| 摘要 |
A jar (10) includes a plurality of pistons (16) secured together to form a piston assembly (23). Piston assembly (23) is movable axially in response to an actuating pressure differential between the jar bore (17) and the borehole (19). Biasing spring (28) biases piston assembly (23) to return to a closed position when the actuating pressure differential is reduced by a predetermined amount. Piston assembly (23) forces a hammer member (32) and a movable anvil portion (30A) axially to cock the jar in response to the applied actuating pressure differential. When the pressure differential is reduced, biasing spring (28) moves anvil portion (30A) against anvil support portion (30B). Detent assembly (47) temporarily limits the velocity of hammer member (32) towards movable anvil portion (30A) after the pressure differential is reduced. Compressed nitrogen (64) in nitrogen chamber (31) biases hammer member (32) towards anvil portion (30A) to deliver a jar impact.
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