Abstract: A hydraulic control system is disclosed. The hydraulic control system may have a pump configured to pressurize a fluid, an actuator, a position sensor associated with the actuator and configured to generate a first signal indicative of a position of the actuator, and a circuit fluidly connecting the pump to the actuator. The hydraulic control system may also have a valve associated with the circuit and configured to move from a first position, at which fluid relief from the circuit is inhibited, toward a second position, at which fluid is relieved from the circuit through the valve, when a pressure of fluid within the circuit exceeds a threshold setting of the valve. The hydraulic control system may additionally have a controller in communication with the position sensor and the valve. The controller may be configured to selectively cause adjust the threshold setting of the valve based on the first signal.

Abstract: A hydraulic circuit for operating a tool is provided that is particularly useful in construction equipment such as an excavator, crane, wheel loader, drilling machine, or others. Furthermore, a control unit and a method for controlling the hydraulic circuit and construction equipment including such a hydraulic circuit is disclosed.

Abstract: An improved double check valve for a construction machine is provided, which can greatly reduce noise and hunting phenomenon by making check valves open and close within a predetermined time difference to correspond to pressure drops that occur due to an external load when a dozer blade working device is operated.

Abstract: A hydraulic control device for an automatic transmission is provided. The hydraulic control device can sets up any gear from a plurality of gears by causing any one of a plurality of frictional engagement elements to selectively carry out an engagement operation. The hydraulic control device includes: a regulator valve that regulates base oil pressure of hydraulic oil supplied from an oil pressure source; a relief valve provided in a lubricating oil passage connected from the regulator valve; and a line pressure switching section that sets up line pressure to low pressure to reduce the amount of lubricating oil in a region in which engagement hydraulic oil pressure does not require high engagement hydraulic oil pressure depending upon an operation state of a vehicle, and sets up the line pressure to high pressure when a target value of the engagement hydraulic oil pressure exceeds predetermined pressure.

Abstract: A tripping control system for use with, for example, turbines, includes a block circuit having two or more redundant blocking valves disposed or connected in series within a pressure supply line to block the supply of hydraulic fluid within the pressure supply line and a bleed circuit having two or more bleed valves connected in parallel between the pressure supply line and a return or dump line to bleed to the hydraulic fluid from the pressure supply line. The blocking valves and the bleed valves are actuated by one or more control valves under the control of a process or safety controller which trips the turbine by first performing a bleed function using the bleed valves, which then causes the block function to automatically actuate. Pressure sensors disposed at various locations in the tripping control system provide feedback to the controller to enable the controller to test each of the block and bleed valves individually, during operation of the turbine, without causing an actual trip of the turbine.

Abstract: A suspension system includes four electronically controlled actuators, one at each of the four wheels. The actuators are each controlled by an electronic control unit. The left front and right front actuators are mechanically connected with each other. The left rear and the right rear actuators are also mechanically connected with each other. The only connection between the front two actuators and the rear two actuators is an electronic communication through the electronic control unit.

Abstract: The valve arrangement for the activation of a structural element has three inlet switching valves through which a pressure-loaded medium can be conducted. These inlet switching valves are connected on their inflow side to a pressure supply by inflow lines and are arranged parallel to one another in flow terms. Moreover, the valve arrangement has a connection element, which is connected to outflow sides of all the inlet valves by pressure lines. A control line acted upon by the medium is connected to the pressure supply. The three switching-valve groups can be activated by the control line, and in each case two switching valves and in each case one inlet switching valve are assigned to each switching-valve group. A activation valve can be interposed in each case between a switching-valve group and the control line. Three outflow lines for the medium can be arranged between an outflow location for the medium and the connection element.

Abstract: The redundant valve system 10 of the preferred embodiment includes a first valve unit 12 and a second valve unit 14. The redundant valve system 10 is preferably used to connect a source 16 to a destination 18 and to connect the destination 18 to a reservoir 20. The first valve unit 12 and the second valve unit 14 are coupled to control fluid flow such that fluid flow is allowed in only one of two given directions at any given time, either from the source 16 to the destination 18 or from the destination 18 to the reservoir 20.

