Abstract: A pilot neutralizing system of a work vehicle may include a pilot neutralizer and a flow control apparatus. The work vehicle may include a frame assembly and an actuating assembly to pivot the frame assembly. The pilot neutralizer is hydraulically coupled between an operator control member and a steering valve to selectively direct a pilot signal to the steering valve and is hydraulically coupled to a reservoir via a reservoir line. The pilot signal is used to switch the steering valve to change a direction of a hydraulic fluid flowing from the steering valve to the actuating assembly. The flow control apparatus is hydraulically coupled to the reservoir line and used to change a draining rate of the pilot signal to the reservoir. When the articulation position reaches a cushion region during steering, the pilot signal drains back through the flow control apparatus to the reservoir.

Abstract: A closed-loop hydraulic circuit associated with a swing mechanism of a machine is controlled to obtain both a pressure control during acceleration and deceleration of the swing mechanism and a velocity control during coasting. In this manner, a system pressure in closed-loop hydraulic circuit is maintained below a maximum allowable pressure during acceleration and deceleration, and the swing mechanism can be rotated at a desired constant speed during coasting. This is achieved by controlling a hydraulic actuator adjusting the displacement of a variable displacement pump in different control modes, depending on a comparison between a desired displacement of the pump and an actual displacement of the same.

Abstract: A regeneration control hydraulic system for an excavator, including at least one hydraulic pump, an actuator, a regeneration oil path, and a regeneration cut-off oil path. The regeneration oil path is configured to send a return oil as a regeneration oil to a cavity having a negative pressure of the actuator. The regeneration oil path is provided with a regeneration valve and a first control valve. The first control valve is configured to control the regeneration oil to enter the cavity having the negative pressure of the actuator when a working device of the excavator retracts inwards, or to control the oil to be discharged from the actuator to the regeneration cut-off oil path when the working device swings outwards. The regeneration cut-off oil path is configured to send the regeneration oil passing through the regeneration valve or the oil discharged from the actuator to other destinations.

Abstract: A manipulator includes an articulated boom configured to be folded out. The articulated boom includes a turntable that can be rotated about a vertical axis, a plurality of boom segments, electrically-actuated proportional valves, and a remote control. The boom segments are pivotable via respective drive assemblies. The electrically-actuated proportional valves are respectively arranged directly on or in proximity to the respective drive assemblies to be controlled. The remote control includes at least one control lever configured to be displaced in a plurality of actuating directions. The manipulator further includes an electronic controller configured to actuate the drive assemblies via a travel command. The travel command indicates a desired movement of the boom tip. The travel command is generated in response to displacement of the control lever into at least one of the plurality of actuating directions. And, the travel command causes actuation of the respective electrically-actuated proportional valves.

Abstract: Methods and apparatus are described for enabling downlink transparent relay in a wireless communication network. In a wireless communications network, a base station and a mobile station may communicate with each other via a relay station, as needed. Transparent relay may allow for relay communication between a base station and a mobile station although the mobile station is unaware of the relay station. However, non-contiguous transmission of a relay station may lead to channel quality measurement and channel estimation degradation during downlink transparent relay. According to some aspects, a base station may schedule a mobile station to a transmission mode that utilizes dedicated pilot signals for downlink transparent relay, and a relay station may transmit data and dedicated pilot signals over the same channel resources as the base station. According to some aspects, the relay station may null common pilot signals transmitted by the base station.

Abstract: A travel control valve includes a valve body and a spool. The valve body includes a first pump port connected on an upstream side from a drive control valve, a first connection port connected on a downstream side from the drive control valve, a second pump port connected to a second pump, and a second connection port connected to a second circuit system. The travel control valve can switch a communication opening between the first pump port and the first connection port to a large opening throttle position in which the communication opening remains smaller than that between the second pump port and the second connection port, and a small opening throttle position in which the communication opening remains smaller than that in the large opening throttle position.

Abstract: The present disclosure provides embodiments directed towards a method and a system for fine control of hydraulic cranes. In one embodiment, a system is provided. The system includes a service pack having an engine. The engine has an operating speed ranging from a low speed to a high speed, a hydraulic pump coupled to the engine, wherein the hydraulic pump is configured to supply a hydraulic output to a hydraulic load, and a control system configured to control the hydraulic output. The control system includes a fine control mode configured to lock the engine in the low speed and control the hydraulic output in proportion to a percentage of a trigger activation.

