A hydraulic drive system raises and lowers an object by supplying and discharging operating oil to and from each of two ports of an actuator and includes a control device, first to third electromagnetic proportional control valves, a hydraulic pump, a control valve, and a lock valve. When a second pilot pressure is output, the control valve causes the operating oil to be discharged from a first port in order to lower the object. The lock valve is disposed so as to be able to prevent the operating oil from being discharged from the first port by closing a path between the first port and the control valve, and only when a third pilot pressure is output, allows the operating oil to be discharged from the first port by opening the path between the first port and the control valve.

A redundant valve manifold system includes at least two automatic valves coupled to one another and at least two automatic isolation valves each corresponding to one of the at least two automatic valves. Each of at least two automatic isolation valves is operatively coupled to one of the at least two automatic valves and isolates the one of the at least two automatic valves when the one of the at least two automatic valves is removed from the system to deliver media to an outlet.

A valve assembly includes a valve moveable between an open position where hydraulic fluid flow is permitted and a closed position where hydraulic fluid flow is blocked. A controller includes a magnetometer adapted to measure a magnetic flux through at least a portion of a solenoid linear actuator that moves the valve. A magnetic flux value measured by the magnetometer corresponds to a linear position of the regulating member relative to the port.

A hydraulic system of a construction machine includes: control valves interposed between a main pump and hydraulic actuators; and first solenoid proportional valves connected to pilot ports of the control valves. The hydraulic system further includes: a brake for a slewing motor; and a second solenoid proportional valve connected to a brake release port of the brake by a secondary pressure line and connected to an auxiliary pump by a primary pressure line. A switching valve including a pilot port connected to the secondary pressure line by a pilot line is interposed between the auxiliary pump and the first solenoid proportional valves.

A hydraulic control loop controls a hydraulic adjusting cylinder. The cylinder has a cylindrical housing and a displaceable piston therein. The piston divides the housing interior into a first and a second hydraulic chamber. A first hydraulic valve supplies the first hydraulic chamber with hydraulic fluid. A hydraulic pressure of the first hydraulic chamber is adjustable by controlling the first hydraulic valve. A second hydraulic valve supplies the second hydraulic chamber with hydraulic fluid. A hydraulic pressure of the second hydraulic chamber is adjustable by controlling the second hydraulic valve. A control device controls the two hydraulic valves. In a position control state, the second hydraulic valve is controlled by a position control signal dependent on the working position of the piston and the first hydraulic valve is controlled by an adjusted position control signal, that is generated on the basis of the position control signal.

A hydraulic system of a construction machine includes: control valves interposed between a variable displacement main pump and hydraulic actuators; and first solenoid proportional valves connected to pilot ports of the control valves. The hydraulic system further includes: a regulator that changes a displacement of the main pump; and a second solenoid proportional valve connected to an auxiliary pump by a primary pressure line, the second solenoid proportional valve outputting a secondary pressure to the regulator through a secondary pressure line. A switching valve is interposed between the auxiliary pump and the first solenoid proportional valves, and includes a pilot port that is connected to the secondary pressure line by a pilot line.

A work vehicle includes: a hydraulic pump driven by an engine; a hydraulic actuator that is driven by hydraulic oil supplied from the hydraulic pump; a switching valve configured to switch from one to the other of a first state in which the hydraulic oil supplied from the hydraulic pump is supplied to a first channel and a second state in which the hydraulic oil supplied from the hydraulic pump is supplied to a second channel; a restriction operation device configured to generate an operation signal that restricts the drive of the hydraulic actuator; and a controller that controls the switching valve. The controller includes: an operation signal acquisition unit configured to acquire the operation signal; and an instruction output unit configured to output, to the switching valve, a control instruction that restricts the drive of the hydraulic actuator with the engine driving, in response to the operation signal.

The subject matter of this specification can be embodied in, among other things, a method that includes actuating a closure member at a predetermined first velocity a predetermined first number of cycles between a first configuration and a second configuration, actuating the closure member at a predetermined second velocity a predetermined second number of cycles between the first and the second configuration, actuating the closure member at a predetermined third velocity a predetermined third number of cycles and the second configuration, actuating the closure member at a predetermined fourth velocity a predetermined fourth number of cycles and the second configuration, and actuating the closure member to the second configuration at a predetermined fifth velocity for a predetermined flushing period.

A valve arrangement has two main valves which are each preloaded by a spring device into a first switching position, and which can each be switched into a second switching position by means of an assigned pilot valve. The pilot medium required for switching is provided with a pilot pressure at a pilot connection of each pilot valve. The main valves are each equipped with a working valve section each of which are fluidically connected to one another. In addition, each main valve contains a monitoring valve section. The monitoring valve sections are designed to provide the venting of at least one pilot connection when the two main valves are in different switching positions. This allows a fluid-actuated actuator to be controlled in accordance with high safety standards.

A hydraulic control loop controls a hydraulic adjusting cylinder. The cylinder has a cylindrical housing and a displaceable piston therein. The piston divides the housing interior into a first and a second hydraulic chamber. A first hydraulic valve supplies the first hydraulic chamber with hydraulic fluid. A hydraulic pressure of the first hydraulic chamber is adjustable by controlling the first hydraulic valve. A second hydraulic valve supplies the second hydraulic chamber with hydraulic fluid. A hydraulic pressure of the second hydraulic chamber is adjustable by controlling the second hydraulic valve. A control device controls the two hydraulic valves. In a position control state, the second hydraulic valve is controlled by a position control signal dependent on the working position of the piston and the first hydraulic valve is controlled by an adjusted position control signal, that is generated on the basis of the position control signal.