A hydraulic system and a method comprising a linear actuator 23 for generating discrete sum forces, chambers A-D for generating discrete force components, at least two charging circuits 3,4 configured to maintain predetermined pressure levels of hydraulic fluid, independent control interfaces 9-16 configured to open and close connections of the first and second charging circuits to the chambers, and an electronic control unit 50 for controlling the control interfaces. At least two control interfaces are proportional valves which are used as shut-off valves and are independently switchable to the open and closed positions in a controlled manner. Moreover, non-throttled control and secondary control are implemented in the hydraulic system and the method.

Provided is a hydraulic pump arrangement including a plurality of motor-pump units connected to a common confluence, wherein each motor-pump unit of the hydraulic pump arrangement includes a pump realized provide pressurized fluid at its outlet; a motor arranged to drive the pump; a bypass valve configured to relieve pressure at the pump outlet; and wherein the hydraulic pump arrangement further includes a controller configured to receive a feedback signal from each motor-pump unit and to actuate the bypass valve of a motor-pump unit on the basis of the motor speed of that motor-pump unit. Further provided is a method of operating such a hydraulic pump arrangement, and a wind turbine including a number of such hydraulic pump arrangements.

A work vehicle includes: a main hydraulic pump that supplies pressure oil to a hydraulic cylinder; an accessory pump that supplies pressure oil to an auxiliary machine; and a confluence switching valve that merges pressure oil of the accessory pump with pressure oil of the main hydraulic pump. The work vehicle is provided with a control device that, in case atmospheric pressure or air density of outside air is lower than a predetermined value, executes confluence limitation control of reducing a confluence flow rate at the confluence switching valve compared to the time in case the atmospheric pressure or the air density of the outside air is higher than the predetermined value, and canceling the confluence limitation control in case rotation speed of an engine becomes higher compared to a predetermined rotation speed value during the confluence limitation control, and the rotation speed value is higher as the atmospheric pressure or the air density of the outside air is lower.

A fluid pump for a linear actuator causes a rod in the actuator to extend or retract by controlling fluid flow 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 check valves that control fluid flow between a driven pump element and each portion of the fluid chamber and a shuttle movable in response to fluid pressure along a shuttle axis extending through the valves. At least one valve includes a valve member movable between a closed position and an open position defining a fluid flow path between the driven pump element and fluid chamber and means for limiting movement of the shuttle towards the valve such that the shuttle may, depending on the position of the limiting means, move the valve member to an intermediate position between the closed and open positions.

A hydraulic control apparatus includes an output-side oil passage into which oil from a first oil passage and oil from a second oil passage flow, and a pressure regulating check valve regulating a hydraulic pressure in the second oil passage. The pressure regulating check valve includes first and second elastic portions housed in a spool hole between a valve body and a bottom of the spool hole. A natural length of the second elastic portion is shorter than a distance between the valve body and the bottom when the valve body closes an inflow hole. The second elastic portion applies an elastic force to the valve body in a state in which the valve body opens the inflow hole.

A hydraulic apparatus for a hydraulic work vehicle capable of supplying pressure oil to any of a bucket cylinder, an arm cylinder, a boom cylinder, a swing cylinder, a blade cylinder, a turning hydraulic motor, a left traveling hydraulic motor, a right traveling hydraulic motor, and a PTO hydraulic motor by a first hydraulic pump, a second hydraulic pump, or a third hydraulic pump. The pressure oil can be branched off from a discharge oil passage of the third hydraulic pump and supplied through an external pipe to a downstream side of a load check valve disposed on an oil passage communicating with a pump port of a PTO control valve for switching supply of pressure oil from the second hydraulic pump to an external hydraulic work machine.

A hydraulic system includes a hydraulic actuator to be operated by an operation fluid, a first hydraulic pump to output the operation fluid, a second hydraulic pump to output the operation fluid, a control valve to which the operation fluid outputted from the first hydraulic pump is supplied, the control valve being configured to control the operation fluid that is to be supplied to the hydraulic actuator, a first fluid tube connecting the control valve to the hydraulic actuator, a second fluid tube to which the operation fluid outputted from the second hydraulic pump is supplied, the second fluid tube being connected to the first fluid tube, and a first switching valve disposed on the second fluid tube. The spool includes a communicating fluid passage being configured to supply the operation fluid to the first inner fluid passage, the operation fluid being received by the pressure-receiving port.

A control system includes a variable displacement hydraulic pump, the pump having an inlet for receiving fluid, an outlet for discharging fluid under pressure, and a pump displacement input, a hydraulic motor having an inlet and an outlet, a fluid circuit including a supply conduit for conducting fluid discharged by the pump to the motor and a return conduit for returning fluid discharged by the motor to the pump, a pump displacement control cooperating with the pump displacement input in order to vary a displacement of the pump, a control circuit in communication with the pump displacement control for controlling the pump output such that the motor is driven at a constant rotational speed, and a system controller in communication with the control circuit and a remote location to transmit and receive information to and from the remote location.

A construction machine is provided which includes a hydraulic closed circuit in which a single rod hydraulic cylinder is driven directly by a bidirectionally tiltable variable displacement pump and can stably speed up the contraction action of the single rod hydraulic cylinder. In the case where a contraction action of a hydraulic cylinder 10 is instructed through an operation lever 30, when a differential pressure obtained by subtracting the pressure of a cap chamber 10a from the pressure of a rod chamber 10b is equal to or lower than a first threshold value a set to a level equal to or higher than a selection setting pressure of a flushing valve 14, a controller 20 closes a rod side selector valve 12b to disable rod assist action for supplying hydraulic fluid from a second hydraulic pump 8 to the rod chamber, and when the differential pressure is higher than the first threshold value, the controller 20 opens the rod side selector valve to enable the rod assist action.

A hydraulic system includes a first system discharge fluid tube that discharges fluid flowing through a first supply fluid tube, a second system discharge fluid tube that discharges fluid, a first control valve, and a second control valve connected to a second supply fluid tube, the first system discharge fluid tube, and the second system discharge fluid tube, configured to be switched between: a supply position that supplies fluid from the second supply fluid tube to the first supply fluid tube; a first stop position that stops supply of fluid from the second to the first supply fluid tube and supplies fluid from the first supply fluid tube to the first system discharge fluid tube; and a second stop position that stops supply of fluid from the second to the first supply fluid tube and supplies fluid from the first supply fluid tube to the second system discharge fluid tube.