Abstract: Roughness or jerkiness in a hydraulic swing circuit in an implement having a plurality of control circuits each having a work performing device (28), (30), (32) including a swing circuit having a hydraulic motor (32), which when under an aiding load may function as a pump, is avoided in a construction that includes a source (10) of hydraulic fluid under pressure and a plurality of control valves (22), (24), (26) for the circuits which are interconnected between the source (10) and the associated work performing device (28), (30), (32). The system includes a pair of hydraulic conduits (34), (36) extending from the control valve (26) for the swing circuit to the hydraulic motor (32). A pair of pilot operated, dual level pressure relief valves (56), (58) are connected oppositely across the conduits (34), (36) at a location between the control valve (26) for the swing circuit and the hydraulic motor (32).

Abstract: A variable priority device for a swing motor in heavy construction equipment including a variable orifice device installed in an arm cylinder-side parallel oil passage of an parallel oil passage for supplying oil pumped by a single pump to a swing motor and an arm cylinder, the variable orifice device serving to perform a switching operation between an orifice state and an orifice release state in response to a pilot pressure for moving the spool of a swing motor control switching valve.

Abstract: Simultaneous operation efficiency in a case where a plurality of actuators are operated by one or a plurality of hydraulic pumps is improved. A delivery pressure passage (1a) of one hydraulic pump (1) and that (1a) of the other hydraulic pump (1) communicate with each other through a first short-circuit passage (39) via a pair of check valves (38, 38), and an unload valve (40) is provided in this first short-circuit passage (39). The load pressure introduction passages (6, 6) on the left and right hydraulic pumps (1, 1) communicate with each other through a second short-circuit passage (36) via a pair of check valves (35, 35), and a relief valve (37) is provided in this short-circuit passage (36).

Abstract: When the pump pressure detected through a pressure detecting line 48 is raised higher than a first predetermined pressure Pd1, a recovery switching valve 44 is shifted to a valve-closed position to cease the recovery function. At this time, the pump delivery pressure detected through a pressure detecting line 51 is higher than a second predetermined pressure Pd1* close to the first predetermined pressure Pd1, and an engine speed increasing device 52 controls an engine controller 11 to increase the rotational speed of an engine 10, thereby increasing the pump delivery rate. Thus, it is possible to make small speed change of an actuator and to increase working efficiency with no deterioration in operability, even when a recovery function is ceased.

Abstract: A device for recovering energy, in particular potential energy in working machines, has a hydraulically actuatable working cylinder linked to a hydropneumatic storage. At least another working cylinder is provided. The two working cylinders are mutually linked by their rod end chambers to transfer fluid and are linked to a hydraulic circuit having at least one pump. The other working cylinder is also linked at its piston end chamber to a hydraulic circuit having a pump. The energy generated by the movements of the working machine can be effectively stored in a failure-proof manner and called back at defined moments in time.

Abstract: A power steering apparatus for a motor vehicle is provided with a metering orifice arranged on a supply passage and a flow control device in parallel relation with the metering orifice. The flow control valve includes a spool and a spring and moves the spool against the force of the spring in response to the pressure difference across the metering orifice for returning an excess part of operating fluid discharged from an engine-driven pump to an intake side of the pump so as to keep the flow rate towards a power assist gear unit almost constant regardless of changes in rotational speed of the pump. A drooping device cooperating with the flow control valve is provided comprising a control orifice at the upstream of the metering orifice and a bypass valve in communication with a spring chamber of the flow control valve retaining the spring.

Abstract: A flow control system is arranged in a hydraulic circuit provided with a variable displacement hydraulic pump, plural actuators and a pump controller. The pump controller controls the displacement of the pump so that a delivery pressure becomes higher by a predetermined value than a maximum load pressure of the plural actuators, whereby the flow rate of pressure oil to the actuators is controlled. The system includes plural valve units connected between the pump and the actuators. Each valve unit has an operating and correcting variable restrictors. The system also includes pressure compensation valves, which are each arranged on an upstream side of a restrictor group consisting of the operating and correcting variable restrictors.

