| 摘要 |
PROBLEM TO BE SOLVED: To secure a good responsiveness by a flow rate control valve system in a small loading condition, while preventing the generation of a cavitation in a large loading condition, by a counterbalance valve system. SOLUTION: A lowering mode is divided to 'a normal lowering mode' and 'a high speed lowering mode' according to the size of a load, and in a large loading time when the safety is preferred than the responsiveness, the first flow rate control valve 21 is selected as 'a normal lowering mode', so as to prevent the generation of a cavitation by a counterbalance valve system. On the other hand, the second flow rate control valve 22 is selected as 'a high speed lowering mode' in a small load time, and a good responsiveness is secured by a flow rate control valve system.
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