Patent ID: 7600563
Filing Date: 2009-10-13
Classification: E21B

Abstract:
1. A pump jack system for reciprocating a pump rod string in an oil or gas well and the like comprising: a ground-engaging base frame, and an upper end of said pump rod string extending upwardly through said base frame; piston drive cylinder assemblies mounted on said base frame for extension on opposite sides of said pump rod, each of said assemblies including inner and outer concentric fluid passages and means for introducing fluid under pressure to each of said passages for reversibly driving said pistons in unison including a directional control valve and a limit switch to regulate the directional flow of fluid under pressure into said cylinders; means operatively connecting said pistons to said pump rod for reciprocating said pump rod in said well, said pistons being operatively connected to said pump rod for reciprocating said pump rod in said well including means for regulating changes in pressure at the beginning of each lift stroke and down stroke; and wherein each of said pistons includes a piston shaft slidable in sealed engagement through an inner concentric piston tube, and an outer piston tube is mounted for reciprocal movement with each of said piston shafts in outer spaced concentric relation to said inner piston tube.