Abstract: A hydraulic circuit suitable for use on power shovel or other construction machines, more specifically a hydraulic circuit for a cylinder in a hydraulic power transmission, of the type which is adapted to control pressurized oil flows to and from two oil chambers in the cylinder by switching the position of a directional control valve in communication with a pressurized oil source. The hydraulic circuit includes a logic valve provided between the directional control valve and a load-holding oil chamber in the cylinder. The logic circuit has first and second ports connected to the directional control valve and said load-holding oil chamber, respectively.

Abstract: A hydraulic lift valve system for fork lift trucks comprising a three way valve including a spool in a bore having a first neutral position, a second lift position and a third lower position. In the second lift position, the spool functions to apply fluid from a source to a cylinder for lifting the fork of the truck only after the pressure exceeds the load pressure and a predetermined value as established by a first poppet valve. Upon shifting to the third position the spool functions to permit exhaust of the fluid in the cylinder and therefore lowering the fork only after a predetermined pressure is established in a pilot valve which permits the first poppet valve to open, thereby insuring that the fork of the lift truck is not lowered unless there is a predetermined load on the fork. By this arrangement, the problem of uncontrolled descent of the fork upon engagement of the fork with an object is obviated.

Abstract: The drive control valve for constant speed is for driving a pneumatic actuator at a constant speed by use of a meter-out control mode, and includes a nonreturn valve for blocking discharged air from its pressure chamber and a relief valve for controlling the air pressure in the pressure chamber so as to be equal to an adjustable set pressure which is constant. When air pressure is supplied to one of the pressure chambers of the pneumatic actuator, the air pressure air discharged from the other pressure chamber is blocked by the nonreturn valve, so that it is discharged to the outside through a relief valve. In this case, however, the air pressure of the pressure chamber on the exhaust side is maintained at a set pressure for the relief valve which is set beforehand, and hence, the flow rate of air discharged from the pressure chamber becomes constant, and the pneumatic actuator is driven at a constant speed.

Abstract: A four-wheel steering system of a vehicle includes a power steering device for steering the front wheels, an oil pressure pump for generating an oil pressure in accordance with a travel speed of the vehicle, and a hydraulic actuator for steering the rear wheels. A first control valve is provided between the pump and the actuator so as to operate upon reception of the oil pressure from the power steering device. This valve introduces the oil pressure from the pump to the actuator in accordance with the oil pressure from the power steering device so that the actuator steers the rear wheels in the same direction as the front wheels. A second control valve is provided between the power steering device and the actuator so as to operate in accordance with the oil pressure from the power steering device.

Abstract: A hydraulically powered actuator (16) for moving a member (28 or 30) into and away from a position at which the member is under a preload is disclosed. A hydraulically powered motor (22) is utilized which is coupled to the member for moving the member to and from the position at which the member is preloaded. A source (40) of pressurized hydraulic fluid is coupled to the hydraulic motor for supplying power to the motor for moving the movable member. A brake (32) is provided which is coupled to the movable member for holding the movable member in the position at which the member is preloaded. A hydraulic fluid control is provided which is coupled to the motor, the brake and the source of pressurized fluid which activates the brake after the motor has moved the member to the position at which the member is preloaded and deactivates the motor while maintaining the member under preload.

Abstract: A braking system for a dumping vehicle having a hydraulic drive system and a hydraulic dump container is disclosed. A two-section control valve is connected by conduit to a hydraulic fluid reservoir and a hydraulic motor. The control valve includes a first valve assembly for controlling the dump container and a second valve assembly for controlling operation and direction of the hydraulic motor. An anti-cavitation valve and relief valve are provided to prevent locking of the vehicle wheels during braking. Walk-behind, riding-step and riding-seat variations of the invention vehicle are disclosed.

