Long stroke pumping unit

Claim 1

In a pumping unit which includes a tower, a drum rotatably supported on said tower, reversible drive means operatively connected with said drum, first and second cables connected to said drum for winding thereon or unwinding therefrom, a rod string attached to said first cable, and a counterbalance attached to said second cable whereby rotation of said drum unwinds one cable and winds the other and thus moves said rod string through downstrokes and upstrokes and simultaneously moves said counterbalance in the opposite direction from said rod string, the combination therewith of improved means connecting said cables to said drum and controlling forces which said cables exert on said drum at the conclusion of each stroke, said connecting means comprising links pivoted at one of their ends to opposite sides of said drum, said cables being attached respectively to the other ends of said links, said drum at the conclusion of a downstroke and an upstroke of said rod string rotating to positions in which said first cable and said second cable respectively unwind completely from said drum and have effectively zero moment arms opposing rotation of the drum to start the ensuing stroke in the opposite direction, said links hanging downwardly from their pivots when the cables to which they are attached unwind completely from said drum.