Abstract: For a valve arrangement of a pneumatically actuated, spring-loaded control cylinder, a non-return valve in pneumatic communication with the control cylinder piston chamber. At very low backpressures in the control cylinder piston chamber caused by leaks of the valve responsible for pressurization of the piston chamber, the chamber is vented by passage of a very small air stream via the non-return valve. In this way, leaks cannot cause a very slow pressure buildup in the control cylinder piston chamber, followed at some time by undesired shifting of the control cylinder. In contrast, in the case of normal pressure buildup, i.e., during switching of the pressurizing valve, the non-return valve is promptly closed and the pressure in the control cylinder piston chamber is not influenced.

Abstract: Disclosed is a hydraulic control system of a transfer system for a machine tool, including a hydraulic pump for generating hydraulic pressure, a first directional control valve for controlling the flow direction of fluid from the hydraulic pump, a first flow speed control part located between the first direction control valve and a rotary cylinder to control the flow speed of fluid flowing therebetween, a second direction control valve controlling a flow direction of fluid fed from the first directional control valve and returned to a fluid tank, and a second flow speed control part for controlling flow speed of the returning fluid in accordance with a port variation of the second directional control valve.

Abstract: A control apparatus controls movement of a lift arm and tool on a skid steer loader. Power actuators are coupled to the lift arm circuit and the tool circuit for moving the lift arm and tool along a path. A sensor is coupled to the skid steer loader for sensing a desired parameter and providing a signal indicative of the desired parameter. A power interrupter is coupled between the power actuators for the lift arm and tool and the sensor and interrupts power to the actuators based on the signal. A manually operable bypass mechanism is coupled to the power interrupter and the power actuators and is used to bypass the power interrupter to allow movement of the lift arm.

Abstract: An auxiliary power steering unit, especially for motor vehicles, contains a control valve (1) made as a rotary slide valve for controlling a pressure medium conveyed by a servopump (3) out of a tank (4) to and from the pressure chambers of a servomotor (2). Control valve (1) reveals two feedback chambers (10, 11) that are connected via one, each, fixed throttle (12, 13) and a common throttle (14) to a pressure line (15) of the servopump (3). The feedback pressure that takes effect in the feedback chambers (10, 11) can be limited to a maximum value by a cutoff valve (18). The cutoff valve (18) is made as pressure balance whose response pressure can be adjusted from the outside without dismantling.

Abstract: An exhaust manifold (25) of a fluid power and control system, the pressure of which is varied when the fluid motor (10) is subjected to a bidirectional positive or negative type load (W). This exhaust manifold (25) is also supplied from a source of exhaust manifold pressurizing oil (29) other than the system pump (18). This source of exhaust manifold pressurizing oil (29) may include a flow amplifying device (57) which is activated when the fluid motor (10), in the form of a cylinder, moves a load in the direction of its piston rod end (11) and when the piston rod end (11) of cylinder (10) is subjected to a negative load pressure and when the pressure in the exhaust manifold (25) drops below a certain minimum preselected level.

Abstract: A control for a hydraulic propeller pitch actuator includes a low power pilot valve responsive to digital electronic input signals to control movement of a hydraulic servomotor driving a higher power servovalve. Negative feedback motion is delivered from the servomotor to both the pilot valve and the servovalve.

Abstract: A hydraulic circuit for a backhoe loader having two double-acting cylinders for the arm and bucket of the loader and respective directional valves for the cylinders. There are heavy demands on the oil pump of the system when the two cylinders are moved simultaneously from one extreme position to another which requires substantially two whole cylinder volumes of oil. The cylinders are arranged in parallel relative to the pump. A first source of pressure medium displaced from one cylinder is used to perform work in the other cylinder and the other cylinder is also supplied with a second source of pressure medium directly from a pump. The line section through which the first source of pressure medium is supplied is shunted to a tank by valving apparatus upon a predetermined pressure being reached to freely accommodate the simultaneous movements of the cylinders.

