaft and to a pressure gauge and pressure bleed valve, thereby allowing the operator to use the same tool to cut, gauge, and purge the section of pipeline to be abandoned.

Abstract: Provided is a thermal energy network system including: a first thermal station that stores first thermal energy using a first heat source and supplies the first thermal energy to a first demand source used for residence or commerce; and a second thermal station that stores second thermal energy using a second heat source and supplies the second thermal energy to a second demand source used for industry, wherein the first thermal station and the second thermal station manage a base load of a thermal energy network, and the first thermal energy and the second thermal energy are transferred between the first thermal station and the second thermal station as needed.

Abstract: A system for gas hydrate production. The system includes a tubular having a plurality of ports. The plurality of ports includes a first port configured to automatically open at a first differential pressure, and to remain closed at differential pressures below the first differential pressure. A second port configured to remain closed at the first differential pressure, and to automatically open at a second differential pressure greater than the first differential pressure; wherein the second port is located uphole of the first port. Also included is a method of improving methane hydrate production.

Abstract: Systems and methods provide pneumatic control of a slam shut valve system.

Abstract: A slam-shut safety device having a disc arrestor includes a valve body, a valve seat between an inlet and an outlet, and a reset pin shiftable between untripped and tripped positions. A valve disc support includes has a threaded stem and is operatively coupled to the reset pin. A valve disc fits on the stem of the support and shifts in response to movement of the valve disc support between an open position and a closed second position in which the valve disc is seated against the valve seat. A threaded nut is securable to the threaded portion of the stem of the valve disc support, and an arrestor spring is positioned on the stem of the valve disc support and is secured by the threaded nut. The arrestor spring is arranged to apply a biasing force to valve disc.

Abstract: A fuel-injection device in a turbomachine is disclosed. The device includes a high-pressure pump supplying a flow control valve, whose outlet is connected via a pressurization and cut-off valve to a fuel-injector feed pipe. The valve is connected to the inlet and to the outlet of the pump in order to define two fuel pressurization thresholds, one of which is used to start-up and restart the turbomachine and the other is used for operating the turbomachine from an idle speed and for commanding an equipment with variable geometry.

Abstract: A centralized automatic fluid or gas spill prevention and shut-off valve system that prevents line ruptures comprising means to reduce fluid pressures, such as gas, to appropriate levels, a continuous monitoring of downstream conditions, an immediate stop system of major spillage caused by excessive flow wherein said immediate stop system automatically shuts off the flow of fluids, means for timed shut off of minor fluid flows that exceed a predetermined amount of time and a restarting system that restarts when overflow conditions are corrected, wherein said restarting system works automatically or manually.

Abstract: A manifolded fail-safe hydraulic control system provides fail-safe operation of a pipeline valve using no more than a total of 45 proprietary parts in the system. The system controls the operation of a spring return actuator, which in turn strokes the pipeline valve from the normal operating position to the fail-safe position, or from the fail-safe position to the normal operating position. The system enables the valve to automatically stroke to its fail-safe position without external power.

Abstract: Provided are a flow meter and a flow-rate control system using the same that is capable of measuring a flow rate in a minute flow-rate region with excellent measurement accuracy by preventing or suppressing the generation of bubbles and in which accumulation of the fluid and the bubbles is less likely to occur.

Abstract: Featured is an automatic high-negative pressure relief valve and its use in combination with an apparatus for draining fluid from a body. In broad terms the negative pressure relief valve includes a biasing mechanism, a moveable member acted upon by the biasing mechanism and a seating surface. When the pressure within a chamber, in which a portion of the relief valve is in fluid communication with, is less than a predetermined negative pressure, the moveable member is moved by the biasing mechanism to sealing engage the seating surface and when the pressure is at or above the predetermined value, the restoring force of the biasing mechanism is overcome and the moveable member moves away from the seating surface. In an exemplary embodiment, the biasing mechanism is a spring, diaphragm or wave washer.

Abstract: A valve activation assembly which mechanically collapses a collapsible member, such as a buckling pin, in response to both overpressure and underpressure conditions of a pressurized fluid. A retention member retains the valve member in a selected position with respect to the fluid, such as an open or closed position. A piston assembly is configured to mechanically collapse the collapsible member both when a fluidic pressure upon the piston assembly exceeds a first level, and when a fluidic pressure upon the piston assembly falls below a second level. Upon collapse of the collapsible member, the valve member releases the valve member, allowing the valve member to move to a different selected position (such as closed or open, respectively). A third piston member and a biasing member thereon can also be utilized. In some embodiments, a fluid is preferably held in compression between selected piston members.

