| 摘要 |
PROBLEM TO BE SOLVED: To save energy by eliminating the need of a pump for a pilot pressure source. SOLUTION: When control valves 7, 8, 9 are kept in neutral positions, a fluid from a pump P is led into a tank T via. a bleed-off passage 11. When the control valves are changed over, the working fluid is supplied into actuators. The control circuit comprises pilot primary pressure passages 17, 18 for leading a pilot primary pressure into the control valves, a high-pressure selection circuit 19 selecting the maximum load pressure of the load pressures of the actuators, and a connection passage 20 connecting the downstream side of a bleed-off valve 10 in the bleed-off passage 11 to the high-pressure selection circuit 19. When the control valves are neutral, a pressure is generated in the bleed-off passage 11, and the pressure is used as the pilot pressure source. When the actuators are controlled and the bleed-off circuit is cut off, the pressure in the high-pressure selection circuit 19 is used as the pilot pressure source. COPYRIGHT: (C)2007,JPO&INPIT
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