A valve (V, V1, V2) includes a housing (VG) and a piston (VK) displaceably guided therein. A first end (VK1) of the piston (VK) can be acted upon by a force, with the aid of which the piston (VK) is displaceable against a spring (F) acting upon a second end (VK2) of the piston (VK). The valve (V, V1, V2) has four switching conditions, in which four ports (A, B, P, T) in the housing (VG) are selectively connectable to one another or blocked with respect to one another. In a first switching condition, none of the ports (A, B, P, T) are connected to one another. The spring (F) is configured in such that, in the absence of an application of force onto the first end (VK1), the piston (VK) is held in a position, which corresponds to the first switching condition of the valve (V, V1, V2).

The subject matter of this specification can be embodied in, among other things, an electrohydraulic positioning control system that includes a shuttle valve configured to direct fluid flow between a selectable one of a first fluid port and a second fluid port, and a fluid outlet configured to be fluidically connected to a fluid actuator, a first servo valve controllable to selectably permit and block flow between the first fluid port, a fluid source, and a fluid drain, a second servo valve controllable to selectably permit and block flow between the second fluid port, the fluid source, and the fluid drain, a first servo controller configured to provide a first health signal and control the first servo valve based on a second health signal, and a second servo controller configured to provide the second health signal and control the second servo valve based on the first health signal.

A hydraulic circuit includes a pump connected to a tank for supplying hydraulic liquid under pressure to a component via a directional control slide valve provided with a feed port connected to an inlet of the component and with a return port connected to an outlet of the component. The hydraulic circuit further includes a pressure limiter connected to the inlet of the component and the tank, and a feed control system for the hydraulic component including a pressure sensor installed upstream of the hydraulic component downstream of the feed port for supplying information about the pressure of the hydraulic liquid and a setpoint pressure. The feed control system further including an actuator for controlling the movement of the directional control slide valve, and a control unit for generating a control signal for the actuator based on information about the pressure measured at the feed port.

Exemplary control valves that may be configured as a load sense, closed-center, and/or open-center valve. The control valve may include optional individual valve force sensing to potentially allow an operator to smoothly operate devices operating on low-load work ports even when a variable displacement pump is inducing pressure to operate a device connected to a high-load work port of a separate valve or worksection in the same stack. This optional force sensing may be employed on any or all worksections associated with any valve stack, and may further be included on one or both workports for any given worksection. Each worksection may include parallel and variable paths of fluid supplied by the pump. Also, flow priority to one or more worksections or external valves in a corresponding hydraulic system is optional and can be customized using the variable flow path and a corresponding fixed restriction.

A hydraulic system includes a hydraulic pump to output an operation fluid, first and second hydraulic devices to be operated by the operation fluid, first and second control valves to control the first and second hydraulic device, respectively, first and second communication tubes connecting the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve, first and second connection fluid tubes disposed on the first control valve, a discharge fluid tube connected to the first control valve, first and second branching fluid tubes branched from the first and second connection fluid tubes, respectively, first and second throttles disposed on the first and second branching fluid tubes, respectively, the second throttle being smaller than the first throttle.

An example valve assembly includes a housing having an accumulator fluid passage configured to be fluidly coupled to an accumulator, a supply fluid cavity configured to be fluidly coupled to a source of fluid, a reservoir fluid cavity configured to be fluidly coupled to a reservoir of fluid, a head fluid cavity configured to be fluidly coupled to a head-side chamber of a hydraulic actuator, and a rod fluid cavity configured to be fluidly coupled to a rod-side chamber of the hydraulic actuator; a main spool that is axially-movable within the housing; and a balancing spool that is axially-movable within the housing based on an axial position of the main spool.

A control device for controlling a hydraulic consumer (2), such as a working cylinder, has at least one control valve (18) having a control spool (20). Control spool (20) is guided in a valve housing (22) in a longitudinally movable manner and is actuated by an electric motor (24). Electric motor (24) can be controlled by control electronics (MC), which receive input signals from a sensor device (58, 60, 62) detecting at least one operating state of the consumer (2).

An example valve assembly includes a housing having an accumulator fluid passage configured to be fluidly coupled to an accumulator, a supply fluid cavity configured to be fluidly coupled to a source of fluid, a reservoir fluid cavity configured to be fluidly coupled to a reservoir of fluid, a head fluid cavity configured to be fluidly coupled to a head-side chamber of a hydraulic actuator, and a rod fluid cavity configured to be fluidly coupled to a rod-side chamber of the hydraulic actuator; a main spool that is axially-movable within the housing; and a balancing spool that is axially-movable within the housing based on an axial position of the main spool.

A hydraulic circuit includes a pump connected to a tank for supplying hydraulic liquid under pressure to a component via a directional control slide valve provided with a feed port connected to an inlet of the component and with a return port connected to an outlet of the component. The hydraulic circuit further includes a pressure limiter connected to the inlet of the component and the tank, and a feed control system for the hydraulic component including a pressure sensor installed upstream of the hydraulic component downstream of the feed port for supplying information about the pressure of the hydraulic liquid and a setpoint pressure. The feed control system further including an actuator for controlling the movement of the directional control slide valve, and a control unit for generating a control signal for the actuator based on information about the pressure measured at the feed port.

A hydraulic system, mining machine and method of controlling a hydraulic actuator. The hydraulic system (HS) is provided with a control valve (23) for controlling movement direction and speed of a hydraulic actuator (HA) connected to the system. Generated force of the hydraulic actuator is controlled independently relative to the control valve by means of counterbalance valves (Cb1, Cb2) and servo valves (Sv1, Sv2) controlling their opening pressure. The counterbalance valves and the servo valves operate as a meter-out control assembly which controls flow of hydraulic fluid discharged from working pressure spaces (16a, 16b) of the hydraulic actuator. The disclosed system may be implemented to control a mining boom (3) of a mining machine (1).