| 摘要 |
<p>The invention relates to a self-propelled apparatus 1 for replacing main such as a gas main 2, comprising a single double acting hydraulic piston and cylinder combination 3 connected with slidable devices 4, 6 operable by the device for step-by-step movement of the apparatus through the main on alternate strokes of the combination, the devices 4 and 6 being operative in only a forward direction to slide to grip the main, the apparatus drawing a vibratable breaker device 20 (FIG. 2) or 30 (FIG. 3) through the main, the device being vibratable to precess about an axis and the device 30 being vibratable by percussive means longitudinally of the main.</p> |
