US PATENT SUBCLASS 175 / 297
.~.~ Restricted orifice for initially delaying escape of restraining fluid

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

293  DF  BELOW-GROUND (1) HAMMER, OR (2) IMPACT MEMBERS {7}
296  DF  .~ Fluid-operated {1}
297.~.~ Restricted orifice for initially delaying escape of restraining fluid

DEFINITION

Classification: 175/297

(under subclass 296) Apparatus in which said relieving means comprises a restricted orifice through which said fluid may escape when placed under pressure to allow unrestrained movement of said hammer or impact device after a predetermined amount of said fluid has escaped.