US PATENT SUBCLASS 166 / 324
.~.~.~ With fluid pressure equalizing means

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  DF  .~.~ Fluid pressure biased to open position position {3}
324.~.~.~ With fluid pressure equalizing means

DEFINITION

Classification: 166/324

(under subclass 321) Devices in which the valve has means which when operated equalized the pressure on both sides of the valve before the valve is moved to open position.