| 摘要 |
The invention provides a back spin swivelling device for a downhole rod pump, for backing off drive strings which may be under torque. The device of the invention is particularly suited for use with progressive cavity pumps (PCP), and for the release of torque in a drive string through "back spin". The device comprises a housing having an opening at a bottom end adapted to receive a rotatable shaft and having means for attachment to an external support at a top end; said rotatable shaft being partially housed within the housing and projecting from the bottom end of the housing, the shaft having at its bottom end means for attachment to a drive string; and means for mounting the shaft rotatably within the housing. The shaft and the means for attachment to the drive string are substantially symmetrical about their common axis of rotation, and provide no point of articulation between the shaft and the drive string. In a preferred embodiment, the device includes shock absorbing means for damping longitudinal displacements of the shaft. The symmetrical design of the rotating parts and the linear attachment of the shaft to the drive string greatly improve the safety of the device in comparison with rod pulling devices of the prior art, avoiding equipment failure and possible injury due to flying apart of the device under the influence of "wobble" at high angular velocities.
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