US PATENT SUBCLASS 251 / 198
.~.~.~.~ With second expander

Current as of: June, 1999
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251 /   HD   VALVES AND VALVE ACTUATION

157  DF  WITH MEANS TO INCREASE HEAD AND SEAT CONTACT PRESSURE {8}
193  DF  .~ Gate valve {3}
195  DF  .~.~ Bifaced {4}
197  DF  .~.~.~ Faces pressed by subsequently movable expander {2}
198.~.~.~.~ With second expander

DEFINITION

Classification: 251/198

(under subclass 197) Devices including also a second expanding surface which comes into play as the valve approaches or reaches the limit of its closing movement.

(1) Note. This second expanding surface is usually either a

part of a carried expander as in subclass 200 or is fixed to the valve casing as in subclass 202.