A Modern Approach to the Design Calculation of Torque Loadings on a Pumping Unit Gearbox

Design calculation of gearbox torque will improve a pumping unit´s efficiency. The kinematic relation and total loads of polished rod were developed based on the kinematic and dynamic analysis of the pumping system. The method combined the counterbalance effect with the calculated dynamometer cards and torque factors to compute the net gearbox torque. The results show that the dynamic load is relatively small in the CBM wells. And the total deformation of rod and tubing is much smaller than that in oil/gas fields. For unbalanced operation, the well torque has one maximum peak occurring on the upstroke and one minimum valley on the downstroke when the prime motor is operating in a “regenerative power” mode. For balanced operation, the instantaneous net gearbox torque usually has two approximately equal peaks and their magnitudes are just within half of unbalanced torque loadings. Consequently, balance torque loadings can reduce the size of the prime and gearbox, and load the gearbox more uniformly.