Abstract: Servoactuator includes a pair of double-acting linear actuators providing for 360.degree. controlled rotation of an output shaft. The rotary motion of the ouput shaft is employed to sequence high pressure fluid flow and return for the same to the respective ends of the respective actuators so that both actuators continuously develop output force except for end stroke points. Shimmy damping may also be obtained by a bypass-damping valve which comprises a shuttle movable to a first position by high pressure fluid for controlled operation of the servoactuator and to a second position by removal of the high pressure fluid to direct fluid flow between the respective actuators through a damping orifice.

Abstract: A hydraulic flow control apparatus is provided which is adapted to provide a constant pressure differential between a pump and an external load. the apparatus includes a housing, and a balance piston slideably mounted therein. The pump pressure acts to bias the piston in a direction toward a pump bypass position, and the piston is urged in the other direction and toward its operating position by the consumer pressure and a spring. Means are also provided whereby the pressure of the pump necessary to move the piston toward its bypass position and against the force of the spring, may be minimized during operation in the idling mode, to thereby minimize power consumption.

Abstract: A device for hydraulically lifting agricultural implements by a lifting jack, utilizing a pump with constant stroke volume and a stepless distributor. A flow pressure regulator of the pump is piloted by the pressure of the lifting jack, a downstroke valve is provided for lowering the implements, and a relay valve connects to the reservoir the piloting pressure of the regulator in the downward movement of the implements. A reducing valve fed by the flow circuit of the pump feeds at least one pilot electrovalve of the stepless distributor.

Abstract: A hydraulic system including at least one hydraulic cylinder is provided with an anti-cavitation and overload relief valve having a housing, a first chamber within the housing in fluid communication with one end of the cylinder, and a second chamber within the housing in fluid communication with a fluid reservoir. A fluid passageway within the valve housing connects the first and second chambers. A movable valve assembly is positioned within the fluid passageway for operating in a plurality of modes for providing anti-cavitation and overload relief. The valve includes a stationary portion positioned within the fluid passageway between the first and second chambers having a valve seat. The movable valve assembly includes a poppet mechanism for sealingly engaging a valve seat of the movable valve element when the movable valve assembly is operating in first and third modes.

Abstract: A power brake system has a brake booster operable by differential air pressure provided by a source of vacuum and a source of compressed air pressure. The differential air pressure control valve assembly of the invention maintains a substantially constant available differential of air pressure between the vacuum and compressed air pressures available to the brake booster for booster operation. In the charging mode it directs air pressure from an air pressure pump to an accumulator connected to the pressure inlet side of the booster, charging until the desired pressure differential is attained. In the storage mode, the air pressure from the pump is permitted to flow in its usual manner to another device or circuit utilizing the air pressure. This may be, for example, a part of the vehicle engine emission control system. In the pressure relief mode, the control valve vents excess accumulated pressure to exhaust.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher by a constant pressure differential than the pressure required by the largest load being controlled and which while system loads are not being controlled using external source of pressure fully opens pump bypass and reduces the pump bypass pressure to a minimum level.

Abstract: A load responsive fluid control system in which system pump controls permit variation in the level of pressure differential in response to an external control signal and which uses direction control valves equipped with load responsive variable pressure differential positive load controls.

Abstract: PCT No. PCT/US79/01033 Sec. 371 Date Nov. 29, 1979 Sec. 102(e) Date Nov. 29, 1979 PCT Filed Nov. 29, 1979Heretofore the capability of operating a system (10), which supplies fluid to a hydraulic circuit (12), selectively at either a high or a low flow rate with only a single pressurized fluid source (14) has not existed. Such a system (10) includes a control valve structure (16) for controlling delivery of fluid from the source (14) to drive the circuit (12) and a flow control (22) for metering a portion of the fluid to the circuit (12). The capability of operating such a system (10) selectively at either a high or a low flow rate is advantageous in some modes of operation of the circuit (12). Herein, hydraulic circuitry (86) serves for controlling the magnitude of the portion in response to application of a signal thereto and a device (78) is provided for selectively applying the signal to the circuitry (86) for selectively directly controlling the magnitude of the portion.

Abstract: A control valve unit (10) disclosed includes a slide mechanism (14) mounted on a base (40) of the unit, a control member (18) driven by a hydraulic linear actuator (12) controlled by the unit, and a control valve (22) that feeds hydraulic fluid to the actuator and has a deactivator (24) that is engaged and moved by a pair of slides (16a,b) of the slide mechanism under the impetus of the control member movement in order to terminate driving of the actuator at its limits of movement. The slide mechanism includes a slideway on the base and a pair of fixed stops (62a,b) between which the movable slides are supported on the slideway and biased by a helical spring (68) against the stops. The helical spring is aligned with openings (66) in the slides and the control member (18) extends through the spring and the slide openings. Lugs (76a,b) on the control member for moving the slides are preferably adjustable so as to permit adjustment of the limits of actuator movement.

