| 摘要 |
An apparatus for a derrick, comprising two or more hydraulic piston-cylinde r arrangements (10, 11) for raising and lowering a yoke (8) which travels on guide rails (7) in the derrick (1) itself, where two or more wire lines (13) are strung over sheaves (12) rotatably attached to the yoke. The wire lines (13) are attached at one end thereof to the top drive (9) and at the other end thereof are secured to an attachment poin t (14a, 14b) adjacent to a drill floor (2), said two or more wire lines being run in two sets (13a, 13b) of lines. The attachment points (14a, 14b) for each wire set are connected t o a tension equalizer assembly to equalize differences in tension in the wire lines.</SD OAB>
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