| 摘要 |
PURPOSE:To prevent a decrease of a pile-driving force, by a method wherein a free piston is mounted to a cylinder body, a controller for a vertical movement which can ensure a passage having a large cross section and no reduced section part is installed to prevent a weight from delaying in a dropping speed at a stage of downward movement. CONSTITUTION:A device is constituted such that a free piston 28 loosely engages with an upper end at an inner side of an outer cylinder 24, a valve piston 27 having a connecting hole 27a and sliding between the free piston 28 and an inner cylinder 23 is located, and an upper chamber 28a is held therebetween. If fluid enters through a lower port 30 and a weight 29 is positioned at a given level, with switching valves 34 and 35 actuated by a detector 36, the upper chamber 28a is open to a tank, and the switching valve 34 leading to the connecting hole 27a is closed to push upward the valve piston 27. Fluid in a lower cylinder chamber 25 flows to an upper cylinder chamber 26a through an outer annular chamber 26, and the weight 29 is lowered. In this case, the increase of the volume of the upper cylinder chamber 26a is offset to prevent the production of a cavity, and a high-pressure fluid is released in a short time, which results in preventing a decrease of the dropping speed. |