Abstract: The invention relates to a leak control system (1) in two-stringed pipe installations and a method of executing a leak control system comprising one stop valve (2) with an associated flow meter (3) arranged in the supply pipe (4) of the pipe installation, and one stop valve (5) with an associated flow meter (6) arranged in the return pipe (7) of the pipe installation, said stop valves (2,5) as well as associated flow meters (3, 6) being connected to a control box (8), said box (8) comprising one valve monitor (9) connected to each stop valve (2, 5) to control/record the possible state of the individual stop valve (2, 5): open or closed, as well as an executer which, in combination with the control logics of the control box and the operating conditions of the pipe installation, controls/monitors the valve monitors (9) during a given sequence of actions, said leak control system (1) being capable of performing a number of measurements and data collections to evaluate the functionality of the stop valves (2, 5)

Abstract: Apparatus for detecting and abating an overpressure condition and an underpressure condition in a pressurized fluid. A collapsible buckling pin is supported between a valve assembly and a control assembly. The control assembly comprises a retractable support member moveable between an extended position and a retracted position. A biasing member applies a retraction force to urge the support member to the retracted position. A compressive force is applied to the pin by the valve assembly in relation to a pressure of the fluid, and this force nominally retains the support member in the extended position. When the pressure of the fluid exceeds an upper operational limit, the pin is mechanically deformed; conversely, when the pressure falls below a lower operational limit, the pin advances past the support member. In both cases the mechanical displacement of the pin allows the valve assembly to establish a secondary path for the fluid.

Abstract: Featured is an automatic high-negative pressure relief valve and its use in combination with an apparatus for draining fluid from a body. In broad terms the negative pressure relief valve includes a biasing mechanism, a moveable member acted upon by the biasing mechanism and a seating surface. When the pressure within a chamber, in which a portion of the relief valve is in fluid communication with, is less than a predetermined negative pressure, the moveable member is moved by the biasing mechanism to sealing engage the seating surface and when the pressure is at or above the predetermined value, the restoring force of the biasing mechanism is overcome and the moveable member moves away from the seating surface. In an exemplary embodiment, the biasing mechanism is a spring, diaphragm or wave washer.

Abstract: A dual piston/poppet valve in a fuel dispenser works with a two-stage valve to help eliminate errors from an inferential flow meter. When the two-stage valve opens partially, a secondary fuel path is opened in the dual piston/poppet valve. A sensor detects the opening of the secondary fuel path and reports its opening to a control system. The two-stage valve opens fully and a primary fuel path is opened concurrently. During transaction completion, the two-stage valve partially closes, resulting in the closing of the primary fuel path. When the two-stage valve closes completely, the secondary fuel path closes. The sensor detects the closing of the secondary fuel path and reports the closing to the control system. Based on the outputs of the sensor, the control system accepts or declines input from a flow meter.

Abstract: A flow control valve is disclosed wherein a housing defines a flow chamber with an inlet and an outlet. Disposed within the flow chamber is a poppet assembly comprising an inner poppet and an outer poppet. A first spring is selected to bias the outer poppet to seal closed the inlet below a predetermined fluid flow rate. Above the fluid flow rate, the force of the fluid against the outer poppet compresses the spring, breaking the seal and allowing fluid to flow into the fluid flow chamber. Inside the outer poppet is an inner poppet which extends from the outer poppet. A second spring biases the inner poppet predominantly within the outer poppet, but an increased pressure inside the outer poppet collapses the second spring and extends the inner poppet in a fully extended position. Fully extended the inner poppet shuts the outlet of the fluid chamber thereby arresting the flow.

Abstract: A pressure activated valve for a three-way connection between a catheter, an injector and a pressure transducer is disclosed. The valve includes a body that has an inlet for connection to an injector, an outlet for connection to a catheter and a secondary connection for connection to a pressure transducer. The body also includes a seal seat disposed between the secondary connection in both the inlet and the outlet. The body is flexibly connected to a plug seal. The plug seal is disposed between the seal seat in both the inlet and the outlet. The plug seal is movable between an open position spaced apart from the seal seat and biased towards the inlet and the outlet and a closed position against the seal seat thereby isolating the secondary connection from both the inlet and the outlet.

Abstract: A wellhead safety valve control system for opening and closing subsurface and surface safety valves in a predetermined sequence and certain components used with such control system. Dump valves in both latching and non-latching configurations are utilized within the control system. Embodiments of the dump valve may incorporate a time delay feature to ensure the subsurface safety valve is closed after a desired time period following the closure of the surface safety valve in the event of flowline anomalies. Provision is made for independent closure of the surface safety valve without closure of the subsurface safety valve.