Abstract: A hydraulic servo system to control flow rate of working fluid to a hydraulic motor as a function of command includes a spool-type pilot valve with manual or electrohydraulic structure for positioning the pilot valve and control conduits connecting the pilot valve to a flow control valve having lands and chambers between the lands for directing flow to the hydraulic motor, the flow control valve having a cylindrical cavity at one end and being exposed to full system pressure at the other end, a shuttle valve coaxially positioned with respect to the flow control valve having an axial extension extending into the cylindrical cavity, a spring in the cavity which tends to urge the flow control valve in a direction to oppose the system pressure, with control passages connecting opposite sides of the shuttle valve with the flow control valve chambers causing the shuttle valve to select the higher pressure in the flow control valve chambers and causing the spool to seek a position providing the desired flow rate.

Abstract: A locking valve assembly for use with air cylinder and in pneumatic circuits and including a locking valve for selectively locking air pressure in the air cylinder. The locking valve is pilot operated to provide for release of air pressure from the air cylinder and also includes a manual override apparatus for providing for release of the locking valve in the absence of pilot pressure.

Abstract: A fluid pressure-intensifying system of the double-acting type has a recompression valve assembly that meters working fluid of the low pressure hydraulic cylinder to control low pressure piston travel upon reversal at the end of each pressure-intensifying stroke.

Abstract: A hydraulic control system comprising a hydraulic actuator having opposed openings adapted to alternately function as inlets and outlets for moving the element of the actuator in opposite directions, a pump system for supplying fluid, and a directional valve provided to which the fluid from the pump is supplied for controlling flow to and from the actuator. A pair of lines extends from the directional valve to the respective openings of the actuator. A controller alternately supplies a first fluid pilot pressure to pressure reducing valves associated with the directional valve for reducing the pressure from the pump system or any other source and supplying a second reduced pilot pressure to the directional valve for controlling the flow to and from the actuator. Preferably, the directional valve comprises a meter-in valve and a meter-out valve associated with each line to the actuator for controlling flow out of the actuator.

Abstract: A fluid valve structure is provided having spaced first and second inlet sections connected to a source of pressure fluid and a plurality of side by side valve sections between said inlet sections, each having inlet, work and tank chambers intersected by a passage open at opposite ends to a control chamber and a tank chamber at a common pressure, a valve spool movable in said passage and having both ends at a common pressure and grooves adapted selectively to connect the work chamber to the inlet or tank chamber, a lever in the control chamber removably engaging one end of the spool and rotatable about a shaft transverse to the spool axis, and an external handle means operatively engaging the shaft to rotate the lever to move the spool axially in the passage, all of the spool, lever and shaft being fully enclosed with a valve housing in all operative positions.

Abstract: A hydraulic system for raising and lowering a working machine in a working vehicle such as agricultural tractors, which comprises a hydraulic cylinder, a hydraulic pump, an oil tank, a manual valve shiftable between three positions: a stationary position in which a working oil discharged from said hydraulic pump is released into the oil tank; a raised position in which the working oil is supplied into the hydraulic cylinder; and a lowered position in which the working oil supplied into the hydraulic cylinder is passed back into the oil tank, and a check valve for permitting only a flow of the working oil from the manual valve toward the hydraulic cylinder.

Abstract: A flow control and load check valve in a spool valve between a first power core (20) and the motor ports (22,24,26) for controlling the flow therebetween as a function of the differential pressure of the first power core and the inlet pressure. A piston (66) responsive to said two pressure positions a sleeve (76) to determine the flow rate. The sleeve (76) also serves as a load check.

Abstract: The invention relates to a pressurized hydraulic fluid spool valve intended to be stacked against other similar spool valves, having a valve body (1) with a spool (4) adapted for sliding in a bore (5) into which open in the following order: a first intake recess (19) in a central position, two second recesses (21A, 21B) for connection to a hydraulic apparatus situated on each side of the preceding one; two third recesses (T.sub.1, T.sub.2) situated respectively beyond the second recesses, and two fourth recesses (22.sub.1, 22.sub.2) situated respectively beyond the third recesses.

Abstract: A change-over valve for hydraulic walking mine-roof supports comprises a valve housing containing a sealed-off operating piston in which a valve member supported on a helical spring is displaceably arranged, the piston being responsive to the supply of small quantities of hydraulic fluid through an end connection in the housing and having a sealing cone adapted to close a connection of large throughflow cross-section at the opposite end of the housing which also has a side connection for the supply of pressurized fluid to a working cylinder of a mine-roof support, the large throughflow cross-section at the connection thereby guaranteeing brisk pushing-in of a piston rod of a piston in the cylinder.

