Abstract: The invention provides a hydraulic circuit for feeding an actuator (1) comprising first and second chambers (5, 6), the circuit comprising a slide valve (10) with a slide (16) that is movable between first and second extreme positions (18, 19) on either side of a stable central position (17) so that: in the central position, it connects the chambers (5, 6) of the actuator to a return port; in the first extreme position (18), it connects the first chamber (5) to a feed port and the second chamber to the return port; and in the second extreme position (19), it connects at least the second chamber (6) to the feed port. According to the invention, the hydraulic circuit includes pressure-maintaining means (20) for maintaining pressure in the first chamber of the actuator while the slide is passing through the central position on being moved from the first extreme position to the second extreme position.

Abstract: A hydraulic system (600) and method for reducing boom dynamics of a boom (30), while providing counter-balance valve protection, includes a hydraulic actuator (110), first and second counter-balance valves (300, 400), first and second independent control valves (700, 800), and first and second blocking valves (350, 450). The actuator includes first and second corresponding chambers. In a first mode, the second counter-balance valve is opened by the first control valve, and the first counter-balance valve is opened by the second control valve. In a second mode, at least one of the counter-balance valves is closed. A meter-out control valve (800, 700) may be operated in a flow control mode, and/or a meter-in control valve (700, 800) may be operated in a pressure control mode. Boom dynamics reduction may occur while the boom is in motion (e.g., about a worksite). By opening the counter-balance valves, sensors at the control valves may be used to characterize external loads.

Abstract: A fluid pump for a linear actuator is provided. The pump causes a rod in the actuator to extend or retract by controlling the flow of fluid to and from portions of a fluid chamber on either side of a piston disposed within the fluid chamber and supporting the rod. The pump includes a valve structure that enables the pump to redistribute fluid obtained from one portion of the fluid chamber on one side of the piston to the other portion of the fluid chamber on the other side of the piston without first returning the fluid to a fluid reservoir thereby increasing the efficiency of the pump.

Abstract: The invention relates to a functional unit (100) for a brake release device, comprising a recess (111) for receiving a pump assembly (113), an actuating cylinder support (119) for receiving an actuating cylinder arrangement (400), wherein the functional unit (100) is formed as an integral functional block where the actuating cylinder support (119), the recess (111) and a plurality of channels (150, 160, 170, 171, 172, 180, 190) for a hydraulic medium are developed, said channels forming a line arrangement. The invention also relates to a brake release device having such a functional unit.

Abstract: A fluid pump for a linear actuator is provided. The pump causes a rod in the actuator to extend or retract by controlling the flow of fluid to and from portions of a fluid chamber on either side of a piston disposed within the fluid chamber and supporting the rod. The pump includes a valve structure that enables the pump to redistribute fluid obtained from one portion of the fluid chamber on one side of the piston to the other portion of the fluid chamber on the other side of the piston without first returning the fluid to a fluid reservoir thereby increasing the efficiency of the pump.

Abstract: Provided is a hydraulic driving apparatus for a working machine, preventing an excessive decrease in pressure on a meter-in side and moving a load at a stable speed in a lowering direction. The apparatus comprises: a hydraulic pump; a hydraulic actuator; a manipulation device; a working hydraulic circuit including a meter-in flow passage and a meter-out flow passage; a control valve for changing a state of supply of hydraulic fluid to drive the hydraulic actuator at a speed designated by the manipulation device; a meter-in flow adjuster and a meter-out flow adjuster adapted to adjust a meter-in flow rate and meter-in flow rate respectively to respective value corresponding to the speed designated by the manipulation device; and a relief valve. The meter-in and meter-out flow adjusters have respective flow adjustment characteristics such that the meter-in flow rate is greater than the meter-out flow rate.

Abstract: A fluid pressure control device includes a switching valve that operates in conjunction with a control valve by a pilot pressure to switch an operation of an operated check valve. The switching valve includes a spool that moves according to the pilot pressure of a pilot chamber, and a piston that is accommodated in the pilot chamber and imparts a thrust force to the spool upon receiving the pilot pressure. The piston includes a first piston that is slidingly accommodated in the pilot chamber and is acted upon by the pilot pressure, and a second piston whose distal end faces the spool and is inserted into an accommodating hole formed in the first piston. A spherical protrusion is provided on a center of either one of a bottom surface of the accommodating hole of the first piston and a back surface of the second piston.

