A system for braking a displacement-controlled drive system (10), which can be driven by means of an inflow pressure and an outflow pressure at an inflow end and an outflow end thereof, respectively, for a motion, characterized in that by means of an electro-proportional adjustment of at least one valve element (26, 28, 126, 128) an outflow volume flow of the drive system (10) is controlled such that the outflow pressure is decoupled from the motion of the drive system and can be freely preset and coupled to the inflow pressure, which can in that way be lowered to the extent necessary for the motion of the drive system (10).

A control device controls movement of a valve body of a valve device and estimates a flow rate of the valve device; determines, on the basis of an input target flow rate value and the flow rate estimate, whether or not the flow of an operating fluid in the valve device is in a transient flow state; calculates an opening command on the basis of the target flow rate value and an upstream-downstream pressure difference of the valve device; and controls the movement of the valve body. When the control device determines that the flow is not in the transient flow state, it controls the movement of the valve body on the basis of the opening command, and when the control determines that the flow is in the transient flow state, it controls the movement of the valve body on the basis of the target flow rate value.

A fixed displacement hydraulic pump match flow demand control system that includes a spool valve, a plurality of fixed displacement pumps and a control valve is provided. The spool valve includes a spool. The spool is configured to shuttle within a chamber of a housing based at least in part on a pressure difference between a first end and the second end of the chamber. A fluid flow from each fixed displacement pump of the plurality of fixed displacement pumps is in fluid communication with an associated input port to the spool valve. At least one output port of the spool valve is in fluid communication with a hydraulically operated device and at least one of another output port is in fluid communication with a return. The control valve is configured to adjust the location of the spool in the chamber to regulate fluid flow to the hydraulically operated device.

An amplifier is configured for use in a control valve. These configurations provide a pneumatic signal to an actuator that regulates flow through the device. The amplifier may include a variable orifice, or bleed valve, that moves in response to changes in actuating media around steady state. This bleed valve prevents bleed of actuating media at steady state. This feature reduces energy consumption or emissions from the control valve.

A cap with electromagnetic proportional valve, includes a pilot cap mounted on a valve housing and defining a pilot chamber, and an electromagnetic proportional valve mounted on the pilot cap and adapted to control a pressure of a working fluid supplied to the pilot chamber. The pilot cap includes a supply port into which a working fluid of a fluid pressure supply source is supplied, a discharge port from which the working fluid is discharged to the tank, a primary pressure passage which leads the working fluid at a primary pressure to the electromagnetic proportional valve from the supply port, a secondary pressure passage which leads the working fluid whose pressure is reduced to a secondary pressure by the electromagnetic proportional valve to the pilot chamber, and a drain passage which leads the working fluid discharged from the electromagnetic proportional valve to the discharge port.

The present invention provides a work machine including a steering device that is very responsive to switching operations. The work machine includes: a proportional solenoid valve for outputting a first pilot pressure oil with a pressure responding to a steering signal; a solenoid valve for outputting a second pilot pressure oil with a predetermined pressure while the steering signal is outputted from the steering device; a switching valve capable of switching to a first state of outputting the first pilot pressure oil to a directional control valve and a second state of outputting the second pilot pressure oil to the directional control valve, while the first pilot pressure oil is outputted from the proportional solenoid valve and the second pilot pressure oil is outputted from the solenoid valve in parallel; and a controller to switch the switching valve from the first state to the second state in a case where a malfunction is detected in a main circuit ranging from the steering device to the directional control valve via the proportional solenoid valve and the switching valve of the first state.

A work vehicle includes: an operation tool that is operated by an operator; and a controller that determines a target flow rate for hydraulic oil fed to a hydraulic device on a basis of the amount of operation of the operation tool. The controller calculates a bleed-off target flow rate on a basis of the flow rate of hydraulic oil fed from a hydraulic oil pump and the target flow rate for hydraulic oil fed to the hydraulic device, calculates a bleed-off throttle differential pressure on a basis of a pressure of hydraulic oil fed from the hydraulic oil pump and a pressure of hydraulic oil in a hydraulic oil tank, calculates a bleed-off target opening area on a basis of the bleed-off target flow rate and the bleed-off throttle differential pressure, and controls a hydraulic oil control valve such that the bleed-off target opening area is achieved.

A valve assembly includes a linearly moving main slider, a pilot valve, a control oil inlet, and a control oil return. The pilot valve is designed as a 4/3 proportional directional valve, via which a first end face and an opposite second end face of the main slider can be fluidly connected selectively to the control oil inlet or the control oil return so that the main slider (20) is hydraulically movable by adjusting the pilot valve. The pilot valve is electrically adjustable depending on a target current. A position sensor is provided, with which an actual position of the main slider can be measured. A positioner is provided, with which the actual position can be regulated by adjusting the target current to a predefinable target position. The pilot valve is connected to the control oil return via a check valve. The check valve only permits fluid flow from the pilot valve toward the control oil return. The check valve is preloaded to a closed position by means of a first spring so that it opens at a predetermined opening pressure. The leakages at the pilot valve from the control oil inlet toward the check valve are designed to be so large that if the pressure at the control oil inlet exceeds the opening pressure by at least 2 bar, the opening pressure of the check valve is present immediately upstream of the check valve.

A hydraulic drive system raises and lowers an object by supplying and discharging operating oil to and from two ports of an actuator and includes a control device, first to fifth electromagnetic proportional control valves, first and second hydraulic pumps, a first and second control valve, and a lock valve. When a fourth pilot pressure is output, the second control valve causes the operating oil to be discharged from a first port in order to lower the object. The lock valve prevents the operating oil from being discharged from the first port by closing a path between the first port and the second control valve, and when a fifth pilot pressure is output from the fifth electromagnetic proportional control valve per an operating device, discharges the operating oil from the first port by opening the path between the first port and the second control valve, to lower the object.

A valve arrangement for a fluidic supply of a fluid load, with several main valves designed for influencing fluid flows at the fluid ports, and with electrically controllable pilot valves designed for fluidic control of the main valves. A base body is assigned a connection plate lying opposite a connection face and having a fluid passage which leads into an operating port for the connection of a fluid load wherein, between the connection face and the connection plate there is provided a separate passage body which has at least one connection passage for a fluidically communicating link between at least one of the fluid ports and the operating port, and at least one connecting conduit for a fluidic coupling of at least two fluid ports.