Abstract: A working vehicle, wherein flows of hydraulic oil delivered under pressure from two or more hydraulic pumps are joined together and the joined hydraulic oil can be taken out. A working vehicle is provided with two hydraulic pumps independent of each other and adapted to deliver hydraulic oil under pressure, a mode switching valve (230) capable of being switched to a flow joining position (K) at which flows of the hydraulic oil delivered under pressure by the two hydraulic pumps are joined together, PTO ports (260, 261) out of which the hydraulic oil is taken, and a PTO switching valve (240) provided downstream of the mode switching valve (230) and switching flow of the hydraulic oil so that the oil can be delivered under pressure to the PTO ports (260, 261).

Abstract: An hydraulic system for an autonomous multi-set pipeline isolation tool comprising an hydraulic piston; a pump for operating the pistons; an accumulator between each of the hydraulic pistons and the pump; and means for operating the pump. The system also comprises a manifold operable to control the flow of fluid in fluid pipelines to control the operation of the pistons which actuate gripping and sealing means of the autonomous multi-set pipeline isolation tool. The hydraulic system further comprises a controller comprising a number of operational modules which are positioned on a single printed circuit board. The advantage of this is that the size of the hydraulic system may be minimised thereby enabling use of the system within a pipeline having an inner diameter of the order of 0.15 m (6?) and upwards. The manifold of the hydraulic system is also provided with a triple fail safe redundancy mechanism.

Abstract: A mixer drum driving device includes a hydraulic motor that rotates a mixer drum, a first hydraulic pump that is driven by an engine to be capable of supplying working oil to the hydraulic motor, an electric motor, a power supply connected to the electric motor, a second hydraulic pump capable of supplying the working oil to the hydraulic motor on the basis of a driving force of the motor, and a flow dividing valve that divides the working oil discharged from the first hydraulic pump and supplies the working oil to the hydraulic motor and the second hydraulic pump. The second hydraulic pump is configured to rotate the electric motor using the working oil. The electric motor is configured to generate electric power so as to charge the power supply when driven to rotate by the second hydraulic pump.

Abstract: The present disclosure relates to a hydraulic system for a construction machine having an electronic hydraulic pump, and more particularly, to a hydraulic system which temporarily drives the construction machine when an operation of an electronic control unit controlling an electronic hydraulic pump is abnormal, particularly, when the electronic control unit is not able to perform a control because an operative amount of a joystick input to the electronic control unit is not normally transmitted to the electronic control unit.

Abstract: A system and method for calibrating an electronically actuatable hydraulic valve in a work machine may include at least one supply valve and at least one drain valve to be calibrated and a bypass valve in fluid communication with a pump and a fluid source. The at least one supply valve and the at least one drain valve may be calibrated by opening the at least one supply valve and the at least one drain valve, closing the bypass valve, setting the pump to a desired flow output, determining a first current command for the at least one supply valve corresponding to a first target pressure parameter and determining a second current command for the at least one drain valve corresponding to a second target pressure parameter.

Abstract: A circuit for driving a hydraulic cylinder of a construction machine includes: a hydraulic pump; a tank; a control valve; a bottom side line; a rod side line; a quick return circuit having a branch line branched off from the bottom side line and led to the tank and a quick return valve which allows hydraulic fluid to be flowed through the branch line only when the control valve is switched to a contraction driving position; and a recycling circuit which supplies a part of return fluid discharged from a bottom side fluid chamber to a rod side fluid chamber of the hydraulic cylinder. The recycling circuit allows the hydraulic fluid to be flowed only from the bottom side fluid chamber into the rod side fluid chamber of the hydraulic cylinder only when the hydraulic cylinder is switched to the contraction driving position.

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 hydraulic system is disclosed. The hydraulic system may have a unidirectional variable displacement first pump, a first actuator connected to the first pump via a closed-loop first circuit, and a first switching valve disposed between the first actuator and the first pump. The first switching valve may be configured to control a fluid flow direction through the first actuator. The hydraulic system may also have a second actuator connected to the first pump in parallel with the first actuator via the first circuit, and a second switching valve disposed between the second actuator and the first pump. The second switching valve may be configured to control a fluid flow direction through the second actuator. The hydraulic system may further have a modulation valve associated with the first circuit and configured to selectively modulate a pressure of the first circuit during actuation of the first or second switching valves.

