A monitoring device for determining at least one position of a displacement piston (1) which is guided longitudinally movably in a housing (7) and, in the housing (7), delimits at least one fluid chamber (3, 5) with a variable volume, which fluid chamber (3, 5) is connected via a pressure supply connector (9, 11) to a pressure fluid control device (13), is characterized in that a volumetric flow regulating device (45) and, following the latter in the direction of the measuring connector (15, 17), a pressure determining device (47) are connected between the pressure fluid control device (13) and the measuring connector (15, 17) of the assignable fluid chamber (5, 3) of the displacement piston (1), which pressure determining device (47) outputs a measuring signal at least when the displacement piston (1) has reached a predefined end position in the housing (7).

A hydraulic system for a rotary implement, including an oil tank, a main pump, a control valve, and a rotary motor is provided. The oil tank is connected to an oil suction port of the main pump; an oil outlet of the main pump is connected to a P port of the control valve; a T port of the control valve is interconnected with the oil tank; and A and B ports of the control valve are connected to both ends of the rotary motor. The control valve includes a compensation valve connected to the P port and the T port, an electric proportional valve connected to the P port and the compensation valve, and an electromagnetic reversing valve connected to the compensation valve, the T port and the B port.

A hydraulic system for a working machine includes a variable displacement hydraulic pump, a plurality of hydraulic actuators, and a plurality of control valves. Each of the control valves includes an input port, an output port, and a flowrate reduction section. At least one of the control valves includes a flowrate increase section. The hydraulic actuators are a boom cylinder, a working tool cylinder, and an auxiliary actuator. The control valves are a boom control valve for controlling the boom cylinder, a working tool control valve for controlling the working tool cylinder, and a first auxiliary control valve for controlling the auxiliary actuator. The boom control valve and the working tool control valve each include the flowrate reduction section, and the first auxiliary control valve includes the flowrate reduction section and the flowrate increase section.

To keep operability of a hydraulic actuator excellent even in a state pressure has been sufficiently accumulated in a pressure accumulator. In a hydraulic driving device of a work machine including a hydraulic actuator, a tank, a flow control valve, and a pressure accumulator, there are further provided with a first pressure compensation valve that is for controlling difference between front and back pressures of the flow control valve constant and a second pressure compensation valve that is arranged between the pressure accumulator and the tank and is for controlling difference between front and back pressures of the flow control valve and the first pressure compensation valve constant.

A hydraulic control valve assembly to be integrated into a pressure compensated load sensing system including a fluid source is provided. The hydraulic control valve assembly includes a first working unit to control a first hydraulic function of a machine. The first working unit includes a first directional and return flow control in the form of a first spool, a first function flow control to selectively communicate a working pressure of the first function to the fluid source, and a first downstream flow control. The hydraulic control valve assembly further includes a second working unit arranged downstream of the first working unit. The second working unit to control a second hydraulic function of the machine. The first downstream flow control to selectively restrict a flow a fluid from the fluid source to the second working unit.

Provided is a hydraulic drive apparatus for working machine capable of preventing an excessive pressure reduction on a meter-in side and moving a load in a lowering direction at a stable speed requiring no counter balance valve. The apparatus includes a hydraulic pump, a hydraulic actuator for lowering the load, an operating device, a hydraulic circuit including a meter-in flow passage, a meter-out flow passage and a regeneration flow passage, a control valve, a meter-in-flow-rate controller for controlling a meter-in flow rate, a meter-out-flow-rate controller for controlling a meter-out flow rate to one not lower than the meter-in flow rate, a back pressure generator located downstream of the regeneration flow passage in the meter-out flow passage, and a meter-out-flow-rate limiter. The meter-out-flow-rate limiter minimizes a flow passage area of the meter-out orifice when a pressure in the meter-in flow passage falls to or below a permissible pressure.

A hydraulic drive device for cargo handling vehicle has: a tank; a pump for drawing in a hydraulic oil from the tank and supplying the hydraulic oil to hydraulic cylinders; an electric motor for driving the pump; a solenoid-controlled proportional valve disposed between an inlet port of the pump and a bottom chamber of an up-and-down hydraulic cylinder and configured to open with a valve travel depending upon a control input of a descent control of an up-and-down control member; a pressure compensation valve disposed between a branch portion located between the pump and the solenoid-controlled proportional valve and the tank and configured to open with a valve travel depending upon a pressure difference between pressures upstream and downstream of the solenoid-controlled proportional valve; and a valve disposed between the pressure compensation valve and the tank and configured to be switched between an open position and a close position.

A hydraulic control valve assembly to be integrated into a pressure compensated load sensing system including a fluid source is provided. The hydraulic control valve assembly includes a first working unit to control a first hydraulic function of a machine. The first working unit includes a first directional and return flow control in the form of a first spool, a first function flow control to selectively communicate a working pressure of the first function to the fluid source, and a first downstream flow control. The hydraulic control valve assembly further includes a second working unit arranged downstream of the first working unit. The second working unit to control a second hydraulic function of the machine. The first downstream flow control to selectively restrict a flow a fluid from the fluid source to the second working unit.

A hydraulic system for a rotary implement, including an oil tank, a main pump, a control valve, and a rotary motor is provided. The oil tank is connected to an oil suction port of the main pump; an oil outlet of the main pump is connected to a P port of the control valve; a T port of the control valve is interconnected with the oil tank; and A and B ports of the control valve are connected to both ends of the rotary motor. The control valve includes a compensation valve connected to the P port and the T port, an electric proportional valve connected to the P port and the compensation valve, and an electromagnetic reversing valve connected to the compensation valve, the T port and the B port.

Open centre hydraulic distributor, comprising: a free circulation line connecting a supply line from a negative control pump to a discharge; a delivery line connecting the supply line to users; at least one directional valve that intercepts the free circulation line and the delivery line, so that it narrows a transit area of the free circulation line and opens a transit area of the delivery line, and vice versa; a slide valve arranged on the free circulation line downstream of the directional valve; a valve device that is activated when a threshold value of a pressure delta between upstream and downstream of the directional valve is reached, and maintains this pressure delta equal to the threshold value; a negative control line to pick up a pressure signal from the free circulation line downstream of the directional valve and upstream of the slide valve.