| 摘要 |
A primary pipe gripping mechanism and a backup, secondary pipe gripping mechanism are carried in a single tapered slip bowl. The primary gripping mechanism employs smooth surface pipe dies that set against and grip and hold the pipe without damaging the pipe surface. After the primary mechanism is set, toothed dies in the secondary gripping are automatically engaged with the pipe with only a minimal pipe gripping force. Accidental slippage of the pipe through the smooth dies sets the toothed dies down against a wedging surface to grip and hold the pipe to stop its downward movement. A resilient biasing device is used to urge the toothed dies away from the pipe before the smooth dies are set. Movement of the pipe relative to the already set, smooth dies automatically causes the toothed dies to set and grip the pipe to thereby limit the incidence of pipe damage to those situations in which pipe slippage occurs through the primary gripping mechanism.
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