| 摘要 |
An unthreading apparatus is set forth which includes upper and lower mandrels which thread together at a threaded connection which is made of threads having the same pitch as the pipe making up the drill string. There is an internal stem or shaft passing through the upper and lower mandrels. The shaft is provided with upper and lower cylinders, thereby enabling fluid under pressure to be introduced into the cylinders to drive the shaft to and fro. Through a ratchet type mechanism, shaft movement is converted into an unthreading motion for the two mandrels and they unthread, coupling unthreading action to the pin and box at a threaded joint in the drill string above the sticking point of the drill string. This enables the present apparatus to unthread at a particular location because it is locked at that location to straddle a particular threaded joint.
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