Patent classifications
E
FIXED CONSTRUCTIONS
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E21
EARTH OR ROCK DRILLING; MINING
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E21B
EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
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21/00
Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
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E21B21/10
Valve arrangements in drilling-fluid circulation systems
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E21B21/103
Down-hole by-pass valve arrangements, i.e. between the inside of the drill string and the annulus
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