Abstract: Dual flow passage drill stem has a tube radially supported within a drill pipe by a plurality of metal ribs welded to the middle portion of the tube and by elastomer O-rings mounted in spiders disposed around the tube connectors and seated against outwardly facing shoulders in the pipe tool joints. Axial loads are taken by elastomer rings around the tube connectors clamped between outwardly facing annular rabbets at the inner periphery of each spider and an integral flange on the pin tube connector and a threaded flange screwed onto box tube connector. The tube is preloaded in tension and the pipe and elastomer rings are preloaded in compression. The axial support elastomer rings preferably have hour-glass cross sections to increase their damping effect; in addition, the axial support elastomer rings, as well as the radial support O-rings, are preferably made of neoprene, which has a relatively flat curve of force transmission versus frequency.

Abstract: A rotary percussion bit comprises a body having at its upper end a threaded pin adapted to mate with a length of dual conduit drill stem. A plurality of down flow passages for air or other drilling fluid are near the periphery of the body. Inwardly of the down flow passages is an upflow passage. Channels across the lower face of the body connect the down flow and upflow passages. Over the bottom face of the body are located interior boring elements. The face is preferably concave, comprising a plurality of annular steps. At the lower end of the body is disposed a ring on the flat bottom of which are located gage and near gage boring elements. The ring extends down below the outer periphery of the bottom face of the body of the bit. The ring is secured to the body by quick attachable and detachable means in the form of an epoxy cemented straight threaded rotary shouldered connection, the ring having a bevelled lip extending upwardly around the bit body.