| 摘要 |
A single acting hydraulic fishing jar, for use in a tubular drilling string for applying upward jarring forces for dislodging a "fish" from a well, may be run into a well on a drill string to operate a fishing tool in the well bore. The jar has housing members in telescoping relation for longitudinal movement of one relative to the other with a hammer member on one and an anvil member on the other. The housing members enclose a chamber containing an incompressible hydraulic fluid for controlling application of jarring forces. A sliding seal closes one end of the chamber and supports the inner housing member, i.e. mandrel, for sliding movement in the outer housing member. A piston is spaced from the sliding seal so that movement of one relative to the other. Movement of one housing relative to the other in one direction moves the piston toward the sliding seal. The chamber between the piston and the sliding seal has an outlet controlled by a valve member slidably supported for movement on the mandrel. Predetermined relative movement of the housing members engages and moves the valve member to open position permitting flow of fluid from the fluid chamber to substantially eliminate the resistance to further movement of the housing members and thus permit movement of a hammer member on the mandrel to impact an anvil member carried on the outer housing.
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