Abstract: A steering system rotary valve having relatively rotatable spool and sleeve members and including first and second valve groups for controlling the amount of fluid feed to a power cylinder responsive to spool/sleeve rotation and including third and fourth valve groups for controlling feed pressure of fluid discharged from a pump, is provided with blocks arranged between the first and second valve groups and between the third and fourth valve groups to interrupt communication between these groups and also is provided with a variable throttle valve on the downstream side of the third and fourth valve groups so that pressure acting on all the valve groups is substantially equalized to provide uniform pressure on the entire circumference of the spool and the sleeve thereby preventing these members from becoming pressure deformed during the course of rotary valve operation.

Abstract: A pair of orifices of different orifice sizes is provided between each pressure chamber and an accumulator chamber. A larger one serves as a variable orifice and a smaller one as a fixed orifice. The variable orifice becomes effective when a control circuit is functioning properly for variably controlling an axial position of a valve spool. The fixed orifice becomes effective when the control circuit malfunctions and allows the valve spool to be moved into a predetermined position. In another embodiment, a single orifice cooperates with the valve spool to serve as both a variable orifice and a fixed orifice.

Abstract: According to the invention, a valve for use with a variable speed motor and pump in an hydraulic elevator balances a fluid pressure force on a pump side of a control valve with a fluid pressure force on a cylinder side of the control valve before an elevator cab moves either upwardly or downwardly. On the pump side of the valve, a separate circuit, which is controlled by a solenoid, directs the pump fluid pressure force behind the valve until the sum of the fluid pressure acting on the pump side of the control valve overcomes the fluid pressure on the cylinder side of the control valve to open the valve.

Abstract: A valve block in a mine hydraulic system contains a non-return valve which is opened when a hydraulic control signal occurs to connect a pressure fluid feed or return line to a working chamber of an appliance such as a prop. A auxiliary valve is mounted in the block and is operated manually to relieve the working chamber even if the non-return valve remains closed.

Abstract: A load-referenced, pressure reducing valve, and a system which incorporates one or more of such valves provide needed response to rapidly changing hydraulic system load demands which are experienced with automatic control systems. The valve provides rapid response for pressure regulation by providing the load pressure to one side of the valve so that immediate, load referenced valve adjustment occurs instantly upon change of load conditions at a system load, and pressure regulation begins immediately without need for fluid flow.

Abstract: A valve body of a variable throttle valve is connected directly to a gear box of a power steering system so that an outlet port of the variable throttle valve communicates with a return port of the gear box. Such construction permits arrangement of the variable throttle valve with respect to the gear box to be carried out without using any piping, coupling and the like.

Abstract: For the relief of a highly pressurized hydraulic liquid in a working chamber of pilot controlled 2/2 poppet valve is used. The working chamber is further connected to a pressure relief valve, the output of which is connected to a control conduit extending between a control chamber of the 2/2 poppet valve and the pilot valve. The apparatus of the invention requires a shorter period of time for the pressure relief without the danger of relief noise.

Abstract: Disclosed is a pressure actuator such as a vacuum actuator comprising a valve unit including a plurality of solenoid valves and a diaphragm unit including a diaphragm defining a pressure chamber, air pressure within the pressure chamber being adjusted by selective activation of the solenoid valves which communicate the pressure chamber with pressure sources of different pressure levels, in which a casing of the actuator defines an accommodating chamber for accommodating the solenoid valve unit and a wall surface of the chamber is provided with ribs for guiding and positioning the solenoid valve unit inside the chamber. The ribs may be adapted to make a sliding contact with a side surface of the yokes of the solenoid valves and a smooth surface a printed circuit board which is attached to the solenoid valve unit. Alternatively or additionally, the ribs may be adapted to be fitted into a gap between a pair of adjacent yokes of the solenoid valves.

