Abstract: A hydraulic valve in a load responsive pressure flow compensated system for operating a header height cylinder including a lockout check valve which is opened by an accompanying plunger experiencing pressure in an adjacent motor port. Said plunger includes a metering notch opening to drain when the plunger is actuated, said metering notch is sized larger than the flow-sensing notch on the valve spool so that while lowering the machine header, the pressure compensating means of the system does not go to full pressure compensation level but rather stands by at the low pressure level relieved across the lockout actuating plunger. The valve further includes metering notches in the control valve spool which are so shaped that a FLOW vs. TIME curve of the spool from the neutral position to an operating position has a plateau at a time interval from zero which is substantially equal to one-half of the cycle time of the natural frequency of the machine.

Abstract: A protective fluid system having a fluid pump and a fluid control valve and a fluid protective valve and a fluid motor all connected together. The protective valve is responsive to a loss of pressure in a fluid line, such as when the line breaks, and the valve then closes to avoid the reaction of the fluid motor which may be a powered cylinder assembly under the influence of a load, and thus the load does not fall or otherwise move when the pressure is lost in the cylinder assembly.

Abstract: The hydraulic apparatus includes a valve which is closable to prevent fluid from flowing out of a cylinder chamber when the pressure of the fluid drops below a predetermined level, and a transmitter which opens the valve so as to keep the chamber pressure constant when a piston slidably received in the chamber moves due to heat-caused expansion of the fluid in the chamber. The apparatus is disclosed in the context of an aircraft spoiler control system.

Abstract: A control apparatus for a hydraulic power consumer, particularly in agricultural machines, has a pressure medium reservoir which is connected with a member for supplying pressure medium from the reservoir to the user to thereby move the latter from a stationary position. This member is subject to pressure oscillations which result from a pressure difference which is created in this chamber on displacing of the consumer from the stationary or neutral position. In order to eliminate undesirable oscillations of the user on displacement of the latter from the stationary position the arrangement is provided with a member for damping these pressure oscillations.

Abstract: The present invention relates to a hydraulic brake booster and a shuttle valve which is operable to limit the pressure communicated to a pressure chamber within the hydraulic brake booster. The shuttle valve is disposed within a control valve which is operator-actuated to communicate pressurized fluid to the pressure chamber so as to provide a power assist to braking via a piston responsive to pressurized fluid in the pressure chamber. The shuttle valve is exposed to the pressure chamber and movable relative to the control valve when the pressure in the pressure chamber is above a predetermined value in order to terminate or decrease communication of pressurized fluid to the pressure chamber. At the same time the shuttle valve cooperates with the control valve to reopen communication to an outlet as the control valve operates to close communication thereto during braking.

Abstract: An improved hydraulic control circuit is disclosed for use in crawler type vehicles and the like in which relief valves as used in conventional circuits are eliminated. The resulting hydraulic circuit is not apt to be damaged by surge pressures and high pressures in the return passages, are simple in their design and more convenient to fabricate.

Abstract: A hydraulic system for raising and lowering a load by means of a fluid motor includes a counterbalance valve which controls the flow of fluid to and from the motor. The counterbalance valve has a pilot operated metering orifice which passes fluid from the motor when the load is lowered and a compensator valve which maintains a fixed pressure differential across the metering orifice. This results in a fixed flow of fluid through the metering orifice when the load is lowered.

Abstract: A pneumatic actuator in which a piston and a cylinder define an annular gap therebetween axially connecting two portions of the cylinder cavity otherwise separated by the piston. When compressed air is admitted to one of the cavity portions, an O-ring in an annular groove of the cylinder wall is expanded by the compressed air and seals the gap, and the piston is moved against the restraint of a strong compression spring. When the air backing the O-ring is vented, the air pressure in the cylinder drives the O-ring back into the groove, and air thereafter escapes quickly from the one portion of the cavity through the gap and into the other cavity portion which is open to the atmosphere. The resulting quick movement of the piston by the expanding compression spring is transmitted to a device outside the cylinder for operating the same.

