| 摘要 |
PCT No. PCT/AU89/00401 Sec. 371 Date Mar. 22, 1991 Sec. 102(e) Date Mar. 22, 1991 PCT Filed Sep. 14, 1989 PCT Pub. No. WO90/03488 PCT Pub. Date Apr. 5, 1990.A pneumatic percussion hammer for attachment to a drill tube is coaxially constructed about an outflow tube which is mounted therein for axial removal and replacement when worn. A cylindrical piston moves axially between a top sub wherein a drill stem is screwed, and an anvil of a bit at the bottom. A casing and the piston are configured to valve the flow of pressurized air therethrough for reciprocating motion of the piston and an outflow that carries debris through the outflow tube and drill stem.
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