A hydraulic system includes: a cylinder in which an interior of a tube is divided by a piston into a first pressure chamber and a second pressure chamber; a first bidirectional pump connected to the first pressure chamber by a first supply/discharge line; a second bidirectional pump connected to the second pressure chamber by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and an electric motor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

A hydraulic system includes a hydraulic pump to output an operation fluid, first and second hydraulic devices to be operated by the operation fluid, first and second control valves to control the first and second hydraulic device, respectively, first and second communication tubes connecting the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve, the supply fluid tube being configured to supply the return fluid to the second control valve, first and second connection fluid tubes disposed on the first control valve, a discharge fluid tube connected to the first control valve, first and second branching fluid tubes branched from the first and second connection fluid tubes, respectively, first and second throttles disposed on the first and second branching fluid tubes, respectively, the second throttle being smaller than the first throttle.

A gangway comprises a fixed platform and a support structure connected to the fixed platform in a manner that allows the support structure to rotate with respect to the fixed platform between a raised stowed position and a lowered deployed position. A self-raising assembly is operative to rotate the support structure from the deployed position to the stowed position. The self-raising assembly includes at least one fluid actuated cylinder connected between the fixed platform and a distal end of the support structure. A raising actuator is usable by an operator to cause operation of the cylinder in a manner that rotates the support structure toward the stowed position.

[Problem to Be Solved] To make it possible to control supply, discharge, and recycled flow rates independently of each other for the boom cylinder in a construction machine comprising first and second boom spool valves respectively connected to first and second hydraulic pumps. [Solution] When the boom cylinder (8) is contracted, the first boom spool valve (16) is configured to control the recycled flow rate from head side a chamber (8A) to rod side oil chamber (8B), the second boom spool valve (17) is configured to control the discharge flow rate from head side oil chamber (8A) to oil tank (15), and both first and second boom spool valves (16, 17) are configured not to supply pressure oil from first and second hydraulic pumps (11, 12) to the boom cylinder (8).

A hydraulic system including a first cylinder conduit configured to couple to a cylinder, a second cylinder conduit configured to fluidly coupled to the cylinder, and a bypass conduit fluidly coupled both to the first cylinder conduit upstream of the cylinder and to the second cylinder conduit downstream of the cylinder. The bypass conduit is configured to enable intermittent fluid flow of a hydraulic fluid from the first cylinder conduit to the second cylinder conduit while bypassing at least a portion of the cylinder.

A forklift truck includes a carriage that moves up and down by a mast assembly in a multi-stage structure including an outer mast, a first inner mast accommodated in the outer mast, and a second inner mast accommodated in the first inner mast. The forklift truck includes a first lift cylinder configured to move the first inner mast up and down; a second lift cylinder configured to move the second inner mast up and down and having a pressure reception area less than a pressure reception area of the first lift cylinder. A first lift hydraulic line supplies hydraulic oil to the first lift cylinder. A second lift hydraulic line supplies hydraulic oil to the second lift cylinder. A pressure regulating valve is provided to increase a pressure of the hydraulic oil to a pressure capable of driving the second lift cylinder.

A hydraulic circuit is disclosed. The hydraulic circuit may include a hydrostatic pump to provide, at a flow rate, a fluid to a hydraulic motor, wherein the hydrostatic pump has a displacement, and wherein the hydraulic motor drives a swinging element; a swing circuit pressure sensor to sense a circuit pressure of the hydraulic circuit; a pilot pressure actuator to control, based on a supply pressure, the displacement of the hydrostatic pump; a pilot pressure override valve to control the supply pressure; and a controller configured to adjust, based on sensed signals and with the pilot pressure override valve, the supply pressure, wherein the sensed signals include: a circuit pressure signal based on the circuit pressure sensed by the swing circuit pressure sensor; and a sensed swing speed signal based on a swing speed of the swinging element sensed by one or more machine sensors.

A hydraulic system includes a first electric machine connected to a first hydraulic machine and a second electric machine connected to a second hydraulic machine. An output side of the second hydraulic machine is connected to an input side of the first hydraulic machine. A hydraulic consumer is hydraulically coupled to an output side of the first hydraulic machine via a supply line and is powered by the first hydraulic machine. A return line hydraulically couples the hydraulic consumer to an input side of the first hydraulic machine. The second hydraulic machine provides a flow of hydraulic fluid to the input side of the first hydraulic machine if a requested flow from the first hydraulic machine exceeds a flow of the return line and recuperates energy if the requested flow from the first hydraulic machine is lower than the flow of the return line.

Method for controlling a hydraulic system for a working machine, the system including a first electric machine connected to a first hydraulic machine the first hydraulic machine including an input side and an output side a second electric machine connected to a second hydraulic machine the second hydraulic machine including a high-pressure side and a low-pressure side the high-pressure side connected to the input side; a hydraulic consumer coupled to the output side via a supply line and configured to be powered by the first hydraulic machine; a first return line hydraulically coupling the hydraulic consumer to the input side and to the high-pressure side; wherein the method includes detecting a return flow from the hydraulic consumer through the first return line; and controlling the second hydraulic machine to maintain a pressure in the first return line at a pressure level higher than a predetermined minimum pressure level.

An example valve assembly includes a first workport fluidly coupled to a first actuator; a second workport fluidly coupled to the first actuator; a third workport fluidly coupled to a second actuator, wherein the third workport is fluidly coupled to the first workport via a first fluid passage; a fourth workport fluidly coupled to the second actuator, wherein the fourth workport is fluidly coupled to the second workport via a second fluid passage; and a spool axially movable in a bore within the valve assembly, wherein when the spool is shifted axially in a first axial direction, pressurized fluid is provided to the first workport and to the third workport via the first fluid passage, and when the spool is shifted axially in a second axial direction opposite the first axial direction, pressurized fluid is provided to the second workport and to the fourth workport via the second fluid passage.