According to an embodiment, a variable pressure device includes a channel constituting unit and a switch valve mechanism. The channel constituting unit constitutes a channel including a first regulator and second regulators that are arranged in series to the first regulator and are in parallel to one another. The switch valve mechanism selectively connects the second regulators to the first regulator. Opening areas of the second regulators are different from one another.

A fluid system includes a variable-speed and/or a variable-torque pump to pump a fluid, at least one proportional control valve assembly, an actuator that is operated by the fluid to control a load, and a controller that establishes a speed and/or torque of the pump and a position of the at least one proportional control valve assembly. The pump includes at least one fluid driver that provides fluid to the actuator, which can be, e.g., a fluid-actuated cylinder, a fluid-driven motor or another type of fluid-driven actuator that controls a load. Each fluid driver includes a prime mover and a fluid displacement assembly. The fluid displacement assembly can be driven by the prime mover such that fluid is transferred from the inlet port to the outlet port of the pump.

A fluid pressure control device includes a switching valve configured to switch an operation of an operate check valve, a relief valve configured to open when a pressure in a load-side pressure chamber reaches a predetermined pressure, and a relief discharge passage configured to lead a relief fluid discharged from the relief valve to a tank. The switching valve includes a piston giving thrust to a spool upon receipt of a pilot pressure on a back surface, a drain chamber defined by the spool and the piston, and a drain passage allowing the drain chamber and a spring chamber to communicate with the relief discharge passage. The relief fluid discharged from the relief valve is discharged to the tank through the relief discharge passage and does not operate the switching valve.

A fluid system includes a variable-speed and/or a variable-torque pump to pump a fluid, at least one proportional control valve assembly, an actuator that is operated by the fluid to control a load, and a controller that establishes a speed and/or torque of the pump and a position of the at least one proportional control valve assembly. The pump includes at least one fluid driver that provides fluid to the actuator, which can be, e.g., a fluid-actuated cylinder, a fluid-driven motor or another type of fluid-driven actuator that controls a load. Each fluid driver includes a prime mover and a fluid displacement assembly. The fluid displacement assembly can be driven by the prime mover such that fluid is transferred from the inlet port to the outlet port of the pump.

A flow control device for a construction machine including a first hydraulic cylinder and a second hydraulic cylinder connected to a hydraulic pump, which is connected to an engine. A first control valve and a second control valve are also included. A regeneration flow path is configured to supplement and reuse hydraulic fluid that returns to a hydraulic tank during a retractable drive of the first hydraulic cylinder. A regeneration valve is installed in the regeneration flow path. A pressure compensation type flow control valve is installed in a meter-in flow path of a spool of the first control valve, and is configured to limit the flow rate of the hydraulic fluid supplied from the hydraulic pump to the first hydraulic cylinder during a combined operation of the first and second hydraulic cylinders.

A work machine to cut timber including a control system, a felling head, a hydraulic motor configured to adjust the position of the felling head, and a spool valve operatively connected to the hydraulic motor, the spool valve being configured to move the felling head responsively through operation of the hydraulic motor. A machine controller coupled to the operator controller and the spool valve executes stored program instructions to generate a first control signal responsive to an operator control signal provided by the operator controller, generate a second control signal as a function of the generated first control signal, adjust a position of the spool of the spool valve in response to a concurrent receipt of the first control signal and the second control signal by the first proportional control valve and the second proportional control valve to move the felling head through operation of the hydraulic motor.

A work machine to cut timber including a control system, a felling head, a hydraulic motor configured to adjust the position of the felling head, and a spool valve operatively connected to the hydraulic motor, the spool valve being configured to move the felling head responsively through operation of the hydraulic motor. A machine controller coupled to the operator controller and the spool valve executes stored program instructions to generate a first control signal responsive to an operator control signal provided by the operator controller, generate a second control signal as a function of the generated first control signal, adjust a position of the spool of the spool valve in response to a concurrent receipt of the first control signal and the second control signal by the first proportional control valve and the second proportional control valve to move the felling head through operation of the hydraulic motor.

An object is to provide a cylinder device which can be used over a long period of time. The cylinder device includes a damper, a pump, a motor and an external tank. The damper has a cylinder, a first bracket, a piston, a piston rod and a second bracket. The piston is slidably inserted into an interior of the cylinder. The piston rod is inserted into the cylinder and connects the piston to an end located in the cylinder. The pump is disposed at one of right and left sides with respect to a central axis of the cylinder. The motor is disposed at the one side which is the same side as the pump with respect to the central axis of the cylinder. The external tank is disposed at the other side with respect to the central axis of the cylinder.