US PATENT SUBCLASS 175 / 234
.~ With longitudinally spaced valve seats

Current as of: June, 1999
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175 /   HD   BORING OR PENETRATING THE EARTH

232  DF  WITH MEANS MOVABLE RELATIVE TO TOOL BELOW GROUND TO STOP FLOW TOWARD BORE BOTTOM {8}
234.~ With longitudinally spaced valve seats {1}
235  DF  .~.~> Seat engaged to stop upward flow

DEFINITION

Classification: 175/234

(under subclass 232) Apparatus in which at least two surfaces are spaced along the bore axis, said surfaces being adapted to cooperate with relatively movable flow stopping means.

(1) Note. The longitudinally spaced valve seats may both cooperate with a single movable means, and may be engaged to stop either upward or downward flow.