Abstract: A hydraulic motor 100 includes a switching valve 3 which is connected to a pilot passage 54 by which a pressure fluid is introduced into a back pressure chamber 21 of a relief valve 2 and takes a first changeover position 3a where the back pressure chamber 21 is connected to a tank 102 or a second changeover position 3b where the pilot passage 54 is connected to the back pressure chamber 21. By this switching valve 3, the pressure fluid supplied to a hydraulic motor mechanism 1 is introduced into the back pressure chamber 21 via the pilot passage 54 when the hydraulic motor mechanism 1 is in operation, whereas the back pressure chamber 21 is connected to the tank 102 as the pressure in the pilot passage 54 becomes not higher than a predetermined pressure when the hydraulic motor mechanism 1 is being braked.

Abstract: A travel control device for a work vehicle includes: a hydraulic pump; a plurality of hydraulic motors connected to the hydraulic pump in parallel through a closed-circuit connection, that drive different wheels with pressure oil delivered from the hydraulic pump; a slip detection device that detects a slip occurring at each of the wheels; and a flow control device that reduces, upon detection of a slip occurring at any of the wheels by the slip detection device, a quantity of pressure oil supplied to a hydraulic motor for driving the wheel at which the slip has been detected, among the plurality of hydraulic motors.

Abstract: A hydraulic motor 100 includes a switching valve 3 which is connected to a pilot passage 54 by which a pressure fluid is introduced into a back pressure chamber 21 of a relief valve 2 and takes a first changeover position 3a where the back pressure chamber 21 is connected to a tank 102 or a second changeover position 3b where the pilot passage 54 is connected to the back pressure chamber 21. By this switching valve 3, the pressure fluid supplied to a hydraulic motor mechanism 1 is introduced into the back pressure chamber 21 via the pilot passage 54 when the hydraulic motor mechanism 1 is in operation, whereas the back pressure chamber 21 is connected to the tank 102 as the pressure in the pilot passage 54 becomes not higher than a predetermined pressure when the hydraulic motor mechanism 1 is being braked.

Abstract: Circuit for controlling a double-action hydraulic drive cylinder includes a directional control valve having working ports A and B, a pump port P, and a tank port T, wherein the directional control valve has a neutral position in which pump port P is blocked and working ports A, B are connected to tank port T. A pressure-limiting valve and a controllable load-holding valve are connected to the piston space in parallel, and a regeneration check valve is connected in series between a connection point for the parallel components and the rod space. A first precharge valve is connected between the working port A and the connection point, and a first bypass check valve is connected anti-parallel parallel with the first precharge valve and the load-holding valve. A second precharge valve is connected in series with the directional control valve between the tank port P and the rod space.

Abstract: Provided is a driving motor controlling device of a construction machine, including a driving motor which is included in the construction machine having a swivel joint interposed between an upper body and a lower body, and is connected to a pump and a tank through the swivel joint, and a motor control valve which switches a state for connecting the pump and the tank to the driving motor such that the driving motor is controlled to a stop state, a normal rotation state, or a reverse rotation state, wherein the motor control valve has a neutral position for the stop state, a normal rotation position for the normal rotation state, and a reverse rotation position for the reverse rotation state, and is switched to the neutral position, the normal rotation position, or the reverse rotation position, based on a command from a control device manipulated by a operator and a pressure of an inflow side of hydraulic oil into the driving motor, wherein the motor control valve is disposed in the lower body in which the dri

Abstract: A hydraulic valve assembly for an excavator including a hydraulic valve movable along a longitudinal axis to control a flow of fluid, a flange coupled to the hydraulic valve, the flange including a receptor, and a locking mechanism movable between a locked orientation and an unlocked orientation. In the locked orientation, the locking mechanism cooperates with the receptor to inhibit movement of the hydraulic valve along the longitudinal axis and in the unlocked orientation the hydraulic valve is free to move along the longitudinal axis.