Abstract: A vehicle mounted hydraulic system is provided with a flow control system that allows and maintains sufficient fluid flow through the pump, regardless of pump speed or fluid usage requirements by the hydraulically operated devices, to prevent cavitation or undue pump wear.

Abstract: In all hydraulic systems, it is important to remove all entrained air, dirt and other impurities from the system prior to normal operation. In the subject invention, a method of purging and/or preconditioning a hydraulic system is provided and includes the steps of connecting a shunt line between opposite ends of respective fluid actuators and operating the respective valve mechanisms to force fluid from the source of pressurized fluid through the respective valve mechanisms across the respective shunt lines and back to the reservoir. Likewise, the subject invention provides a method to purge the signal control system of any entrained air, dirt and other impurities. The method also provides an easy process of "warming up" the system or totally replacing all of the fluid in the system with another type of fluid, such as fluid for arctic conditions. The method of purging the signal control system includes selectively connecting a bypass line between the reservoir and the signal control system.

Abstract: Hydrostatic transmissions are useful for propelling a machine to do work and travel relative to the ground. In performing work functions and during travel it is desirable to adjust machine speed to aid in handling the machine. The subject hydrostatic transmission control system includes a infinitely adjustable creeper hand lever which can be moved to any desired position and be maintained in the selected position until moved by the operator. A spring biased inching pedal can be used in combination with the creeper lever to further adjust the machine speed. This arrangement of components provides a control system for the hydrostatic transmission which can be adjusted and maintained at a desired setting.

Abstract: A hydraulic drive system comprises a controller (12) and several condition sensors. A boom-up target flow rate setting section determines a boom-up target flow rate based on signals from a pressure sensor (11) and a rotational speed meter (16), a pump delivery rate detecting section determines a pump delivery rate based on signals from a tilt angle sensor (15) and the rotational speed meter (16), a differential pressure detecting section and a center bypass flow rate calculating section determine a center bypass flow rate based on signals from pressure sensors (9, 10), a boom cylinder calculating section determines a boom cylinder flow rate from the pump delivery rate and the center bypass flow rate, and a first pump target displacement volume calculating section calculates a first pump target tilt angle .theta..sub.1 in accordance with the difference between the boom-up target flow rate and the boom cylinder flow rate. In this case, .theta..sub.1 is larger than a second pump target tilt angle .theta..sub.

Abstract: A hydraulic recovery device in a hydraulic system having a pump (1) driving a plurality of actuators through a plurality of control valves (2, 3), the hydraulic recovery device comprising a variable resistance valve (6, 60) in a first line being controlled by a control signal (Px), a third line, a check valve (7) disposed in the third line for allowing the hydraulic fluid to flow only in a direction from the first line toward the second line.

Abstract: The present invention relates to a hydraulic circuit and to an apparatus for generating pressure which use a positive-displacement pump provided with a flywheel, one-way valve for discharging the delivery of the pump into a tank, a pilot line for a first valve, delay valve for delaying the opening of the first valve, and second valve for actuating the opening of the first valve by closing the pilot line and connecting the delay valve to the tank and for actuating the closure of the first valve, connecting the pilot line to the delay valve.

Abstract: A hydraulic drive system has a consumer of hydraulic power connected to a pressure medium source, e.g., a hydraulic motor 1. The consumer can be actuated by a control valve 4 throttling in intermediate positions; its width of opening is determined by a pressure difference formed at the control valve 4. The pressure difference is derived from a control pressure to be prescribed and the load pressure of the consumer. The consumer can thus be driven with a definite power or a definite torque. To limit the movement speed of the consumer, it is proposed to reduce the control pressure as a function of the speed of movement. The control pressure is present in a control pressure line 7 or 8, which empty at a charging space of the control valve 4, active in the opening direction. A drain line 16 branches from the control pressure line 7 or 8, in which a multiway valve spring-loaded in the closing direction and throttling in intermediate positions is located.

