To achieve improvement in work efficiency of calibration work and improvement in calibration accuracy, by performing control so that the time taken to increase the sweep of an applied current becomes substantially constant, upon the calibration of a valve opening position current value when a valve operated by electrical current applied to an electrical actuator opens a flow passage. There is provided a predicted value calculating means for predicting a calibration value of a valve opening position current value on the basis of information concerning valve opening position current values, and the sweep starting current value is set so that the time taken to increase the sweep to a predicted value predicted by the predicted value calculating means from a sweep start becomes a fixed time.

A rail maintenance vehicle includes a frame, a workhead, an actuator, a pilot valve, and a throttling valve. The frame includes wheels that travel along rails. The actuator extends and retracts the workhead with respect to the frame. The pilot valve receives a fluid and controls the flow of the fluid to at least one output. The throttling valve adjusts a pressure of the fluid at an output relative to a pressure of the fluid at an input. The pilot valve and the throttle valve are coupled such that the fluid travels through the pilot valve and the throttling valve to cause the workhead to be extended or retracted.

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 load-sensing control arrangement for a first and second hydraulic consumer has a variable displacement pump having load-sensing regulation, to which the highest respective load-sensing pressure of consumers is reported. The first consumer has the highest load pressure in normal operation and therefore the highest load-sensing pressure dependent on the load pressure. A pressure reducing valve is arranged in the pressure medium flow path between the variable displacement pump and the first consumer. A spring force from a regulating spring and a regulating pressure dependent on the load pressure of the first consumer are applied in the opening direction of a valve gate in this pressure reducing valve and pressure is applied directly downstream from the pressure reducing valve in the closing direction thereof. A pressure equivalent of the spring force of the regulating spring and the regulating pressure are greater than a pressure of the variable displacement pump.

A hydraulic drive system includes an oil supply device, an oil return device and a hydraulic cylinder circuit component. The circuit component includes a hydraulic cylinder, a first and a second two-position two-way electromagnetic directional valves. The cylinder includes a first chamber and a second chamber that has a piston rod. A first port of the first valve connects with the first chamber and a first port of the second valve connects with the second chamber. When the oil supply device connects to a second port of the first valve and a second port of the second valve connects to the oil return device, the piston rod is extended outwards. When the oil supply device connects to the second port of the second valve and the second port of the first valve connects to the oil return device, the piston rod is retracted.

A hydraulic system of a work machine includes a first hydraulic actuator, a first control valve, a first oil passage, a second hydraulic actuator, a second control valve, a second oil passage, and a bypass oil passage. The first control valve is connected to the first hydraulic actuator to control the first hydraulic actuator. The first oil passage is connected to the first control valve to supply hydraulic oil to the first control valve. The second control valve connected to the second hydraulic actuator to control the second hydraulic actuator. The second oil passage connects the second control valve and the first hydraulic actuator via the first control valve. Hydraulic oil returning from the first hydraulic actuator to the first control valve is to be supplied to the second control valve through the second oil passage. The bypass oil passage connects the first oil passage and the second oil passage.

A rail maintenance vehicle includes a frame, a workhead, an actuator, a pilot valve, and a throttling valve. The frame includes wheels that travel along rails. The actuator extends and retracts the workhead with respect to the frame. The pilot valve receives a fluid and controls the flow of the fluid to at least one output. The throttling valve adjusts a pressure of the fluid at an output relative to a pressure of the fluid at an input. The pilot valve and the throttle valve are coupled such that the fluid travels through the pilot valve and the throttling valve to cause the workhead to be extended or retracted.

Particular embodiments of the inventive technology disclosed herein relate to the use of a dynamic valve to reduce motion caused by impulse force applied to a positioned component. Typically, the inventive technology finds application in an internally pressurized positioning system. At times, use of the inventive technology may lead to cost savings by, e.g., allowing for the use of smaller diameter positioner actuators and/or a reduced internal pressure.

The invention relates to a valve unit for the exclusive hydraulic actuation of the locking means of a mechanical quick-changer for attachments of a construction machine, wherein the valve unit comprises a feed pressure connector for applying the feed pressure, a first valve unit outlet for connecting an unlocking pressure line, a second valve unit outlet for connecting a locking pressure line, at least one discharge to the tank, and at least two switchable directional valves, with the feed pressure connector being connected or connectable to the second valve unit outlet via a serial connection of the at least two switchable directional valves.

A fluid system is provided that includes a first actuator, a second actuator and a valve system. The valve system includes a first control valve, a second control valve and a transfer valve. During a first mode of operation, the transfer valve is configured to fluidly couple the first control valve to the first actuator and fluidly couple the second control valve to the second actuator, and the transfer valve is also configured to fluidly decouple the first control valve from the second actuator and fluidly decouple the second control valve from the first actuator. During a second mode of operation, the transfer valve is configured to fluidly couple the first control valve to the first actuator and the second actuator, and the transfer valve is also configured to fluidly decouple the second control valve from the first actuator and the second actuator.