Abstract: An apparatus for rotating a tubing string within an oil well. The apparatus includes an outer housing having an upper end, a lower end and a generally hollow interior where the lower end may be used to attach the outer housing to the casing bowl of an oil well. The apparatus further includes a drive assembly and a tubing string hanger generally disposed within the interior of the outer housing. The drive assembly has a generally hollow rotating gear mandrel and a drive gear. The tubing string hanger has a lower end for attaching to and supporting a tubing string. The tubing string hanger engages the rotating gear mandrel such that rotation of the rotating gear mandrel causes rotation of the tubing string hanger. The tubing string hanger, and a tubing string attached thereto, may be withdrawn from the oil well and through the outer housing without withdrawal of the rotating gear mandrel or the drive gear.

Abstract: An apparatus for rotating a tubing string of a pumping wellhead is described which includes a housing having a first end, a second end, and an interior. The first end has a stationary external coupling communicating with the interior. The second end is adapted for attachment to a wellhead. A drive assembly is disposed in the interior. The drive assembly includes a rotatable tubular member having a first end and a second end. The first end of the tubular member is disposed within the interior of the housing in fluid communication with the stationary external coupling. The second end of the tubular member extends past the second end of the housing thereby providing a rotatable coupling engagable with a tubing string. The drive assembly rotates the tubular member. Bearings are disposed between the tubular member and the interior of the housing thereby facilitating rotation of the tubular member. Dynamic seals are disposed between the tubular member and the interior of the housing.

Abstract: A jar tool having a mandrel and a housing substantially surrounding said housing. The mandrel and housing are splined such that they may move longitudinally relative to each other. First and second pairs of abutment faces for the jar and bump strokes respectively, are provided between the mandrel and the housing. Both sets of abutment faces are enclosed within the jar tool.

Abstract: A variable displacement pump has a swashplate controlled by a pair of pistons. A shuttle valve communicates the highest pressure pump workport to an operator-controlled displacement control valve. A pressure-responsive override valve is connected in series between the displacement control valve and the pistons. When an override pressure is achieved, the override valve blocks communication of the control valve with the pair of pistons and communicates the pump workports directly to the pistons for rapid destroking.

Abstract: A hydrostatic drive system includes a hydraulic motor driven by a variable displacement axial piston pump with alternative intake and output ports. A charge pump generates a charge pressure which is communicated only to the pump intake port via a charge valve unit. The pump displacement is controlled by a swashplate which is moved by servo pistons which receive fluid from a displacement control valve. A three check valve unit communicates the higher of pump intake, outlet and charge fluid pressures to an inlet of the displacement control valve.