| 摘要 |
PURPOSE:To produce a most favorable state in terms of strength per area, by installing each selector valve in position between each stretch working oil chamber as well as between each contraction working oil chamber. CONSTITUTION:A selector valve 34, whose oil passage to a hydraulic cylinder at the upper stage side is opened in time of a hydraulic cylinder at the lower stage side being fully stretched, is installed in position between stretch working oil chambers 26a and 31a of hydraulic cylinders 26 and 31. Then, a selector valve 37, whose oil passage to the hydraulic cylinder at the lower stage side is opened in time of the hydraulic cylinder at the upper stage side being fully contracted, is installed in position between contraction working oil chambers 26b and 31b. With this constitution, in time of being extended or contracted from or to the most base stage boom member in consecutive order, these cylinders are contracted from the forefront boom member in order so that a most favorable state in terms of strength per area is producible. |
