| 摘要 |
A pneumatic downhole impact drill having a porting system for automatically supplying pneumatic pressure fluid from a fluid delivery tube received within a coaxial bore in the impact piston to the opposite ends of the piston operating cylinder as the piston reciprocates. The porting system comprises an annular set of equiangularly spaced outlet ports in the fluid delivery tube and two sets of radially extending bores in the piston having first and second, axially spaced, annular sets of equiangularly spaced inlet ports which cooperate with the outlet ports in the delivery tube. The number of inlet ports in the piston in each set thereof, is different than the number of outlet ports in the supply tube and the combined angular widths of the ports of each set of inlet ports and the outlet ports is substantially greater than 360 DEG to provide substantial fluid communication therebetween at all relative angular positions of the piston and fluid delivery tube.
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