Abstract: A downhole rotary pump driven by a polished rod and a string of sucker rods from the earth's surface by a variable or fixed frequency, three phase electric motor, is controlled by measurements of power consumed by the electric motor and by measurements of the rotary speed of the polished rod, the combinations of such measurements being indicative of the torque exerted on the polished rod. Determinations of such torque being either within or outside of predetermined upper and lower torque limits are used to either maintain the rotary speed of the downhole pump, or to vary the rotary speed of the downhole pump, or alternatively, to completely shutdown the downhole pump. Power generated by the motor is monitored and the measured value of power may also be used to terminate motor operation when a low power limit is exceeded.

Abstract: A tubular mandrel is provided as a sleeve around the portion of the rod string polish rod extending through the stuffing box housing. The mandrel is coupled to the polish rod so that they rotate together. Bearings stabilize the mandrel within the housing. Stationary rotary seal means are provided in the housing to seal against the now-stabilized mandrel. Leakage and seal wear are improved when compared with the prior art approach of using compressed packing in direct contact with the polish rod to provide the rotary seal.