Abstract: To provide a hydraulic drive system for a work machine capable of securing a favorable operability in the case where hydraulic fluid discharged from a hydraulic actuator is regenerated for driving other hydraulic actuator.

Abstract: A double valve includes a first unitary valve assembly and a second unitary valve assembly. Each unitary valve assembly includes a first outlet port, a second outlet port, and a spool. A first pilot assembly and a second pilot assembly are coupled to the first unitary valve assembly and the second unitary valve assembly, respectively. A plate is coupled to the unitary valve assemblies and includes a passage to provide a first common outlet passage that is coupled to the respective first outlet ports of the unitary valve assemblies and a second common outlet passage that is coupled to the respective second outlet ports of the unitary valve assemblies. When the spools are in a first position, fluid flows through the first common outlet passage, and when the spools are in a second position, the fluid flows through the second common outlet passage.

Abstract: A shovel according to an embodiment of the present invention is a shovel including a boom cylinder and an arm cylinder. The shovel includes a hydraulic motor driven by hydraulic oil flowing out of the boom cylinder, a regenerating oil passage configured to supply the hydraulic oil flowing out of the boom cylinder to the hydraulic motor, a reusing oil passage configured to supply the hydraulic oil flowing out of the boom cylinder to the arm cylinder, and a reusing flow control valve configured to control a flow rate of hydraulic oil flowing in the reusing oil passage.

Abstract: A solenoid valve including a spool received within a housing. The spool is configured to move to multiple positions within the housing. The housing includes supply ports, exhaust ports, and outlet ports. When the spool is in a specific location, two outlet ports are in fluid communication with each other.

Abstract: The invention discloses a valve arrangement for supplying pressure medium to a hydraulic load (2) having a directional valve (8), which has an inflow measuring diaphragm (10, 12) and a directional part (14, 16) flowing in the flow direction. The directional valve is associated with an individual pressure scale (18). In a return from the load, a load-lowering valve (44, 46) is provided, to which a pilot pressure is applied in the opening direction. According to the invention, said pilot pressure is tapped in channel between the pressure scale and the directional part.

Abstract: A hydraulic valve device includes a fluid connection arrangement (10) having different connections and a mobile control (18) for at least partially controlling connections of the fluid connection arrangement (10). The control (18) is provided with load reporting and load detecting connections (32, 38; 34, 36). According to the displacement position of the control (18), at least one part of the connections of the fluid connection arrangement (10) are interconnected in a fluid-guiding manner. The control can then be brought with precision into the required functional positions, with a favorable dynamic driving behavior.

Abstract: A positioning system includes an actuator, valve (preferably pneumatic), position sensor and an electronic valve controller, integrated in a single unit. Continuously variable setpoints are possible within the range of operation. A preferred control circuit includes a signal converter, a ramp generator to smooth the shape of the command or target value signal applied, a position feedback sensor to report the actual position of the actuator, a controller, and a driver, containing an H-bridge, for controlling the pneumatic valve which feeds air into the actuator mechanism. Integration of all these components into a single unit shortens signal paths, improves resistance to electrical noise, and permits faster response time.

Abstract: The invention concerns a hydraulic valve arrangement (1) with a working connection arrangement having a first working connection (A) and a second working connection (B), both working connections (A, B) being connectable with a hydraulic consumer (2), a supply connection arrangement having a pressure connection (P) and a tank connection (T), a first valve arrangement with a first valve (12), closing the pressure connection (P) or connecting it in a controlled manner with the first working connection (A) or the second working connection (B), a second valve arrangement with a second valve (16), closing the tank connection (T) or connecting it in a controlled manner with the first working connection (A) or the second working connection (B), and a control arrangement controlling the first valve arrangement and the second valve arrangement. In such a valve arrangement, it is endeavoured to achieve improved operation behaviour.

Abstract: A distributing valve for a speed governor of a turbine is provided, the distributing valve having a structure to reliably vent air therefrom. The distributing valve is disposed such that the direction of movement of a plunger is horizontal, with air vent valves being provided at the highest portion of each of ports of the distributing valve, to facilitate reliable venting of air out of a pressure oil system. Also provided is a structure of the distributing valve to facilitate machining or assembly of the distributing valve.

