Sometimes, however, crank-balanced units can become prohibitively heavy due to the need for counterweights. Lufkin Industries offer "air-balanced" units, where counterbalance is provided by a pneumatic cylinder charged with air from a compressor, eliminating the need for counterweights.

Depending on the size of the pump, it generally produces 5 to 40 litres (1 to 9impgal; 1.5 to 10.5USgal) of liquid at each stroke. Often this is an emulsion of crude oil and water. Pump size is also determined by the depth and weight of the oil to remove, with deeper extraction requiring more power to move the increased weight of the discharge column (discharge head). The prime mover runs a set of pulleys to the transmission, often a double-reduction gearbox, which drives a pair of cranks, generally with counterweights installed on them to offset the weight of the heavy rod assembly. The cranks raise and lower one end of an I-beam which is free to move on an A-frame. On the other end of the beam is a curved metal box called a horse head or donkey head, so named due to its appearance. A cable made of steel—occasionally, fibreglass—, called a bridle, connects the horse head to the polished rod, a piston that passes through the stuffing box. verifyErrors }}{{ message }}{{ /verifyErrors }}{{