| 摘要 |
<p>A down hole hammer comprising: a substantially cylindrical casing (11) having a top sub (10) at one end and a drill bit support (12) at the other; a central passageway extending through the top sub, casing and drill bit support (12); a central tube (14) coaxial with the casing and extending from the bottom of the top sub (10) to the top of the bit support (12) thereby defining an annular space between its outer surface and the internal face of the casing (11), its inner bore forming part of the central passageway; an annular piston (16) reciprocatively accommodated within the annular space for movement between an impact position at which said piston abuts the drill bit support (12), and a raised position at which said piston (16) is spaced from the drill bit support (12); fluid porting means (20 and 32) being provided to said annular space to effect the reciprocation of the piston (16) between the raised and impact positions, the exhaust from the annular space during reciprocating of the piston (16) being exhausted into the central passageway; a fluid bypass (19, 25, 26, 27, 29) extending between the top sub (10) and the drill support (12) and having an outlet opening (28) into the central passageway of the drill bit support (12) and being directed towards the top sub (10).</p> |