Abstract: A mechanical leak arresting valve is disclosed in which fluid through the valve is limited to a range between a predetermined minimum flow rate and a predetermined maximum flow rate, and where both a small or large downstream leak mechanically causes the valve to lock closed. The present invention uses a locking mechanism triggered by a pressure differential resulting from the downstream leak to block the flow of fluid through the valve until the fluid source upstream is stopped. Reduction of the upstream pressure by the stopping of the fluid source automatically resets the valve without further manipulation.

Abstract: A valve actuator with an emergency shutdown feature incorporates shutdown of the valve when a sensed line pressure is outside of high- and low-pressure trip points. The actuator can be manually tripped. The actuator can be tripped in the event of a fire or, incorporating a solenoid, a trip can be accomplished with an appropriate signal. Once tripped, the actuator requires manual reset. The normal open and closed operation of the valve cooperates with a clutching mechanism which is part of the trip system. The preferred embodiment of the clutching system is a torsion spring or springs which normally allow movement in one direction but not in the other unless acted upon by the tripping system.

Abstract: A wellhead safety valve control system for opening and closing subsurface and surface safety valves in a predetermined sequence and certain components used with such control system. Dump valves in both latching and non-latching configurations are utilised within the control system. Embodiments of the dump valve may incorporate a time delay feature to ensure the subsurface safety valve is closed after a desired time period following the closure of the surface safety valve in the event of flowline anomalies. Provision is made for independent closure of the surface safety valve without closure of the subsurface safety valve.

Abstract: An indicator for a pilot, particularly a two-line pilot to visually indicate whether a pilot has responded to a pressure condition within a flowline which pressure condition is outside a predetermined range. The visual indication also indicates whether the pressure condition is above or below the predetermined range.

Abstract: A gas flow safety valve assembly having a main housing of generally solid rigid construction with a main interior chamber divided into an upper compartment and a flow through compartment by a primary diaphragm. Further, the main housing includes an inlet passage leading into the flow through compartment and an outlet passage leading out of the flow through compartment. Upon a gas flow pressure within the flow through compartment dropping below a predetermined minimum acceptable gas flow rate, the primary diaphragm is downwardly displaced resulting in the engagement of a primary displacement member connected thereto with a lever element pivotally positioned within the main housing.

Abstract: A two line pilot valve used to exhaust hydraulic fluid from a control circuit when the operating conditions within which a flowline is intended to operate are outside of predetermined limits. The pilot exhausts fluid within a control circuit to a reservoir which allows a dump valve to dump fluid from an actuator which causes the actuator to close the flowline. The pilot has a first poppet sleeve which contacts an o-ring. When the poppet sleeve and o-ring separate, fluid is allowed to pass from the inlet port of the pilot to the exit port and thereby exhaust the fluid of the control circuit.

Abstract: A propane gas distribution system according to the present invention substantially enhances safety by providing a gas lockout device within the enclosure containing the distribution lines to the propane appliances for closing off a gas distribution line in response to either a sensed low pressure level or a sensed high pressure level. The closure member within the lockout device is biased closed, but is normally prevented from closing by a stop member which in turn is held in position until the unsafe low pressure or unsafe high pressure condition exists. A security control member is utilized for restricting the re-opening of the lockout device to select personnel, which typically would be a propane company representative. According to the method of the present invention, gas from the high pressure source is regulated and output to a low pressure gas distribution line.

Abstract: An emergency shut-down system to close a gate valve in a pipeline and therefore terminate flow. The closing action is initiated when a pilot valve senses pressure in the pipeline outside predetermined limits. This reduces the signal pressure in the system which, in turn, causes a fluid dump from the gate valve actuator which closes the gate valve and terminates fluid flow in the pipeline. The system is reactivated by manually pumping the system which re-opens the gate valve and allows fluid flow in the pipeline to again continue.

Abstract: The improved valve of the present invention is a self-contained emergency safety shutdown valve which does not require the attendance of an individual or an outside power source for its emergency shutdown. The valve illustrated is a gate valve with the gate movable between positions opening and closing flow through the valve and having a stem which is controlled by a ball shaft extending through a rotary ball nut with means for preventing rotation of ball nut in one direction and means urging stem, gate and ball shaft in a direction closing flow through the valve. The control means controlling the release of the rotation preventing means is controlled by both high and low pressure responsive devices which are interconnected to a plunger for operating the release and to a plunger for sensing the pressure downstream of the valve.

