| 摘要 |
PURPOSE:To prevent shield jacks from being operated by leakage of selector valves and, at the same time, to make it possible to additionally select without retracting the shield jacks. CONSTITUTION:Selector valves 10 and pilot check valves 12 allowing the current to pushing side lines of jacks from the selector valves are provided respectively to pushing side lines 5 of the jacks of a plurality of hydraulic shield jacks 4. A drawing side line 6 of every jack is commonly used, and a pressure ejecting valve 8 is so provided that a pilot pressure opening line 16 is opened to eject confined pressure to an oil tank from a pilot line in order to eject automatically pressure confined to the pilot line 7 with pulling operation of the shield jacks through the pressure confined to a pulling side line. According to the constitution, the extension of the shield jacks by leakage is prevented, and the additional selection of the shield jacks can be made without retracting a shield machine. |
