A pumpjack (also known as nodding donkey, pumping unit, horsehead pump, beam pump, sucker rod pump (SRP), grasshopper pump, thirsty bird and jack pump) is the overground drive for a reciprocating piston pump installed in an oil well.
It is used to mechanically lift liquid out of the well if there is not enough bottom hole pressure for the liquid to flow all the way to the surface. The arrangement is commonly used for onshore wells producing relatively little oil. Pumpjacks are common in many oil-rich areas, dotting the countryside and occasionally serving as local landmarks.
Depending on the size of the pump, it generally produces 5 to 40 litres of liquid at each stroke. Often this is an emulsion of crude oil and water. The size of the pump is also determined by the depth and weight of the oil to be removed, with deeper extraction requiring more power to move the heavier lengths of sucker rods (see diagram at right).
A pumpjack converts the rotary mechanism of the motor to a vertical reciprocating motion to drive the pump shaft, and is exhibited in the characteristic nodding motion. The engineering term for this type of mechanism is a walking beam. It was often employed in stationary and marine steam engine designs in the 18th and 19th centuries.