Abstract: A pressure responsive pilot control valve has a spool which is movable by a metal diaphragm sensing the pressure in a flowline. The spool includes two poppet seal rings mounted thereon, the poppet seal rings having concentric axes and which are used for opening and closing fluid ports. The fluid ports are opened and closed for the purpose of sending a signal to a latching relay valve to bleed off a shut in valve actuator which will terminate flow in the flowline. The poppet seal rings of the pilot move responsive to a high or a low pressure condition. A low pressure spring is provided for measuring a low pressure condition and a high pressure spring is provided for measuring a high pressure condition.

Abstract: An emergency shut-down system to close a gate valve in a pipeline and therefore terminate flow. The closing action is initiated when a pilot valve senses pressure in the pipeline outside predetermined limits. This reduces the signal pressure in the system which, in turn, causes a fluid dump from the gate valve actuator which closes the gate valve and terminates fluid flow in the pipeline. The system is reactivated by manually pumping the system which re-opens the gate valve and allows fluid flow in the pipeline to again continue.

Abstract: A flow control device insertable into a pressurized fluid line upstream of the fluid utilization device for automatically terminating the flow thereto upon the occurrence of any one of a number of predetermined conditions, such as a leakage in or to the utilization device, an excessive quantity of the fluid supplied to the utilization device, and/or the supply of the fluid at an excessive rate to the utilization device. The control device is electrically controlled by a power supply which is normally disconnected from the control system and is connected thereto only when there is flow to the utilization device, so as to conserve the energy of the power supply when no fluid is flowing to the utilization device.

Abstract: A latching trip valve for opening and closing a safety device. The trip valve is operable manually and from the pressure of a pilot circuit which monitors the operating conditions of a pipeline. A floating seat is movable under the influence of a longitudinal movable poppet and its included seal means. The floating seat and seal means forms a closed passage until the pressure of the pilot circuit decreases whereas the passage is opened.

Abstract: A method and apparatus monitor fuel pressure in a heating system where a controller controls actuation of fuel valves. A fuel pressure limit signal is provided to the controller for determining if the fuel pressure crosses predetermined thresholds. In order to avoid nuisance shut-downs, the fuel pressure limit signal is ignored by the controller for a predetermined time interval after the controller has actuated a fuel valve.

Abstract: The device comprises a body consisting of a top half shell and a bottom half shell, coupled to one another through the interposition of a resilient membrane which defines a pressure control chamber and a pressure reducing and metering chamber, communicating with a delivery gas outlet, the bottom half shell defining a coupling end piece with the valve of the gas pressure vessel, and a quick coupling being moreover provided, operating between the end piece and the valve, which quick coupling is adapted to operatively engage with the operating handle of a gas control valve of the adjusting device for preventing the adjusting device from improperly engaging with or disengaging from the gas pressure vessel as the gas control valve means is in its open position.

Abstract: In order to control the tightness of a central heating system (10, 11) which may be connected to a district heating system (1, 2), the system is provided with a flow meter (8, 9) and a valve (6, 7) in the flow (3) and return pipes (4), respectively. Hereby it becomes possible to monitor the liquid flow through the flow meters (8, 9) and in a control unit (15) to compare the signals from the flow meters (8, 9) in order subsequently to produce a signal for an electric motor on the inflow valve (6) when a certain limit value is exceeded in order to shut off the flow of water into the system (10,11) and to a signalling device (16), if any.

Abstract: In a gas pressure regulator a switch valve is provided in a throttle nozzle between an inlet passage and a pressure sensing chamber containing a diaphragm controlling a lever arrangement. The pressure regulator is capable of both pressure reduction and automatic shut off if there is a leak due to gas line damage or other conditions. Preferably a restoring mechanism is provided to reset the regulator after its automatic shut off.

Abstract: A surface pipeline safety valve having a tubular member telescopically movable in the housing for controlling the movement of a valve closure member, a rod piston and cylinder assembly contacting and moving the tubular member in response to pressure in the bore of the housing in which the second side of the assembly is in communication with the atmosphere. High and low pressure responsive mechanisms for closing the valve. Seals in the assembly and high and low pressure responsive mechanisms are replaceable from the exterior of the housing.

Abstract: A valve system for a hydraulically controlled starting friction clutch for motor vehicles, a clutch pressure control valve that controls the clutch pressure as a function of the torque demand of the driver, a valve arrangement that modulates a pressure dependent upon the engine speed and that delivers it to the clutch pressure control valve, a shuttle valve 11, a throttle orifice 12 and an accumulator 13 associated with the clutch pressure control valve 1. The shuttle valve 11 comprises a valve member 15 disposed in a valve bore 14 with three control lands 16, 17 and 18 and a spring 19 that acts upon one end of the valve member 15. A pressure signal Ppitot dependent upon the speed is applied by way of lines 21 and 22 between the first control land 16 and the second control land 17 and between the second control land 17 and the third control land 18 and is supplied by way of outlets 23 and 24 and a line 10 to the clutch pressure control valve 1. A pressure signal P.sub.