Abstract: Disclosed is an air filter unit for a pressure actuator such as a vacuum actuator for a speed control of an automobile comprising a solenoid valve unit including a plurality of solenoid valves and a diaphragm unit including a diaphragm defining a pressure chamber, air pressure within the pressure chamber being adjusted by selective activation of the solenoid valves which communicate the pressure chamber with pressure sources of different pressure levels. A filter element holder defining a pair of receptacles for receiving filter elements therein is attached to the solenoid valve unit so as to intercept air flow from an external air source into the vacuum chamber by way of the solenoid valves. The filter element for a vent valve which is frequently used is finer in structure than that for a safety valve which is less frequently used and is required to be capable of rapid introduction of air into the vacuum chamber.

Abstract: An electromagnetic proportioning valve is provided having two coils and an armature which can be displaced by either coil in one of two possible directions, in which case a seat valve on whose valve bodies the magnetic force generated in the armature acts, is located on each side of the armature.

Abstract: The servo device for controlling flow (10) situated in a branch hydraulic line (6), incorporates in a body (11) an inlet passage (12) and an outlet passage (9) connected by an intermediate passage (13) forming a seat (14) for a valve component (15) which is pushed against its seat by a spring (26) and by an electromagnetic actuator (16) via a push-rod (23) which is slidingly sealingly mounted in a bore (22) between the intermediate passage (13) and an internal chamber (19) which is connected to the inlet passage (12).

Abstract: A fluid machine comprises a cylinder block mounted on a rotary shaft, a rotary plate an axis of which is intersecting with an axis of the rotary shaft by an acute angle, a gear engaging mechanism for engaging the rotary plate with the rotary shaft to cyclically rotate the same, a piston supported by the rotary plate and inserted into a throughhole provided in the cylinder block a suction system and a delivery system for effecting suction and delivery operation by a rotation of the cylinder block and the piston, a spherical contact portion disposed between the rotary plate and the rotary shaft and adapted to receive thrust generated between the same, and a passage for leading to the spherical contact portion a high-pressure working gas including lubricating oil generated in the delivery system.

Abstract: An electro-hydraulic height corrector for motor vehicles comprising a hydraulic distributor having ducts connected, one to a pressurized supply source, another to suspension cylinders and another to an exhaust circuit, and means for connecting these different ducts together, and means sensitive to the position of the suspended part of the vehicle with respect to the none suspended part thereof.

Abstract: A control valve includes a monolithic valve body incorporating dual digital valves and dual by-pass valves interconnected with each other by ducts within the valve body and providing for either controlled or uncontrolled actuation of a piston in either a forward or a reverse direction of movement.

Abstract: An air actuator device is provided for manually operable hydraulic valves having a valve spool moving in a bore in a valve housing in the form of an actuator housing adapted for attachment on the valve housing and having a bore carrying a piston coaxially engageable with the spool end, spaced openings in the actuator housing communicating with the bore therein to introduce air to act on opposite sides of the piston and resilient means on at least one side of the piston normally urging the piston and spool to a closed position.

Abstract: Step control apparatus for a fluid motor includes a plurality of devices each responsive to an external signal for initiating movement of the fluid motor. Also included is a mechanism for stopping movement of the fluid motor upon movement thereof a discrete step. Thus, a sequence of external signals applied to the devices effects movement of the fluid motor in a stepping mode. Optionally, an assembly may be provided for effecting movement of the fluid motor in a free-running mode.

Abstract: The invention relates to a hydraulic steering system of the type having a servomotor controlled by a steerable valve assembly which directs metered quantities of pressurized fluid to the servomotor and has a feedback arrangement for stopping the flow of fluid when the steering motion is stopped. The system involves an arrangement wherein the metering unit is arranged downstream from the servomotor and an auxiliary valve is provided for automatically accommodating normal conditions as well as emergency pump failure conditions and overpressure conditions caused by the servomotor reaching an extreme end position in the operation thereof.

