Importance

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Abstract

A hydraulically-driven pumping unit for pumping a working fluid includes a pair of double-acting hydraulic piston-cylinder (HPC) assemblies, each having a central axis, a hydraulic cylinder, a piston, and a rod coupled to the piston for axial movement relative to the first hydraulic cylinder. The pumping unit also includes a hydraulic fluid source and an exhaust path for hydraulic fluid. The two hydraulic cylinders are coupled to the hydraulic fluid source and the exhaust path such that the movements of the two pistons are synchronized. The two HPC assemblies are configured for phase-shifted operation such that when pumping unit is reciprocating the two pistons and rods, the a first pair of the pistons and rods always has a different combination of axial position and direction of travel than does a other pair of the pistons and rods. During phase-shifted operation, at least one of the two rods is moving to extend further beyond the corresponding hydraulic cylinder at all times.

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First Claim