| 摘要 |
A reverse percussion device (30) for use with hydraulic percussive drills is provided. The reverse percussion device (30) includes a cycling piston (34), valve (36) and anvil (38). The piston (34) and valve (36) move in opposing directions between low and high pressure passages automatically until a lodged drill bit (18) is freed, thereby facilitating removal of the drill bit (18) from the drilled hole and eliminating alternate loosening and tightening of drill string threads (14). The reverse percussion device (30) preferably includes an automatic disabling feature which causes the reverse percussion operation to cease when the bit is free to retract normally.
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