| 摘要 |
Well head shut-off device having a housing with a bore for connection to the upper end of production tubing, upper and lower shoulders in the bore and an annular pack-off element with an internal tapering expansion member driveable reciprocably between the shoulders whereby compression of the pack-off element against the shoulders expands the element tightly between the bore and a cylindrical shaft passing through the middle of the pack-off element, whereby a pack-off can be achieved at upper or at lower positions. This allows rapid pack-off to be achieved regardless of the direction in which the pack-off member is driven.
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