Abstract: The present invention includes a hydraulic pump (11), a variable displacement hydraulic motor (5) for traveling driven by pressure oil from the hydraulic pump (11), a motor displacement control means (17, 18) for adjusting a displacement of the hydraulic motor (5) in correspondence to a drive pressure at the hydraulic motor (5), an operating member (22) through which a forward travel command and a backward travel command for the vehicle are issued, a control means (12) to be driven in response to an operation of the operating member (22), for controlling a flow of pressure oil from the hydraulic pump (11) to the hydraulic motor (5), a reverse operation detection means (41A, 41B) for detecting a reverse operation of the operating member (22) performed to a reverse side opposite from a direction along which the vehicle is advancing, and a cavitation preventing means (25A,25B) engaged in operation so as to prevent occurrence of cavitation at the hydraulic motor (5) when the reverse operation at the operating mem

Abstract: The invention relates to a hydrostatic drive (1) and to a method of braking a hydrostatic drive (1). In the hydrostatic drive (1), in a closed circuit a hydraulic pump (3) is connected by a first and a second working line (11, 12) to a hydraulic motor (4). The hydrostatic drive (1) comprises a brake actuation device (37) as well as at least one pressure relief valve (26, 30), which is connected to the working line disposed downstream of the hydraulic motor (4). The hydraulic pump (3) upon detection of an actuation of the brake actuation device (37) is adjustable to a braking delivery rate. The hydraulic motor (4) is adjusted in dependence upon the actuating intensity of the brake actuation device (37) in the direction of a larger absorption volume if the actuating intensity of the brake actuation device (37) increases.

Abstract: The invention relates to control of a hydrostatic gearbox, comprising a hydraulic pump (2), provided for pumping in a first pump-side main line (5a) or a second pump-side main line (6a). The hydrostatic gearbox further comprises a hydraulic motor (3), connected to a first motor-side main line (5b) and a second motor-side main line (6b). The first pump-side main line (5a) and the second pump-side main line (6a) may be connected to the first motor-side main line (5b) or the second motor-side main line (6b) by means of a brake valve unit (19). The first motor-side main line (5b) or the second motor-side main line (6b), arranged downstream of the hydraulic motor (3), may be connected to a tank volume (12) in a throttled manner, depending on the pressure therein.

Abstract: A hydraulic hybrid powertrain system includes a power plant generating a high pressure fluid at an output, at least one drive motor responsive to the high pressure fluid for generating rotary motion at an output, and a mode selection device connected to the power plant output and the drive motor for selecting a mode of operation from a plurality of drive motor modes of operation including at least two of a drive mode, a neutral mode, a reverse mode and a park mode. The system includes a control device connected to the power plant and the drive motor for controlling operation of the drive motor in the plurality of modes of operation, a selectively actuated brake device for interrupting high pressure fluid flow to the drive motor, and a check valve bridge circuit for connecting the drive motor to a low pressure fluid source when the brake device is actuated.

Abstract: The invention pertains to an electrohydraulic servo door drive for operating a door, a window, or the like, with a hold-open function, where a valve is installed in the hydraulic circuit to implement the hold-open function. To create an electrohydraulic servo door drive which requires less space and can be produced at lower cost, it is provided according to the invention that the valve is designed as a hydraulically controlled hold-open valve.

Abstract: A hydraulic circuit branch includes a hydraulic actuator, such as a cylinder, and an assembly of one or more electrohydraulic proportional valves connected in series between a pressurized fluid supply line and a tank return line. The force acting on the hydraulic actuator is determined by sensing fluid pressures produced by the hydraulic actuator. Pressures in the supply and tank return lines also are sensed. The sensed pressures and a desired velocity for the hydraulic actuator are employed to determine an equivalent flow coefficient, which characterizes fluid flow through the hydraulic circuit branch, either a conduction or restriction coefficient may be derived. The equivalent flow coefficient is used to determine how to activate each electrohydraulic proportional valve to achieve the desired velocity of the hydraulic actuator. The equivalent flow coefficient also is employed to control the pressure levels in the supply and tank return lines.

Abstract: The flow of fluid to a hydraulic actuator is controlled by a valve assembly which operates in different metering modes at various points in time. The metering mode to use in selected in response to the hydraulic load that acts on the valve associated with the hydraulic actuator. Specifically the load is determined and then compared to threshold levels associated with the different metering modes to choose the metering mode for use a given point in time.