Abstract: A hydraulic drive system for hydraulic working machines has a variable displacement hydraulic pump, at least one actuator driven by the hydraulic fluid, a directional control valve of center bypass type for controlling the flow of the hydraulic fluid, a center bypass line for connecting the center bypass passage of the control valve to a reservoir and a fixed restrictor disposed in the center bypass line. A first control signal that determines a first target displacement of the hydraulic pump is determined by using the pressure generated by the fixed restrictor. A second control signal is generated for determining a second target displacement of a hydraulic pump. A third control signal, which is the larger one of the first and second control signals, provides a target displacement that is applied to a pump regulator that controls the displacement of the hydraulic pump.

Abstract: An inertial body drive mechanism which is arranged to prevent a reversing motion of a hydraulic motor 1 after an inertial rotation and which is capable of stopping the hydraulic motor 1 quickly together with an inertial body. An oil chamber 26 of a reversing motion preventive valve 21 and an oil reservoir chamber 34 of an oil suction feeder 32 are communicated with each other through a tank conduit 27 with a throttle 38. Operating oil is supplied into and out of the oil chamber 26 by way of the oil reservoir chamber 34 of the oil suction feeder 32 in relation with displacement of a piston operating in response to oil pressure acting in a pilot chamber 33. When inertial rotation of the hydraulic motor 1 is once stopped, operating oil is supplied from the oil reservoir chamber 34 to the oil chamber 26 thereby sliding the reversing motion preventive valve 21 from a closed position (a) to an open position (b) to prevent reversing motions of the hydraulic motor 1.This application is a designated filing under 35 U.

Abstract: A hydraulic door operator includes a reversible hydraulic pump driven by an electric motor and connected in a closed loop to a reversible hydraulic motor which operates the door. A bypass valve assembly is connected across the loop between the pump and hydraulic motor. The bypass valve assembly is operative when fluid is delivered by the pump to drive the motor in one direction so that a portion of the fluid flow is bypassed from reaching the motor. When the pump is operated to deliver fluid to drive the motor in the opposite direction, the bypass valve assembly is inoperative. When operative, the bypass assembly will cause the motor to be driven at a slower speed than it will be driven when the bypass valve assembly is inoperative.

Abstract: A hydrostatic transaxle having a hydrostatic transmission includes a plate-like dump valve disposed between the transaxle housing or in a recess formed therein, adjacent a fluid conduit that connects the pump and motor of the transmission, the dump valve having fingers which unseat valves in the conduit to relief pressure therein. A rod having an offset portion extends through a bore in the dump valve, the rotation of the rod and offset portion urges the fingers of the plate-like dump valve towards or away from the conduit valves. The settling chamber disposed within the transmission includes protrusions upwardly projecting from the bottom of the chamber which trap particulates suspended in the hydraulic fluid that circulate through the system. A magnet is likewise disposed in the settling chamber adjacent the protrusions for attracting and holding magnetic particles and debris circulated by the hydraulic fluid.

Abstract: A hydrostatic rotary power transmission system that provides a stable rotation rate at very slow rotation speeds is provided. The system operates in two speed control modes, one being a normal mode for use in the rotation rate range of 50 rpm to the maximum rated speed and a second or fine speed control mode for use in the rotation range of <1.0 to 250 rpm. In the normal control mode, the rotation speed is a function of the displacement of the hydrostatic pump. In the fine speed control mode, the motor rotation rate is a function of the flow rate through a proportional-flow valve that is downstream of the motor.

Abstract: A clutch valve is constituted with a valve cylinder fitted in and fixed to the center of a cylinder block in a manner to form with the cylinder a third ring-shaped oil passage and a second ring-shaped oil passage to communicate with a first ring-shaped oil passage and a valve body slidably fitted in the valve cylinder in a switchable manner to communicate between the third and second ring-shaped oil passages and/or shut them off from each other.