Abstract: A selectable flow divider drive system includes a hydraulic fluid reservoir and a plurality of drive motors in fluid communication with the hydraulic fluid reservoir. A hydraulic pump is connected between the hydraulic fluid reservoir and the plurality of drive motors and directs hydraulic fluid from the hydraulic fluid reservoir to the plurality of motors. The hydraulic pump is operable in a high flow condition and a low flow condition. A flow divider component is interposed between the hydraulic pump and the plurality of motors. The flow divider component selectively divides hydraulic fluid flow to each of the plurality of drive motors, where a flow divider of the flow divider component is sized for the low flow condition of the hydraulic pump. A bypass valve is disposed upstream of the flow divider that selectively bypasses the flow divider when the hydraulic pump is operated in the high flow condition.

Abstract: A hydraulic control device for a work vehicle includes: a hydraulic pump that supplies pressure oil; an arm drive actuator that drives, with pressure oil supplied from the hydraulic pump, an arm attached to the work vehicle so as to swing the arm; a bucket drive actuator that drives, with pressure oil supplied from the hydraulic pump, a bucket attached to a front end of the arm, so as to swing the bucket; an arm drive pressure oil control valve that controls drive of the arm drive actuator by controlling pressure oil supplied from the hydraulic pump to the arm drive actuator; a bucket drive pressure oil control valve that controls drive of the bucket drive actuator by controlling pressure oil supplied from the hydraulic pump to the bucket drive actuator; an arm operation unit that controls the arm drive pressure oil control valve; a bucket operation unit that controls the bucket drive pressure oil control valve; an operating state detection unit that detects operating states of the arm drive actuator and the

Abstract: Disclosed are a system for driving a boom of a hybrid excavator, and a method for controlling same. The disclosed system comprises: an electric motor operating by means of a motor or generator; a capacitor for storing electricity generated by the electric motor; a hydraulic pump motor driven by the electric motor to supply working oil to a boom; a boom control valve having a closed circuit for selectively connecting/disconnecting a discharge line and an inlet line of the hydraulic pump motor to/from a head or a load of the boom; a main pump driven by a driving source arranged separately from the motor so as to supply working oil to a bucket, driving motor, or arm; a boom-assisting valve, which connects a discharge line of the main pump to the discharge line of the hydraulic pump motor, such that working oil discharged from the main pump and the hydraulic pump motor can be combined; and a control unit for controlling the electric motor, the hydraulic pump motor, and the boom control valve.

Abstract: A control arrangement for use in a hydraulic control system including a control valve having at least two movable elements. The control arrangement is configured to control the positions of the two movable elements such that fluid from a common fluid pressure source is applied to both of the control surfaces of an actuator to drive the actuator. In an embodiment, the control surfaces have different effective areas.

Abstract: First and second mechanical hydraulic valves are disposed between a pump and the cap side chamber of an actuator and the pump and the rod chamber of the pump. The first and second valves are actuated as a result of respective pressure differentials applied across the valves. A controller controls flow from a pump in response to a commanded motion to control movement of the actuator, and cause the valves to open. The valves are disposed in their no-flow positions when the pump is not operative, and when the hydraulic system of off or locked out to hold a load.

Abstract: An electro-hydraulic actuator (EHA) includes a hydraulic circuit having a plurality of pressure compensated flow control valves for allowing a maximum flow rate through the fluid conduits regardless of the loads imparted on the actuator. In one embodiment of the EHA, a plurality of combination manual override/thermal expansion valves that simplify the manufacture of the EHA.

Abstract: This invention consists of two or more fixed displacement hydraulic pump/motors mounted on a common input shaft hydraulically connected to two or more fixed hydraulic pump/motors mounted on a common output shaft. The relative displacements of the pump/motors are chosen such that by selectively activating the individual pump/motors, the transmission ratio can be changed in the case when the input devices and acting as pumps driving the output devices as motors (conversely when driving the vehicle in reverse). Further, a hydraulic accumulator and reservoir are attached in a manner that allows the pressurized fluid to augment the flow produce by the input pumps in order to increase the transmission ratio. Similarly, the transmission ratio can also be reduced by causing the input pumps to pump fluid into the accumulator at the same time they are pumping fluid through the output motors.