Abstract: A fluid pressure system incorporating a piston and cylinder actuator which is initially moved from right to left and is reversed at the left hand end of its stroke by a switching valve upon receiving a signal through a passage from a sensing valve which becomes hydraulically balanced during a no-flow condition of the system and is displaceable to a switch initiating state during that condition by a small force originating from a light spring, or the actuator or from the operation of another valve in the system.

Abstract: A control valve (10) is disclosed for use in controlling a winch motor (12) on a winch. The control valve (10) is employed with a conventional operating valve (32). When the operating valve is in the neutral position, the control valve (10) acts as a hydraulic brake and an unloading valve for a brake cylinder (20). When the operating valve (32) is moved to raise a load with the winch, the control valve provides a flow path to and from the winch motor (12) to rotate the motor to raise the load and provides sufficient hydraulic pressure in the brake cylinder chamber (18) to release the brake even if the winch has no load. When the operating valve is operated to lower the load, the control valve (10) acts as an over center valve to prevent the load and winch from running away from the winch motor (12). The control valve (10) accomplishes each of these functions with only a single valve spool (132) slidable in a valve housing (100).

Abstract: A valve unit for use in a load sensing system having a fluid operated cylinder. The valve unit permits positioning of an implement between the raise, lower, neutral and float positions and also provides for throttling of fluid flow to the cylinders as well as priority flow to the system. Float is obtained through a lock check valve which includes a main poppet maintained in a seated position by a spring biased pilot poppet. A pilot piston is positioned coaxially opposite the main poppet and is responsive to fluid pressure in the valve to act upon the pilot poppet and unseat the main poppet. In the float position, the fluid pressure within the valve may be stand-by pressure which acts upon the pilot piston to allow it gradual decent of the implement. The pilot pressure is communicated to the pilot piston through a centrally located passage. The location of the passage permits additional lock check valves to be easily added as needed.

Abstract: A pressure compensated flow control valve (10) embodying the concepts of the present invention is particularly suited for use as a component within the hydraulic system of a fork lift truck (11) in order to permit an unrestricted flow of fluid therethrough to raise the forks (18), either with or without a load (19), and to control the flow of fluid therethrough in order to govern the speed at which the forks (18) lower a load (19). During the lowering of the load (19) the valve (10) is properly responsive to actual, apparent and/or transient loading changes. The valve (10) employs a spool (95) slidable within a cavity (75). The spool (95) has a piston portion (96), and a sleeve (135) is slidably mounted on the skirt (125) of the piston (96).

Abstract: A fluid valve structure is provided having spaced first and second inlet sections connected to a source of pressure fluid and a plurality of side by side valve sections between said inlet sections, each having inlet, work and tank chambers intersected by a passage open at opposite ends to a control chamber and a tank chamber at a common pressure, a valve spool movable in said passage and having both ends at a common pressure and grooves adapted selectively to connect the work chamber to the inlet or tank chamber, a lever in the control chamber removably engaging one end of the spool and rotatable about a shaft transverse to the spool axis, and an external handle means operatively engaging the shaft to rotate the lever to move the spool axially in the passage, all of the spool, lever and shaft being fully enclosed with a valve housing in all operative positions.

Abstract: There is disclosed a spool type direction control valve for controlling the oil flow direction in a hydraulic circuit including a pressure source, a hydraulic cylinder and a spool member. A flow control mechanism is provided in an oil passage connecting one of the oil chambers of the hydraulic cylinder to the spool member. The flow control mechanism comprises a poppet type piston adapted for opening and closing the oil passage. When the spool member is switched over for supplying the pressure fluid to the other oil chamber of the hydraulic cylinder, the pilot pressure from the pressure source is caused to act on the piston in the valve opening direction, while the back pressure of the discharge side pressure fluid corresponding to the load acting on the one oil chamber is caused to act on the piston in the valve closing direction, so as to control the discharge flow of the pressure fluid from the one oil chamber.