Abstract: A plunge valve for closing and for opening a connection in a hydraulic conduit comprises a plunge (37) which is slidably movable in the hydraulic conduit (5, 5A) under the influence of the pressure in a section (5A) of the conduit on the inlet side of said conduit adjacent to the plunge between a first, open position, when the pressure in said section (5A) is high, in which position the plunge is withdrawn and communication is established, and a second, closed position, in which the pressure in said section is low, in which position the plunge shuts off said connection.

Abstract: The present invention is directed to a hydro-mechanical or electro-hydro-mechanical control system utilized for positioning a mechanical device. The control system incorporates an open-center control valve for selectively controlling the differential pressure applied to and the differential flow between input ports of a power output transducer in response to a mechanically applied rotational inputs. The power output transducer is then utilized to position a mechanical device. The control system is a closed loop circuit adapted to supply hydraulic fluid at a desired supply pressure to the control valve. The supply pressure is varied in relation to the absolute value of the pressure differential or load pressure exerted across the input ports of the power output transducer.

Abstract: A switching arrangement for controlling the speed of hydraulic drives, wherein a speed of the drive is assigned to a corresponding flow rate of a hydraulic medium. The flow rate is determined by a preselected pair of phased nozzles placed in the inlet and outlet lines. The nozzle flow rates are selected such that switching between a series of nozzle pairs creates a smoothly changing speed of the hydraulic drive, thus eliminating jolting during starting and braking.

Abstract: A low breakout power transfer unit for transferring power between first and second hydraulic systems includes first and second pump/motor units to allow fluid flow between the first and second pump/motor units and the first and second hydraulic systems, respectively. The transfer unit includes a detection device for sensing fluid flow demand in the hydraulic systems and values for automatically isolating the pump/motor units from the hydraulic systems when the detection means senses substantially no fluid flow demands in a hydraulic system. The transfer unit includes a bypass device for each pump/motor unit for recirculating pumped fluid in excess of fluid flow demand.

Abstract: The present invention relates to a valve assembly for the supply of users in hydraulic control systems with pressurized fluid for the load pressure (LS) independent control of several simultaneously actuated hydraulic users wherein the ratio of the partial flows once set is maintained at undersupply of the system with the pressurized fluid. When the demand of the users exceeds the maximum output flow of the variable displacement pump, the (high) priority users receive the demanded quantity whereas the low priority users receive a reduced quantity by switching the control pressure for the low (i.e. no) priority users via a directional control valve and a pressure relief valve to a lower pressure level. Only when undersupply of the entire system occurs, i.e. when the maximum output flow of the variable displacement pump is no more sufficient despite the limitation of the control pressure for the low priority users, then the presently flowing partial flows of all users are reduced proportionally.

Abstract: A device for controlling the variable capacity motor incorporated in a hydraulic drive vehicle, wherein a control valve for reducing the oil pressure for controlling the motor is provided to pilot hydraulic piping extending from a control pump or controlling the capacity of the motor, and changeover valves are provided for performing changeover between operation and non-operation of the pressure reduction valve. The above structure serves to control the minimum capacity of the variable capacity hydraulic motor while reducing the pressure of pilot oil introduced from the control pump and, when a pressure in the main circuit exceeds a preset value, the changeover valves operate even when the pressure reduction valve is in operation so as to cancel such operation for continuously controlling the vehicle.

Abstract: A method and device for regulation of the output power of a fluid power motor involving the bypass of a selected portion of the supplied pressure fluid to the motor exhaust as a means of effectively reducing the available pressure drop across the motor and thereby its power output.

Abstract: A hydraulic drive system for civil-engineering and construction machines has reverse motion check valves and a regulator for selectively limiting outflow of the hydraulic fluid through the reverse-motion check valves. This prevents unusual operation of the valves in certain environments, such as in a low-temperature environment and in an environment where the civil-engineering and construction machine is operated on an incline.

