A hydraulic circuit of a construction machine including center bypass passages, into which a pressurized oil from hydraulic pumps is supplied, includes a directional control valve group in tandem with the center bypass passages; a bleed-off valve on a downstream side of each center bypass passage; and a merging circuit that merges the pressurized oil supplied into one center bypass passage and that in another center bypass passage, wherein each directional control valve includes a first internal passage that flows the pressurized oil into the center bypass passages, and a second internal passage that supplies the pressurized oil to a hydraulic actuator, wherein the center bypass passages and the first internal passage form a parallel passage, wherein an opening area of the bleed-off valve is changed, wherein the merging circuit includes a merging directional control valve that controls an inflow direction of the pressurized oil to be merged.

Disclosed is a hydraulic construction machinery capable of operating a travel apparatus and a swing apparatus, when same are to be operated in combination, by means of working fluids supplied at the maximum discharge flow rate from a plurality of hydraulic pumps. A hydraulic construction machinery according to the present invention comprises: first and second hydraulic pumps; travel and swing motors connected to the first hydraulic pump; a hydraulic actuator connected to the second hydraulic pump; a main control valve comprising a first control valve and a second control valve, the first control valve controlling a working fluid supplied from the first hydraulic pump to the travel and swing motors, and the second control valve controlling the working fluid supplied from the second hydraulic pump to the hydraulic actuator; a first regulating valve, disposed on the most upstream side of a supply channel of the second hydraulic pump, for switching when the travel and swing motors are operated simultaneously so that the working fluid of the first hydraulic pump is supplied to the travel motor and the working fluid of the second hydraulic pump is supplied to the swing motor; a second regulating valve, disposed on the most downstream side of a supply channel of the second hydraulic pump, for switching when the travel and swing motors are operated simultaneously so as to close the most downstream opening of the supply channel of the second hydraulic pump; and an electronic proportional valve for outputting a control signal, corresponding to a control signal from a controller, to the first and second regulating valves when a manipulation signal, sensing whether the travel and swing motors are manipulated, is entered in the controller.

A hydraulic system according to one aspect of the present disclosure includes: control valves interposed between a main pump and hydraulic actuators; and solenoid proportional valves connected to pilot ports of the control valves. Among the solenoid proportional valves, a first solenoid proportional valve and a second solenoid proportional valve are connected to a pair of pilot ports of a particular control valve, respectively. The first solenoid proportional valve and the second solenoid proportional valve are directly connected to an auxiliary pump. The solenoid proportional valves except the first solenoid proportional valve and the second solenoid proportional valve are connected to the auxiliary pump via a switching valve. The switching valve includes a pilot port that is connected, by a switching pilot line, to a first pilot line between the first solenoid proportional valve and the particular control valve.

A bucket raising/lowering and opening/closing device (11) of a deep foundation excavator (1) includes a raising/lowering cylinder (12), a first raising/lowering sheave (14) and a first opening/closing sheave (15) that move in an expansion/contraction direction of the raising/lowering cylinder (12), a second raising/lowering sheave (17), a second opening/closing sheave (20), an opening/closing cylinder (18) that moves the second opening/closing sheave (20) to be closer to and to be separated from the first opening/closing sheave (15), a raising/lowering rope (24) that is wound around the first raising/lowering sheave (14) and the second raising/lowering sheave (17), and an opening/closing rope (25) that is wound around the first opening/closing sheave (15) and the second opening/closing sheave (20). In addition, provided are a slack adjustment cylinder (26) that expands and contracts to adjust the slack of the opening/closing rope (25), and a slack adjustment sheave (28) that moves in a direction of being closer to and being separated from the second opening/closing sheave (20) in response to an expansion/contraction movement of the slack adjustment cylinder (26).

A shovel includes a lower traveling body, an upper turning body turnably mounted on the lower traveling body, an engine provided in the upper turning body, a hydraulic pump and a hydraulic oil tank provided in the upper turning body, a plurality of hydraulic actuators driven by the hydraulic pump, and a hydraulic circuit connected to the hydraulic pump, wherein the hydraulic circuit includes a plurality of control valves configured to control flows of hydraulic oil between the hydraulic pump and the plurality of hydraulic actuators, and a unified bleed-off valve configured to collectively control bleed-off flowrates of the plurality of control valves, wherein the hydraulic circuit is configured so that a discharge pressure of the hydraulic pump becomes equal to or less than a predetermined pressure during start-up of the engine.

A working machine includes a fan motor driven with hydraulic fluid, the fan motor including a first port and a second port, a bypass fluid passage connecting the first port of the fan motor and the second port to each other, a flow rate control valve provided on the bypass fluid passage to control a flow rate of the hydraulic fluid flowing in the bypass fluid passage, a drain passage configured to drain the hydraulic fluid upstream of the flow rate control valve, and an unloading valve shiftable between a full-closing position to close the drain passage and a full-opening position to open the drain passage.

A method is provided for compensating for the flow rate of a variable capacity-type hydraulic pump such that, when a manipulation lever is manipulated, a discontinuous section, which has no change in the discharge flow rate of the hydraulic pump, is eliminated.

Disclosed is a hydraulic system for performing land preparation works by means of a simultaneous boom-up and arm-in operation. The hydraulic system according to the present invention includes: an arm cylinder and a boom cylinder that are connected to first and second hydraulic pumps, respectively; a first boom control valve that is disposed in the discharge flow path of the second hydraulic pump; a second boom control valve that is disposed in the discharge flow path of the first hydraulic pump and causes the working fluid of the first hydraulic pump to converge with the working fluid which is supplied from the second hydraulic pump to the boom cylinder; a first arm control valve that is disposed in the discharge flow path of the first hydraulic pump; a second arm control valve that is disposed in the discharge flow path of the second hydraulic pump and causes the working fluid of the second hydraulic pump to converge with the working fluid which is supplied from the first hydraulic pump to the arm cylinder; a recycle valve that is disposed in the flow path between the working fluid inlet port of the first arm control valve and a hydraulic tank; and a second boom control valve spool having a parallel pressure section in which the boom-up pilot pressure does not increase with respect to the boom-up strokes during the simultaneous boom-up and arm-in operation.

A hydraulic system includes a first hydraulic device to be operated by an operation fluid, a second hydraulic device, the second hydraulic device being configured to be operated by the operation fluid, a first control valve to control the first hydraulic device, a second control valve disposed on a downstream side of the first control valve and configured to control the second hydraulic device, a communication tube connecting the first hydraulic device to the first control valve, the communication tube being configured to supply a return fluid that returns from the first hydraulic device to the first control valve, a supply fluid tube connecting the first control valve to the second control valve and being configured to supply the return fluid to the second control valve, and a connection fluid tube disposed on the first control valve, the connection fluid tube connecting the communication tube to the supply fluid tube.

A shovel includes a lower traveling structure, an upper swing structure swingably mounted on the lower traveling structure, an engine mounted on the upper swing structure, a hydraulic pump configured to be driven by the engine, and processing circuitry configured to determine a command value by energy saving control and to control a flow rate of hydraulic oil discharged by the hydraulic pump according to the command value. The processing circuitry is configured to control the command value.