| 摘要 |
A bit (2) in a down-the-hole drill rod (4) is driven down by a hammer (8) under the action of hydraulic pressure applied intermittently through fluid (19) to a stem (9) of the hammer. Compressed gas is applied through passages (15, 12, 13) to act between the hammer and bit for the return stroke of the hammer. The bit may be flushed by the gas through passage (6) or by the hydraulic fluid through a passage in the hammer. No internal valve is, therefore, required. <IMAGE> |