Abstract: The invention relates to a system for powering the driving actuator of an aircraft undercarriage, the system including a hydraulic generator capable of delivering fluid under pressure to one or the other of two chambers of the driving actuator. According to the invention, the power supply system includes a safety device enabling any overloading of the actuator rod under the effect of pressure peaks to be avoided: said device comprises two pressure relief valves, the first valve limiting the pressure delivered to the annular chamber and being under the control of the pressure in the full-section chamber, and the second pressure relief valve being of the differential type and continuously controlling the pressure difference between the two chambers of the actuator. The invention is applicable to providing very safe power supply systems for aircraft undercarriages.

Abstract: When a hydraulic circuit for driving actuators of a construction machine or the like includes a single hydraulic pump and a plurality of direction changeover valves connected to the hydraulic pump for controlling the respective actuators, operation of one of the direction changeover valves may result in undesirable change in the output oil pressure of the other direction changeover valves. The inventive hydraulic circuit includes means for driving a regulator of the hydraulic pump in response to any oil puressure change at the inlets of the direction changeover valves corresponding to the output oil pressure change, thereby compensating for the pressure change.

Abstract: A hydraulic system for a vehicle that includes an implement such as a bucket that is operated by a hydraulic actuator and a directional valve which controls flow from a load sensing variable displacement pump. A hydraulic bucket shake circuit is provided which is selectively operable to force the pump to a maximum displacement condition thereby providing standby pressure and flow to the directional valve so that the directional valve can be operated rapidly in order to shake the bucket and dislodge mud, clay and debris from the bucket or to allow penetration into frozen ground.

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: A Hydraulic control circuit and a hydraulic control apparatus therefor are disclosed to preferentially feed fluid in a controlled amount or below to a first circuit system and feed fluid in an excessive amount exceeding the controlled amount to a second circuit system, and change over a pressure generated to a pilot pressure. Changing-over of control valves which are provided in the second circuit system permits a pilot pressure to be generated in the circuit. When any trouble occurs in the control valves, fluid fed to the second circuit system is unloaded, to thereby eliminate a possibility that an actuator is unexpectedly actuated.

Abstract: A hydraulic control system includes a pump, a hydraulic motor and a motor hydraulic circuit interconnecting the pump and the motor. The circuit includes a first hydraulic fluid line extending between the pump and an inlet of the motor and a first control valve located in the fluid line for selectively allowing the flow of fluid between the pump and the motor inlet. A second hydraulic fluid line extends from an outlet of the motor to the first control valve. A circuit is provided for allowing a flow of fluid between the first and second fluid lines. Located in the circuit is a flow control orifice for slowing a flow of fluid between the first and second fluid lines.

Abstract: The present invention relates to an electrically actuated and controlled auxiliary hydraulic system for controlling the flow of hydraulic fluid under pressure to mounted attachments on a skid steer loader. In one embodiment, an electrically actuated auxiliary control valve is coupled to the front and rear mounted attachments through an electrically actuated diverter valve. In a second embodiment, a front and a rear auxiliary control valve is coupled to the front and rear mounted attachments. An operator can select between control of either the front or rear attachments by selectively actuating the forward, reverse and latch switches on the control handles. A mode control switch electrically coupled to an auxiliary mode control circuit allows the cyclical selection between the disable mode, the momentary mode, and the latch mode. In the disable mode, the actuation of the forward, reverse or latch switches has no effect.

Abstract: A hydraulic circuit supplies a controlled hydraulic flow rate to a hydraulically operated automotive component, such as, a power steering unit for satisfying the characteristic function thereof. The hydaulic circuit includes therein a flow control valve unit. In the flow control valve unit, throttle passages are provided each for throttling a hydraulic flow fed from a pump to increase its speed. Orifices are further provided in the flow control valve unit to regulate a hydraulic flow rate to be supplied toward the hydraulically operated automotive component. Each orifice functions to allow less hydraulic flow rate to pass therethrough toward the hydraulically operated automotive component corresponding to increasing speed of a hydraulic flow just upstream thereof.

