| 摘要 |
A drilling jar to be installed in a set of drill collars in a drill string is disclosed. In the illustrated embodiment, first and second tubular members telescope relative to one another. At the upper end of the lower tubular member, a set of protruding lugs match shoulders having undercuts which permit relative rotation of the two tubular members through part of a turn, thereby permitting the two members to axially telescope whereby locking or unlocking the telescoping movement is controlled. The lower tubular member has an upwardly facing shoulder which is abutted against the lower end of the upper tubular member. This permits the two to be reciprocated and banged together to create a jar for the drill string. A dual jarring activity is developed by a cam actuated radially yieldable collet-type release mechanism that allows relative linear movement of the tubular members and permits selected jarring activity independently of or in conjunction with the lugged locking and releasing portions thereof.
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