Abstract: A valve assembly for controlling the flow of pressurized fluid supplied to an actuating cylinder having a piston driven by the pressurized fluid along a stroke path therewithin, the pressurized fluid being applied to alternative driving sides of the piston. The valve assembly comprises a first and a second valve pistons, which cooperate to block the supply of pressurized fluid to the current driving side of the piston when the piston reaches the end of its stroke path, thereby limiting the pressure of the pressurized fluid supplied to the driving side to a level reduced compared to a pressure level applied to drive said piston. If a leak occurs within the actuating cylinder at the end of the stroke path of the piston, it will be at the reduced pressurized fluid pressure.

Abstract: A hydraulic transformer is disclosed. The hydraulic transformer may have a housing, and a first pumping mechanism disposed within the housing and rotated in a first direction by fluid pressure. The hydraulic transformer may also have a second pumping mechanism disposed within the housing and rotated by the first pumping mechanism in the first direction to increase the fluid pressure. The hydraulic transformer may further have a common shaft connecting the first and second reversible pumping mechanisms. One of the first and second pumping mechanisms may also be rotated in a second direction opposite the first by fluid pressure. The other of the first and second pumping mechanisms may also be rotated by the one of the first and second pumping mechanisms in the second direction to increase the fluid pressure.

Abstract: A hydraulic brake apparatus includes a tandem brake master cylinder having a rod piston moving in response to a brake pedal, and a floating piston moving in response to the rod piston; a separation valve provided in a hydraulic brake circuit connecting the brake master cylinder and brake wheel cylinders in order to establish and shut off communication between the brake master cylinder and the brake wheel cylinders; a pressure control valve unit for controlling fluid pressure to be supplied from an external fluid-pressure supply source to the brake wheel cylinders while the separation valve is in a shutoff condition; and a stroke simulator mechanism for allowing an idle stroke of the rod piston and an idle stroke of the floating piston while the separation valve is in the shutoff condition. The idle stroke of the floating piston starts during the idle stroke of the rod piston.

Abstract: A spool-out type booster brake valve device for industrial vehicles is configured to allow hydraulic working fluid to be supplied not only to a booster chamber but also to a master chamber thereby eliminating the need to use a separate brake fluid reservoir tank for supplementing brake fluid in the master chamber. The brake valve device is used in an industrial vehicle equipped with a fluid pump, a reservoir tank and a brake actuator. The brake valve device includes a valve body having an inlet port, a drain port, a brake port, a booster chamber communicatable with the pump via the inlet port and a master chamber communicatable with the brake actuator via the brake port. The master chamber is connected to the inlet port to receive working fluid from the pump. A valve spool is slidably fitted in the valve body through the booster chamber and the master chamber, the valve spool being shifted between an idle position and an operating position.

Abstract: A microturbine fabricated by a three-level semiconductor batch-fabrication process based on polysilicon surface-micromachining. The microturbine comprises microelectromechanical elements formed from three polysilicon multi-layer surfaces applied to a silicon substrate. Interleaving sacrificial oxide layers provides electrical and physical isolation, and selective etching of both the sacrificial layers and the polysilicon layers allows formation of individual mechanical and electrical elements as well as the required space for necessary movement of rotating turbine parts and linear elements.

Abstract: The present invention provides for a control system 20 of a hydraulic construction machine for enhancing a responsibility and stability of a work implement movement The control system 20 comprises a variable displacement type hydraulic pump 2, a hydraulic actuator 7 driven by hydraulic fluid delivered from the pump 2, a flow control valve 5 for controlling the flow rate of the hydraulic fluid to the hydraulic actuator 7 in response to a an amount of an operating lever 8, the variable bleed valve 14 disposed in the bleed-off hydraulic circuit 13 through which exhausts the hydraulic fluid supplied to the hydraulic actuator 7 and a controller 15 for controlling the flow rate through the variable bleed valve 14.

