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Valve apparatus
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Patent number 5,338,001
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Issue date Aug 16, 1994
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Halliburton Company
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Craig W. Godfrey
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E21 - EARTH DRILLING MINING
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Valve
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Patent number 5,050,839
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Issue date Sep 24, 1991
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Otis Engineering Corporation
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Rennie L. Dickson
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E21 - EARTH DRILLING MINING
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Valve control system
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Patent number 4,880,060
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Issue date Nov 14, 1989
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Halliburton Company
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Kenneth L. Schwendemann
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E21 - EARTH DRILLING MINING
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Valve
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Patent number 4,522,370
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Issue date Jun 11, 1985
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Otis Engineering Corporation
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Timothy J. Noack
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E21 - EARTH DRILLING MINING
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