A new means of achieving a valve float position in a closed centered hydraulic control valve. The valve has a main spool position whereby pressure compensator load sense control pressure is drained to tank through the main spool. Secondly, a pin acts on the pressure compensator to prevent the main pump flow from reaching the main section spool. Finally, the new spool position adds a connection from the consumer to tank, enabling a float position.

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 hydraulic system includes an output fluid tube connected to a hydraulic pump to output operation fluid, and an unload valve to be switched to output operation fluid or to stop outputting operation fluid, the unload valve being connected to the output fluid tube. The hydraulic system includes a hydraulic actuator to be actuated by operation fluid, a control valve to control operation fluid to be supplied to the hydraulic actuator with use of a pilot fluid that is operation fluid applied to a pressure-receiving portion of the control valve, a pilot fluid tube connected to the pressure-receiving portion of the control valve, an operation valve to change a pressure of the pilot fluid to be applied to the pilot fluid tube, and a warm-up fluid tube connected between the unload valve and the pilot fluid tube.

A system and method for detecting the functional state of a piloted or direct-operated isolation valve in a hydraulic circuit is presented. In some examples the hydraulic circuit is a steering circuit and the isolation valve provides selective isolation between a hydraulic actuator and one or more metering valves. In some examples, the isolation valve assembly is movable between a first position, in which fluid flow between the metering valve and the actuator is enabled, and a second position, in which fluid flow between the metering valve and the actuator is blocked. When the isolation valve assembly is moved to one of the first and second positions, an inlet port and a pressure sensing port of the isolation valve assembly are placed in fluid communication with each other. When the isolation valve assembly is moved to the other of the first or second position, a second inlet port and the pressure sensing port are placed in fluid communication.

Different exemplary control systems for a hydraulically powered load-handling clamp, of the type usually mountable on industrial lift trucks or automatically guided vehicles, are disclosed. The disclosed systems variably limit a hydraulic force, by which load-clamping arms move a load substantially transversely, automatically depending on the weight of the load being moved, so as to avoid excessive transverse force applied to fragile loads.

A hydraulic control circuit includes a pressure regulator valve, a first pilot valve, a second pilot valve, and a third pilot valve. A first pilot pressure is introduced as a source pressure into the primary solenoid valve that generates a primary signal pressure and a secondary solenoid valve that generates a secondary signal pressure. A second pilot pressure is introduced as a source pressure into a lock-up solenoid valve that generates the lock-up signal pressure. A third pilot pressure is introduced as a damping pressure into a primary regulator valve that controls a primary pulley pressure according to the primary signal pressure, and into a secondary regulator valve that controls a secondary pulley pressure according to the secondary signal pressure.

Disclosed are an adjustable load pressure compensation balancing system, an end cover, and a counterbalance valve. The adjustable load pressure compensation balancing system comprises: an adjustable orifice control module and a counterbalance valve control module, wherein the adjustable orifice control module is used for receiving control oil generated when a luffing system descends and oil from a descending cavity of a luffing cylinder; the counterbalance valve control module is used for receiving the control oil generated when the luffing system descends; the pressure applied to the counterbalance valve control module by the control oil is maximum when the luffing system starts to descend, and then decreases gradually; and the pressure applied to the adjustable orifice control module by the oil from the descending cavity is minimum when the luffing system starts to descend, and then increases gradually.

A hydraulic circuit is disclosed. The hydraulic circuit may comprise an actuation valve configured to actuate a flow of hydraulic fluid to and from the hydraulic consumer, a first control valve in fluid communication with the actuation valve through a first pilot line and configured to displace the actuation valve to a first position when actuated, and a second control valve in fluid communication with the actuation valve through a second pilot line and configured to displace the actuation valve to a second position when actuated. The first pilot line and the second line may each have a fixed minimum back pressure sufficient to maintain dissolved air in the hydraulic fluid.

A shovel includes a turning hydraulic motor, a hydraulic cylinder, a pilot circuit, a hydraulic control valve, a variable throttle, and a controller. The turning hydraulic motor is driven with hydraulic oil supplied from the hydraulic pump to drive a turning body of the shovel to turn. The hydraulic cylinder is driven with the hydraulic oil supplied from the hydraulic pump. The pilot circuit controls a pilot pressure in accordance with the operation of an operation lever. The hydraulic control valve controls the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder in accordance with the pilot pressure supplied from the pilot circuit. The opening of the variable throttle varies in accordance with the operating state of the operation lever. The controller changes the opening of the variable throttle.

A method for controlling a valve spool that includes providing a control valve having a first end and a second end with a spool disposed therebetween, a hydraulic component, a controller, a first control circuit and a second control circuit, selectively controlling the pressure in the first end and the second end with the controller, identifying an active state, with the controller, and applying an active pressure to both the first end and the second end with the corresponding first control circuit and second control circuit during the active state, and identifying a first command, with the controller, and providing a command pressure to the first end through the first control circuit and a release pressure to the second end through the second control circuit during the first command. Wherein, the spool is moved within the control valve and the hydraulic component is engaged during the first command.