Abstract: A continuously active pressure accumulator power transfer system for a vehicle or a like comprises an engine, a pump driven by the engine, a main pressure accumulator maintained at a substantially constant fluid pressure and fluid volume by the pump during operation, a fluid motor for propelling the vehicle which is supplied with driving fluid pressure from the pressure accumulator and auxiliary units for operating the vehicle. The auxiliary units are also operated by fluid pressure from the pressure accumulator. The fluid motor(s) and the auxiliary units are operated directly by fluid pressure from the accumulator without any direct connection with the engine.

Abstract: A detachable intake neck connection for a pump which prevents aspiration of air into the hydraulic pump if a suction line is missing. The hydraulic pump has a first neck bore that, communicates with a suction chamber, which tightly receives an intake hose nipple of a suction line. The pump has a second neck bore for a pressure line, this second bore communicates with a pressure chamber. A connecting bore 31 that communicates with the pressure chamber of the pump begins at the neck bore for the intake hose nipple and is tightly closed by the intake hose nipple introduced into the neck bore. If the intake hose nipple is missing, the pressure chamber of the pump is short-circuited to the suction chamber through the connecting bore. A buildup of pressure in the pump and hence pumping of air is therefore precluded, the hydraulic pump is usable for instance for hydraulic vehicle brake systems, in which for safety reasons, the aspiration of air into the brake system must be prevented.

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 refuse collection vehicle has a pair of hoists which can be operated together to lift a large container by both hoists and which can also be operated separately for the lifting of a small container by each hoist, a hydraulic liquid circuit which includes a respective control valve for each hoist, respective inlets on the control valves are interconnected by a duct which includes a flow-restrictor to permit hydraulic liquid flow to one control valve to be supplemented at a relatively low rate from hydraulic liquid flow to the other control valve, so that to operate the hoists together both control valves are operated together.

Abstract: A hydraulic circuit, for use with i.e. a backhoe implement of a work vehicle. The circuit includes an engine, first through third pumps driven by the engine and a plurality of actuators. The invention is characterized by a relief pressure switchover device for selectively providing a first mode for realizing a low relief pressure in the first and second feed oil passages and a second mode for realizing a high relief pressure in the same and a relief pressure control device for causing the relief pressure switchover device to automatically provide the first mode when the third pump is loaded and causing the switchover device to automatically provide the second mode when the third pump is unloaded.

Abstract: A hydrostatic transmission is provided of the type including a pump (15), a motor (17), and a pintle assembly (35) defining high (61) and low (63) pressure fluid conduits. In communication with the conduits, the pintle assembly includes a pair of acceleration valves (85, 89), each of which comprises a differential area piston. Adjacent each acceleration valve is a pilot valve means (95) disposed in a pilot bore (105) and including a valve member (115) operable, in response to system pressure in excess of the pressure relief setting of a spring (117) to relieve fluid pressure in a chamber (101), such that the acceleration valve (85) is biased toward an open position (FIG. 5) relieving fluid pressure spikes from the high pressure conduit (61) to the low pressure conduit (63).

Abstract: A continuously variable hydraulic transmission operatively interconnects a transmission mechanism and a clutch mechanism. The hydraulic transmission includes an oil pump having an inlet port and an outlet port and a transmission ratio control member such as a swash plate which is displaceable for varying the transmission ratio between a higher-speed position, a lower-speed position, and a neutral position, an oil motor having an inlet port and an outlet port and drivable by the oil pump, a first oil passage hydraulically interconnecting the outlet port of the oil pump and the inlet port of the oil motor, a second oil passage hydraulically interconnecting the inlet port of the oil pump and the outlet port of the oil motor, a housing accommodating the oil pump, the oil motor, the first oil passage, and the second oil passage, and an oil passage control unit for selectively bringing the first oil passage into and out of hydraulic communication with the second oil passage.