Abstract: A pressure relief valve for the working pressure of a servo-steering mechanism of a vehicle, with a pressure medium connection between a high pressure connection adapted to be placed under a working pressure and a zero connection adapted to be placed under a lower pressure, whose valve-adjusting member is retained in a normal rest position closing off the pressure medium connection during normal conditions by a control device operating as a function of an operating magnitude of the servo-steering mechanism and which upon exceeding a critical value of the operating magnitude is adapted to be displaced into a by-pass position more or less opening up the pressure medium connection; the control device thereby operates in dependence on the load of the servo-steering mechanism while the by-pass position is independent of the angle of rotation of the steering shaft of the servo-steering mechanism.

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: Two circuit breakers or circuit breaker modules are actuated by hydraulic jacks fed by supply and drain valves operated by a single closing-operation control unit. A differential pressure detector is subjected to the pressure of the two jacks. In the event of a relative variation in the jack-operating times, the free piston of the detector actuates a switching device which connects the supply and drain valves to the drain tank, thus preventing the complete performance of any non-simultaneous operation of the circuit breakers.

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: Hydraulic control.The unit is characterized in that it is provided, between an inlet well and an outlet well for pressurized fluid, with an obturator urged in the closed position by a resilient member arranged to act against the pressurized fluid in the inlet well in a chamber communicating with a conduit issued from the outlet well and separated from a return conduit by a relief valve which is urged in the closed position by a spring and by the fluid pressure prevailing in the inlet well.Application to transfer-machines with one single hydraulic station.

Abstract: A control valve adapted for use in working machines for hydraulically controlling the lifting movements of the working machine such as a rotary blade or plow connected to a power machine, said control valve comprising essentially a change-over valve for connecting or shutting off a cylinder port to or from a pump port or tank port by a spool operation, and a compensator for guiding cylinder port pressure into an oil chamber of a plunger on the spring loaded side for bypassing the pump discharge oil opposedly to the pump pressure, and characterized by provision of a passage for connecting the oil chamber of the compensator on said spring loaded side into the tank port or cylinder port through said change-over valve, whereby when said change-over valve is at its neutral or dropping position, said oil chamber is communicated with the tank port, and when said valve is at its elevating position, said oil chamber is communicated with the cylinder port.

Abstract: A flow control valve in fluid communication with a variable orifice which is utilized to control speed of a fluid motor, the valve providing a constant pressure drop across the variable orifice whereby consistent control of speed of the motor may be maintained.

Abstract: A regulation system for steam turbines which includes a servomotor controlled by a servovalve (1) and two safety valves (31, 31') controlled by two electrically-operated valves (19, 19'). When the control inlet (7) of the servomotor is connected to the drain pipe (6) by at least one of the safety valves, the high-pressure fluid supply to the servovalve is simultaneously cut and the high-pressure fluid source is thereby prevented from discharging directly into the drain pipe. This enables high-pressure fluid sources having a low discharge rate to be used.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher by a constant pressure differential than the pressure required by the largest load being controlled and which while system loads are not being controlled automatically reduces the pump bypass pressure to a minimum level lower than the constant pressure differential of the load responsive control.

Abstract: Fluid control valve apparatus is provided having a directional control valve for metering passage of fluid from a supply passage to a feeder passage for first actuator. A pressure compensating valve is provided for regulating flow through the directional control valve and for delivering excess fluid to a compensating valve output port for power operation of a second actuator. A main relief valve is connected to the first actuator feeder passage downstream from a metering portion of the directional control valve for sensing a first actuator stall condition. The main relief valve, when actuated, delivers fluid to a tank from a supply passage, through the metering portion of the directional control valve, and a relief passage including the main relief valve upon sensing an overload condition. The rate of flow through the relief passage is subject to limitation only by the metering portion of the direction control valve.

Abstract: A hydraulic system including at least one hydraulic cylinder is provided with an anti-cavitation and overload relief valve having a housing, a first chamber within the housing in fluid communication with one end of the cylinder, and a second chamber within the housing in fluid communication with a fluid reservoir. A fluid passageway within the valve housing connects the first and second chambers. A movable valve assembly is positioned within the fluid passageway for operating in a first mode to block fluid flow between the first and second chambers, for operating in a second mode to permit fluid flow from the first chamber to the second chamber only when the pressure in the first chamber exceeds the pressure in the second chamber by a first predetermined amount, and for operating in a third mode to permit fluid flow from the second chamber to the first chamber only when the pressure in the second chamber exceeds the pressure in the first chamber by a second predetermined amount.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher by a constant pressure differential than the pressure required by the largest load being controlled and which while system loads are not being controlled using external source of pressure fully opens pump bypass and reduces the pump bypass pressure to a minimum level.

