The construction machine includes: a control valve that switchingly supplies hydraulic fluid from a hydraulic pump to a hydraulic actuator; a control valve drive device that supplies pilot secondary hydraulic fluid to the control valve in accordance with an operation of an operation lever device; a pilot hydraulic pump that supplies pilot primary hydraulic fluid to the control valve drive device; a pressure accumulation device that recovers return hydraulic fluid returned from the hydraulic actuator. The construction machine further includes: a check valve provided in a line between the pilot hydraulic pump and the control valve drive device; a pressure reducing valve that supplied the hydraulic fluid accumulated in the pressure accumulation device; a flow rate reduction device; and a controller that controls the flow rate reduction device in accordance with the pressure in the line between the check valve and the control valve drive device.

The present invention relates to a hydraulic control valve for construction machinery that is used to maintain secondary pilot pressure which is formed proportionally to the switching of a switching device so as to be equal to or below a setting pressure of a pilot pump. The hydraulic control valve of the present invention includes: a port of the pilot pump into which the pilot pressure flows; a tank port to which the pilot pressure is drained; a valve body at which a secondary pilot pressure port that selectively communicates with the port of the pilot pump and the tank port is formed; the switching device that is pivotally mounted on the valve body; a pilot control valve that is linked through pressurization of the switching device and has a spool which forms the secondary pilot pressure proportional to the amount of switching of the switching device by communicating the port of the pilot pump and the secondary pilot pressure port with each other during the switching; a valve spring that elastically supports the spool so as to communicate the secondary pilot pressure port and the tank port with each other; and a check poppet that is disposed in an openable and closable manner at a pilot passage whose inlet side communicates with the secondary pilot pressure port and whose outlet side communicates with the port of the pilot pump.

A zoned fluid control system in a valve manifold system has a plurality of manifold blocks connected together and a plurality of control valves mounted to the manifold blocks with the control valves being electrically actuated and pilot pressure operated. The plurality of manifold blocks forms at least first and second separate pilot pressure passages of a respective first zone and second zone not connected to each other for supplying a respective first set and second set of control valves with independently controlled pilot pressure. A pilot supply valve selectively supplies pilot pressure and shuts off pilot pressure to the second pilot pressure passage without affecting the pilot pressure to the first pilot pressure passage thereby disabling the second set of control valves as a separate zone independent from the first set of control valves.

A bypass line (35) having one end side connected to a pilot delivery line (23) between a pilot pump (16) and a throttle (32) and the other end side connected to the pilot delivery line (23) between a check valve (33) and a pressure reducing valve type pilot valve (25) so as to bypass the throttle (32), a gate lock valve (27), and the check valve (33) provided in order from a pilot pump (16) is provided in the pilot delivery line (23). A lock switching valve (36) shutting down a flow of a pilot pressure oil from the pilot pump (16) through the bypass line (35) at a normal time and allowing the flow of the pilot pressure oil through the bypass line (35) when a pressure generated in the pilot delivery line (23) exceeds a predetermined pressure between the gate lock valve (27) and the check valve (33) is provided in the bypass line (35).

In a closed loop control method for an electropneumatic field device, an electronic target value input of a command variable corresponding to a target value of a control center is received by the open loop and/or closed loop control electronics, an electronic output for a manipulating variable to pilot the electropneumatic converter is generated by the open loop and/or closed loop control electronics; and, in a predetermined operating condition of the field device, the manipulating variable is determined by a closed loop control algorithm based on the command variable and on another controlled variable different from an actual control member position measurement value.

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 bypass line (35) having one end side connected to a pilot delivery line (23) between a pilot pump (16) and a throttle (32) and the other end side connected to the pilot delivery line (23) between a check valve (33) and a pressure reducing valve type pilot valve (25) so as to bypass the throttle (32), a gate lock valve (27), and the check valve (33) provided in order from a pilot pump (16) is provided in the pilot delivery line (23). A lock switching valve (36) shutting down a flow of a pilot pressure oil from the pilot pump (16) through the bypass line (35) at a normal time and allowing the flow of the pilot pressure oil through the bypass line (35) when a pressure generated in the pilot delivery line (23) exceeds a predetermined pressure between the gate lock valve (27) and the check valve (33) is provided in the bypass line (35).

A hydraulic system for a working machine includes a first hydraulic apparatus to be activated by the operation fluid, a second hydraulic apparatus being configured to be activated by the operation fluid, a first operation valve to control the operation fluid to be supplied to the first hydraulic apparatus, a second operation valve to control the operation fluid to be supplied to the second hydraulic apparatus, a first fluid tube connecting the first operation valve to the first hydraulic apparatus, a second fluid tube connecting the first operation valve to the second hydraulic apparatus, a third fluid tube connecting the first fluid tube to the second fluid tube, and an outputting fluid tube connected to any one of the first operation valve and the second operation valve and configured to output the operation fluid supplied from any one of the first fluid tube and the second fluid tube.

A hydraulic system for a work machine includes a hydraulic pump to supply a pilot fluid, and a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure. The pilot pressure is a pressure of the pilot fluid supplied from the hydraulic pump. The hydraulic system includes a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions. The hydraulic system includes a pressure applying device to apply a second pilot pressure to the hydraulic switch valve. The second pilot pressure is lower than the first pilot pressure.

The construction machine includes: a control valve that switchingly supplies hydraulic fluid from a hydraulic pump to a hydraulic actuator; a control valve drive device that supplies pilot secondary hydraulic fluid to the control valve in accordance with an operation of an operation lever device; a pilot hydraulic pump that supplies pilot primary hydraulic fluid to the control valve drive device; a pressure accumulation device that recovers return hydraulic fluid returned from the hydraulic actuator. The construction machine further includes: a check valve provided in a line between the pilot hydraulic pump and the control valve drive device; a pressure reducing valve that supplied the hydraulic fluid accumulated in the pressure accumulation device; a flow rate reduction device; and a controller that controls the flow rate reduction device in accordance with the pressure in the line between the check valve and the control valve drive device.