| 摘要 |
A jar mechanism (1, Fig 1) has a jar rod 2 which is releasably secured via a latch key 3 and a latch sub 4 to a piston 5. The piston 5 has a shaft 6 and a body 7. The latch sub 4 is secured to the shaft 6 by a roll pin (8 fig 2). The shaft 6 and body 7 are secured together in a fluid chamber 9 in a piston housing 10. When an upward jar is to be exerted the jar rod 2 is pulled slowly upward. The pulling force exerted on the jar rod 2 is transmitted to the piston 5 via the latch key 3 and latch sub 4 so that the piston 5 is moved through the fluid chamber against the resistance of the fluid. As the movement of the piston 5 is slow due to the restricted fluid flow, time is available to pull up to a desired force before the piston reaches the other end of the fluid chamber 9. Continuation of the pulling force forces the latch key 3 out of the jar rod 2 so that the rod 2 is released from the piston 5 and rapidly accelerates until a shoulder 37 hits the anvil shoulder 11a of the anvil sub (11, Fig 1). This creates the upward jarring force. The jar(1, Fig 1) may then be reset. A balance piston 32 may be provided to accommodate any thermal expansion of fluid in the fluid chamber 9 . Likewise, the jar rod (2', Fig 9A,9B) may also have an acircular cross section which may lodge against faces(202, Fig 9B) in the anvil sub(11', Fig 8B) so that turning forces may be transmitted from the jar rod(2', Fig 9A,9B) to the anvil sub (11', Fig 8B). |
