A lift arm lifting and lowering mechanism cylinder case provided with a cylinder portion into which oil is fed, a piston slidable inside the cylinder portion to define a hydraulic chamber and receiving hydraulic pressure of the hydraulic chamber on a front surface, a safety valve provided to the piston to discharge the oil inside the hydraulic chamber to the outside when the hydraulic pressure of the hydraulic chamber becomes greater than or equal to a predetermined value, and a lift arm supported by the cylinder case and rotatable in conjunction with movement of the piston, in which the piston includes an oil passage allowing communication between a rear surface of the piston and the front surface, and the oil passage includes a containing portion provided to open on the axially front surface side and capable of containing the safety valve, and a non-containing portion provided on the axially rear surface side relative to the containing portion and incapable of containing the safety valve.

To reduce an increase in the electric power consumption of an electric motor according to the state of an electric power source at the start of driving of an actuator, and make it possible to use devices in an appropriate state in an electrically driven hydraulic construction machine including a driving system that drives a hydraulic pump by using the electric motor. For this purpose, a controller 50 sets a target relief pressure of a relief valve 3 to a normal relief pressure Pn (first relief pressure) when an operation lever device 44 is not being operated and a storage amount SOC(t) of a battery 62 (the state quantity of an electric power source) is equal to or larger than a threshold S1, and sets the target relief pressure to a reduced relief pressure Pr(t) (second relief pressure) lower than the normal relief pressure Pn (first relief pressure) when the operation lever device 44 is not being operated, and the storage amount SOC(t) of the battery 62 (the state quantity of the electric power source) is smaller than the threshold S1.

A valve unit (V) has a valve housing (50) that includes a supply oil passage (55) configured to receive operating oil from a hydraulic pump, and a pressure adjustment valve (Va) configured to adjust the pressure of the supply oil passage (55). The pressure adjustment valve (Va) includes a pressure adjustment valve body (61) configured to open and close the supply oil passage (55), a compression coil spring (62) that keeps the pressure adjustment valve body (61) at a closed position when the pressure of the supply oil passage (55) is smaller than a set value and allows the pressure adjustment valve body (61) to open when the pressure of the supply oil passage (55) is not smaller than the set value, and a restriction member (63) configured to, when the pressure adjustment valve body (61) becomes open against the urging force of the spring (62) in response to a pressure of the operating oil, abut against the pressure adjustment valve body (61) to restrict movement of the pressure adjustment valve body (61).

A fluid pressure valve according to an embodiment of the present invention is applicable to a fluid pressure servo mechanism. The fluid pressure valve includes a housing having a housing member, the housing member being formed integrally so as to have a first port, a second port, and a flow path connecting between the first port and the second port.

A method and control system operable to control movement of a work implement of a work vehicle. The control system includes a reservoir that retains fluid, a pump in fluid communication with the reservoir, and an actuator in fluid communication with the pump. The actuator has a first side and a second side. A control valve is fluidly positioned between the pump and the actuator, a first proportional relief valve is fluidly positioned between the pump and the first side of the actuator, and a second proportional relief valve is fluidly positioned between the pump and the second side of the actuator. The first proportional relief valve is configured to permit flow of fluid from the first side of the actuator to the reservoir when a pressure at the first side of the actuator exceeds a pressure set point.

A valve for controlling a hydraulic cylinder on a work machine may include a raising position configured for placing a pump in fluid communication with a cap end of the hydraulic cylinder. The valve may also include closed center position configured for closing off fluid communication to the cap end line and the rod end line. The valve may also include a lowering position configured for placing the pump in fluid communication with the rod end of the hydraulic cylinder. The valve may also include a snubbing position configured for placing the cap end in restricted flow fluid communication with the tank and for placing the rod end in restricted flow fluid communication with the tank.

Hydraulic valve circuitry adapted for hydraulic connection to a lift truck having a mast and at least one lift cylinder for alternately raising and lowering the mast. The hydraulic assembly is also adapted for hydraulic connection to an attachment to the lift truck, the attachment having opposed clamps actuated by respective clamp cylinders. The hydraulic assembly preferably comprises a valve circuit capable of causing the at least one lift cylinder to be an accumulator.

A hydraulic drive system of a construction machine includes: a boom control valve connected to a boom cylinder by a boom raising supply line and a boom lowering supply line; a pump that sucks hydraulic oil through a suction line, and delivers the hydraulic oil through a delivery line; a regenerative valve that brings the boom raising supply line and the suction line into communication with each other through a regenerative line when a boom lowering operation is performed; and a controller that controls an accumulator switching valve. The controller: switches the accumulator switching valve to a pressure accumulation position when a pressure accumulation condition is satisfied; switches the accumulator switching valve to a pressure release position when a pressure release condition is satisfied; and switches the accumulator switching valve to a neutral position when neither the pressure accumulation condition nor the pressure release condition is satisfied.

A hydraulic system in a work machine includes a hydraulic pump to supply pilot hydraulic oil. A work hydraulic actuator is to move a work device of the work machine. A control valve is to control the work hydraulic actuator based on a pilot pressure of the pilot hydraulic oil. A target pilot pressure of the pilot hydraulic oil is input through the work operation device to control, according to the target pilot pressure, the pilot pressure supplied from the hydraulic pump to the control valve. A pilot oil path connects the work operation device and the control valve to supply the pilot pressure to the control valve. A drain oil path is divided from the pilot oil path. A pressure adjustment valve is provided in the drain oil path to adjust the pilot pressure to be less than the target pilot pressure when a condition is satisfied.

A hydraulic system includes first and second valve assemblies connected to a common pump. The first valve assembly includes a main valve housed inside a manifold. A pressure compensator valve maintains a constant pressure drop across a variable orifice of the main valve. A pressure limiter valve is in communication with the main valve and the pressure compensator valve, and allows an actuator connected to the first valve assembly to operate independently of the second valve assembly so that fluid flow to a work port of the first valve assembly is not interrupted by operation of the second valve assembly.