Abstract: A compensated control valve assembly for control of fluid flow to and from a fluid motor, which may be of a cylinder type and is subjected to positive and negative loads. During control of negative load the controlled pressure level of a pressure reducing valve mechanism handling the fluid flow at negative load pressure is varied upstream of an outflow metering orifice arrangement, positioned at the outlet of the fluid motor, in response to pressure at the inlet of the fluid motor, while maintaining this controlled pressure constant at each specific level. The pressure differential across an inflow metering orifice arrangement, positioned at the inlet of the fluid motor, is maintained at a constant preselected level by a positive load pressure compensating control device.

Abstract: This double acting check valve allows hydraulic power steering oil to flow from the power steering pump through the valve to the power steering gear in normal operation. During an impact load at the tire, the piston in the gear forces the oil from the gear to the check valve which controls or meters the oil flow and pressure so that the impact is not transmitted back to the steering wheel. In the event that the impact load is severe and pressures build up within the power steering gear, as a result, the blow off valve opens to allow such back flow to reduce or eliminate damage to the gear housing.

Abstract: A hydraulic distributor in the body of which there is provided a central hole and supply, a discharge, a working, and bypass conduits, said conduits being connected to the central hole. In central hole there is disposed a plunger which is provided with central and end rings. Between the rings there are shaped profile necks and in one of the ends of the plungers there is provided a bypass groove. The working conduits are arranged perpendicularly to the central hole in the distributor body, and non-return valves are disposed in them. The spaces formed by the profile necks in the walls of the central hole are interconnected by an auxiliary conduit. In one embodiment of the distributor, the auxliary conduit is provided in the central ring of the plunger. In another embodiment of the distributor, the auxiliary conduit is provided in the body of the distributor.

Abstract: A compensated direction flow control valve arrangement provided with a direction control spool for control of fluid flow to and from a fluid motor, which may be of a cylinder type and is subjected to positive and negative loads. During control of negative load the upstream of the outflow metering orifice, positioned at the outlet of the fluid motor, is maintained at a controlled constant pressure level by a pressure reducing valve handling the fluid flow at negative load pressure. The outflow metering orifice is made independent of the direction control spool and its effective flow area is made responsive and varies with the pressure at the inlet of the fluid motor. The pressure differential across a metering orifice, positioned at the inlet of the fluid motor, is maintained at a constant preselected level by the positive load compensator.

Abstract: Electrohydraulic regulating device, particularly for aircraft controls, iuding a regulating cylinder having a regulating piston therein capable of being loaded at either end thereof for the positioning of which necessary volumes of operating fluid can be supplied separately to either end space of the cylinder by means of magnetically-operable valves; a computer by which switch pulses of variable duration to be fed to the magnetically-operable valves are determined in dependence on the specified adjustment distance of the regulating piston; restrictors which determine the throughput of operating fluid through the magnetically-operable valves and sensors which after the switching of a respective magnetically-operable valve generate electrical signals which are fed back to the computer purely as a confirmation of operation. The restrictors are so arranged in an operating fluid circuit that, on movement of the piston, operating fluid flows through only one of the restrictors.

Abstract: The invention is a lockout valve used in a hydraulic circuit to prevent leakage in a static condition; the lockout valve does not require outside force to hold the lockout open once flow across the lockout is established due to the positioning of an orifice ring around the poppet upstream of the poppet seat with the closing area acting on the poppet in conjunction with a spring which senses the pressure downstream of the orifice ring so that when there is sufficient flow across the orifice ring, the force created by the opening area on the poppet, which is located upstream of the orifice ring, will exceed the combined force of the spring and the closing area so that the lockout valve will remain open without an outside force so long as sufficient flow is maintained across the poppet.

Abstract: An improved hydraulic system for material handling implements is disclosed which functions to permit a hydraulic fluid actuator to be locked in a fixed, load-supporting condition. The system includes a locking circuit which comprises a normally open check valve in parallel flow relation with a pressure relief valve provided in close association with a return port of the fluid actuator. The locking circuit further comprises a normally closed pressure release valve which can be selectively operated to create a pressure differential across the check valve to close the check valve, and thereby prevent flow of fluid from the fluid actuator to maintain the actuator in a load-supporting condition.