Abstract: In a hydraulic apparatus, an operating oil delivered from a fixed delivery hydraulic pump is divided into two parts, one of which is discharged into an oil tank by passing through a serial circuit consisting of a normally open valve and an orifice and the other of which is supplied to a piston-cylinder means by passing through a parallel circuit consisting of a normally closed valve and a check valve. When the normally closed valve is closed and the normally open valve is gradually closed, the piston is raised while gradually increasing in velocity. On the other hand, when the normally open valve is totally opened to stop the piston and the normally closed valve is gradually opened, the piston is lowered while gradually increasing in velocity. When the valves are operated to cause the piston to move vertically, the impact applied thereto at the time when the valve opening is large is largely mitigated by using said orifice.

Abstract: A closed center programmed valve system having a load sense fluid source for control of the raising and lowering of load means by a raise and a lower normally closed two stage valve assembly. Each of the second stages of the valve assemblies has a poppet with a parabolic contour which is dimensioned to provide substantially linear flow rate change for minimized shock when the respective valve is actuated to the valve closed state. The load sense for the load means is taken from the outlet of the raise second stage without the requirement of a separate actuated valve or land with a load sense signal being applied to the fluid source during the time the raise valve assembly is actuated to the valve open state.

Abstract: A pump system includes a source of fluid under pressure conveyed into a fluid chamber containing meshing gears which are rotated by the pressurized fluid to, in turn, transmit rotation to a unitary valve member positioned in a housing. Rotation of the gears also displaces fluid at a preselected flow rate through an inlet port of the housing and into a first inlet port of the rotary valve member. During the first one half cycle of rotation of the rotary valve member, fluid is conveyed through a first set of aligned outlet ports of the valve member and the valve housing to a water pump for displacing a water piston. The water piston is displaced to convey water through a first conduit. During the second one half cycle of rotation of the rotary valve member, fluid is conveyed through a second set of aligned outlet ports of the valve member and the valve housing to displace the water piston in an opposite direction to convey water through a second conduit.

Abstract: A control unit for a hydraulic actuated elevator consists of a valve device in the hydraulic circuit wherein the circuit includes a pump, a hydraulic cylinder and its piston for raising and lowering an elevator cab and a reservoir for the hydraulic fluid. The valve device features a rotary disc serving as a valve element slidable to positions which open and close ports leading respectively to the reservoir and the cylinder. A reversible electric motor in a cab demand circuit has a rotary drive to the rotary disc, as, for example, by a pinion and gear, for rotating the rotary disc in response to the cab demand circuit serving to start and stop the motor. In one position of the rotary disc, with both ports closed, hydraulic fluid is passed directly into the cylinder for up travel of the cab. In an intermediate position with the port to the cylinder closed the fluid is locked in the cylinder in stop position of the cab.

Abstract: A valve structure is provided for use in an integral hydraulic pump and valve assembly having a housing adapted to be integral with a pump housing with spaced apart low pressure and high pressure ports corresponding to the low pressure inlet port and high pressure outlet port of said pump, a low pressure chamber, a high pressure chamber and a cylinder chamber in said housing spaced apart and generally parallel to one another, a transverse bore in said housing intersecting said chambers, valve means movable axially in said bore, said valve means having an annular groove intermediate its ends capable of connecting said low pressure and high pressure chambers in a first neutral position, capable of connecting all of said chambers in a second position and connecting only the low pressure chamber in a third position, detent means in said housings extending into said bore and annular groove in the valve member, detent engaging means in said groove intermediate its ends and stroke limiting means extending into the b

Abstract: The control device is applicable as a hydraulic regulating valve for controlling a power lift unit of a tractor and comprises a mechanically actuated preliminary selector valve operable for reciprocal movement to close or open pressure fluid supply into a control chamber counteracting a reciprocal main pressure control valve that is spring loaded against the control chamber. To avoid permanent choking resulting from pressure changes due to the movement of the control edges, a section of the preliminary control slide is recessed to such an extent as to exert elastic extension when subject to increased pressure, the extension being within the limits of elasticity of the material of the slide.