Abstract: An electronically controlled pipe fracture safety device for operating devices which are fed by a hydraulic pump and which are actuated by a control slide value by means of hydraulic cylinders. Control lines branch off from lines which lead from the hydraulic pump via a control slide valve to the hydraulic cylinders, the control lines feeding the hydraulic medium to a differential flow monitor, on the piston of which a permanent magnet is fastened. The latter, by means of a reed contact as a result of a pressure difference existing between the control lines, which pressure difference is brought about by damage or fracture of a line, produces a signal in the NOR gate, the latter forming the input of a scoring logic. This signal retransmits a self-holding signal to NAND-gates which form a flip-flop. The self-holding signal causes deenergization of a relay and consequently an interruption of the current flow to the control slide valve and brings about the locking position of the latter.

Abstract: The hydraulic lifting device for harvesting machines includes a hydraulic cylinder-piston unit mounted on the wheel frame of the machine and supporting most of the weight of the harvesting apparatus so that the latter abuts against the ground with residual weight only. The cylinder-piston unit is controlled by a multi-way selector valve and a locking valve unit connected in a first working pipeline system. The hydraulic device further includes a pressure limiting valve for setting a reference pressure for the hydraulic cylinder-piston unit, the limiting valve being connected in an additional working pipeline that is branched upstream the limiting valve to a nonreturn valve and therefrom is connected by a direct conduit to a hydraulic accumulator and the hydraulic cylinder-piston unit.

Abstract: An actuator device for actuating ejector of a scraper comprising a first actuator having a long stroke, a second actuator having a short stroke, said first and second actuators being connected and fixedly secured in series so that the piston rod of said second actuator can be brought into contact with the piston of said first actuator, and valve means which normally permits the communication between the delivery side of a hydraulic pump and a pressure chamber of said first actuator and which also permits the communication between the delivery side of said pump and the pressure chamber of said second actuator when the pressure within the pressure chamber of said first actuator has increased beyond a predetermined value.

Abstract: A method of temporarily maintaining the position of a hydraulically, pneumatically or electrically driven drive apparatus by sensing the movement of the drive apparatus and then supporting the drive apparatus by the components to be controlled.

Abstract: The invention relates to a fluid pressure supply system for controlling a servomotor and in particular the forward speed of the servomotor, such as the raising speed of a fork lift truck, independently of the actual loading on the servomotor. This is accomplished with the combination of a pressure responsive regulating and reducing valve and a throttle valve in the supply branch of the circuit. The pressure regulating and reducing valves have setting elements that are loaded in opening directions by desired value springs and by a pilot pressure tapped between the reducing valve and the throttle valve.

Abstract: A hydraulic system including a hydraulic pump, a hydraulic motor having at least one port and a hydraulic reservoir. A main spool valve is interposed between the motor and the pump and reservoir and has a spool shiftable between positions connecting the pump to the port, connecting the reservoir to the port, and blocking fluid flow to or from the port. A single combination check and flow control valve is interposed between the main spool valve and the port. A fluid responsive surface opens the combination valve to permit relatively free flow of fluid therethrough when the spool is in the first mentioned position thereof. A pressure responsive surface and a control valve provides for partial opening of the combination valve to meter fluid flow therethrough when the spool is in the second position thereof. A spring is operative to close the combination valve to prevent fluid flow therethrough when the spool is in the last mentioned position thereof.

Abstract: A combination pressure reducer and flow control valve which includes a valve body and cover means having an upstream port and a downstream port, and two parallel fluid flow passages interconnecting said ports. An adjustable differential pressure valve means is operatively mounted in a first one of said two parallel fluid flow passages for reducing the upstream pressure of fluid entering the upstream port to provide a reduced downstream pressure at the downstream pressure port. A check valve means is operatively mounted in the second one of said two parallel fluid flow passages and it is operative to check the flow of fluid through said second one of said two parallel fluid flow passages when fluid is flowing through said first one of said two parallel fluid flow passages, and to allow flow of fluid through said second one of said two parallel fluid flow passages when fluid is exhausted into said downstream port and out the upstream pressure port.

Abstract: A valve controls fluid flow to a fluid jack by movement of a single valve spool to a first position. A check valve and bypass valve cooperate to pass fluid exhausted from the fluid jack to a tank bypassing the single valve spool. Movement of the bypass valve is controlled by developing a controlled pressure drop between the fluid in the fluid jack and the fluid between the check valve and the single valve spool in response to the valve spool being moved to a second position.

