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 hydraulic drive system raises and lowers an object by supplying and discharging operating oil to and from two ports of an actuator and includes a control device, first to fifth electromagnetic proportional control valves, first and second hydraulic pumps, a first and second control valve, and a lock valve. When a fourth pilot pressure is output, the second control valve causes the operating oil to be discharged from a first port in order to lower the object. The lock valve prevents the operating oil from being discharged from the first port by closing a path between the first port and the second control valve, and when a fifth pilot pressure is output from the fifth electromagnetic proportional control valve per an operating device, discharges the operating oil from the first port by opening the path between the first port and the second control valve, to lower the object.

A hydraulic control apparatus is disclosed that controls a hydraulic pump in a construction machine in which a hydraulic actuator is connected to the hydraulic pump via a directional control valve of a closed center type, and in which a position of the directional control valve is changed according to an operation amount of an operation member. The hydraulic control apparatus includes a virtual negative control pressure calculating part configured to calculate, based on the operation amount of the operation member and a discharge pressure of the hydraulic pump, a virtual negative control pressure when a negative control system is assumed; and a part configured to calculate a control command value for the hydraulic pump based on the virtual negative control pressure.

A prime mover and a plurality of hydraulic actuators, a hydraulic machine having a rotatable shaft in driven engagement with the prime mover and comprising a plurality of working chambers, a hydraulic circuit extending between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold. The hydraulic machine being configured to actively control at least the low-pressure valves of the group of one or more working chambers to select the net displacement of hydraulic fluid by each working chamber on each cycle of working chamber volume, and thereby the net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal, wherein the apparatus further comprises a controller configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators.

[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 load sense open center hydraulic system provides efficiency and operator feedback and includes one or more constant flow-open center valves (218); respective one or more parallel power cores (238) operatively coupled to the one or more constant flow-open center valves; a variable capacity pump (246) directly fluidly connected to the one or more parallel power cores; and a pressure compensated flow control fluidly connected between the variable capacity pump and the one or more constant flow-open center valves. The one or more constant flow-open center valves are not fluidly coupled to a fixed capacity pump.

Disclosed is an apparatus for improving excavating operation characteristic and grading operation characteristic of an excavator. The apparatus includes a solenoid valve group and a hydraulically controlled selector valve. An oil controlling output A1 of the solenoid valve group is configured in series with oil controlling input a1 of the hydraulic control valve. An oil controlling output A2 of the solenoid valve group is configured in series with a pilot control end XBa2 of a multi-port valve group. An oil return port T1 of the solenoid valve group is connected to the hydraulic oil tank. An oil controlling output b1 of the hydraulically controlled selector valve is connected to a pilot control end XAb2 of the multiplexer valve group, and an oil return port T2 of the hydraulically controlled selector valve is connected with the hydraulic oil tank. The apparatus improves operational efficiency and control comfortability.

It is to provide a control valve that can make the valve body smaller and the structure simplified and the hydraulic pressure system equipped therewith. The plural number of parallel feeder oil paths that are respectively connected to the plural number of pumps and are not cut off by displacement of spools is provided in the valve body in a linearly through all spool holes. For each section, a connection oil path is provided to connect any one side of parallel feeder oil paths to the bridge circuit B of the internal spools. Parallel feeder oil paths can be positioned in a simple shape, but also, just by properly providing connection oil paths, without depending on each section belonging to any of pump systems, positioning of section can be freely done within the valve body. Making the valve body smaller and the structure simplification can be executed.

A hydraulic block includes multiple pairs of actuator ports connectable to a hydraulic actuator and a discharge oil passage for discharging work oil returned from the hydraulic actuator to the outside. The charge oil passage includes a first oil passage corresponding to a predetermined actuator port of all the actuator ports and a second oil passage corresponding to non-predetermined actuator ports other than the predetermined actuator ports. The first oil passage is disposed in parallel with the second oil passage.

Provided is a hydraulic drive system including: first and second pumps; a first main supply fluid line and an optional supply fluid line leading to the first pump; a second main supply fluid line leading to the second pump; a main manipulating device for the main actuator; an optional manipulating device for the optional actuator; a bleed-off flow rate regulating section to change the bleed-off flow rate for the second pump; and a bleed-off control section to operate the bleed-off flow rate regulating section to change the discharge flow rate of the second pump in accordance with a control operation applied to the main manipulating device and to make a bleed-off flow rate in a specific combined manipulation state with simultaneous performance of a specific main control operation and an optional control operation be smaller than that in a single main manipulation state.