Abstract: In a continuously variable transmission with a toroidal variable speed drive, in which a roller is supported pivotably between two toroidal disks for transmitting motion between the two toroidal disks at transmission ratios which depend on the pivot position of the roller according to pressure forces acting on a hydraulic actuating piston, for the purpose of varying the transmission ratio, two regulating slide valves are provided, each including a regulating slide with control edges to act upon the hydraulic actuating piston via a hydraulic medium under the control of the regulating slide valves each controlling the pressure in one of the chambers arranged at opposite ends of the actuating piston.

Abstract: A swing speed compensation device is provided for use with a flow sharing hydraulic system. The present invention is mounted within the metering spool of a flow sharing valve and includes a poppet that is attached to a spring retainer. The spring retainer encases a compression spring which pushes against a plug and has a drain hole that, depending upon the position of the spring retainer and poppet combination, can vent excess pressure within the present invention to a hydraulic pump tank. When a flow sharing hydraulic system starts or stops, there is a rush in the fluid flow that can cause a spike in the system pressure. The present invention absorbs this pressure spike, allowing for the fluid flow to gradually increase or decrease as the system starts or stops.

Abstract: By means of a method and a device for controlling a lift cylinder (2) of working machines, wherein the hydraulic oil from the pressure cylinder space (12) is forced via a control element (3) into the suction cylinder space (11) during lowering by an external force, it is possible in particular to achieve automatic changeover between normal operation and an operating condition in which an additional force in vertical direction can be exerted.

Abstract: In a machine tool by pulse drive of a hydraulic system, a piston of a hydraulic cylinder is connected with a table, and an outflow valve and an inflow valve, which form a pair, are respectively connected with a right and a left hydraulic chamber. When the feed table is moved to the right, for example, control is conducted so that the valve-opening period of one valve can be a portion in the middle of the valve-opening period of the other valve. Since a portion of pressure in the hydraulic chamber is canceled, an effective pressure, the pulse width of which is narrow, remains. Accordingly, even in the case where a common inexpensive electromagnetic valve is used, it is possible to accomplish a smooth feed motion.

Abstract: A fast-acting valve includes a valve body and a spool slidably mounted within the valve body between first and second limit positions. Both the spool and the valve body have a flow passage which come into alignment with the valve spool at a position intermediate the first and second limit positions and spaced therefrom by a given distance. That given distance allows the spool member to accelerate in travel from the first and second limit positions to the valve open position so that the opening of the valve (and closing) occurs quite quickly. Reciprocating movement of the valve spool relative to the valve body can be provided by springs mounted in opposing ends of the valve body bore in cooperation with solenoids mounted on opposing sides of the valve body. The fast-acting valve may be modified into the form of poppet valve or a cartridge valve.

Abstract: A fluid control valve system for controlling the flow of hydraulic fluid supplied to and discharged out of an actuator having first and second actuator ports, comprising: a valve housing having a pressure sensing chamber for sensing the pressure of the hydraulic fluid introduced therein and a pressure port for introducing a hydraulic fluid; a valve spool axially movably received in the valve housing; valve spool operating means having the valve spool axially moved and including a force motor, a piston rod having the valve spool slidably received thereon and driven by the force motor, and a fixed piston firmly connected with the piston rod; and resiliently urging means for resiliently urging the valve spool along the center axis of the valve housing, the valve spool being urged by the hydraulic pressure of the hydraulic fluid in the pressure sensing chamber and the resiliently urging means to assume operation positions consisting of normal operation positions where the hydraulic pressure of the hydraulic fluid

Abstract: The present invention relates generally to agricultural machinery and, more particularly, to a device for controlling a double-acting steering cylinder of a steering system, having two working connections of the steering cylinder, wherein the working connections are each connected by means of an input pipe or an output pipe to a valve unit, which comprises two switching valves that can be moved alternately into a first switching position and into a second switching position and the steering cylinder in the first switching position of the first switching valve admits a fluid at the first working connection and the steering cylinder in the second switching position of the second switching valve admits the fluid at the second working connection.

Abstract: A hydraulic circuit for a boom cylinder in a hydraulic shovel has a pressurized discharge fluid from a hydraulic pump that is driven by an engine, the pressurized discharge fluid supplied via a directional control valve for a boom into a retraction pressure chamber and an extension pressure chamber of a boom cylinder for swinging the boom upwards and downwards. A relief valve is included in a circuit for connecting the retraction pressure chamber of the boom cylinder to the boom directional control valve, the relief valve having a relief set pressure. A switching device is included for switching the relief set pressure to a low pressure as well as to a high pressure if the directional control valve is set at a position that is other than a neutral position thereof, when the engine is driven, the switching device being adapted to switch the relief set pressure to a high pressure when the engine is halted.

