| 摘要 |
PCT No. PCT/AU87/00362 Sec. 371 Date Apr. 24, 1989 Sec. 102(e) Date Apr. 24, 1989 PCT Filed Oct. 26, 1987 PCT Pub. No. WO88/03220 PCT Pub. Date May 19, 1988.A pneumatic percussion hammer casing (10), a top sub (23) connected to the outer tube of a double tube drill stem, an air feed pipe (19) extending from the top sub (23) co-axially into the casing and co-axially about an air outflow pipe (21) connected at its upper end to the inner drill stem tube, its lower end slidable in an air passage (38) through bit (31) the shank of which (32) is slidable in a driver sub (33) at the lower casing end and topped by an anvil (35), a passage (43) having ducts (39,44) extending to the exterior of the bit (31). A tubular piston (27), slidable in the casing (10) co-axially about the air outflow pipe (21) engages, when brought down onto the anvil (35), tube (37) rising from passage (38) through the bit, shank and anvil. Annular chambers (11, 12, 13) are formed within the casing (10) and the axial passage of the piston is divided into upper and lower passages (29,30). Piston (27) is formed with ports (45, 46, 47, 48) to act as a valve for effecting reciprocating movement, impacting the anvil (35) on its downstrokes, but if the casing (10) is raised to lift the bit (31) from its work face, the anvil (35) and piston (27) descent so that the hammer is in a state of balance and automatically ceases operation.
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