Abstract: An electrohydraulic proportional valve wherein an electromagnetic force motor sends a mechanical signal to a pilot actuator which moves a main spool. The pilot actuator includes a pilot spool slidably received in a pilot sleeve. A feedback spool which is movable with the main spool has a camming surface against which the pilot sleeve rides. A load check valve is provided that isolates the load pressure from system pressure when desired.

Abstract: A device for controlling a consumer, in particular a hydromotor includes a restrictor, preferably an electrohydraulic proportional directional control valve, and a control valve operating on the basis of a releasable non-return valve. The control valve is provided with an actuating cylinder-and-piston unit having control ports and a biasing spring for the piston. The control valve also has a connecting port which is connected with a connecting port of the restrictor. In order to substantially simplify the structural design of the device, a flow regulator is installed between the control port of the control valve and the connecting port of the restrictor which is connected with the consumer. The control sides of the flow regulator and the control valve are connected through a throttle with a supply container. The space of the cylinder-and-piston unit adjoining the control side of the control piston is connected with another connecting port of the control valve and with the restrictor.

Abstract: A modulation valve for controlling flow to a fluid consuming device which valve provides a gradual buildup of fluid pressure and during at least part of the buildup restricts flow to the consuming unit. The valve includes a slide movable by a spring on one end and fluid pressure on the other. The slide has a blind bore on the pressure end which is adapted to move over a projection having a restricted passage therethrough. In at least one position of the slide, fluid flow to the consuming unit is through the projection and through a passage in the slide to the consuming unit. In another position of the slide, fluid flow is through the blind bore and through the passage in the slide to the consuming unit.

Abstract: A control arrangement for a hydraulic motor has an adjustable pressure medium supply device with a container, an unblockable check valve with a control connection, a plurality of chambers including a supply chamber, a motor chamber, first and second return chambers, and a control chamber, a control slider displaceable relative to the chambers, wherein a control conduit extends from the supply device and leads to the control chamber, a first pressure control member is arranged on the control slider so that in a lowered position of the latter the first pressure controlling member is located between the control chamber and the second return chamber and the control slider in its raised position blocks the control chamber, and a second pressure controlling member located between the control chamber and the motor chamber and opening into the latter.

Abstract: A leak-detecting hydraulic system is disclosed for operation of a fluid actuator associated with a front-end loader, a backhoe, or a like implement on a material handling device. Notably, the system includes a leak-detection circuit which normally acts to prevent movement of the implement associated with the actuator by gravity in the event of a failure in one of the hydraulic fluid lines operatively connected with the actuator. Additionally, the system preferably includes a selectively operable float valve which permits fluid flow which bypasses the leak-detection circuit, thus desirably permitting operation of the implement associated with the actuator in a "floating" mode.

Abstract: To assure adjustability under all internal pressure conditions a hydraulic damper having a hollow piston rod, a piston on the end of the rod slidable in a fluid filled tube and cooperating with the latter in defining inversely variable volume compression and rebound chambers, and at least two relief valves on the piston connected to the compression chamber for passing fluid thereto at two different levels of pressure relief, includes a right cylindrical valve spool in the piston rod bore rotatable between a plurality of control positions corresponding to pressure relief at the different relief pressure levels, first passages between the rebound chamber and the piston rod bore, second passages between each of the relief valves and the piston rod bore, first circumferentially symmetrically arrayed ports in the valve spool registerable with the first passages to always connect the rebound chamber to the valve spool, second circumferentially symmetrically arrayed ports in the valve spool to selectively connect re

Abstract: A sequencing valve utilized with a tractor-propelled planter having two row arms which pivot downward to the ground in an alternating sequence as the planter changes directions in the field. The sequencing valve is connected with the conventional hydraulic system which raises and lowers the planter at the end of each row so as to automatically lower alternate marker arms. This is achieved by pressurizing opposite ends of the sequencing valve spool for longitudinal movement through a cam means, causing the spool to rotate during movement in one direction whereby alternating lowering of the planter arms is achieved each time the planter is hydraulically lowered to the ground.

