| 摘要 |
A reverse circulation, pneumatic drilling assembly wherein the bit assembly is operatively connected to a dual wall pipe assembly. A supply of compressed air is conducted through the annulus of the dual wall pipe assembly to a down hole pneumatic hammer. Exhaust air from the down hole hammer is directed to the bit assembly for continuous removal of drilling debris through a central evacuation tube of the dual wall pipe assembly. Sections of the dual wall pipe are joined by hex head couplings which are quickly and easily engaged and disengaged.
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