A counter pressure valve arrangement for controlling a pressure level of a hydraulic fluid in a return line from a hydraulic actuator arrangement. The counter pressure valve arrangement comprises a counter pressure valve having: a moveable valve member; a counter pressure regulating port configured for being connected to the hydraulic actuator arrangement via the return line; a tank port configured for being connected to a tank or low pressure reservoir for storing low pressure hydraulic fluid; and a pump port configured for being connected to a source of pressurised hydraulic fluid. A first position of the valve member effects fluid communication between the pump port and the counter pressure regulating port for supplying pressurised hydraulic fluid to the return line, and a second position of the valve member effects fluid communication between the counter pressure regulating port and the tank port for discharging hydraulic fluid from the return line to the tank.

A hydraulic circuit for the transmissions of industrial and agricultural vehicles. The circuit comprises a feed pump driven by an internal combustion engine; a lubricating circuit; a main pressure regulator capable of bringing about a first change in the pressure of the working fluid in the circuit, this change in pressure being capable of regulation in relation to a first regulation pressure; a maximum pressure regulator for the lubrication circuit capable of bringing about a second change in pressure of the working fluid depending upon a second regulating pressure; and means for regulating regulation of the first and second regulating pressures.

A travel control device is provided with hydraulic pumps of a variable capacity type that are driven by an engine; hydraulic motors that are driven by discharged oil from the hydraulic pumps; traveling devices that are rotation-driven by the hydraulic motors; a travel operation lever that is operated so as to instruct a traveling operation; a first control valve for generating a charged hydraulic pressure by adjusting the discharged oil from a charge pump and a second control valve for generating a capacity control hydraulic pressure in accordance with the operation of the travel operation lever. The first control valve is designed to pressure-adjust and generate a charged hydraulic pressure in accordance with the rotation speed of the engine, and the hydraulic pump is subjected to a variable capacity control process by a capacity control hydraulic pressure that is pressure-adjusted and generated by the second control valve.

Provided is a pump device and a hydraulic actuator that can reduce the number of steps of performance measurement. The pump device includes: a switching valve for switching a flow of oil to a first chamber or a second chamber of a cylinder device, the inside of which is segmented into the first chamber and the second chamber by a piston; an up blow valve (first chamber-side relief valve) that relieves pressure of a first chamber-side flow path connected to the first chamber; and a down blow valve (second chamber-side relief valve) that relieves pressure of a second chamber-side flow path connected to the second chamber.

A forklift truck includes a carriage that moves up and down by a mast assembly in a multi-stage structure including an outer mast, a first inner mast accommodated in the outer mast, and a second inner mast accommodated in the first inner mast. The forklift truck includes a first lift cylinder configured to move the first inner mast up and down; a second lift cylinder configured to move the second inner mast up and down and having a pressure reception area less than a pressure reception area of the first lift cylinder. A first lift hydraulic line supplies hydraulic oil to the first lift cylinder. A second lift hydraulic line supplies hydraulic oil to the second lift cylinder. A pressure regulating valve is provided to increase a pressure of the hydraulic oil to a pressure capable of driving the second lift cylinder.

A valve has a housing which has at least two fluid openings, through which fluid can flow, and a further opening, at least one valve seat which is assigned to one of the fluid openings, and at least one closure member which is adjustable to release and/or close the at least one valve seat, the at least one valve seat which adjoins a cavity through which fluid can flow being formed on a housing part. The valve includes a sensor device which closes the opening in a fluid-tight manner and can acquire data about the fluid is arranged in the further opening. A valve island is furthermore described.

A forklift truck includes a carriage that moves up and down by a mast assembly in a multi-stage structure including an outer mast, a first inner mast accommodated in the outer mast, and a second inner mast accommodated in the first inner mast. The forklift truck includes a first lift cylinder configured to move the first inner mast up and down; a second lift cylinder configured to move the second inner mast up and down and having a pressure reception area less than a pressure reception area of the first lift cylinder. A first lift hydraulic line supplies hydraulic oil to the first lift cylinder. A second lift hydraulic line supplies hydraulic oil to the second lift cylinder. A pressure regulating valve is provided to increase a pressure of the hydraulic oil to a pressure capable of driving the second lift cylinder.

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 quick coupler circuit for attaching and detaching an attachment to a quick coupler includes a coupler cylinder, an actuator, a first hydraulic pump, a boosting valve, a coupler changeover valve, and a changeover switch. The boosting valve switches to a boosting position and the coupler changeover valve switches to a lock-side position when the changeover switch switches to a lock position. When the changeover switch switches to a hold position, the boosting valve switches to a non-boosting position and the coupler changeover valve switches to the lock-side position. When the changeover switch switches to an unlock position, the boosting valve switches to the boosting position and the coupler changeover valve switches to an unlock-side position.

A hydraulic system may include a reservoir of hydraulic fluid, a hydraulic pump, a directional control valve, a hydraulic work loop, a bypass valve, and a hydraulic motor, as well as a plurality of hydraulic conduits interconnecting such components. When excessive hydraulic backpressures are encountered, the system may employ one or more bypass valves and one or more bypass conduits to automatically, and in an on-demand manner, return some or all of the hydraulic fluid from the hydraulic motor to the hydraulic reservoir without the hydraulic fluid passing through flow constrictions causing the excessive hydraulic backpressures.