Abstract: A hydraulic circuit branch includes a hydraulic actuator, such as a cylinder, and an assembly of one or more electrohydraulic proportional valves connected in series between a pressurized fluid supply line and a tank return line. The force acting on the hydraulic actuator is determined by sensing fluid pressures produced by the hydraulic actuator. Pressures in the supply and tank return lines also are sensed. The sensed pressures and a desired velocity for the hydraulic actuator are employed to determine an equivalent flow coefficient, which characterizes fluid flow through the hydraulic circuit branch, either a conduction or restriction coefficient may be derived. The equivalent flow coefficient is used to determine how to activate each electrohydraulic proportional valve to achieve the desired velocity of the hydraulic actuator. The equivalent flow coefficient also is employed to control the pressure levels in the supply and tank return lines.

Abstract: A valve device (10) for at least one hydraulic motor suitable for driving a mass of large inertia. The device includes first and second ducts (12, 14) serving to be connected to respective ones of the two main ducts (feed or discharge) of the motor, and an auxiliary duct (15) connected, for example, to a booster duct. The device can have two configurations, depending on which of the main ducts has the higher pressure, in which configurations the main duct at high pressure is isolated, while the main duct at low pressure is connected to the auxiliary duct. The device includes time delay means (36, 46, 38, 48) suitable for limiting the speed of transition between one and the other of the first and second configurations when the difference between the pressures in the first and second main ducts (12, 14) changes sign.

Abstract: A hydraulic drive unit is disclosed which can prevent the occurrence of cavitation at the time of turning OFF of a hydraulic motor without greatly modifying the circuit configuration and the entire system and which, as a result, can improve the deceleration feeling of the hydraulic motor and prevent the occurrence of a low noise.

Abstract: A hydraulic system controls the flow of fluid to and from several functions on a machine. Each function has a valve assembly through which fluid is supplied under pressure from a source to an actuator and through which fluid returns from the actuator to a shared return line connected by a return line metering valve to the system tank. There are several regeneration modes of operation in which fluid exhausted from one port is supplied into the other port of the same actuator, which eliminates or reduces the amount of hydraulic fluid that must be supplied from the source. In some regeneration modes, input fluid for an actuator is obtained from another hydraulic function via the shared return line. In these regeneration modes an electronic controller operates the return line metering valve to restrict fluid from flowing into the tank from the shared return line, so that the fluid will be available to be supplied into an actuator port.

Abstract: The present invention provides a hydraulic controller comprising: a plurality of switching spools; a plurality of cylinder ports of a switching valve; a compressed oil passage common to the switching valves having an intermediate chambers, at least a check valve in correspondence with at least a part of said switching spools, and said check valve being positioned between said intermediate chambers and said cylinder ports, so that said switching spools being positioned in a neutral position to close said passage and also being movable to adjust opening degree of said passage, wherein auxiliary ports are provided between the cylinder ports and a tank line; flow rate adjusters are also provided between the auxiliary ports and the tank line for adjusting an opening degree of the passage; pressure detectors are provided in the switching valves for detecting pressures of oils in the intermediate chambers; a maximum pressure selector operatively linked to said pressure detectors for selecting a maximum pressure from

Abstract: The present invention relates to a backpressure control circuit for a hydraulic drive device, which reduces the loss in drive power and which can suppress cavitation. Thus, the backpressure control circuit for hydraulic drive devices is a hydraulic drive circuit: for supplying to a hydraulic motor pressurized oil discharged from a hydraulic pump through a direction changeover valve, which is switched upon receipt of a pilot pressure; and for permitting at the time of braking by the hydraulic motor, a throttle valve to throttle return oil from the hydraulic motor and oil discharged from the hydraulic pump to generate a backpressure to supply pressurized oil to the hydraulic motor via a check valve for prevention of cavitation.

Abstract: Cylinder drift resulting from internal leakage of a recycling circuit, which recycles oil returned from the arm cylinder of a hydraulic shovel to the hydraulic supplying end, is reduced by an hydraulic circuit which includes a recycle valve attached directly to a control valve. When working fluid is returned from a rod chamber of arm cylinder into the control valve, the recycle valve recycles a part of the working fluid through a recycle selector valve to the hydraulic supplying end. A pilot operated check valve is disposed in the oil channel that connects the rod chamber and recycle selector valve together. When extending arm cylinder of the hydraulic shovel, pilot pressure from control valve shifts a pilot selector valve in such a direction as to open pilot operated check valve. When control valve is at the neutral position, pilot selector valve is shifted back to the return position and closes pilot operated check valve so that return oil of arm cylinder is prevented from working on recycle selector valve.