Abstract: A valve control system for controlling the operation of a pressure fluid-activated device such as a hydraulic cylinder includes a valve housing having an internal, sealed valve chamber therein. A valve spool is slidably disposed for lengthwise movement within the valve chamber, the valve spool having a valve member for selectively admitting a pressure fluid through passages in the vale housing. A movable handle for manual operation of the valve is connected to the valve spool by a connecting mechanism, whereby movement of the handle causes lengthwise movement of the valve spool relative to the valve housing. A neutral-centering tactile feedback mechanism applies a return force to the handle when the handle is in an operative position. The return force varies in proportion to the pressure of the pressure fluid within the valve, which pressure actuates the device. The feedback mechanism ceases to apply the return force when the handle returns to a neutral position.

Abstract: A fluid control apparatus which communicates a fluid cylinder with a fluid supply passage and a return passage, and a piston of the fluid cylinder is connected to a spoiler of an airplane.The fluid control apparatus comprises a hydraulic passage and a check valve. The hydraulic passage is capable of communicating with cylinder chambers located at both sides of the piston. The check valve is opened by hydraulic pressure generated by backward movement of the piston.The fluid control apparatus has a blow down valve characteristic so that the piston is allowed to move only in one direction by an external force when supply of fluid to the actuator is stopped because at least one of the supply passage and the return passage is damaged.The fluid control apparatus further has a retainer and a manually operable member.The retainer communicates the return passage with the hydraulic passage capable of communicating with cylinder chambers of the actuator.

Abstract: The device comprises a lever movable by the operator between at least two working positions and a neutral position to achieve, by means of an hydraulic actuator of double acting follower type, of the gear ratios in one stage of the gear box. The actuator comprises a piston slidable between two working positions and one neutral position to actuate engagement means and defining two chambers; and a shaft connected to the lever by means of a motion transfer unit and shaped as an hydraulic distributor in such a way that in the neutral position of the lever the chambers are connected to a discharge opening so as to determine the neutral position of the piston, and in a manner and in an operative position the stroke of the shaft causes communication of one chamber with the opening and of the other with an inlet opening for a fluid under pressure such that the pressure will translate the piston in the same direction and with the same stroke as the shaft. (FIG. 4).

Abstract: A valve assembly for an energy transfer unit comprises a source of hydraulic fluid, a reciprocating valve member reciprocable from an open position to a closed position, a slidable sleeve assembly whereby the hydraulic fluid is selectively allowed to force the valve member into the open position or into the closed position, and a solenoid, for selectively operating the slidable valve assembly to provide for the open or closed position. The slidable sleeve assembly comprises a first sleeve half portion and a second half portion, each sleeve half portion having at least one fluid-passing aperture defined therein. Two chambers are provided, an upper chamber and a lower chamber, for selectively receiving pressurized fluid therein. Whether the valve member is in the closed position or in its open position depends upon whether or not fluid is entering or exiting the respective upper chamber and lower chamber.

Abstract: The invention concerns an electrical reversing switch, which is especially suited for switching of high-frequency electrodes. This switch has an over mounted pneumatic cylinder, which moves on pistons arranged on both sides, and thus produces electric contacts.

Abstract: A fast acting valve actuator for actuating an intake or exhaust valve in an internal combustion engine of a type which is hydraulically powered and command triggered is disclosed and includes a cylinder with a power piston having a pair of opposed working surfaces or faces reciprocable within the cylinder along an axis between first and second extreme positions. A cylindrical control valve is located radially intermediate the reservoir and the cylinder, and is movable upon command to alternately supply high pressure fluid from a reservoir of high pressure hydraulic fluid to one face and then the other face of the power piston causing the piston to move from one extreme position to the other extreme position. The cylindrical control valve may be a shuttle valve which is reciprocable along the axis of the power piston between extreme positions with control valve motion along the axis in one direction being effective to supply high pressure fluid to move the piston in the opposite direction.

Abstract: A valve with four passages controls a piston (15) disposed in a cylinder (16). Between the body (1) of the valve and the cylinder (16) is disposed a plate (23) having passages (24, 25) which are used and a passage (26) which is not used in FIG. 1. By turning plate (23) 180.degree., the passage (24) is located in the non-use position, while the passage (26) connects the conduits (19 and 13) in such a way as to cause the space (21) of the cylinder (16) to communicate continuously with an exhaust orifice (6).

