| 摘要 |
A down hole hammer comprising cylindrical casing (12), a top sub (11) mounted at one end of the casing and a drill bit support (14, 15, 16) mounted at the other end of the casing, a space defined within the casing between the top sub and the drill bit support, a piston (17) slidably received within the space for reciprocation between an impact position at which the piston is in engagement with a drill bit (13) which is to be supported from the drill bit support and a raised position at which the piston is adjacent the top sub, the top sub comprising a single element having a first portion which closes the one end of the casing and is adapted to be connected to a drill string to receive pressurised fluid from the drill string, a second portion comprising an annular sleeve (26) which is receivable in the space to form the inner wall of the casing for at least a portion of the length of the space, the sleeve defining ducts which are connected to the first portion, the sleeve cooperating with the external radial face of the piston during reciprocation of the piston within the space to enable the delivery of the pressurised fluid from the first ducts into the space to effect reciprocation of the piston within the hammer.
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