Abstract: A control valve is provided between a direction-changeover valve and an actuator in a fluid-pressure operating system. This control valve includes a body having an inlet and an outlet; a fluid passage interconnecting the inlet and the outlet; a valve body and a valve seat which are cooperative with each other to define a clearance therebetween and positioned within the fluid passage; a spring for resiliently urging the valve body toward a constrictive position to where a diminished clearance is defined between the valve body and the valve seat; and pressure responsive means for displacing the valve body in an opposite direction against the force applied by the spring thereby enlarging the clearance and bringing the valve body to its fully open position. An adjusting rod enabling adjustment of the first position of the valve body is provided, and a pilot piston operates under a pilot fluid pressure applied through a pilot port for forcing the valve body to its fully open position.

Abstract: A fluid supply circuit for supplying three motors includes means for sequentially connecting two of the motors to the supply conduit of the third motor as the pressure in the supply conduit rises through first and second threshold levels. The circuit includes a manual override for suppressing the automatic sequential action. The circuit is applied to the control of the booms and bucket of a hydraulic excavator, and provides for semi-automatic digging.

Abstract: A control circuit for a hydraulic cylinder and shaft assembly to regulate movement of the shaft relative to one end of the cylinder. The circuit has a fluid pressure supply and associated reservoir and a metering valve with interconnected normally closed passage means connected at one end to the one cylinder end and at an opposite end to the reservoir. The fluid pressure supply, in a first condition, supplies fluid under pressure to the one cylinder end, and, in a second condition supplies piloting fluid under pressure for actuating the metering valve to regulate the fluid flow from the one cylinder end to the reservoir through the normally closed passage means.

Abstract: A combination pressure regulating and flow control valve which includes a valve body and cover means having an upstream port and a downstream port, and a fluid flow passage interconnecting said ports. An adjustable pressure regulator valve means is operatively mounted in said fluid flow passage. A check valve means is operatively mounted in parallel with said adjustable pressure regulator valve means, and it is operative to check the flow of fluid through said fluid flow passage when fluid is flowing through said fluid flow passage from the upstream port to the downstream port, and force it through the regulator valve means, and to allow flow of fluid through the check valve means when fluid is exhausted into said downstream port and out the upstream pressure port.

Abstract: An arrangement for controlling the flow of a hydraulic fluid between a pump, a user and a fluid reservoir includes a main control slide, an auxiliary control slide accommodated in a compartment provided in one end of the main control slide, a flow-regulating valve arranged in parallel to the main control slide between the pump and the fluid reservoir and a holding valve arranged in a pressure conduit section between the main control slide and the user. The main control slide is shiftably received in a bore which has a plurality of annular chambers arranged therealong. The main control slide has a plurality of lands separated by respective recesses, the lands, depending on the position of the main control slide, establishing or interrupting the communication between the respective chambers.

Abstract: A fluid circuit including an actuator, a flow-direction change-over valve and a pressure source. The actuator includes a piston-rod-side chamber and a piston-head-side chamber which are partitioned by a piston. In a fluid path leading from the piston-head-side chamber to the flow-direction change-over valve, there is provided a flow-rate-control, pressure-regulating valve assembly for regulating a fluid pressure to be fed into the piston-head chamber, thereby saving energy required for a return stroke of a piston. In another fluid path leading from the piston-head-side chamber to the flow-direction change-over valve, there is provided a check valve and throttle valve assembly. The check valve in the valve assembly may be of a type which allows the flow of a fluid only in the direction towards the piston-head-side chamber (a meter-in control) or may be of a type which allows the flow of a fluid only in the direction from the piston-head-side chamber (meter-out control).

Abstract: A hydraulic motor and control system therefor which includes a pump for delivering fluid to a control valve, the control valve having a Float position which connects a first end of the motor to a sump, a First position for applying fluid from the pump to power the motor in a first direction by delivering fluid to the first end of the motor via a flow path and a Second position in which the motor moves in a second and opposite direction. A conduit connects the control valve to the sump. A check valve is provided in the flow path which always allows flow therethrough towards the first end of the motor and normally blocks reverse flow therethrough and also a mechanism for opening the check valve to allow reverse flow therethrough responsive to operation of the control valve in the Float position and in the Second position.

Abstract: A hydraulic motor and control system which comprises a pump delivering fluid to a control valve. The control valve has a Float position which connects a first end of the motor to sump, a First position for applying fluid from the pump to power the motor in a first direction by delivering fluid to the motor's first end via a flow path and a Second position in which the motor moves in a second and opposite direction. A conduit connects the control valve to the sump. A check valve is provided in the flow path which always allows flow therethrough towards the motor's first end and normally blocks reverse flow therethrough. A mechanism opens the check valve to permit reverse flow therethrough responsive to operation of the control valve in the Float position and in the Second position.