Abstract: The disclosure relates to a new valve and a hydraulic system incorporating such valve. A mode-selection assembly on the valve is adjustable between an open-loop position for system purging and a closed-loop position for normal system operation. A sealing member moves with the spool and with the mode-selection assembly in the open-loop position, the sealing member may be urged against a stationary abutment member in the valve. Such cooperative sealing member/abutment member contact blocks the closed-loop flow path and causes fluid to be "rerouted" to tank rather than back to the pump. The system is thereby temporarily converted to open-loop configuration for purging and is restored to closed-loop configuration by moving the mode-selection assembly to the closed-loop position. The new valve is particularly useful in hydraulic steering circuits for boats.

Abstract: Cavitation in axial piston motors (20) caused to act as a pump by an aiding load (28), and the related difficulty of loss of hydrostatic film (52), and tipping or hammering of motor slippers (64), can be reduced by a method which includes the step of recirculating hydraulic fluid from the supply port (18) of the motor (20) to the return port (30) of the motor (20) upon the occurrence of an aiding load (28).

Abstract: A tilt cylinder for tilting an outboard engine has first and second cylinder chambers. A pair of on/off valves is movably disposed in respective fluid passages connected to a hydraulic pump and the first and second cylinder chambers, respectively. The on/off valves are operatively combined with respective shuttle valves which have respective oil passages in facing relationship to the on/off valves, respectively, and respective ball valve bodies for selectively opening the oil passage into communication with each other. When the hydraulic pump is actuated to develop a working oil pressure buildup, one of the on/off valves is opened by the working oil pressure buildup to establish an oil supply passage from the hydraulic pump to one of the first and second chambers, and the other of the on/off valves is opened by the coacting shuttle valve which is moved by the working oil pressure buildup to establish an oil return passage from the other of the first and second chambers to the hydraulic pump.

Abstract: A hydrostatic drive system including a pump and a hydraulic motor in an open circuit which includes a feed line and a control valve in the feed line on the inflow side of the hydraulic motor to control the quantity of hydraulic pressure medium supplied to the hydraulic motor. A brake valve is located in the open circuit on the outflow side of the hydraulic motor to receive hydraulic pressure medium flowing out of the hydraulic motor. The control valve and the brake valve are constructed for independent actuation so that the functions of the control valve and the brake valve can be reversed when the direction of rotation of the hydraulic motor is reversed and the actuating pressure on the brake valve in the braking phase depends on the inflow pressure to the hydraulic motor independently of the actuating pressure on the control valve.

Abstract: A hydraulic system for controlling the contract force of a hydraulic device. A proportional pressure relief valve acts as pilot valve for a main valve that controls the lowering process. The proportional pressure relief valve is provided with a solenoid whose voltage can be varied. A pressure sensing line is also applied to the same side of the valve as the solenoid for biassing the valve against a spring.

Abstract: In the case of a hydraulic control device for an oscillating load moving system comprising a double-acting hydroconsumer (V), which is adapted to be selectively connected to a pressure source (P) or to a reservoir (T) via two separate main lines (9, 10) and a control valve (C), and further comprising a load supporting valve (H), which is arranged in at least one main line (10) between the control valve (C) and the hydroconsumer (V) and which is adapted to be opened from the other main line (9) via a pilot line (16), a damping device (X), which consists of a bypass line (23) and an interference throttle aperture (D2), is connected to the pilot line (16) of the load supporting valve (H). The pilot line (16) has provided therein a throttle aperture (D1) which is smaller than the interference throttle aperture (D2).

Abstract: An apparatus includes a feed cylinder having a first end port and a second end port. A feed cylinder is located within the feed cylinder and is movable in a drive direction in response to fluid pressure applied to the first end port, and is movable in a return direction in response to fluid pressure applied to the second end port. A feed pump selectively displaces fluid between the first and the second end ports. A variable overcenter device controls fluid pressure offset, independent of the feed pump, between the first end port and the second end port. An adjustment device automatically adjusts the variable overcenter device during travel of the feed cylinder in the drive direction to a value corresponding to an amount of force required to displace the feed cylinder in the return direction.

