<P> In the early days, pumpjacks worked by rod lines running horizontally above the ground to a wheel on a rotating eccentric in a mechanism known as a central power . The central power, which might operate a dozen or more pumpjacks, would be powered by a steam or internal combustion engine or by an electric motor . Among the advantages of this scheme was only having one motor to power all the pumpjacks rather than individual motors for each . However, among the many difficulties was maintaining system balance as individual well loads changed . </P> <P> Modern pumpjacks are powered by a prime mover . This is commonly an electric motor, but internal combustion engines are used in isolated locations without access to electricity, or, in the cases of water pumpjacks, where three - phase power is not available (while single phase motors exist at least up to 60 hp, providing power to single - phase motors above 10 horsepower can cause powerline problems, and many pumps require more than 10 horsepower). Common off - grid pumpjack engines run on natural gas, often casing gas produced from the well, but pumpjacks have been run on many types of fuel, such as propane and diesel fuel . In harsh climates, such motors and engines may be housed in a shack for protection from the elements . Engines that power water pumpjacks often receive natural gas from the nearest available gas grid . </P> <P> 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 assist the motor in lifting 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 . </P> <P> The cranks themselves also produce counterbalance due to their weight, so on pumpjacks that do not carry very heavy loads, the weight of the cranks themselves may be enough to balance the well load . </P>

Where does the oil from a pump jack go