Abstract: A control unit for controlling the supply of fluid to a hydraulic jack, the control device including a main valve having a valve member normally held closed by pressure in a pressure chamber, the pressure chamber being fed with fluid through a bore in a valve member of the main valve. In one embodiment, a valve spindle slides in the bore to stop it being blocked. In another embodiment, designed to control a double-acting jack, the main valve is associated with a second similar main valve the pressure chamber of which is fed from the first main valve instead of through a bore in its valve member.

Abstract: A self-responsive fluid means for anti-cavitation, such as when a fluid motor is rotating in a manner beyond that induced by the fluid pressure fed thereto, and thus the motor itself acts in the nature of a pump to produce a cavitation effect. Thus, there is a fluid motor, a valve controlling flow thereto, a pump, and an additional valve which directs the exhaust from the fluid motor and back to the motor itself, under certain conditions of operation, all to avoid the cavitation effect. The latter valve includes two fluid inlet openings and a movable closure which controls fluid flow to a fluid outlet opening; and pressure relief valve are incorporated in that valve and thus permit and control flow to the reservoir when pressure is at a certain magnitude.

Abstract: A pressure governor valve having a casing with an inlet on the primary side and an outlet on the secondary side thereof. A passage is formed in the casing and communicates the inlet with the outlet. A pressure governor valve is mounted in the casing for closing said passage on the inlet side thereof, and a flow control valve is interposed at an intermediate portion of the passage between the outlet and the pressure governor valve.

Abstract: The self-actuating fluid holding system includes a fluid pump and two fluid valves and two fluid motors all fluid-flow connected together. The valves are arranged to sense the proportionate flow therethrough and to the two motors, and when the flow is out of proportion, such as when one of the connecting lines or a connection breaks to permit the fluid to leak, then the valves have shut off closures which protect the system against fluid leakage.

Abstract: An arrangement for controlling a hydraulic motor having a movable member with opposite faces to be impinged by pressure fluid, in which first valve means serve to direct pressure fluid against a respective one of the opposite faces to thus control the direction of movement of the movable member, and in which second valve means connected in a hydraulic circuit with the first valve means serve to control the speed of the motor in connection with control means actuated by the movable member for controlling the change of the speed dependent on the position of this member.

Abstract: A fluid power system including a fluid power cylinder having a piston and fluid ports at its opposite ends, a directional valve for selecting the direction of piston actuation, and a metering control valve coupled between the directional valve and the cylinder. The control valve includes a cylinder section having a control piston therein and a valve body connected to the cylinder section and having a valve spool-receiving cavity therein. The valve body has first and second fluid ports therein communicating with the cavity, one of the valve body ports being coupled to one of the power cylinder ports and the other being coupled to the directional valve. A valve spool is disposed in the valve body cavity operatively connected to the control piston and movable therewith, the spool having a passage therein.

Abstract: A fluid source for delivering fluid to a control valve having Float, First direction and Second direction positions. A piston-bore check valve allows flow to the motor and normally blocks reverse flow, the piston having its first end biased against a seat. A control chamber communicates with the piston's second end. Flow is restricted between the motor's first end and the control chamber and there is a full flow path between the motor's first end and the bore to provide a force acting against the piston's first end. The control chamber connects with a sump. A drain valve entry port communicates with the motor's first end and an exit port thereof communicates with the sump to provide either entry port-exit port connection or blocking. A mechanism moves responsive to shifting of the control valve to shift the drain valve to connect the entry and exit ports when the control valve is in a Float or a Lower position and to block such connection in a Raise or Neutral position.

Abstract: A pressure-reducing device which incorporates, in a hydraulic actuating system provided with more than one circuit module, a flow rate control valve which is set at a lower flow rate value than the fluid supply rate from the hydraulic source and is installed in the supply side of a circuit module so as to control precisely the maximum working pressure of any of the said circuit modules thereby assuring that the maximum working pressure is at a value lower than the maximum pressure value set by a main relief valve installed in the fluid supply side leading from the hydraulic source. A relief valve is installed in the lower stream of the said flow rate control valve so as to control its maximum working pressure.

