| 摘要 |
A jar ( 10 ), for use in a downhole toolstring comprising: a hollow housing ( 11 ); a jar mandrel ( 13 ); a latch sub ( 14 ); one or more latch keys ( 16 ); a cam surface ( 17 ); a chamber ( 23 ); a compression spring; and an adjuster ( 24 ). The hollow housing ( 11 ) supports, moveably retained therein, the jar mandrel ( 13 ). The jar mandrel ( 13 ) and the latch sub ( 14 ) are releasably securable together by means of the one or more latch keys ( 16 ), and each latch key ( 16 ) is moveable between a latching position, in which the latching sub ( 14 ) and the jar mandrel ( 13 ) are connected together, and a release position permitting separation thereof. The cam surface ( 17 ) engages each latch key ( 16 ) to move it from its latching position to its release position when the jar mandrel ( 13 ) occupies a preselected position in the housing ( 11 ). The compression spring ( 24 ) is constrained within the chamber ( 23 ) and acts between the latch sub ( 14 ) and the hollow housing ( 11 ) to bias the jar mandrel ( 13 ) when connected to the latch sub ( 14 ) away from the predetermined position; and the adjuster ( 27 ) includes an adjuster mandrel ( 47 ) that is rotatable relative to the hollow housing and has an external portion ( 49 ) that is engageable from outside the hollow housing ( 11 ) via a side thereof. An adjuster portion ( 51 ) is threadedly connected to the jar mandrel ( 13 ) such that rotation of the adjuster mandrel ( 47 ) relative to the jar mandrel ( 13 ) alters the length of the chamber ( 23 ) and hence the degree of compression of the compression spring ( 24 ).
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