Abstract: In accordance with an illustrative embodiment of the present invention, a hydraulic drilling jar includes a mandrel and a housing movable between extended and retracted relative positions to deliver jarring blows to a struck object, a piston on the mandrel that slides in a cylinder in the housing, and a restriction assembly on the housing having an internal seal that engages an enlarged section of the mandrel to enclose a high pressure, oil-filled chamber between the piston and the restriction assembly, the restriction assembly including a pin check valve that provides a very slow leakage of oil from the high pressure chamber while the enlarged section of the mandrel is engaged with the seal. An oil-filled compensating chamber on the opposite side of the restriction means from the high pressure chamber has its pressure equalized with the pressure inside the mandrel by ports through the wall of the mandrel.

Abstract: Apparatus for repairing insulation of an insulated conductor comprising a split yoke; an elongate, substantially cylindrical cavity formed in the mating surfaces of the yoke; an elongate, split, substantially cylindrical conductor mold or insert removably positioned in the cavity; an injection molding unit communicating with an opening in the conductor insert through an injection bore in the yoke to inject insulator into the conductor mold through such bore; a heating element within the yoke to melt the injected insulator over an area comprising the central area of the conductor mold; and a cooling element within the yoke to cool the ends of the conductor mold while the central area is heated, whereby the heat applied to the insulated conductor within the conductor mold does not extend to insulated conductor outside the yoke. In an optional embodiment, a tensioning device can be used to maintain the insulated conductor under tension during the repair.