Abstract: A two-stage regulator valve, particularly for regulating the operation of single acting hydraulic lift motors in lift trucks, which embodies a spool valve controlling first and second ports in the valve body and responsive at one end to lift motor fluid pressure. At the opposite end the valve is responsive first to the force of a first spring which closes the spool on one port when lift motor fluid is below a predetermined pressure, and secondly, following predetermined compression of the first spring during which both ports are opened to exhaust pressure fluid from the lift motor, to the added combined force of a lift motor pressure responsive piston and a second spring. The piston forms with the spool valve a differential area response to said fluid pressure and together with the second spring regulates the position of the spool valve so as to variably restrict the other port to control the exhaust from the lift motor inversely as a function of the fluid pressure therein.

Abstract: A fluid cylinder assembly includes a cylinder and a piston slidably disposed in the cylinder, the cylinder having a cylinder bore closed at both ends by end caps. One of the end caps is provided therein with a flow control valve assembly for controlling the fluid flow from the cylinder bore during a working stroke of the fluid cylinder assembly. The flow control valve assembly comprises a poppet valve having a pair of poppets on a valve rod and a spool valve movable in response to the operation of the poppet valve. The poppet valve is shiftable by a solenoid alternately energized and de-energized by an electric control circuit which is closed just before contact of a cutter on the piston rod with a workpiece.

Abstract: The present invention relates to a control device for a controlled non-return valve provided in large hydraulic distributors. During the mode of operation where the double acting hydraulic ram is in a non-movable state, a means is utilized to communicate a control pressure to the one-way non-return check valve to positively maintain the check valve in a closed state thereby eliminating the accidental opening of the return valve and maintaining the double acting hydraulic ram in its initial position.

Abstract: A cylinder locking apparatus primarily intended for use on counter-balanced lift trucks incorporating lift cylinders of the single-acting type, comprising a positive sealing poppet-type check valve which operates in the normal manner when the system is in the raise mode, but which in the lowering mode is operable by controlled pilot means triggered manually by the system's main control valve spool, thus permitting the load to be lowered by gravity.

Abstract: A motor grader including a main frame mounted on steerable wheels, a drawbar frame mounted on the main frame, a working implement carried by a circle gear rotatably mounted on the drawbar frame and a hydraulic control circuit is described. An improvement in the control of the working implement is disclosed in which continuous downward force is exerted on the circle gear at all times during operation by hydraulic rams. Preferred embodiments of the invention are described wherein the force is exerted by hydraulic means including wear surfaces in contact with the circle gear and wherein the hydraulic control circuit is adapted to provide automatic operation.

Abstract: A safety valve for use in a compressed air line having a supply valve and a control valve, to prevent inadvertent sudden shifting of the controlled part when the line is exhausted and later repressurized. The safety valve comprises a normally closed piston-operated poppet valve, the piston chamber and outlet port being connected to the supply port through a bypass with an adjustable restriction upstream of the valve member. In one embodiment, the adjustable restriction comprises a replaceable plug threaded in the valve body. In a second version, the adjustable restriction comprises a needle valve mounted in a housing cover.

Abstract: A main valve controls the flow to a load in a first or second direction depending upon the signal applied to a pilot valve. A spool of the main valve is biased to a central position blocking flow by springs. A throttle valve having an adjustable restrictor area is connected in one line between the main valve and the load. The restrictor area is adjusted in correspondence to an input signal. The spool is moved to a first or second extreme position by the pilot valve. The pressure difference developed across the throttle valve is applied to the spool in a direction to force the spool towards the central position. The spool is balanced at a predetermined pressure difference across the throttle valve.

Abstract: An oscillatory electro-hydraulic system for a material handling bucket and including two hydraulic cylinder assemblies connectable with the bucket for tipping the bucket, and including a hydraulic pump and control valve and pressure relief valve and a reducing valve, all for directing flow to the respective cylinder assemblies. An electric system is interconnected with the assemblies and with one of the control valves, for controlling the flow of fluid to one of the two cylinder assemblies.

Abstract: A compensated work port fluid valve is provided wherein a directional control valve having an inlet chamber, an outlet chamber and a work chamber is provided with a compensator valve connected to the work chamber and having a pressure sensing compensator valve controlling the flow of fluid from the work chamber to a work port to maintain constant pressure at the work port.