Abstract: A slewing control device for a hydraulic slewing crane adapted to supply a discharge oil from a hydraulic pump through a slewing control valve to a slewing motor and control a rotational direction and a rotational speed of the slewing motor. The slewing control device includes a brake pressure control valve for variably controlling a discharge pressure of the slewing motor, an acceleration pressure control valve for variably controlling a suction pressure of the slewing motor, and a controller for outputting to both pressure control valves a pressure control signal to be determined according to an operational condition of the crane upon braking of a slewing body and controlling both the discharge pressure and the suction pressure of the slewing motor to control a pressure differential therebetween. Accordingly, even when a braking torque is small, the slewing body can be smoothly braked to be stopped at a target position accurately with no oscillation of a suspended load remaining.

Abstract: A hydraulic actuator is driven by hydraulic fluid discharged from a hydraulic pump, for controlling driving of the actuator. A valve has a meter-in circuit for introducing the hydraulic fluid discharged from the hydraulic pump into the actuator. The valve also has a meter-out circuit for returning fluid from the actuator, into a tank. The meter-out circuit is provided with a main valve for controlling the return fluid from the actuator, and a pilot circuit including a variable restrictor. When the main valve is closed, the pilot circuit is closed, and when the main valve is open, its degree of opening varies depending upon an amount of restriction of the variable restrictor. A controller varies the amount of restriction of the variable restrictor valve in accordance with the driving pressure of the actuator.

Abstract: The invention relates to a braking valve arrangement for a hydrostatic drive operated in open circuit, in particular for vehicle drives, wherein a hydraulic pressure medium is supplied to the hydraulic motor from the hydraulic pump via a reversing directional control valve as desired through one of two branches each containing a pressure limiting valve and a braking control valve, and the pressure medium is discharged to the tank through the respective other of the two branches. The braking control valve controls the flow of hydraulic medium through the respective branch depending on the pressure in the respective other branch and has parallel with it a non-return valve opening into the hydraulic motor.

Abstract: A control block, having few moving parts and few bores, for the hydraulic drive of an airplane control surface comprises a primary spool valve 2 which is shifted by two electromagnetic valves I, II to determine the direction of rotation of a hydraulic motor 18. A prolongation 20 of primary spool valve 2 is located in a pressure chamber D and bears two annular pistons 22, 24 which are always a minimum distance apart. Space 26 is adapted to be connected via a control valve 34 with the return line of the hydraulic system. The position of slide 36 of control valve 34 is influenced by an electromagnetic valve III to change the pressure of the fluid in space 26 and thereby move the primary spool valve either into a position in which the fluid lines are completely opened (for the "fast speed" mode), or to move it into a position in which the fluid lines are throttled (for the "creep speed" mode).

Abstract: A drill feed control system for controlling the force exerted on a drill string having substantial weight. A feed cylinder, which has a first end and a second end, is connected to the drill string. Fluid is pumped from a reservoir to displace the feed cylinder. A first conduit is connected to the first end while a second conduit is attached to the second end. A variable displacement pump displaces fluid from the reservoir, within the first conduit, to the first end of the feed cylinder. A feed pressure control regulates the pressure of the variable displacement pump. An overcenter valve, which is connected to the second conduit, restricts the fluid exiting the second conduit. A relief valve controls the flow of fluid to a pilot conduit which extends between the first conduit and the overcenter valve. An orifice or check valve to release the pressure is connected to the pilot conduit such the the pressure in the pressure conduit will respond to a pressure increase or decrease in the first conduit.

Abstract: Cushioned swing circuits sometimes have a restricted passage between the motor conduits to allow the implement controlled by the swing circuit to coast to a stop. However, opening and closing of the restricted passage was manually controlled, thereby requiring an additional manipulative step by the operator. The present cushioned swing circuit includes a cushion valve moveable to an open position to establish communication through vent line means when a pressure differential greater than a predetermined level is generated in one of the motor conduits connecting a directional control valve to a hydraulic motor. The cushion valve is retained in the open position for a predetermined limited time after the pressure differential drops below the predetermined level so that the inertia generated pressure in the circuit is dissipated through the vent line means.

Abstract: The invention relates to a safety arrangement for a controlled drive which is connected to a conduit with impressed pressure. When the safety arrangement responds the machine is separated via shutoff valves from the inlet and outlet and a via a switchover valve the pivot angle of the machine is set to the maximum value so that the largest possible braking torque can be automatically set.

