US PATENT SUBCLASS 210 / 118
.~.~.~ Non-closing, e.g., sand valve

Current as of: June, 1999
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210 /   HD   LIQUID PURIFICATION OR SEPARATION

97  DF  FLOW, FLUID PRESSURE OR MATERIAL LEVEL, RESPONSIVE {14}
109  DF  .~ Discharge of treated material {5}
117  DF  .~.~ Check valve controlled {2}
118.~.~.~ Non-closing, e.g., sand valve

DEFINITION

Classification: 210/118

(under subclass 117) Apparatus comprising a variable restrictor responsive to flow direction whereby flow increases during backwash.