Abstract: A directionally controllable air cylinder has a set of circumferentially disposed air passages formed at each end of a closed tube. A sleeve manifold surrounds the tube and is pneumatically sealed thereto by means of a plurality of O-rings. The O-rings are positioned such that they selectively expose the sets of air passages to the manifold for receiving compressed air and to the atmosphere for venting. The direction of piston movement is determined by the set of passages exposed to compressed air. A pilot piston moves the manifold in response to a pilot air signal in one embodiment and an electrically operated solenoid moves it in another version. The manifold may also be manually or mechanically moved to operate the air cylinder. Hydraulic cylinders utilizing fluids, other than air, are also disclosed.

Abstract: A pneumatic reciprocator includes a cylindrical air cylinder concentrically mounted within a cylindrical manifold. A cylindrical sleeve valve is concentrically mounted for movement along the manifold by a pair of spaced O rings. Two sets of circumferentially arranged air holes in the manifold are alternately covered and uncovered by the O rings as the sleeve valve is moved to selectively pressurize and vent opposite sides of the piston in the air cylinder. Movement of the sleeve valve is controlled by stops on the movable bed of a surface grinder that is controlled by the air cylinder.

Abstract: A hydraulic system has a rotary valve which controls multiple hydraulic dces such as double-acting piston type actuators and which prevents deactivated devices from creeping. The valve has an outer housing and a rotatable inner member which form high pressure inlet, low pressure outlet, and control stages. The control stages utilize partial commutators (part circumferential grooves) and ports on the valve member selectively to couple control ports of the housing respectively to the inlet stage or the outlet stage by rotating the inner valve member (the control ports being connected to the hydraulic devices). At the inlet and outlet stages, the valve member has full annular commutators which communicate continuously with a high pressure inlet port and a low pressure vent port of the housing as the valve member is rotated. The valve member also has internal passageways which connect each control stage partial commutator and fluid port to either the inlet commutator or the outlet commutator.

Abstract: A hydraulic operated control system for remotely operating a walk-behind soil compactor. A remotely operated three-position valve is connected to the pressure line of the hydraulic system of the soil compactor and serves to control the flow of hydraulic fluid to opposite ends of a hydraulic cylinder unit that is operably connected to a hydraulic pump which operates the speed and direction control for the compactor. The cylinder unit includes a piston that is slidable within the cylinder and the piston is biased to a neutral position by springs. Through remote operation of the valve, hydraulic fluid will be directed to either end of the cylinder to provide direction and speed control for the compactor. A deadman switch is located on the remote control panel and manual release of the deadman switch will open the hydraulic circuit between the opposite ends of the cylinder to prevent fluid from being directed to the cylinder and will enable the springs to return the cylinder to a neutral no speed position.

Abstract: A hydraulic control valve having a valve housing including a cylindrical valve bore, the valve bore being in communication with a supply port, a discharge port and first and second delivery ports each with first and second openings to the valve bore. A valve pin is slidable within the valve bore, the valve pin including first and second pin grooves operable to establish communication between the supply port and either of the delivery ports to the exclusion of the other delivery port, the supply port and discharge port communication being establishable through corresponding valve bore openings of respective delivery ports. Supply port communication with one of the delivery ports is establishable simultaneously with discharge port communication with the other delivery port.

Abstract: An improved jam compensating control valve (45) includes a spool (65) which blocks and unblocks a flow passage through the valve. The spool is slidably disposed within an inner sleeve (60) which, upon jammed interengagement with the spool moves therewith, thereby connecting drain passsages (180, 182, 185, 190 and 195) in the surface of the spool with outlet passages (120 and 125) communicating with an associated actuator (5) for actuator draining in response to such valve jamming.

Abstract: A rotating servomotor apparatus for use in rotating guide vanes in a hydraulic machine, wherein for the purpose of suppressing occurrence of flow-induced vibrations, there is provided a bearing to support wicket gates, a rotating servomotor which includes a movable spindle projecting in the axial direction and which has a plurality of movable partition members, a cylinder having a plurality of stationary partition members disposed around the spindle, and a plurality of compartments partitioned between the movable partition members and the stationary partition members; and a first distributing valve connected to one side of plural compartments within the cylinder of the rotating servomotor means, a second distributing valve connected to the other side of plural compartments within the cylinder of the rotating servomotor means, wherein the respective distributing valves have valve piston members sized and arrangeable with respect to fluid inlets and outlets to define a neutral position in which fluid is supplie

Abstract: The control valve for an hydraulic actuator is provided with a particular operating state for venting the hydraulic system, which state is attainable positively whenever the hydraulic pressure is inadequate, e.g., in the case of venting or presence of air bubbles; a pressure-monitoring element permits positively the slide element of the control valve to be placed into the venting disposition, in that a particular stop on the slide rod cooperates with a plunger extending from the monitoring cylinder and being subject to the differential force between a spring and system pressure.