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: An arrangement in the dropping of pressure in either chamber of a double acting booster steering servomotor is provided, such pressure drop starting at a predetermined point toward the end of travel of the servomotor piston in either direction. The invention is characterized by a respective bypass valve in each chamber, spring biased to closed position, and engageable by the piston, to be opened gradually. The piston force is exerted on the bypass valves through a respective spring so as to effect the gradual opening instead of the abrupt opening effected in the prior art. Opening of the bypass valves effects connections which shunt the servopump output to the system oil tank via a differential pressure valve as taught in Lang U.S. Pat. No. 3,878,763 to prevent strong mechanical stresses on the steering linkages at the ends of steering movement. Shunt control takes place through desirably small flow lines and bypass valves which heretofore have been found to produce undesirably abrupt operation.

Abstract: In an auxiliary power steering system, a steering linkage actuated limit valve assembly is maintained depressurized in its inactive state by one-way check valves blocking flow from the pressurized chambers of the steering servomotor and by by-pass valves which control the connection of the differential pressure operated valve to the vented chambers of the servomotor.

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 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 system for a fluid pressure-actuated cylinder or the like includes a pump supplying fluid from a reservoir to a control valve which may be selectively operated to cause cylinder extension or retraction and to immobilize the cylinder at a selected position. A unidirectional flow device connects an accumulator to the flow passage between the control valve and cylinder to smooth pressure fluctuations which can otherwise occur when the control valve is closed and which can otherwise produce erratic cylinder motions. Means are provided to relieve excessive pressure in the accumulator, at times when the control valve is shifted to release fluid from the cylinder, without in the process causing unwanted cylinder drift from feedback of the fluid from the accumulator to the cylinder.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher by a constant pressure differential than the pressure required by the largest load being controlled and which while system loads are not being controlled automatically reduces the pump bypass pressure to a minimum level lower than the constant pressure differential of the load responsive control.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher than the pressure required by the largest load being controlled. To obtain unidirectional flow, load sensing passages of individual valve spools are connected by check valves with the load responsive control, which is capable of fast response, without large control leakage from the load sensing circuit, in the direction to reduce fluid flow supplied to the system loads.

Abstract: A pressure responsive check valve permits fluid flow therethrough in a first direction and blocks fluid flow therethrough in the reverse direction until the fluid pressure at the blocked side exceeds a preselected pressure level at which time the check valve is controllably opened for reverse flow therethrough.

Abstract: A control valve arrangement is disclosed for regulating fluid communication between a source of fluid under pressure and a double-acting hydraulic motor, including a housing defining a bore, an inlet chamber in communication with the bore and the pressure source, a pair of service chambers in communication with the bore and the hydraulic motor for actuation thereof, and a plurality of drain passages in communication with the bore, a pressure transmitting circuit defined in the housing and in communication with the bore, a relief valve which is in responsive communication with the pressure transmitting circuit for variably controlling the pressure in the inlet chamber, and a spool reciprocably disposed in the bore of the housing and having a plurality of lands for blocking communication between the inlet chamber and the service chambers in a neutral position, with the spool having metering slots for communicating fluid from the inlet chamber radially outwardly to a selected one of the service chambers and to t

Abstract: A valve operator is disclosed for controlling an inlet valve to a large fluid-driven turbomachine such as a steam turbine. Such a valve is subject to a fast closing requirement under emergency trip conditions and at other times, the valve may be required to provide a precise steam flow regulating function. The present invention responds to these various requirements by providing a valve operator capable of fast closing by means of a disk-dump valve within the valve operator for rapid hydraulic fluid evacuation. In addition, the precise control of steam flow is accomplished by including a double-acting hydraulic cylinder within the valve operator.

Abstract: This invention relates to a three-way hydraulic valve, stable in two positions, intended for distributing a liquid containing impurities, comprising a ball valve whose ball is located in the first way, the inlet for said liquid, and has a seat located between the first and the second way, the pressure of said liquid applying said ball on said seat, a conical needle valve, a calibrated spring applying said needle on a seat located between the second and third way, said seat being of diameter smaller than that of the seat of said ball valve, and a manoeuvring rod outside the valve body, with which said needle is fast and which comprises an extension abutting on said ball and maintaining it open when the needle is closed.

