The beginnings of steam technology are usually traced to a 1698 invention of Thomas Savery, in Devon, England. His "Miner's Friend" used high-pressure steam to evacuate a metal chamber; when the steam was condensed by injecting cold water into the chamber, the resulting vacuum drew water upward from a flooded mine. The cycle then recommenced by forcing that water out with more steam.
The first true "engine" using steam was invented about 1712 by another Englishman, Thomas Newcomen. His "atmospheric engine" operated on the low-pressure steam, which was used to displace the air from a cylinder. Again, water was injected to condense the steam, but this time the vacuum caused a piston to move downward. When the piston was attached to a pivoted beam, this action could be used to lift a pump rod on the other end. The Newcomen engine acted only in one direction, pulling the piston down; it was raised by counterweights on the pump rod. By the mid-18th century this rather inefficient engine was widely used for pumping water but had no other application.
The broader application of steam power began with several key improvements by the Scot James Watt, in the 1760s and '70s. His "separate condenser" increased the efficiency of the Newcomen engine by allowing the main engine cylinder to be kept hot, shunting the cooler, condensing steam to a small, separate chamber that could be kept cold. Shortly after introducing this improvement, Watt devised the first "double-acting" engine, in which the steam was introduced alternately to both sides of the piston, thus powering the upstroke as well as the down. This made it possible to attach the piston rod to a crank or set of gears to produce rotary motion, making the engine useful for running machinery or even driving the wheels of a carriage or the paddles of a riverboat. By the end of the 18th century, the steam engines produced by Watt and his partner, Matthew Boulton, were powering factories, mills, and pumps both in Europe and America.
Early in the 19th century the Boulton-Watt low-pressure engine, which was relatively efficient but quite heavy in construction, was joined by an important alternative, the high-pressure steam engine pioneered by Richard Trevithick in Britain and Oliver Evans in the United States. This design, which could be made in relatively small versions, became the basis for the 19th-century revolution in transportation when applied to railroad locomotives and river- and ocean-going vessels. In its simplest forms the high-pressure engine used the fact that when water is converted to steam it expands to occupy a volume as much as 1,600 times the original. In a confined space, such as an engine cylinder, this expansion manifests itself as pressure and forces a piston back and forth in a cylinder, entering alternate sides of the piston by means of self-acting valves. All work is done through steam pressure, rather than by condensation as in the earlier engines. Trevithick showed in 1804 that the high-pressure engine could be made to operate a locomotive, although it was another quarter-century before locomotives began to be used widely.
The steam engine became the most important prime mover of the 19th century. The low-pressure, condensing form was used in factories, waterworks, mines, and wherever a large, centrally located power source could be useful. The high-pressure version found its most important application in transportation but was also used in shops and other places where a small easily operated and maintained engine was needed. Many variations on both condensing and high-pressure engines were developed in the continuing effort to improve fuel efficiency, reliability, and power-to-weight ratios. These variations included hybrid forms, such as compound and multiple-expansion engines.
Today reciprocating steam engines are rare, having been displaced by steam turbines for large applications such as electrical generation, by internal-combustion engines for transportation and portable power sources, and by electric motors for shop and domestic use.