| 摘要 |
A latch for a telescoping drill string jar is confined in an opening in the jar housing and engages the arbor of the jar to prevent telescoping action for normal drilling. The latch has a number of spring bars, each with a latch lug extending into a latch groove in the arbor. The lugs and the groove have beveled engagement surfaces that urge the spring bars radially outward, into clearance provided, when axial forces on the arbor relative to the housing exceed a preselected amount. The end of the spring bars are restrained in a cup with tubular sides extending along the spring bars to limit the length of spring bar allowed to flex radially outward. The length free to flex determines the average axial force required to release the latch. The ratio of the extending sides of the opposed cups determines the ratio of tension or compresive axial forces required to release the latch. The jar fitted with the latch is free to telescope, to cause jarring, when the lugs clear the groove.
|