Abstract: The invention is concerned with an improvement in a load lifting apparatus which comprises a primary load member pivotally mounted about a generally horizontal axis on a frame, a tilt cylinder and a tilt piston movable relative to one another pivotally connected to the frame and the primary load member to provide impetus for pivotal movement therebetween, a secondary load member movable relative to the primary load member, a lift cylinder and a lift piston movable relative to one another connected to the primary load member and the secondary load member to provide impetus for linear relative movement therebetween, tilt cylinder valve means for controlling flow of pressurized fluid from pump means to the tilt cylinder and lift cylinder valve means for controlling flow of pressurized fluid from the pump means to the lift cylinder. The improvement of the invention provides protection which prevents the apparatus from overbalancing. The improvement operates by sensing a moment created by a load on the apparatus.

Abstract: A load responsive direction and flow control valve for use in fluid power load responsive system. The valve maintains a selected constant flow level for control of both positive and negative loads, irrespective of the change in the load magnitude or change in the fluid pressure, supplied to the valve. When controlling positive or negative loads the valve maintains a constant pressure differential across a flow control metering orifice utilizing a single control slide member, first by throttling fluid entering the inlet chamber and then by throttling the fluid leaving the outlet chamber. The valve may be used with fixed displacement pumps, fixed displacement pumps equipped with differential pressure relief valves, with variable pumps equipped with pressure compensators and variable pumps equipped with differential pressure compensators.

Abstract: System and method to ensure that the pressure in a hydraulic pressure system is at a pre-determined level and is maintained for a pre-determined length of time.

Abstract: An electric and hydraulic servomechanism controlling device comprises a pressure governor valve, a hydraulic servomechanism actuated by the supply of the line pressure regulated by said pressure governor valve, and a change-over valve for shifting an oil passage that connects said pressure governor valve and hydraulic servomechanism. The change-over valve serves also as a pressure reducing valve thereby reducing not only the capacity but also the size of the necessary solenoid.

Abstract: An arrangement for limiting the steering-power in hydraulic servo-steering systems provided with a valve of the type of a three-way three positions valve for controlling a pressure flow from a pressure source to a working space of a preferably higher effective area of a servo-motor or from the working space to a return flow, in which the working space of a preferably lesser effective area is always connected with the pressure source, and the reaction areas with hydraulic reaction areas serve for signalling back a steering sensation to the steering wheel, which reaction areas are arranged to the various effective areas of the servo-motor, and, in combination with respective lever arms, etc., and/or respective reaction areas define a torque dynamometer, etc.

Abstract: In order to automatically switch an open circuit type hydraulic actuating circuit to the meter-in flow control system when the direction of the load is positive or to the meter-out control system when the direction of the load is negative or is reversed to negative, thereby controlling the speed of the load, there is provided a hydraulic actuating system in which an amplifier valve assembly of the type which may produce a main flow whose flow rate is amplified with respect to that of a pilot flow in proportion to the ratio of the opening area of a detector orifice inserted in a pilot flow passage to the opening area of a main orifice inserted in a main flow passage, is hydraulically and operatively combined with a meter-in flow control valve for controlling the flow rate of the pilot supply flow in the amplifier valve assembly, a meter-out flow control valve for controlling the flow rate of the pilot return flow, and a switching valve inserted between the pilot supply and return flow passages and adapted to b

Abstract: Hydraulic control apparatus for controlling the rate of flow of a fluent plastic from an injection nozzle of an injection molding machine wherein an injection ram is connected to a hydraulic piston in a hydraulic cylinder. The control apparatus controls the pressure exerted by a hydraulic fluid in the cylinder by means of a main hydraulic circuit including the cylinder, a valve and a pump connected in series and a main line pressure valve connecting in parallel a plurality of pilot pressure control valves having different pressure set points to the main line. The pilot pressure control valves are operated in sequence by an electrical relay and timer circuit, or a combination of such circuit and limit switches.

Abstract: A cushion valve arrangement for reducing the rate of pressure build up and relieving pressure rebounds in a fluid conduit. The valve housing defines first and second fluid ports, a fluid passage communicating therebetween, and a cushion passage communicating between the fluid passage and the first and second fluid ports. A valve spool is disposed in the fluid passage and defines an axial bore, within which is disposed a slideable valve member. When the pressure and flow suddenly builds up, the valve member is biased to an open position permitting high pressure fluid to pass through the axial bore and radially out through a passage in the spool into the cushion passage from which the fluid flows to the other conduit.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher than the pressure required by the largest load being controlled. To obtain unidirectional flow, load sensing passages of individual valve spools are connected by check valves with the load responsive control, which is equipped with a leakage control, maintaining a relatively constant leakage from load sensing circuit, irrespective of sensing circuit pressure and permitting fast response of pressure compensated load responsive flow control valve without excessive leakage losses.

