| 摘要 |
PURPOSE:To obviate a pilot pump and pilot piping and many open/close valves connected thereto be enabling the changeover of a straight travel valve on a differential pressure between the delivery hydraulic pressure of a secondary pump and the hydraulic pressure at the downstream of the straight travel valve. CONSTITUTION:With transversely running motors 6 and 9 stopped, an actuator is driven. In this case, right and left travel valves 1L and 1R are not operated and an oil circuit leading to the pump pressure receiver 16 of a straight travel valve 15 is shut off with an open/close valve 14, thereby making said valve 15 stop at 'a' position. In this state,when one of turning motor valve 2 as a changeover valve other than the right and left travel valves 1L and 1R and cylinder valves 3, 4 and 5 is operated, a turning motor 7 and a cylinder 8 belong ing to a group 'A' are actuated by hydraulic pressure from a primary pump 12, and cylinders 10 and 11 belonging to a group 'B' are actuated by hydraulic pressure from a secondary pump 13.
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