Abstract: A hydrostatic drive system with a pump and at least one consuming device that is connected to the pump can be actuated by a control valve. The control valve can be actuated as a function of an actuator that specifies a desired speed of movement and a direction of movement of the consuming device. The control valve in the center position, makes possible an unpressurized circulation of the pump. The control valve can be actuated electrically, and there is a sensor that measures the actual speed of movement of the consuming device. The control valve, the speed-of-movement sensor and the actuator are connected with an electronic control that controls the control valve as a function of the direction and speed of movement specified by the deflection of the actuator and of the actual speed of movement of the consuming device as measured by the speed-of-movement sensor. The speed-of-movement sensor may be a delivery flow sensor.

Abstract: The maintenance device consists of a hydraulic insulation unit (2) mounted between the supply circuits of a cylinder (1). The insulation unit (2) comprises a sluice (9) which has, at each of its two openings, an anti-return valve, one of which, the primary valve (11) is hydraulically connected to the outlet chamber (6) of the shaft (7) of the cylinder (1) and opens toward said chamber; and a safety valve (13) opening in the same direction, with the latter valve closing at a different rate than the primary valve closes. The invention is useful for maintaining the shaft of any cylinder in position, particularly a charged cylinder, and it is of interest to manufacturers of hydraulic devices, particularly lifting cylinders, as well as those who use them.

Abstract: An apparatus for controllably actuating a hydraulic actuator is provided. The apparatus is connected between a source of pressurized hydraulic fluid and the hydraulic actuator. The apparatus controllably provides pressurized hydraulic fluid to the hydraulic actuator. The apparatus includes a controller for receiving an operating signal and a load pressure signal and responsively actuating the hydraulic actuator.

Abstract: An apparatus for controllably actuating a hydraulic actuator is provided. The apparatus is connected between a source of pressurized hydraulic fluid and the hydraulic actuator. The apparatus controllably provides pressurized hydraulic fluid to the hydraulic actuator. The apparatus includes a controller for receiving an operating signal and a load pressure signal and responsively actuating the hydraulic actuator.

Abstract: Hydraulic control of reversible hydraulic motors typically requires several different valves to provide for the various operating parameters. The subject hydraulic control circuit has only a pair of electrohydraulic control valves to provide all the typical operating parameters. Operation of the control valves is controlled by a microprocessor in response to receiving command signals from a manually controlled command signal outputting device which establishes a desired fluid flow rate and direction of flow through the control valves.

Abstract: Flow amplified control systems are useful in pilot operated steering systems. The load responsive flow amplified control system includes a directional control valve movable to an operating position to direct fluid from the operating fluid circuit through a variable orifice to a steering motor and to direct control fluid from a control fluid circuit through another variable orifice to be combined with the fluid going to the steering motor. The operating fluid circuit and the control fluid circuit are provided with fluid from a common variable displacement pump. The directional control valve is moved to an operating position by the control fluid acting thereon and is pressure compensated insofar as the flow of control fluid passing through the another variable orifice such that a substantially constant predetermined pressure differential exists across the another variable orifice.

Abstract: A pressure-compensated flow-control valve with an adjustable limiting device controls the maximum speed of a fluid motor and eliminates an additional valving element found in prior art device. The flow control valve includes a flow limiting throttle opening integral with the flow control spool. The spool can be selectively rotated to adjust the effective size of the throttle opening thereby limiting flow through the valve. The spool establishes a constant rate of flow determined by the throttle opening or a directional control valve. By incorporation of the flow limiting function within the flow control spool, the overall cost and complexity of the pressure compensated flow control valve is reduced.

Abstract: A tractor hydraulic control system of the kind comprising a power lift with a hydraulic actuator (12) and a main control valve (17) controlling the supply of fluid from a pump (19) to the actuator, the system including selector valve means (50) interconnected with the main control valve (17) and movable between a first position in which flow to and from the actuator (12) occurs via the selector valve means under the control of the main control valve and the associated system control mechanism (28) and a second position in which the actuator is hydraulically locked in a given position and an external services outlet (51) is placed in communication with the pump. Linkage means (60,61,62) operatively connects the selector valve means (50) and the system control mechanism (28) to condition the main control valve (17) to cause the pump (19) to supply fluid to the external service outlet (51) via the selector valve means on movement of the selector valve means to the second position.

