Abstract: A well pumping unit including a derrick having first and second sheave sets attached near the top thereof, a drive mechanism, a counterweight, a polish rod assembly and cable members. The cable members form a closed loop extending from the polish rod assembly to the first sheave set, to the counterweight, to the second sheave set, to the drive mechanism, to the second sheave set, to the first sheave set and back to the polish rod assembly. The counterweight is suspended by the sheave sets and cable members between the sheave sets. When the drive mechanism operates in a first direction, the polish rod assembly is raised and the counterweight lowered. When the drive mechanism operates in a second direction, the counterweight is raised and the polish rod assembly lowered. The counterweight may be located within the derrick while the polish rod assembly and drive mechanism may be located outside of the derrick. The weight of the counterweight may be adjusted as desired.

Abstract: A reciprocating drive mechanism powered by a rotating prime mover for use, for example, in operating oil well pumps. The drive mechanism utilizes a rotating pinion meshing with an endless arcuate rack gear to convert rotation to reciprocation and includes an assembly to provide a positive engagement between the pinion and rack gear. The prime mover is coupled to a fixed input shaft, the input shaft has the pinion coupled thereto, and an endless arcuate rack gear is rigidly coupled to an output shaft and meshes with the pinion. An arcuate cam is rigidly coupled to the arcuate rack gear and is engaged by a pair of cam followers which are also coupled to the pinion. A transmission shaft, which supports the pinion and cam followers, is parallel to and located a fixed distance from the input shaft, thereby maintaining the cam followers in positive engagement with the cam and the pinion in positive engagement with the rack gear.