Abstract: This disclosure relates to an improved electro-hydraulic pulse motor wherein safety valves are arranged in hydraulic circuits provided for the hydraulic motor part of an electro-hydraulic pulse motor so as to release abnormal high pressure produced in the circuits due to sudden interruption of the operation of an electric pulse motor part of the electro-hydraulic pulse motor. As a result, breakage of the circuits or four way pilot valve part of the electro-hydraulic pulse motor can be avoided.

Abstract: Hydraulic control valve arrangement for controlling the amount of pressure fluid flowing to a consumer, in which the valve member of a first valve, which selectively controls flow of pressure fluid to at least one consumer or from the latter to a return passage, forms a variable throttle between the pressure fluid inlet passage and a consumer passage connected to the consumer, in which the throttle causes a pressure difference, and in which the pressure difference may be maintained substantially constant by a bypass passage between the inlet passage and the return passage in which a second valve member is arranged which is biased by a spring to a closed position and by the pressure difference produced by the variable throttle to an open position.

Abstract: In a vehicle, such as a motor grader, having a work tool operated by at least one hydraulic cylinder, the position of the work tool being controlled by a main control valve, and the work tool being placed in a float condition by actuation of a second control valve, the improvement wherein the operator may override the float condition by actuation of the main control valve.

Abstract: A hydraulic system including a source of pressurized fluid, a plurality of hydraulic motors with a plurality of control valves for directing fluid from the source to the motors, a dual-stage relief valve for the system for normally establishing a first pressure for part of the system for some of the motors and a second pressure for part of the system for the remainder of the motors and responsive to at least a pair of the control valves of the system for establishing the higher pressure includes a balanced resolver valve disposed between the pair of directional control valves and the relief valve and operative to prevent simultaneous communication of the pair of valves with the relief valve.

Abstract: The invention relates to a hydraulic steering apparatus comprising a continuously operating pump, an operating motor for controlling the parts to be steered, a control device which is adjustable by the steering wheel and which, in its neutral position, connects the pump to a tank through a short-circuiting path. The control device has two operating positions in which the pump is connected to one side or the other of the operating motor and connects the other side of the operating motor to the tank. The control device has a control element connected to a steering wheel and a following element connected to a metering motor and these elements are relatively displaceable to a limited extent. Apparatus is provided to prevent the steering parts moved by the operating motor from stroking mechanical abutments.

Abstract: A fluid control circuit for regulating flow from a source of fluid under pressure to a hydraulic motor, including a control valve having a movable spool for communicating fluid entering an inlet chamber from the source with service chambers in communication with the motor, an inlet relief valve selectively pressurizing the inlet chamber in response to spring means and signal fluid received from the service chambers through signal passages. The control valve and its spool are configured to insure that the signal passages are always in positive communication either with one of the service chambers or a drain in order to facilitate manipulation of the spool. The control valve is also adapted to communicate signal fluid to the relief valve prior to communication of either service chamber with the inlet chamber in order to precondition the relief valve and improve response of the motor to manipulation of the control valve.

Abstract: The invention relates to a hydraulic steering unit for automotive vehicles. A main feature of the unit is that pressure relief means are provided for relieving excessively high pressures developed in the unit which are caused by the steered wheels encountering road obstacles. The unit includes a pump, a drain tank and a working motor which is connectable to the wheels to be steered. The working motor has complementary expansible chamber means and a control valve is connected to the motor with a pair of supply and exhaust conduits which are selectively connectable to the pump and the tank by the control valve. A shunt line is provided between the pump and the tank and a pressure relief valve is in the shunt line. A manually operated valve controlled by a steering wheel is connected to the pump and the drain tank. A pair of control lines are connected to the manually operated valve which are selectively connectable to the pump and the drain tank by the manually operated valve.

Abstract: A pressure compensated load responsive flow control valve for use in a system controlling a plurality of loads. The system is powered by a single, fixed displacement pump. The flow control valve is equipped with a load responsive control, which during simultaneous control of multiple loads automatically maintains the pump discharge pressure at a level higher than the pressure required by the largest load being controlled. To obtain unidirectional flow, load sensing passages of individual valve spools are connected by check valves with the load responsive control, which is equipped with a leakage control, maintaining a relatively constant leakage from load sensing circuit, irrespective of sensing circuit pressure and permitting fast response of pressure compensated load responsive flow control valve without excessive leakage losses.