| 摘要 |
A down-the-hole pneumatic drill in which the reciprocating hammer-piston slides over a ported tubular structure mounted centrally in the cylinder of the drill body and providing two longitudinal passages through which passes all the pressure air required below the piston. The tubular structure comprises an outer tube having a close-fitting inner tube within it, the inner tube being formed in its wall with a longitudinal indentation closed at the lower end, one of the passages being defined by the indentation and the wall of the outer tube and the other passage being defined by the interior of the inner tube. The tubular structure is provided with ports controlled by the sliding hammer-piston, certain of these ports being formed by registering holes in portions of the walls of the inner and outer tubes which lie in contact with one another. The drill has a pressure-responsive disc valve at its upper end by which pressure air is distributed alternately into the upper working chamber of the cylinder and, via the indentation, into the lower working chamber to effect respectively the downward power stroke and the return stroke of the piston, the air being exhausted at the end of each stroke through the tubular structure to an exhaust passage at the lower end of the drill body.
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