| 摘要 |
A boom has an inner end pivotally supported in front of the bottom of an oil well drilling derrick to enable the boom to be swung in a vertical plane toward and away from the derrick. A boom extension is hinged to the outer end of the boom on a horizontal axis and extends upwardly from the boom when the latter is in its raised position. Means are provided for swinging the outer end of the boom extension relative to the boom in a direction toward the center of the derrick while the boom is being lowered and away from the center while the boom is being raised. Pivotal means, pivotally connected to the outer end of the boom extension on a horizontal axis, supports clamping means for gripping drill pipe. The pivotal means is positioned to allow the gripped drill pipe to swing across the boom and boom extension as the boom is raised or lowered, whereby drill pipe suspended from the elevators can be moved back and forth between upright position in the derrick and forwardly extending position near its bottom.
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