A single-use pressure-controlled actuator for downhole well tools or mechanisms is provided. The actuator is configured for control of activation/deactivation by agency of wellbore fluid pressure (e.g., pressure levels of drilling fluid or drilling mud in the wellbore). The actuator is further configured for hydraulic actuation by agency of the wellbore fluid. The actuator comprises a plunger displaceably mounted on a sealed cylinder body, with a non-reclosable frangible device closing off wellbore fluid access to an interior of the cylinder body. The frangible device is configured for automatic in response to exposure of wellbore fluid pressures exceeding a predetermined activation threshold. Failure of the frangible device causes exposure of the plunger to the wellbore fluid, resulting in actuated movement of the plunger by hydraulic action of the wellbore fluid.

A hydraulic system includes a poppet control valve having an inlet workport, a function workport, a control chamber, and a poppet arranged between the inlet workport and the control chamber. The poppet is movable between an open position and a closed position. The hydraulic system further includes a pilot control valve. A pressure correlated to the function workport is supplied to a first side of the pilot control valve and a pilot source pressure is supplied to a second side of the pilot control valve. When a pressure in the function workport reaches a setpoint pressure, the pressure correlated to the function workport forces the pilot control valve to a position that increases a flow restriction between the control chamber and the function workport, so that the poppet moves in a direction toward the closed position and limits the pressure in the function workport to the setpoint pressure.

A system for recovering energy from a hydraulic actuator and to a method of operating the system are described. The system may have a hydraulic actuator and a source of hydraulic pressure, comprising a hydraulic pump, in fluid communication with the hydraulic actuator for pressurizing the hydraulic actuator. The system may also have a hydraulic accumulator assembly for selectively absorbing energy from the hydraulic actuator or via the hydraulic actuator. The system may also have a first one-way valve configured to provide fluid communication between the hydraulic actuator and the hydraulic accumulator assembly. The first one-way valve may be configured to permit a flow of fluid through the first one-way valve from the hydraulic actuator to the hydraulic accumulator assembly. The first one-way valve may also be configured to block a flow of fluid through the first one-way valve from the hydraulic accumulator assembly to the hydraulic actuator.

A neutral valve includes a spool inserted in a housing so as to be movable in a predetermined direction, the spool configured to move to a neutral position set such that a first and second port are connected to each other through a valve passage, a first offset position located at neutral position's first side in the predetermined direction and set such that second port and valve passage are disconnected from each other, and a second offset position located at neutral position's second side in the predetermined direction and set such that first port and valve passage are disconnected from each other. The spool's outer peripheral portion includes a first pressure receiving surface receiving first port's fluid pressure to be pushed toward the first side in the predetermined direction and a second pressure receiving surface receiving second port's fluid pressure to be pushed toward second side in the predetermined direction.

A hydraulic drive system for a track device of crawler type has right and left hydraulic track motors. The hydraulic drive system is capable of correcting for skew occurring in the straight line traveling of the track device. A traveling test is conducted upon shipment from a factory. If skew is noted during the test, a plug disposed on the side of a valve opening-side pressure receiving portion of a pressure compensating valve for the track which is lower in speed is removed and, replaced with an adjusting mechanism-mounted plug having an adjusting pin. The pin is operated so as to strengthen a biasing force of a target compensating differential pressure adjusting spring. An opening in the pressure compensating valve is thereby corrected in an opening direction and a flow rate to one of the left and right track motors is thereby adjusted to be equal to the other motor.

A hydraulic drive system (1) including a meter-in compensator (37) and a bleed-off compensator (42) comprises a plurality of sensors (64 to 68), a controller (62), and an outlet pressure switching valve (61). The controller (62) determines whether or not the state of a wheel loader (2) which is detected based on the signals output from the sensors (64 to 68) meets a predetermined steering limiting condition. When the controller (62) determines that the state of the wheel loader (2) meets the steering limiting condition, it outputs a command signal to the outlet pressure switching valve (61). The outlet pressure switching valve (61) reduces the flow rate of the hydraulic oil flowing to steering cylinders (18L, 18R), in response to the command signal in such a manner that the flow rate becomes lower than that corresponding to the operation amount of a handle of a steering device (35).

A pilot type switching valve includes: a housing bore formed in a valve body, the housing bore having an opening end; a spool slidably housed in the housing bore, the spool being configured to allow or block a flow of the working fluid to a first relief valve; a pilot chamber to which pilot pressure biasing the spool in the valve opening direction is guided; and a spring configured to bias the spool in the valve closing direction. The spool has a bottom surface on which the pilot pressure acts in such a manner that the spool is biased in the valve opening direction, and the area of the bottom surface is smaller than the sectional area of the housing bore.

Shock absorber used for damping a control flow which is to be directed to the control valve belonging to a hydraulic system or is to be directed to the adjustable valve of the flow through which absorber the flow of the hydraulic fluid can be directed at least in one direction. The absorber is a stopper which restricts the run of the flow to be damped which stopper is equipped with one or several ducts which let the flow go through the mentioned stopper when the other orifice of the mentioned duct is blocked with a plate in such a way that bending of the mentioned plate opens access for the flow through the mentioned stopper due to the pressure of the flow coming along the mentioned duct.

A fluid pressure control device includes a switching valve configured to switch an operation of an operate check valve, a relief valve configured to open when a pressure in a load-side pressure chamber reaches a predetermined pressure, and a relief discharge passage configured to lead a relief fluid discharged from the relief valve to a tank. The switching valve includes a piston giving thrust to a spool upon receipt of a pilot pressure on a back surface, a drain chamber defined by the spool and the piston, and a drain passage allowing the drain chamber and a spring chamber to communicate with the relief discharge passage. The relief fluid discharged from the relief valve is discharged to the tank through the relief discharge passage and does not operate the switching valve.

A pump discharge amount is divided in accordance with switch amounts of respective switch valves by leading load pressures of actuators to which compensator valves are connected to respective first pressure chambers of the compensator valves, leading a maximum load pressure selected by a selection unit to respective second pressure chambers of the compensator valves, and controlling respective openings of the compensator valves in accordance with respective pressure actions between the respective pressure chambers. A drain passage is provided to connect the first pressure chamber of the compensator valve to a tank, and a flow dividing ratio modification valve is provided to control a pressure in the first pressure chamber.