Abstract: A four-way poppet valve having a housing provided with a pair of parallel bores, and a pair of valve stems slidably supported within the bores, each valve stem having one or more elastomeric poppets thereon for controlling fluid flow. A supply port communicates with one of the bores, whereby flow therethrough is controlled by the respective shiftable valve stem through intermediate passages to the second bore, which second bore communicates with both the exhaust port and a pair of load ports. The shiftable valve stem in the second bore respectively controls flow between the ports which communicate therewith. The bores, and the valve stems associated therewith, define various chambers which cooperate with the poppets on the respective valve stems for confining therein fluid pressure so that the valve poppets, when in a closed or seated condition, are always urged in the seated direction by the fluid pressure.

Abstract: The invention relates to an automatic rigging arrangement for an actuation system wherein the rigging arrangement includes in combination a differential length feedback device that has a moveable inner member and an outer member, with the outer member secured at its ends respectively to a power drive unit and an actuator, the moveable inner member being controllingly coupled to a power drive control and secured to an actuator position feedback member of the actuator to thereby provide via the moveable member of an actuator position feedback input signal to a signal summing means associated with the power drive control. The feedback input signal being proportional to an actuator position and the signal summing means being responsively coupled to the power drive unit to receive as an input, a signal representative of a given position commanded.

Abstract: A sectional hydraulic valve has clamped together an inlet section, an outlet section and at least one working section which can be integral with the inlet and/or outlet sections. Fluid supply and return passages are formed in the sections and are in register at each junction where there are formed contiguous planar sealing surfaces. A depressed area is provided in one of the surfaces surrounding the contiguous planar sealing surfaces of the supply and return passages and a groove containing a sealing ring is formed in one of surfaces around the depressed area. A drain passage leading to a low pressure region opens into the depressed area and should there be leakage between the sealing surfaces of the supply and return passages, particularly as a result of the presence of high pressure in said passages, the leaked fluid merely passes into the depressed area and flows through the drain passage to the low pressure region without subjecting the sealing ring to pressure and possible leakage there past.

Abstract: A compressed air motor comprises a cylinder with a piston slidable in said cylinder and connected to a compressed air inlet through a slide valve mechanism which alternately admits respective opposite sides of the cylinder with compressed air for driving the piston in the opposite direction, and which also alternately vents the side of the cylinder in which the piston is moving. The construction includes an action rod mounted for movement in a direction parallel to the piston on each side thereof which is contacted by the piston after predetermined movement thereof. A snap-action lever mechanism is connected between the action rod and the slide valve mechanism so that the action rod, through the snap-action lever mechanism reverses the slide valve during each motion of the piston. The action rod member is returned to its starting position during the return movement of the piston by means of a stop member connected to an extension of the piston.

Abstract: Hydraulic servo-mechanism having a housing in which is defined a cavity with an input member and an output member mounted coaxial therein and each supporting a single sprocket. In a bore of the housing having its axis perpendicular to that of the input and output members, a distribution spool is slidably disposed, with push rod and means facing its respective ends for imparting movement thereto. A double sprocket is rotatably mounted at each outer end of the respective push rod means. The housing rotatably supports another double sprocket which is disposed in substantially the same plane as the sprockets of the input and output members. A first chain meshes with the sprocket of the input member and a first set of the teeth of each of the double sprockets. A second chain meshes with the sprocket of the output member and a second set of the teeth of each of the double sprockets.

Abstract: A safety steering system to control torque rotation for boats having directable propeller outboard motors capable of pivoting about a vertical axis. An arm extending from the motor is connected to a flexible cable having two ends, a first end connected to a steering device and a second end connected to the arm. An actuator control valve interposed along the flexible cable is capable of locking the arm in a single position when no force from the cable is being exerted on the arm. The control valve has a valve body with a central bore therethrough and a first external port and a second external port in fluid communication with the central bore. A hydraulic piston-cylinder is connected between the end of the motor arm and a tab in the motor well. The hydraulic cylinder has a first chamber of confined liquid and a second chamber of confined liquid.