Abstract: A hydraulic operating circuit for working members of earth-moving machines includes linear and rotary hydraulic actuators each of which is associated with a respective hydraulic distributor supplied from a principal supply and with a pressure compensator of the load-sensing type. A re-supply circuit is also associated with one or more of the rotary actuators for integrating the leakage and includes two anticavitation valves and a valve for boost-feeding the anticavitation valves from the principal supply.

Abstract: A prime-mover driven variable-rate pump of relatively great flow capacity is in delivery and return-circuit connection to an intermittently loaded hydraulic motor. A fixed-rate pump of substantially less capacity is continuously driven by the prime-mover, to charge a hydraulic accumulator, there being a safety relief to sump when a predetermined high-pressure threshold is reached. The accumulator is exclusively connected to the inlet of the variable-rate pump, being isolated by check valves from delivering any reverse flow to the fixed-rate pump and from delivering any reverse flow to the return portion of the motor-driving circuit. In said return portion, and between its check valve and the motor, a "dump" valve is operable for transient diversion of return flow to sump, thereby transiently enabling enhanced load-accelerating torque from the motor; this valve is preferably pressure-operated to "dump" position upon a load-reflecting pressure rise in the supply line from the variable-rate pump to the motor.

Abstract: Hydraulic control circuit for working members of earth-moving machines including linear and rotary hydraulic actuators associated with respective hydraulic distributors for the operation of respective working members. The rotary hydraulic actuators with their distributors are grouped in a circuit separate from the linear hydraulic actuators and are provided with braking valve means constituted by a single counterbalance valve connected in a common discharge line, the opening of which is controlled by a pilot pressure signal corresponding to the lowest supply pressure for the rotary actuators.

Abstract: A compensating valve arrangement is connected between a throttling direction control valve or proportioning valve which controls fluid flow from a pressure source to a load. The compensating valve is provided with a pressure reducing valve, check valves and throttling points between the pressure supply and the control piston of the compensating valve to compensate for surges, prevent sudden driving of the load and prevent leakage.

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 hydrostatic drive system with an adjustable pump is provided with branch lines from a main delivery line to several consumers, an arbitrarily actuatable switch in each branch line, an adjustable parallel connecting restrictor in each branch line with an adjusting element loaded on one side by pressure from either the main delivery line or the branch line and on the other side by a spring and control pressure and a source of common control pressure furnishing the control pressure to the adjusting element through a check valve.

Abstract: The mechanism comprises a hydraulic circuit having a power driven pump; a reservoir for hydraulic fluid, and a motor for each wheel or two or more coaxial wheels of the carriage. The motor has a movable driven member therein and ports for the infeed and outfeed of fluid therethrough. There are connecting means between the pump, the reservoir and the ports whereby the fluid can be circulated through the motor to drive the driven member thereof. There is also a connection between the driven member of the motor and the corresponding wheel or wheels whereby the motion of one is directly transmitted to the other and vice versa, depending on which is being driven at faster speed. In addition, there are means in the hydraulic circuit for varying the speed of the driven member, and means whereby the vehicle operator can control the speed varying means to adjust the rotational speed of the respective wheel or wheels of the carriage in relation to the speed of the vehicle.

Abstract: Means are disclosed for dissipating supercharge pressure in a hydraulic system including a reversible pump (18) directly connected to a hydraulic cylinder (22). Supercharge pressure results from unequal areas on either side of a piston (24) of a single-ended hydraulic cylinder (22). When the piston moves towards the blind end of the cylinder (22), more fluid is displaced from the cylinder than is admitted to the cylinder on the opposite side of the piston. Means responsive to a pressure at a first port (82) of the pump (18) opens a passage between the second port (76) of the pump (18) and a fluid reservoir (16), allowing fluid in excess of the pump's intake requirements to pass to the reservoir (16). In a first embodiment of the invention, a rocker mechanism (60) is actuated by a piston (66) responsive to pressure at the first port (82) pressing against a first end (20) of the rocker mechanism (60), the second end (74) of the rocker mechanism (60) displacing a check ball (38) of a keep-full valve.

Abstract: A counterbalance valve for controlling the flow of fluid from a hydraulic motor when a load is lowered has a pilot operated valve which modulates the flow of pressure fluid to and from a control port connected to main valve poppet to thereby set the opening of the poppet.