| 摘要 |
PROBLEM TO BE SOLVED: To sufficiently ensure pressure oil required for boom lifting and improve boom lifting even in the case of the simultaneous operation of bucket closing, arm closing and boom lifting, and to enhance workability. SOLUTION: In a hydraulic circuit composed of the first hydraulic circuit, which contains each direction control valve in boom two-speed, slewing and arm one-speed and in which the direction control valves are connected in parallel respectively, and the second hydraulic circuit, which comprises each direction control valve in boom one-speed, a bucket and arm two-speed and in which the direction control valves are connected in parallel respectively, slewing variable priority circuits are installed in the downstream of the direction control valves for slewing in parallel oil passages for the first hydraulic circuit, one pilot control sections of the slewing variable priority valves are communicated with pilot valves for slewing, and the other pilot control sections of the priority valves are communicated with pilot valves for a boom through direction changeover valves changed over at pilot pressure from pilot valves for the bucket.
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