| 摘要 |
A pneumatic downhole impact drill having a porting system for automatically and sequentially supplying pneumatic pressure fluid from a fluid delivery tube received within a central coaxial bore in an impact piston to the opposite ends of the piston operating cylinder as the piston reciprocates and for selectively and automatically connecting the non-impact end of the cylinder to exhaust via the coaxial bore in the piston as the piston reciprocates. The porting system provides two separate paths for supplying pneumatic pressure fluid to the non-impact end of the cylinder and employs annular porting grooves and internal drilled porting bores in only the non-impact end of the piston to minimize stress concentration from piston impact.
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