Abstract: A fluid flow control valve system to be used to control a hydraulic lifting mechanism used on elevators and the like. The valve system includes an inlet conduit from the pump and an inlet-outlet to and from a jack connected together by a conduit with a one-way valve operable in the direction from the pump to the jack, a first by-pass chamber connected to the pump side of the one-way valve and a second by-pass chamber connected to the jack side of said one-way valve, outlets to the pump sump from each by-pass chamber, and a movable gate control mechanism for controlling the exit of pressurized fluid from the first by-pass chamber or the second by-pass chamber through the outlets to the pump sump. Hydraulic fluid from the pump when the first chamber is sealed, passes through the one-way check valve. When the second chamber is also sealed, the fluid will provide pressure to a jack to lift a load. With the first chamber gate opened at least a portion or all of the fluid passes back to the sump.

Abstract: A dashpot assembly has a movable cylindrical element mounted within a housing. The movable element has a chamber with a first opening for restricting flow of fluid into the chamber and a second opening for permitting rapid flow of fluid out of the chamber. An enlarged head is disposed inside the chamber and is coupled to a poppet with a spring coupled between the poppet and the movable element. When the poppet moves in a direction away from the movable element, the enlarged head closes the second opening and pulls the element. Fluid then flows into the chamber only through the restricted first opening, thereby damping the rate of movement of the poppet. When the poppet moves in a direction toward the movable element, the enlarged head opens the second opening and the spring is effective to move the element in the same direction; fluid flows unrestricted through the second opening, thereby permitting an undamped movement of the poppet.

Abstract: A hydraulic system for precise positioning of a control device, such as a valve actuator. A double-acting, hydraulic cylinder, which operates the control device, is held in any set position by a hydraulic lock ensured by one-way check valves which prevent interflow between the chambers on opposite sides of the piston. Occurrence of a signal indicating a need to change position activates one of two three-way directional control valves allowing exhaust flow from the appropriate cylinder volume. Connected in parallel in the exhaust line is a plurality of on-off valves, each having a flow capacity that is some multiple of that of the next smaller valve, e.g. twice as large. This provides a wide range of distinct and precise flow capacities to provide close and instantaneous control over rate of movement of the positioning device.

Abstract: The hydraulic fluid control apparatus has velocity control means and pressure control means. The apparatus has hydraulic fluid entry means for receiving hydraulic fluid and hydraulic fluid discharge means for supplying pressurized hydraulic fluid to hydraulic power means such as an hydraulically actuated oil well drill string power tong. The velocity control means is operatively associated with the hydraulic fluid entry means and serves to establish a desired predetermined velocity for the hydraulic fluid. The pressure control means is operatively associated with the hydraulic fluid discharge means for selectively limiting the exit pressure of the hydraulic fluid through the discharge means to predetermined levels. The pressure control means includes valve means adapted to divert pressurized fluid from the hydraulic fluid discharge means when the hydraulic fluid pressure exceeds predetermined levels.

Abstract: A programmed valve system for positioning control having a first two stage valve assembly operable for raising a load and a second two stage valve assembly for lowering the load. Each of the second stages has a poppet with a parabolic contour which is dimensioned with orifice parameters to provide substantially linear flow rate change for minimized shock when one of the second stage poppets closes and the other opens. In the raise assembly, the pilot stage outlet orifice has a cross-sectional area substantially larger than that of the inlet orifice so that the second stage poppet opens much more rapidly than the closing thereof thereby to minimize overshoot when the pilot stage is actuated to the open position.

Abstract: A closed center programmed valve system having a load sense fluid source for control of the raising and lowering of load means by a raise and a lower normally closed two stage valve assembly. Each of the second stages of the valve assemblies has a poppet with a parabolic control which is dimensioned to provide substantially linear flow rate change for minimized shock when the respective valve is actuated to the valve closed state. The load sense for the load means is taken from the outlet of the raise second stage without the requirement of a separate actuated valve or land with a load sense signal being applied to the fluid source during the time the raise valve assembly is actuated to the valve open state.

