Pumpjack

[2] 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.

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 horsepower or 45 kilowatts,[4] providing power to single-phase motors above 10 horsepower or 7.5 kilowatts can cause powerline problems, notably voltage sag on startup,[5] and many pumps require more than 10 horsepower).

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.

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.

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.

The polished rod has a close fit to the stuffing box, letting it move in and out of the tubing without fluid escaping.

The bridle follows the curve of the horse head as it lowers and raises to create a vertical or nearly-vertical stroke.

The piston then reaches the end of its stroke and begins its path upwards again, repeating the process.

As the gas-laden fluid enters the well bore through the perforations, the gas bubbles up the annulus (the space between the casing and the tubing) while the liquid moves down to the standing valve inlet.

The technology is simple, typically using a parallel-bar double-cam lift driven from a low-power electric motor, although the number of pumpjacks with stroke lengths 54 inches (1.4 m) and longer being used as water pumps is increasing.