A control device for a hydraulic machine such as a revolving excavator work machine having a structure that can cope with such an engine output decreasing environment as a work under a low atmospheric pressure at a high altitude without generating noise caused by engine rotation number increase. The control device corrects a control output value to be applied to an electromagnetic proportional valve for load-sensing valve control in a load-sensing type pump control system, based on a detected state quantity related to the engine output decreasing environment. When an engine speed-sensitive pump control system is adopted, a control output value generated based on a detected decrease in the actual engine rotation number is combined with a control output value generated by the load-sensing type pump control system.

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 (4), 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 safety system for a machine includes a pressurizing device; at least one hydraulic cylinder, the at least one hydraulic cylinder including a pressure chamber and a piston having a head and a rod, the piston being movable within the pressure chamber along a longitudinal direction; a first pressure sensor and a second pressure sensor being designed to measure the pressure within the pressure chamber via a first channel having a first opening and a second channel having a second opening, which both extend into the pressure chamber, and are spaced apart as seen in the longitudinal direction; a seal device arranged circumferentially around the head of the piston, and a hydraulic system being fluidically connected to a head side and a rod side of the at least one hydraulic cylinder, the hydraulic system being fluidically connected to a hydraulic fluid reservoir and the pressurizing device.

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 provides relief pressure operation for a lift cylinder and/or top cylinder in an implement linkage of a utility vehicle. A relief pressure control valve has a first position providing a connection between a variable displacement pump and one side of the hydraulic cylinder, and a second position providing a connection between that side of the hydraulic cylinder and a drain or reservoir. A connection carries an indication of the pressure in the hydraulic cylinder chamber as a load-sensing signal to control adjustment of the pump.

An actuated valve system includes a valve including a flow controlling valve element, an actuator assembled with the valve and including an inlet port in fluid communication with a fluid driven actuator member operatively connected with the valve element and movable from a normal position to an actuated position in response to pressurization of the inlet port to at least a minimum actuating pressure, a pilot valve operable to supply pressurized fluid to the actuator inlet port in a first position and to exhaust pressurized fluid from the actuator inlet port through an exhaust port in the pilot valve in a second position, and a backpressure arrangement in fluid communication with the actuator inlet port to retain a positive pressure smaller than the minimum actuating pressure against the actuator member when the pilot valve is moved to the second position.

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.

In an exemplary method of monitoring performance of a fluid driven actuator for a valve, pressurized fluid is supplied through an actuator supply line to an inlet port of the actuator during a first time period to operate the actuator. Changes corresponding to a fluid flow condition in the actuator supply line are measured during the first time period, and the measured changes are analyzed to identify a non-compliant condition in at least one of the valve and the actuator. An output communicating the identified non-compliant condition is then generated.

There is provided a hydraulic driving device for working machine having operability handling a change in burden weight in a front working device due to a loaded burden and the like when the working machine that accumulates energy in an accumulator and recovers and regenerates the energy performs an operation of lowering the front working device. A hydraulic driving device 5 includes a main pump 101, a boom cylinder 3, a tank 20, a flow rate control valve 6, an accumulator 300, a first differential pressure control valve 201, and a second differential pressure control valve 202. The first differential pressure control valve 201 is located between the boom cylinder 3 and the accumulator 300. The first differential pressure control valve 201 performs control on discharge oil from the boom cylinder 3 such that a differential pressure between before and after the flow rate control valve 6 becomes a target differential pressure. The second differential pressure control valve 202 is located between the accumulator 300 and the tank 20. The second differential pressure control valve 202 performs control on the discharge oil such that a differential pressure between an upstream pressure and a downstream pressure of the flow rate control valve 6 and the first differential pressure control valve 201 becomes the target differential pressure. The first and the second differential pressure control valves 201 and 202 are configured such that the target differential pressure increases according to an increase in pressure of the discharge oil.

A marine hydraulic system and method of use for reducing cyclic loading of the pump(s) and motor(s) and an amount of accumulator storage required in a hydraulic system. A closed loop logic controller comprising at least one control algorithm for each pump/motor pair utilized in a single hydraulic system is utilized to reduce load fluctuations on the motors, allow the use of common pressure compensated, variable displacement (VDH) pumps, reduce the number and/or volume of system accumulators and equalize wear throughout the system.