Exact kinematic and torsional analysis of Rotaflex pumping units

• The paper deals with the special long-stroke sucker-rod pumping unit Rotaflex.
• First paper to accurately describe the kinematic behavior of Rotaflex units.
• Exact formulae derived for polished rod displacement, velocity, and torque factor.
• Exact formulae presented for rod-, counterbalance-, and inertial-torques.
• Method is devised for optimum counterbalancing of Rotaflex units.

Long-stroke sucker-rod pumping units are completely different from the traditional beam pump mechanisms and usually have polished rod stroke lengths greater than 24 ft. Due to the low pumping speeds they require significantly less torque than beam pumping units. One of the most successful long-stroke pumping units available today is the Rotaflex, a completely mechanical device. The operation of these units is significantly different from that of the beam pumping units and provides several advantages over those.The paper, for the first time, presents a thorough investigation of the kinematic performance of Rotaflex pumping units and develops exact formulae for the calculation of polished rod position, velocity, acceleration, and torque factor functions. The recommended formulae provide a theoretically sound description of the unit׳s kinematic behavior and can serve as a sound basis for the calculation of gearbox torques. The possible torques on Rotaflex units is defined and the calculation of each torque component is presented. The calculations of permissible loads as well as the possible ways of ensuring ideal counterbalancing are fully described. An example is included to illustrate the calculation of kinematic parameters and the loading conditions of the gearbox for a sample case.