US PATENT SUBCLASS 166 / 321
.~.~ Fluid pressure biased to open position position

Current as of: June, 1999
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166 /   HD   WELLS

316  DF  VALVES, CLOSURES OR CHANGEABLE RESTRICTORS {5}
319  DF  .~ Fluid operated {4}
321.~.~ Fluid pressure biased to open position position {3}
322  DF  .~.~.~> Retrievable
323  DF  .~.~.~> Locked open or closed
324  DF  .~.~.~> With fluid pressure equalizing means

DEFINITION

Classification: 166/321

(under subclass 319) Devices in which fluid pressure acts on a surface of the valve to urge the valve to open position. The fluid acting on the valve may be the flow line fluid acting on surfaces of the valve of unequal areas or the fluid may be a control fluid distinct from the flow fluid.