Abstract: A polarity control valve enables the undiscriminating interconnection of a pressure line and a return line to two available ports to provide fluid pressure at an output line and a return connection through a return port. This feature of interconnecting either the pressure line or the return line to any of the two available ports is achieved by a pressure positionable spool mounted in a ported sleeve. The spool is positionable between one of two positions depending upon which port is connected to the pressure line. By controlling the distribution of lands on the spool the position thereof always establishes a fluid path from the pressure line to an output port connected to a fluid pressure responsive component. Fluid returning from the component is likewise directed by means of the positionable spool to the return line.

Abstract: A hydraulic engine having a fluid pump for pumping a fluid medium under pressure to a fluid motor connected to the pump for being actuated by the fluid medium under pressure received from the pump. A control system regulates operation of the pump and motor so as to permit appropriate variation of speed of an output shaft of the motor. The fluid motor is a reciprocating motor, the piston of which is connected directly to a mechanism for translating the reciprocating motion into rotary motion, while the reciprocating movement of the pistons simultaneously actuates valves for sequentially directing the fluid medium under pressure to opposite ends of the piston in order to obtain a double-acting piston and cylinder operation.

Abstract: In working cylinders whose power stroke can be shifted to different operating positions in two consecutive steps, the invention provides a control cylinder which is actuated independently of the generation of working pressure. The control cylinder acts on a joint lever which alters the distance between two separate parts of the power transmission to the tool and thus the effective length of the transmission. This arrangement has the advantage of small working volumes and low energy consumption.

Abstract: A fail-safe fluid control valve including a first sleeve fixedly accommodated in a valve housing, a second sleeve reciprocably movably received in the first sleeve. The first and second sleeves are suitably grooved and ported, and the valve spool is formed properly with annular flanges. When there occur such abnormal conditions that the second sleeve and the valve spool are jammed or stuck to each other, the second sleeve is adapted to be moved in unison with the valve spool to actuate the fail-safe fluid control valve under entirely the same conditions as normal conditions.

Abstract: A fluid flow control valve which includes a body formed to define a chamber having inlet, outlet and actuating ports for supplying and receiving fluid to and from external hydraulic machinery to be actuated and including a valve spool formed with several lands and slidably arranged in the chamber for controlling the flow of fluid through the ports, in which the lands and ports are located and arranged so that some of said ports transmit fluid only from said chamber outward while the remainder of the ports transmit fluid only from the ports into the chamber, and which also includes a matrix of restrictors interposed in each of those ports which transmits fluid outward from the chamber, and in which the lands are arranged to control the flow of fluid through only those ports which transmit fluid outward while leaving the flow of fluid into the chamber through the remaining ports unimpeded for all positions of the spool.

Abstract: A hydraulic exciter of vibrations for a vibratory compactor includes an exciter containing a piston which is movable to and fro in the cylinder and either the piston or the cylinder is connected to a compacting member. The movement of the piston in the cylinder is brought about either by an alternating source of hydraulic fluid pressure which forces fluid alternately into and out of the exciter cylinder to move the piston to and fro or by means of a uni-directional source of hydraulic fluid under pressure formed by a hydraulic pressure pump together with a control valve in between the pump and the exciter cylinder. The control valve is operated to switch the supply of hydraulic fluid to and fro in the cylinder from one side of the piston to the other to produce the relative to and fro movement of the piston in the cylinder. The control valve has means for varying its speed of operation to vary the frequency of the vibrations produced by the exciter.

Abstract: Control system including an hydraulic valve and cylinder and including apparatus for indicating to the operator the exact point when pressure fluid starts to flow to the cylinder.

Abstract: A steering shaft, linked with the dirigible wheels of an automotive vehicle and coupled with a hydraulic servomotor for rotation in either direction under the control of a main valve, has two abutments for alternately opening two normally closed ancillary valves in respective limiting positions of the shaft, these ancillary valves being inserted in branches of two feeder lines extending from the main valve to respective cylinder chambers of the servomotor. Either ancillary valve, when opened, connects one cylinder compartment of a differential valve to the feeder line then under low pressure, the other compartment of that differential valve being connected to a supply conduit whereby a pressure difference is created across a spring-loaded piston in that valve whose two compartments are interconnected by a bleeder line. The piston, upon being displaced by this pressure against its spring force, vents the supply conduit to the low-pressure side of the fluid source to arrest the servomotor.