GB1370337A - Mechanical jar - Google Patents

Abstract

1370337 Boring earth &c SCHLUMBERGER TECHNOLOGY CORP 15 Oct 1971 [20 Oct 1970 (3)] 48002/71 Heading ElF A jar comprises a mandrel 21 telescopic within a housing 20, an anvil 26 on the mandrel, a hammer 25 on the housing, and tripping mechanism 32 preventing relative motion of the mandrel and housing until a predetermined force is applied, the tripping mechanism comprising a laterally deformable sleeve 35 having threads 36 held into engagement with threads 37 on the mandrel or housing by locking means 45 released by longitudinal movement of the housing or mandrel relative the sleeve, and resilient means 34 resisting movement of the housing or mandrel relative the sleeve so that when the predetermined force is applied the lock means is released and violent impact accurs between the hammer and anvil. The housing and mandrel are respectively attached to the drill pipe 14 and collars 12. After the drill pipe is lowered to cock the tripping mechanism (as shown) an upward strain is taken on the drill pipe to move the housing upwardly relative to the mandrel and sleeve 35, the movement being resisted by the resilient means 34. When the predetermined force is reached the locking sleeve 45 has moved with the housing so that release grooves 48 are positioned laterally opposite threads 47 on the sleeve 35 which deforms laterally under the camming action of the threads 36, 37 to release the mandrel so that the hammer strikes the mandrel to jar in an upward direction. An upper resilient means 33, a hammer 27 and an anvil 28 permit downward jaming. The predetermined force is adjusted by means of screw jacks (not shown) compressing the resilient means. Spaces within the jar are filled with lubricant.