Abstract: In a drill boom pivotally supporting a rock drilling apparatus, hydraulic parallel motion means is provided which includes a hydraulic pilot cylinder for sensing the setting of the elevation angle of the drill boom. During elevating of the drill boom the hydraulic pilot cylinder is furthermore used as an additional elevating cylinder.

Abstract: The invention may be used with a boom or the like which is raised and lowered by double-acting hydraulic cylinder means provided with a pilot-actuated safety valve at its bottom such that the boom can only go down when pilot pressure (normally from the downthrust line) is applied to this safety valve. The main manual valve has a four-position spool which provides a float position reached by moving through the lowering position. As the main valve is moved to the float position, its manual actuation mechanism actuates an auxiliary valve to supply pilot pressure to the safety valve to open the safety valve to allow the cylinder to achieve the desired floating action. This pilot pressure supply is through a shuttle valve which alternatively lets pilot pressure be applied to this safety valve as here stated or, from the downthrust, without ever connecting the two sources.

Abstract: A unitary pilot-operated bi-directional cylinder lock valve and pressure-compensated flow control valve arrangement, having a common housing with internal porting connecting a pair of oppositely acting normally closed check valves operated to open by fluid pressure in one direction thereagainst on the inlet side and by a common free-floating inlet-pressure-responsive pilot piston therebetween. Also in the common housing and ported in line with each of the check valves are two pressure-compensated flow control valves which restrict fluid flow through the check valves as a function of flow pressure. The pressure-compensated flow control valves are also oppositely acting and each senses and acts to reduce fluid flow in response to pressure build-up in an opposite direction from that of the other.

Abstract: A differential pressure sensing valve has an axially shiftable spool including axially-spaced spool areas on which a pair of pressure sources connectable with such valve act in a predetermined direction with spool shifting force. Biasing means normally biases such spool with spool shifting force in a direction opposite to the predetermined direction. The opposite spool shifting forces are substantially balanced over the normal operating range of the pressure sources for maintaining such spool in an operating position for normal flow of fluid through the valve. Such opposite spool shifting forces are substantially unbalanced for shifting such spool out of such operating position when the pressure sources substantially deviate from their normal operating range.

Abstract: A counterbalance valve assembly for controlling the lowering of an actuator driven load including a housing with a passage connected to deliver fluid to or from one side of the actuator. A main pilot-operated lock check valve is provided in this passage to selectively block flow from the actuator when it is desired that the load be held and also to move to an open position permitting return flow from the actuator with the open valve defining an orifice. The speed of the load is controlled by maintaining a constant pressure drop across this orifice with a compensator valve upstream of the main check valve, which serves the purpose of throttling flow from the actuator to the check valve.

Abstract: A load supporting hydraulic system having a pilot operated main control valve is provided with pilot controlled load check valve operative to permit free flow of fluid from said control valve toward the load supporting means of the system in response to pilot pressure and to block fluid flow from the load supporting means toward the control valve. The system includes vent valve means operative with the main control valve to permit the load check valve to be opened by fluid pressure in the load supporting means to allow fluid flow therefrom to the reservoir.

Abstract: A hydraulic load lifting system having a vented load check valve disposed in the main control line connected between the load supporting end of a hydraulic motor and a spool-type control valve to normally isolate the load generated pressures from the control valve is provided with venting apparatus which is operative to selectively prepressurize the main control line between the control valve and the load check valve prior to the venting of the load check valve and the shifting of the control valve to effect the lowering of a load being supported by the hydraulic motor so as to substantially balance the pressures on the opposite sides of the load check valve to prevent momentary load drop and hydraulic hammering.

Abstract: A pressure reducing valve mechanism maintains pressure in one of the service passages of a control valve at a desirably low value except at times when the control valve element is actuated to a position effecting flow of pressurized supply fluid to said service passage for delivery to a motor governed by the control valve.

Abstract: A safety valve for use in a compressed air line having a supply valve and a control valve, to prevent inadvertent sudden shifting of the controlled part when the line is exhausted and later repressurized. The safety valve comprises a normally closed piston-operated poppet valve, the piston chamber and outlet port being connected to the supply port through a bypass with an adjustable restriction upstream of the valve member. In one embodiment, the adjustable restriction comprises a replaceable plug threaded in the valve body. In a second version, the adjustable restriction comprises a needle valve mounted in a housing cover.