A hydraulic drive system includes a swing directional control valve 81 and a third boom directional control valve 82 that are connected to a third hydraulic pump 33. Furthermore, the hydraulic drive system includes: a second auxiliary directional control valve 84 that is connected to the third hydraulic pump 33, and is connectable with a second special hydraulic actuator 64 for driving special attachments; and a first selector valve 96 that is connected to the third hydraulic pump 33 upstream of the second auxiliary directional control valve 84, and is connectable with an additional hydraulic pump 97. The first selector valve 96 switches the hydraulic fluid source of the second special hydraulic actuator 64 connected to the second auxiliary directional control valve 84 at least between the third hydraulic pump 33 and the additional hydraulic pump 97. Operability for combined operation of a special attachment can be improved in the hydraulic drive system equipped in advance with an auxiliary directional control valve that is connectable with an additional hydraulic actuator for driving the special attachment.

An apparatus for controlling a hydraulic machine, for example a turbine, pump or pump turbine, using variable-speed driven fixed displacement pumps. The apparatus includes a device for carrying out an emergency shut-off that is characterized by low energy consumption and high efficiency while guaranteeing all the operation-relevant and safety-relevant requirements of a hydraulic machine.

A fluid pressure cylinder driving device includes a switch valve, a high pressure air supply source, an exhaust port and a check valve. When the switch valve is at a first position, a head side cylinder chamber communicates with the high pressure air supply source, and a rod side cylinder chamber communicates with the exhaust port. When the switch valve is at a second position, the head side cylinder chamber communicates with the rod side cylinder chamber via the check valve, and the head side cylinder chamber communicates with the exhaust port.

Lever neutrality is determined by whether or not operation levers are at a neutral position based on operation signals from operation levers. Pilot pressures are computed based on the operation signals from the operation levers; and pilot pressure signals are converted to current signals. A current interruption controller controls interruption and communication of the current signals to the solenoid proportional valves; and an operating condition is determined by determining whether a construction machine is in a manual operation state or a semiautomatic operation state. At least one hydraulic actuator is controlled to assist the operation of the operator, and when it is determined that the construction machine is in the semiautomatic operation state, the current interruption controller interrupts the current signals to all of the solenoid proportional valves only when it is determined that all the operation levers are at the neutral position.

A dual spool valve and methods of controlling hydraulic fluid that is moved to a hydraulic actuator of an aircraft. The dual spool valve may include ports to receive and discharge hydraulic fluid. The dual spool valve may also include first and second valve sections that are selectively positionable to control the flow of hydraulic fluid into and out of the actuator. One position provides for hydraulic fluid to move through closure lines. Method of controlling the dual spool valve may provide for selectively positioning the valve sections to control the flow of hydraulic fluid, and to position the valve sections to move hydraulic fluid through a closure line during certain circumstances.

A hydraulic apparatus includes a first valve manifold that provides a shutdown capability and a second valve manifold that provides an overspeed control capability. The hydraulic apparatus advantageously further employs a hydraulic appliance that includes a check valve and a bypass apparatus. The hydraulic appliance enables the second valve manifold to additionally provide as an alternative function a redundant shutdown capability, thereby obviating the need to have three separate valve manifolds.

Distributed trailing edge wing flap systems are described. An example wing flap system for an aircraft includes a flap and an actuator. The flap is movable between a deployed position and a retracted position relative to a fixed trailing edge of a wing of the aircraft. The actuator is to move the flap relative to the fixed trailing edge. The actuator is hydraulically drivable via first pressurized hydraulic fluid to be supplied by a hydraulic system of the aircraft. The actuator is also hydraulically drivable via second pressurized hydraulic fluid to be supplied by a local power unit. The local power unit is selectively connectable to an electrical system of the aircraft. The electrical system is to power the local power unit to supply the second pressurized hydraulic fluid.

A controller (25) of the hydraulic excavator (1) includes a signal separation section (150) that separates each of target speed signals for a plurality of front members (8, 9, 10) into a low frequency component and a high frequency component, a high fluctuation target speed calculation section (143) that allocates the separated high frequency components preferentially to a front member having a relatively small inertial load to calculate high fluctuation target speeds individually for the plurality of front members, a high fluctuation target actuator speed calculation section (141c) that calculates high fluctuation target speeds individually for the plurality of actuators from the high fluctuation target speeds for the plurality of front members, a low fluctuation target actuator speed calculation section (141b) that calculates low fluctuation target speeds individually for the plurality of actuators from the low frequency components separated by the signal separation section, and an actuator controller (200) that controls the plurality of actuators individually based on values obtained by adding the high fluctuation target speeds and the low fluctuation target speeds.

A portable hydraulic power unit includes a fluid tank supported on a frame, a first pump configured to draw hydraulic fluid from the tank and a second pump configured to draw hydraulic fluid from the tank. The portable hydraulic power unit further includes a two-way valve disposed on a high-flow line extending from an output of the second pump, the two-way valve movable between an open state and a closed state. The two-way valve is electrically-actuated and configured to shift to the open state based on a hydraulic fluid pressure in a combined flow line downstream of the first pump and the second pump exceeding a threshold pressure level. The two-way valve directs the output of the second pump back to the fluid tank when the two-way valve is in the open state.

To achieve the improvement of recovery efficiency from a rod end oil chamber to a head end oil chamber during extending operation of a stick cylinder, and at the same time, to prevent an operation speed of the stick cylinder from being impaired when recovery is impossible., as well as to achieve the reduction of the number of parts, in a construction machine equipped with a stick. It is configured such that a first region Y1 at which a discharge valve passage 14g is opened while being throttled and a second region Y2 at which the discharge valve passage 14g is wider opened than at the first region Y1 are provided, in an operating position of a stick control valve 14 during extending operation of the stick cylinder, and if recovery from the rod end oil chamber 9b to the head end oil chamber 9a during extending operation of the stick cylinder 9 is possible, the stick control valve 14 is caused to be positioned at the first region Y1, and if the recovery is impossible, positioned at the region Y2.