Abstract: An improved pilot control relay valve is disclosed to monitor pressure conditions in a pressurized system and to cause the system to shut down in response to detection of operating pressures excessive of an acceptable pressure range. Accurate monitoring is provided for by dual-piston action, with one of the pistons actuating a visual indicator mounted on the slide valve of the control relay valve, and with the second piston coaxially mounted within the first piston.

Abstract: The housing (5, 6) of the regulator contains a medium-pressure chamber (10) to which gas is supplied from the cylinder when a self-closing cylinder valve (2) is open and which communicates with the regulator outlet (14) through a further valve (b 13), and a low-pressure chamber (23) in open communication with the outlet. The medium-pressure chamber (10) has a diaphragm wall (15) with a spindle (16) for controlling the cylinder valve (2). The low-pressure chamber (23) has a diaphragm wall (22) for controlling the further valve (13) through a connecting rod (20) carried by the diaphragm wall and coacting at its upper end with a manual selector (21) and at its lower end with the valve opener spindle (16). By means of the selector the connecting rod may be locked in a raised position in which the cylinder valve (2) is closed.

Abstract: A conduit-break valve for a double conduit (10, 11) has a pressure relief device (28) with a pilot controlled check valve (41, 42) with a control piston (37) which is actuated by the pressure in the space (26) between the double conduits (10, 11) and opens the check valve (41, 42) when a limit value determined by the spring (43) thereof is exceeded. The check valve (41, 42) thereby relieves the pressure in a fluid lock which is formed by a piston and cylinder mechanism (17, 18) the cylinder (18) of which is normally kept closed by the check valve (41, 42) and the piston (17) of which is connected to the main valve member (16) of the main valve, whereby said valve member will be moved to closed position by the action of a pressure spring (19) when the check valve (41, 42) is opened.

Abstract: Disclosed is a pressure controller for sensing changes in a service pressure and controlling a control pressure in response to such changes. The pressure controller includes a valve body having a control inlet and a bleed outlet with a passage therebetween. A valve seat is positioned in the passage and a valve member is reciprocatingly mounted in the valve body for movement between a closed position in engagement with the valve seat and an open position out of engagement with the valve seat. The controller includes a releasable latch for latching the valve member in the closed position. The controller includes a release mechanism for releasing the latch in response to changes in service pressure to allow the valve member to move to the open position.

Abstract: A three position, high and low, block and bleed fluid pressure sensor, wherein a piston contained within a cylinder is urged in one direction by a fluctuating sensed fluid pressure and opposed by a single spring located within said cylinder housing. The cylinder housing includes inlet and outlet ports, and at least one venting port. When the equilibrium of the forces between the spring and the fluid port pressure places the piston in a first position, the inlet and outlet port are allowed to communicate by way of an internal passageway formed within the piston and the sensed fluid may pass therethrough. When the pressure exerted by the fluctuating port pressure is greater or lower than the desired range, the piston will assume a second or third position wherein the inlet and outlet ports are misaligned whereby the inlet port is blocked and the outlet port merely discharges residual fluid through one of the venting ports.

Abstract: A high pressure in-line test valve (42) is positioned to block off a first fluid pressure source (10) acting on a control valve means (32 and 34) and to provide communication with an alternate test fluid pressure source (138) for testing the control valve means. The test valve (42) has a central bore (70) in which a depressible piston (78) is positioned for longitudinal movement between a seated extended position (FIG. 2) blocking the first fluid pressure source and simultaneously communicating test fluid to the control valve means, and an unseated retracted position (FIG. 3) re-establishing communication between the first fluid pressure source and the control valve means and simultaneously blocking the alternate fluid pressure source (138) with a dual sealing means.

Abstract: A relay valve for controlling fluid flow to and from a valve actuator included in a safety system for a flowline such as a production line of an oil or gas well. The relay includes a slide valve (60) which is manually pushed inwardly to the open or set position and held therein by pilot fluid which is also applied to the valve actuator. A visual indicator mounted on a knob (102) of the slide valve is operated by fluid applied to a passage (96) formed in the slide valve. A vent port (82) prevents pilot pressure from moving the slide valve from the closed position to the open position. A modified relay valve (150) has separate inlet ports (198 and 200) for receiving pilot fluid and actuator fluid and a vent port (206) which is in direct fluid communication with the pilot port in the closed position of the slide valve.