| 摘要 |
A plurality of valve structures are incorporated in a drill pipe string for drilling a well into the earth utilizing air as the drilling fluid. A first valve is located in the drill pipe string just above the drilling bit, and an additional valve or valves are located in upwardly spaced relation within the drill collar string. Each of the valves has a valve member held in a position allowing the flow of air through the valve by a fusible support, and when the support melts, the valve member will shift to a position closing the valve. The valve just above the bit is combined with a float valve to prevent the upward flow of fluid into the drill string, while the valve or valves spaced upwardly in the drill collar string are full opening valves which allow the running of instruments through the drill string to selected locations above the bit. The additional upwardly spaced valve or valves include a flap held in a position to one side of the bore through the valve body by a fusible retainer. When the fusible retainer melts, releasing the flap, the flap seats on the sleeve to shut off the flow of fluid through the valve and through the drive pipe string and cause an increase in pressure of air above the closed valve.
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