Abstract: A hydraulic control arrangement for hydraulic consumer includes a multiple position valve having a control slide movable by proportional magnets between a neutral position and a plurality of working positions, in which the magnets may be remote controlled from an analog desired value signal and in which a stop valve is provided in a control circuit leading from the consumer to an over-pressure valve, which in turn is connected, upstream of the multiple position valve, parallel to the consumer between a pressure conduit connected to a source of pressure and a return conduit connected to a tank.

Abstract: A hydraulic control system for use in machine tools, construction machines, hoists and the like, with a driven unit the hydraulic circuit of which is controlled by one or more electromagnetically positioned slide valves, and with an arrangement for automatically regulating the velocity of the hydraulic drive unit regardless of fluctuations in the pressure of the oil supply and similar disturbances. The regulating arrangement includes a potentiometer mechanically controlled by a flow meter interposed in the hydraulic circuit; and an electric comparator the inputs of which are connected to the potentiometer and to a desired-flow-value selector, respectively, and the output of which controls the valve electromagnet(s). In this manner the difference signal developed by the comparator is used to change the setting of the valve in a correcting sense. Several implementations for this regulating circuit and for the design of the flow meter and the valves are disclosed.

Abstract: A valve system for an unbalanced load having a first two stage valve assembly operable for raising the load and a second two stage valve assembly for lowering the load. Each of the second stages has a poppet with a parabolic contour which is dimensioned with orifice parameters to provide substantially linear flow rate change when the second stage poppet moves for substantially zero flow jerk. In addition, the raise valve assembly has a pilot line coupled directly to the load so that high pressure oil is instantly available to actuate the second stage poppet. The lower valve assembly has a dashpot to decrease the rate of opening of that second stage poppet.

Abstract: A fluid pressure supply apparatus includes a fluid pressure source, a fluid supply circuit to receive fluid under pressure from the fluid pressure source, and a fluid return circuit. These circuits are to be coupled to an hydraulic motor through first and second fluid paths. The supply apparatus further includes first means to couple the fluid supply circuit to the first fluid path to cause the hydraulic motor to be operated by the fluid pressure in a predetermined sense, and second means simultaneously to couple the second fluid path either to the fluid supply circuit, to provide a regenerative coupling for the motor, or to a fluid return path. This latter coupling is initially to the second fluid path, the second means being arranged to transfer that coupling from the fluid supply circuit to the fluid return path during operation of the motor in the predetermined sense.

Abstract: A fill and vent valve assembly has a bore in a first member and a cylindrical stem of a second member positioned within the bore. A blind bore extends inwardly from an inner end of the stem and has an internal threaded section. First and second passages in the stem communicate the blind bore with a passage device which communicates the bore of the first member with a fluid chamber. A fill valve has an external threaded section threaded into the internal threaded section of the stem and is movable between a first position at which a valve seat of the valve is in sealing engagement with the inner end of the stem and the first and second passages are blocked from communication with ambient and a second position at which the valve seat is spaced from the inner end and the second passage is in communication with ambient for purging air from the fluid chamber in response to fluid being forced through the fill valve and into the fluid chamber through the first passage.

Abstract: A hydraulic control device for use in a hydraulic system having a pump supplying fluid from a reservoir to a working circuit. The control device detects leaks in the working circuit by monitoring the level of hydraulic fluid in the reservoir. In the event of a drop in the level of hydraulic fluid beyond a predetermined low level, the control device automatically diverts the fluid output side of the pump to the fluid input side to prevent further loss of fluid in the working circuit and to safeguard against cavitation in the pump due to the low level of fluid in the reservoir. The control device also senses excessive pressure peaks in the working circuit and operates to relieve the excessive pressure peaks by automatically venting a portion of the fluid on the output side of the pump to the reservoir.