Abstract: A power steering pump includes a housing defining an opening containing a sliding vane rotor, a cam ring and pressure plates located at each axial side of the rotor and having inlet ports connected to a source of low pressure fluid and outlet ports connected to a power steering system. The pressure control valve opens and closes an orifice of constant size connecting the pump outlet to a power steering gear. An electronically variable orifice arranged in parallel with the fixed orifice connects the pump and outlet to the power steering gear. When the control valve opens sufficiently, the pump outlet is connected to the inlet through a diffuser arranged to draw low pressure fluid into a high velocity stream of bypass fluid. Kinetic energy of the stream is used to increase static pressure in the fluid supplied to the pump inlet.

Abstract: A hydraulic circuit system comprising a hydraulic-fluid supply source, at least one hydraulic actuator operated by hydraulic fluid from the hydraulic-fluid supply source, a flow control valve for controlling the flow of the hydraulic fluid to be supplied to the actuator and a pressure control element for maintaining the differential pressure across the flow control valve at a predetermined value.

Abstract: A proportional directional control valve in combination with a pressure compensator flow rate control valve opening towards a reservoir and a pressure unloading valve in the load- pressure- carrying control line for the compensator valve are provided to actuate the telescopic cylinder of a tipper truck. The valve device is connected to a pump of constant displacement. The operating speed of the telescopic cylinder is independent from the load to be lifted and the driving speed of the pump. Upon reaching a predetermined load pressure the pressure unloading valve is activated and the load pressure engaging the compensator valve towards closing direction is reduced via the reservoir such that the compensator valve opens and the pump displacement volume returns to the reservoir.

Abstract: A hydraulic circuit for a hydraulic shovel includes a variable displacement hydraulic pump; selector valves communicated with the variable displacement hydraulic pump; actuators communicated with the selector valves; variable relief valves provided in a discharge oil passage of the variable displacement hydraulic pump and also provided in input oil passages of some of the actuators; a pilot hydraulic pump communicated with the variable relief valves through pilot oil passages; a solenoid valve provided in the pilot oil passage for changing set pressures of the variable relief valves; a regulator for controlling a discharge quantity of the variable displacement hydraulic pump; and a pilot oil passage for communicating the solenoid valve with the regulator.

Abstract: An apparatus for controlling the distribution of drive power in a motor vehicle includes a pair of pressure regulating valves, a pair of regulated pressure passages interconnecting the pressure regulating valves, respectively, and torque transmission clutches which transmit drive power to a pair of drive wheels, and a shut-off valve mechanism disposed between the regulated pressure passages for selectively bringing the regulated pressure passages into and out of each other.

Abstract: In a hydraulic drive, in which a double-acting working cylinder (10) is connected to the hydraulic power source by very long working lines (20, 22), it is proposed to connect a bypass line (36) containing a normally closed bypass valve (38) to the ends of the working lines (20, 22) nearest the cylinder. The bypass valve (38) is periodically opened to allow the fluid contained in the working lines (20, 22) to be completely replaced.

Abstract: A single hydraulic pump (6) is employed in a vehicle for supplementing fluid to a hydrostatic transmission (1) and for supplying fluid to a fluid-operated clutch (2) and to high pressure-actuated hydraulic actuators (3, 4, 5). Fluid discharge path (7) of the pump is connected to the hydrostatic transmission through a pressure-reducing valve (8). Fluid drain path (9) of the reducing valve is fashioned to a fluid supply path for the clutch. A second fluid supply path (11) is connected to the discharge path for supplying fluid to the hydraulic actuators and include a relief valve (12) or orifice (12A) for maintaining fluid pressure in the discharge path higher than the output pressure of the reducing valve. A high pressure relief valve (10) for establishing fluid pressure to be applied to the actuators is connected to the discharge path for minimizing a discharge pressure required to the pump.