Abstract: A hydraulic control system is provided including a fluid reservoir, a variable displacement pump having a fluid input in fluid communication with the reservoir and having a fluid output, and a fluid actuated displacement control mechanism for controlling the displacement of the pump. A control valve is placed in fluid communication with the fluid output of the variable displacement pump and with the reservoir and is adapted to control the flow of fluid to a fluid actuated device. The control valve includes means for developing a control pressure signal.

Abstract: An open center type control valve for a hydraulic motor, wherein pressure fluid from a source is caused to flow from the valve inlet to a motor port at a substantially uniformly metered rate despite fluctuations in the load on the governed fluid motor, due to the operation of a flow control mechanism which regulates bypass of excess fluid through the open center passage to the valve outlet in accordance with variations in the pressure differential between the inlet and outlet end portions of the open center passage.

Abstract: A fluid drive assembly has a pump, a variable displacement motor, a fluid circuit connecting the pump to the motor, and an actuator device for controlling the displacement of the motor. The actuator device is movable between a first position at which the displacement of the motor is at a preselected maximum and a second position at which the displacement of the motor is at a preselected minimum. A control system for the fluid drive assembly includes a source of fluid at a first preselected pressure value. A valve device is connected to the source of fluid and to the actuator device for controlling the fluid flow therebetween and is movable between a first position at which the source of fluid is in communication with the actuator device and a second position at which the source of fluid is blocked from communication with the actuator device.

Abstract: A control device for a hydrostatic drive, especially for a fork lift truck, in which an engine drives a reversible variable delivery pump which supplies fluid to a fluid motor connected to the drive wheels of the lift truck. A reversible actuator is connected to a control element for the pump and is connected through a reversing valve with a further engine driven pump. The rate of movement of the actuator is controlled in the opposite directions of movement thereof. The truck includes a lift cylinder supplied by a still further engine driven pump, and when the lift cylinder is under pressure, the rate of movement of the actuator is controlled at a still slower speed of movement in at least one direction of movement.

Abstract: For automatically terminating the operation of the vibrator in a self-propelled roller compactor when the vehicle is at rest or travelling slowly, a variable displacement pump driving the hydraulic motor of the vibrator is provided with a servo control mechanism including a spring-neutralized linear actuator capable of adjustably varying the per-cycle displacement of the pump by receiving hydraulic fluid pressure from another pump. Provided between the servo control mechanism and the said other pump is an on-off valve which is closed when the vehicle speed becomes less than a predetermined value, with the result that the actuator is neutralized to zero the displacement of the variable displacement pump. The on-off valve can be operated from an operator controlled shift lever, so as to be closed when the lever is in or adjacent a neutral position.

Abstract: A load responsive direction and flow control valve for use in fluid power load responsive system. The valve maintains a selected constant flow level for control of both positive and negative loads, irrespective of the change in the load magnitude or change in the fluid pressure, supplied to the valve. System is powered by a single fixed or variable volume pump. The direction flow control valve is equipped with a load responsive control which automatically regulates pump discharge pressure to maintain either a constant low pressure level or low pressure differential at the motor exhaust. The pump discharge pressure is either regulated by bypassing of excess flow to reservoir, or by a special load responsive control, which varies the pump displacement. Direction control valve may also be equipped with a control responsive to load pressure for controlling negative loads and an inlet pressure throttling control for simultaneous control of multiplicity of loads.

Abstract: A load-responsive hydraulic system is provided in which the effective output of a fixed displacement pump is controlled by a bypass valve having three fluid-responsive areas.The first fluid-responsive area is pressurized by pump pressure; and the directional control valve of the system includes a first fluid flow path which pressurizes the second fluid-responsive area with the load-actuating pressure of a fluid motor when the fluid motor is receiving pressurized fluid from the pump. Thus, the bypass valve is load responsive.The directional control valve also includes a second fluid flow path which controls a fluid pressure which is applied to the third area; so that, the force balance of the bypass valve is changed by the force developed by the third area; and the difference between pump pressure and load-actuating pressure, while operating the system, is greater than the difference between pump pressure and sump pressure at standby.