Abstract: A pneumatic throttle control configuration provides synchronized start-up and independent shut-off of multiple pneumatic tools. Each tool includes a throttle control assembly having a manually operable throttle valve which selectively admits air to the vane motor of the tool and a spring-biased piston operably coupled to the throttle valve which maintains it in an open position in response to air pressure in a control line which interconnects the tools. The vane motor includes a governor controlled valve which opens at a predetermined motor speed and provides air to the control line and the pistons of each tool of the multiple tool arrangement, thereby opening every throttle valve. Each pneumatic tool may then operate and stall independently. When the last tool stalls, the control air flow to all tools is terminated and the throttle valves close.

Abstract: A counterbalance valve connects a source of hydraulic fluid to a power piston-cylinder unit for positioning and/or holding a load such as a pivoted bucket arm of earth moving equipment. A directional control valve is operable to reverse the supply connection to the cylinder unit and to operatively close the connections thereto to hydraulically lock the cylinder unit and attached load in place, with a highly restrictive bleed passageway. The counterbalance valve has a first valved passageway between a pair of ports which includes a check valve to provide one directional flow between the two ports. A dual poppet valve unit includes a pair of parallel passageways in parallel with each other and with the first passageway. The double poppet valve includes a main poppet valve having a valve stem with a piston head and a spaced member of a larger effective area.

Abstract: A multi-way valve for precisely controlling supplying pressure to a load device, comprising a housing and a control slide slidably mounted in the housing. The housing has annular, internal passages axially spaced along the length of the housing, with first and fifth passages located on opposite sides of second, third and fourth passages in fluid communication with a supply tank, the load device and a fluid pressure source, respectively. The control slide is slidably mounted in the passages and has parts axially spaced along the slide and axially separated by annular grooves, and an internal, longitudinal passages. First and second springs are coupled to opposite ends of the slide and bias the slide to a middle, rest position. First and second control chambers are located in the housing adjacent the slide opposite ends for applying varying pressures to the slide opposite ends.

Abstract: A bar stock feeder has a pneumatic circuit with positive feed and vacuum circuits and uses an air pump to provide vacuum from a pressure line, and is entirely mounted within a single base pedestal to present a readily operable control panel.

Abstract: A load supporting hydraulic system having main control valve provided with a load check valve and a vent valve; the load check valve, which has a hose connection to the main control valve, is operative to permit free flow of fluid from the control valve toward the load supporting chamber of the system and to block fluid flow from the load supporting chamber toward the control valve, whereas the vent valve is operative with the control valve to permit the load check valve to be opened by fluid pressure from the load supporting chamber to allow fluid flow therefrom thru the hose connection and control valve to drain. A cancelling valve is added to the system to override the vent valve upon failure of the hose connection and reblock fluid flow from the load supporting chamber toward the hose connection and control valve.

Abstract: A fluid flow controlling device includes a flow control that is interposed between the valve spool of a directional control valve and the work port channel of the directional control valve, and that is effective to control fluid flow to and from one motor port of a fluid motor in proportion to respective sizing of first and second fluid flow paths by the valve spool. The fluid flow controlling device is preferably used in load responsive hydraulic systems.

Abstract: A hydraulically operated pump jack utilizing dual hydraulically operated piston and cylinder assemblies for pivoting the beam of the pump jack and including a unique control arrangement associated with a reversing valve for controlling operation of the piston and cylinder assemblies. The control arrangement includes a hydraulically operated holding valve incorporated into each of the conduits between the reversing valve and the hydraulically operated piston and cylinder assemblies combined with a control piston and cylinder assembly for controlling the operation of the holding valves. A manually operated valve assembly is also incorporated into each conduit to enable conversion of either or both of the piston and cylinder assemblies from double acting to single acting.

Abstract: The invention relates to a fluid pressure supply and exhaust system for controlling a two part servomotor wherein relative loads are anticipated for one side of the servomotor. The system has a switching valve unit for selecting parallel supply and exhaust branches to direct supply fluid to the servomotor side subjected to negative loading. There are pressure regulating and throttling valves in the supply branch and a reducing valve in the exhaust branch. The supply pressure downstream from the throttle valve is directed to the reducing valve with a valve closing effect so that a sharp negative load will simultaneously reduce the supply pressure to the servomotor while increasing the throttling of the return flow.

