A hydraulic system includes a hydraulic pump to output an operation fluid, a hydraulic apparatus to be activated by the operation fluid, an operating member to operate the hydraulic apparatus, an operation valve to determine a pressure of the operation fluid in accordance with operation of the operating member, the operation fluid being supplied to the hydraulic apparatus, a first fluid tube connecting the hydraulic pump to the operation valve, a first working valve disposed on the first fluid tube, the first working valve being configured to change an opening aperture of the first working valve, a first outputting fluid tube connected to a section of the first fluid tube between the operation valve and the first working valve, and a second working valve disposed on the first outputting fluid tube, the second working valve being configured to change an opening aperture of the second working valve.

A hydraulic valve includes: two spools arranged in a valve main body individually movable in an axial direction and in parallel with each other, end parts thereof being housed in a common pressure chamber, and having respective guide shaft parts on the end parts thereof; a return spring provided between each of the spools and the valve main body, so that a flow of oil is controlled by a movement of the two spools with respect to the valve main body against a spring force of each of the return springs in a case where a pilot pressure is supplied to the pressure chamber; and a coupling member that is arranged in bridged between the guide shaft parts of the two spools and that is pressed in a direction of becoming closer to the spools by the return springs.

An auto guide vehicle (20) that conveys a cart (10), wherein the auto guide vehicle (20) is provided with: a fluid pressure cylinder (22) that is able to be extended and retracted vertically, and that applies an upward pressing force to the floor surface of the cart (10); a fluid pressure supply device (70) that supplies a fluid to the fluid pressure cylinder (22); pressure regulating means (50) that regulates the fluid pressure of the fluid supplied from the fluid pressure supply device (70) to the fluid pressure cylinder (22); a control board (40) that outputs a fluid pressure command value to the pressure regulating means (50); and a pressure sensor (100) that detects the fluid pressure of the fluid supplied to the fluid pressure cylinder (22); wherein the control board (40) computes derivatives of the fluid pressure detected by the pressure sensor (100), estimates a timing at which the cart begins to leave the ground based on a pattern of the computed derivatives, and computes the command value by multiplying a coefficient less than one by the fluid pressure detected by the pressure sensor (100) at the estimated timing.

An example valve includes: a main piston comprising: a channel that is fluidly coupled to a first port of the valve, a pilot seat, and one or more cross-holes fluidly coupled to a second port of the valve; a pilot check member configured to be subjected to a fluid force of fluid in the channel of the main piston acting on the pilot check member in a proximal direction; a solenoid actuator sleeve comprising a chamber; a first setting spring disposed in the chamber and configured to bias the solenoid actuator sleeve in a distal direction; and a second setting spring configured to bias the pilot check member in the distal direction, such that the first setting spring and the second setting spring cooperate to apply a biasing force in the distal direction on the pilot check member toward the pilot seat against the fluid force.

A hydraulic system in of a work machine includes a hydraulic pump to supply pilot hydraulic oil in a hydraulic oil reservoir. A travel pump is to drive a travel motor according to a pilot pressure of the pilot hydraulic oil. A target pilot pressure of the pilot hydraulic oil is input through a travel operation device to control, according to the target pilot pressure, the pilot pressure supplied from the hydraulic pump to the travel pump. A pilot oil path connects the travel operation device and the travel pump to supply the pilot pressure to the travel pump. A drain oil path is divided from the pilot oil path. A pressure adjustment valve is provided in the drain oil path to adjust the pilot pressure to be less than the target pilot pressure when a condition is satisfied.

A system for controllably moving a work implement of a work vehicle having a hydraulic fluid pump for providing fluid to the work implement, the system comprising: at least one operator command tool to produce an operator command signal to move the implement of the work vehicle; at least one sensor to sense a cylinder speed signal indicative of a speed of a hydraulic cylinder coupled to the implement; at least one valve to modulate the fluid flow of the hydraulic cylinder; and a controller.

A hydraulic system for a work machine includes a tank to store an operation fluid, a hydraulic device to be operated by the operation fluid, a control valve to control the hydraulic device, a first fluid tube connecting the hydraulic device and the control valve, the first fluid tube being to supply the operation fluid from the control valve to the hydraulic device, a second fluid tube branching from the first fluid tube and connected to the tank, a switch valve provided to the second fluid tube, the switch valve being to control a flow rate of the operation fluid, and an oil cooler provided to the second fluid tube between the switch valve and the tank.

A method of controlling hydraulic fluid flow to an implement of a material handling vehicle includes coupling a boom arm to a vehicle frame for rotation about the vehicle frame, rotating a boom arm with respect to the vehicle frame with an actuator, coupling an attachment to the boom arm for rotation with respect to the boom arm, sensing a pressure of fluid in the actuator, communicating the sensed pressure to a control system, determining a baseline pressure of the attachment based upon the sensed pressure of the fluid in the actuator, and limiting fluid flow to the actuator with a control valve in response to the sensed pressure of the fluid in the actuator being above the baseline pressure.

A method of controlling hydraulic fluid flow to an implement of a material handling vehicle includes coupling a boom arm to a vehicle frame for rotation about the vehicle frame, rotating a boom arm with respect to the vehicle frame with an actuator, coupling an attachment to the boom arm for rotation with respect to the boom arm, sensing a pressure of fluid in the actuator, communicating the sensed pressure to a control system, determining a baseline pressure of the attachment based upon the sensed pressure of the fluid in the actuator, and limiting fluid flow to the actuator with a control valve in response to the sensed pressure of the fluid in the actuator being above the baseline pressure.

An example valve includes: a piston movable between a neutral position and an actuated position, wherein in the neutral position: a second port of the valve is fluidly coupled to a first port, and a third port is fluidly decoupled from the second port; a solenoid actuator sleeve movable between an unactuated state and an actuated state, wherein in the actuated state, the solenoid actuator sleeve allows pilot fluid to apply a fluid force on a piston in a distal direction; a first feedback spring; and a second feedback spring disposed in series with the first feedback spring, wherein the first feedback spring and the second feedback spring cooperate to apply a biasing force in a proximal direction on the piston against the fluid force, wherein the piston is configured to move to the actuated position based on a relationship between the fluid force and the biasing force.