1491393 Boring earth &c. BAKERDRILL INC 7 April 1976 [7 July 1975] 14033/76 Heading E1F Apparatus for obtaining formation samples from the bottom of a borehole H includes a bit 10 mounted in a housing 10, the bit 10 having passages 16, 15 into which cuttings are conducted by fluid discharged into the hole H in the region of the bit, and a sealing sleeve 24 on the housing 20, fluid being directed above and below the sleeve 24 to provide a zone of static fluid around the sleeve 24 creating a fluid barrier to the movement of cuttings past the sleeve 24. As described the drill is a pneumatically operated percussive down-the-hole drill which is fixed to a rotating concentric dual drill pipe string (not shown), compressed air being supplied down the annulus between the inner and outer pipes and the cuttings being returned up the inner pipe, the inner pipe being connected via tubes 73 and 75 to the passages 15, 16 in the bit 10. Compressed air passes from the pipe string annulus to inlet passages 90 and then alternately through ports 100, 105 above and below a hammer piston 31 to cause the hammer piston 31 to reciprocate and strike the anvil 11 of bit 10. Air also passes continuously from passages 90 through ports 91, 93 and passages 94, 95, 96 to emerge at 97, the air then passing over the bit 10 to conduct cuttings up the passages 16, 15 in the bit 10. Air from above the hammer piston 31 is exhausted through ports 107, 109 into the annulus between the housing 20 and borehole H. Air from below the hammer piston 31 is exhausted through ports 110, and passages 111, 113, 114, 115, 116 to emerge at outlets 117, 118 below and above the sleeve 24. The areas of outlets 117, 118 are chosen to provide the same pressure at opposite sides of the sleeve 24, thereby resulting in a zone of static air around the sleeve 24 to prevent the cuttings from passing upwardly past the sleeve 24.
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