Abstract: A load check valve is normally employed in association with a double-acting hydraulic cylinder, such as the type used to raise and lower the boom of a construction vehicle. Conventional check valves of the poppet type are difficult to modulate whereas check valves of the spool type generally do not insure leakage control at an acceptable rate during normal operation. The spool-type load check valve (20) of this invention, used in conjunction with additional check valves (60,61), overcomes the latter problem by providing a series of interconnecting passages and chambers (36) for communicating equalized fluid pressure from a cylinder (11) to either end of the spool (27) thereof to provide for minimal leakage.

Abstract: A control arrangement for lifting and lowering a hydraulically operated implement comprises a precontrolled reversing valve and a precontrolled stop block arranged in the fluid pressure stream leading from a source of fluid pressure over the reversing valve to the compartment of a cylinder and piston unit connected to the implement for lifting the latter during feeding of pressure fluid into the compartment and for lowering the implement during discharge of pressure fluid from the compartment. The stop block comprises a releasing piston cooperating with a stop valve of the stop block to alternatingly connect the compartment to a return conduit leading to a tank to discharge pressure fluid from the compartment or to the reversing valve to feed pressure fluid into the compartment. A pressure valve arranged in the releasing piston controls a connection leading from the reversing valve to a damping chamber at one end of the releasing piston which is additionally influenced by the movement of the latter.

Abstract: A hydraulic cylinder arrangement of the type wherein the opposite ends of a cylinder are connected selectively to either a pump or sump by a control valve. Each end of the cylinder is provided with a pair of oppositely acting, uni-directional check valves, each connected to a port on the control valve by an individual conduit. The four check valves are so arranged that all the fluid discharged from either end of the cylinder in response to the reciprocation of the piston therein is constrained to flow to sump before it is pressurized and returned to the cylinder.

Abstract: The invention relates to a hydraulic motor assembly which includes a hydraulic servomotor operable in either direction with a control valve. When the motor is operated in a selected direction, as distinguished from the return direction, it is desired that external forces acting on linkage connected to the piston of the hydraulic motor do not alter the speed of the piston. The control valve has two operating positions and two sets of supply and return passages which facilitate operation of the servomotor in either direction. A brake valve between one of the servomotor ports and the control valve has a scanning port which scans or senses the downstream pressure of either of the control valve supply passages, depending on the control position of the control valve.

Abstract: A speed control and transmission vent valve (10) includes a first valve (12), a second valve (14) having first (64) and second inlets (66), an openable outlet (70) and a spool (62 or 62') movable in response to fluid in the inlets (64,66) between first, second and third positions, a passage (112) connecting the first valve (12) to the first inlet (64), and two-state switch means (16) for communicating fluid in the passage (112) to the second inlet (66) in response to one state of the switch means (16) to move the spool (62 or 62') from the first to the second position and for communicating fluid in the passage (112) to the first inlet (64) in response to a second state of the switch means (16) to move the spool (62 or 62') from the second position to the third position in which a fluid control signal is generated.

Abstract: Disclosed is an electrohydraulic proportional valve comprising an electromagnetic force motor, a pilot actuator assembly, and a main spool and body assembly. The pilot actuator assembly comprises a pilot spool slidably received in a pilot sleeve and a feedback spool which has a camming surface against which the pilot sleeve rides. The camming surface comprises a first portion in which the position of the pilot sleeve is a function of the axial position of the camming surface and a second portion immediately adjacent the first portion in which the position of the pilot sleeve is constant regardless of the axial position of the camming surface.

Abstract: A control system for hydraulic servomechanisms comprising a double-acting jack the working chambers of which are selectively and alternately connectable to a source of pressurized fluid and to a fluid discharge through a reactive switching valve which itself is operated by a control member.According to the invention, there are provided between the valve and each working chamber of the jack means for intercepting the passage of fluid toward said chamber as long as the upstream pressure does not reach a predetermined threshold value.The application may be advantageously used in power-assisted steering systems for automotive vehicles.