| 摘要 |
A Pneumatic impact drilling tool, particularly useful as a downhole pneumatic drill, includes a housing structure adapted to be connected to a string of drill pipe and supplied with compressed air therethrough. A hammer piston reciprocates in the housing structure along flexible feed and exhaust tubes. Compressed air is directed alternately to the upper and lower ends of the hammer to effect its reciprocation in the housing. The hammer is operable to strike an anvil bit member repeatedly to effect a drilling motion. At the upper end of the housing there is provided a removable annular plug member surrounding the tubular support in which the feeder tube is positioned. The annular plug member defines the volume of the space above the hammer piston and is related to the size of the feeder tube so that the feeder tube and plug member together determine the volume of air utilized at any selected air pressure and the timing of operation of the hammer position. The feeder tube and plug member are removably positioned on the supporting member as a set and maybe replaced with like sets of feeder tubes and plug members of different size to permit the operation of the drilling tool at various selected air flow rates and air pressures.
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