| 摘要 |
Hydraulic tongs, used to screw oilfield tubulars together, are equipped with torque control means which enable the tongs to rotate the tubulars and then gradually apply torque until a preselected torque value is reached, hold the torque at this value a desired period of time and then release the torque. In one form of the invention, a tong control restricts the power of the tong motor to enable low torque rotation while limiting the maximum torque which can be produced by the tong motor. A hydraulic cylinder placed in the tongs' restraining line is controlled to shorten, hold or extend the line. When the line is shortened, the tongs are pulled in a direction which increases the torque to a value above the maximum torque produced by the tong motor. The system allows heavy, powerful tongs to be used to accurately apply and hold a wide variety of selected torque values.
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