| 摘要 |
<p>A bidirectional hydraulic drilling jar (12) includes an elongated mandrel (42) telescopingly disposed within a body (22) and defining spaced apart fluid chamber (62, 66) separated by a restricted bore portion (64) of the body. The mandrel (42) is provided with spaced apart positive mechanical seal assemblies (96, 98) engageable with the restricted bore portion (64) to form a hyraulic dashpot to retard movement of the mandrel (42) in each direction over a limited stroke length so that the spring tension or weight of the drill stem may become effective to deliver an impact blow when the seal assemblies (96, 98) move out of sealing engagement with the restriction (64). Back-to-back check valves (104, 186) are arranged to bridge the respective seal assemblies to reduce the length of stroke required to cock and trip the jar in each direction. A separate orifice or flow restricting passage (101, 103) is provided across the seal assemblies so that the retarding effect is independent of coacting seal surfaces between the mandrel and the jar body. Rotary driving torque and impacting in the upward drection are absorbed by a replaceable mandrel sleeve member (72). The positive mechanical seals (96, 98) include a spiral cylindrical seal ring (130) which is backed on its inner diameter by a piston ring type seal member (146) so that a radially expandable substantially zero gap seal is provided between the opposed fluid chambers when the seal assembly is effectively engaged with the bore restriction in the body. </p> |
