How the Steam Locomotive and Steam Technology Work

By: Robert Lamb & Yara Simón  | 
A sepia-toned photo of a vintage steam locomotive beginning its journey from the station
A vintage steam locomotive begins its journey from the station. ryasick / Getty Images

To witness the incredible power of steam, you don't have to look any further than the eruption of geysers or the explosion of gasses that occurs when lava reaches the ocean. Early man witnessed such sights and has long sought to control the raw power of steam through technology ranging from the basic tea kettle to the steam locomotive to the modern nuclear power plant.

Regardless of the level of technology involved, steam power comes down to one basic principle: When water heats up to the point of vaporizing, the vaporized water takes up more space than the liquid water did. This is because solids, liquids and gases are each held together by different levels of molecular forces. In solids, the molecules are compact. In liquids, they're further apart. And in gases like steam they're even further apart.


If you heat a can of soup in a fire, the liquid contents will vaporize and eventually expand to the point where the can will explode to release the pressure inside. When this pressure is used to perform a particular task — like turning a turbine or causing a kettle to whistle — steam technology is harnessing steam power. The methods of heating, containing, channeling and using steam have changed, but the basic principle remains the same.

Learning to harness the power of steam has been a long process. Greek mathematician Hero theorized the use of steam technology in the second half of the first century. However, it would be well over 1,600 years before the first practical steam engine came about, leading the way for the invention of the steam locomotive. Powered by steam engines, these locomotives harnessed the energy of steam to propel trains across vast distances.


Early Steam History

The earliest known records of steam technology date back to Alexandria in A.D. 75. Mathematician Hero, also known as "Heros" or "Heron," wrote three books on mechanics and the properties of air and presented plans for a simple steam engine.

Hero's design called for a hollow sphere with bent tubes emerging from either side of it. This mechanism was then filled with water and mounted above a fire. As the heat caused the water inside the sphere to vaporize, steam was forced to vent through the two tubes. This steam-powered propulsion caused the sphere to rotate — like a wheel turned by bottle rockets.


Hero's method for transforming steam power into motion was the foundation for later steam technology. However, a great number of scientific advancements were necessary before the concepts behind his steam turbine could be put to practical use. Although people like Leonardo da Vinci toyed with the idea of steam power (the inventor suggested in 1495 that steam power could fire a projectile), advancements in engineering and more accurate measurements of temperature and time helped pave the way for the coming age of steam.

In 1606, Giovanni Battista della Porta of Naples recorded his theories about the role of steam in creating a vacuum. He theorized that if water converted to steam inside a closed container resulted in increased pressure, steam condensed to water inside a closed chamber would result in decreased pressure. This new understanding of steam played a vital role in future developments.

In 1679, French scientist and mathematics professor Denis Papin managed to turn della Porta's theory into reality through a surprisingly domestic project: the "Digester or Engine for Softening Bones." The sealed cooking pot was essentially the first pressure cooker. Papin expanded on this device by adding a sliding piston to the top of a closed cylinder full of water. When heated, the expanding steam pushed the piston up. As the steam cooled and became liquid again, the resulting vacuum pulled the piston back down.


The First Steam Engines

In the late 17th century, England faced a timber crisis as shipbuilding and firewood consumed forests. The ships were necessary for trade and defense, but coal was a suitable substitute for firewood. However, producing more coal meant digging deeper coal mines, which increases the likelihood of water seeping into the mines. There was suddenly an urgent need for new methods of pumping water out of mines.

In 1698, Thomas Savery, a military engineer, obtained a patent for a steam pump and began pitching his "Miner's Friend" to anyone who would listen. The device consisted of a boiling chamber that routed steam into a second container where a pipe with a non-return valve descended into the water that needed to be removed. Cold water was poured over the container of steam and as the water vapor inside cooled to a liquid state, the resulting vacuum drew up water from below. The sucked-up water was unable to flow back past the non-return valve and was then drained through another pipe.


Unfortunately for Savery, the steam pump hadn’t been as successful as he hoped in the mining industry. Most of his sales were made to private estates that wanted to drain excess water and repurpose it for home and garden needs. Because the steam chamber's heating and cooling had to be managed manually, the engine was somewhat impractical. The engine could also only draw up water from a limited depth — a deep mine required a series of engines installed at various levels.

However, in 1712, the blacksmith Thomas Newcomen and assistant John Calley, a glassblower and plumber, created a more effective steam-powered pump system. The Newcomen Engine combined Savery's separation of the boiler and steam cylinder with Papin's steam-driven piston.

While Savery sought to replace conventional horse-driven pumps with his engine, Newcomen sought to use a steam-driven pump to do the work of horses. Newcomen's engine was similar to Savery's. It included a steam-filled chamber that was cooled by a quick injection of cold water to create a vacuum-inducing change in atmospheric pressure.

This time, however, the force of the vacuum pulled a piston down and pulled a chain that activated a pump on the other end of a suspended beam. When the water in the piston cylinder turned to steam again, it pushed the piston up and a weight on the other side of the beam reset the pump.


Watt and the Steam Engine

James Watt revolutionized steam technology with his early steam engine.
Hulton Archive/Getty Images

While the Newcomen Engine and Savery's "Miner's Friend" certainly employed steam technology, the steam engine is generally credited to the work of one man: James Watt.

Trained as an instrument maker in London, Watt eventually found employment near Glasgow University in Scotland. When one of the University's Newcomen Engines needed repairs, Watt found himself elbow-deep in the inner workings of steam technology. Watt soon recognized a basic design flaw: Time, steam and fuel were wasted by having both heating and cooling take place inside the piston cylinder.


Watt solved the problem by creating a separate condenser. He added a chamber separate from the cylinder (which he also insulated), where steam would be cooled to create the necessary vacuum. This separation allowed the piston cylinder to remain at the same temperature as the entering steam with no energy wasted heating it and the water inside. Additionally, the separate condenser could be kept at a much lower temperature and required less cooling.

After partnering with Matthew Boulton, Watt produced a faster, more fuel-efficient engine using the separate condenser. The pair's attempt to find new uses for their successful engine led to two more crucial inventions — the double-acting engine and the fly-ball governor.

The fly-ball governor created an automated method of opening and shutting steam valves to a piston. Sun and planet gear were fixed to a wheel-driven shaft. As steam power caused the rod to spin, the two balls spun outward from the shaft. When they reached their highest point, they caused the steam valve to shut. As their spinning slowed, they spun back toward the rod and caused the valve to open again. This transformed the motion in the steam engine from back and forth — reciprocating motion — into the circular motion required to operate a wheel.

The double-acting engine helped make the steam engine more efficient by harnessing the power of formerly idle steam to push down pistons.


The Cornish Engine

Steam powered the Industrial Revolution. Power looms were used in textile manufacturing in 1844.
Hulton Archive/Getty Images

James Watt's steam engine and other innovations set the stage for the Industrial Revolution — beginning with the textile industry in the late 18th century. People had long processed wool by hand and later, with the aid of water mills. But a number of new inventions soon saw factories powered by steam.

The Boulton and Watt engine was incredibly successful but other inventors were still intent on improving the technology. However, Boulton and Watt commanded a monopoly over the steam engine business as their engine was protected by strict patents.


Patent royalties cost mining companies a great deal of money. Inventor Richard Trevithick noticed the plight of the mines in his native Cornwall and set out to create an engine that avoided Boulton and Watt's patented technologies. Trevithick believed he could create an engine that did away with Watt's separate condenser by using high-pressure steam.

While the use of high-pressure steam had been theorized, it had not been executed successfully. Eighteenth-century boilers were incapable of withstanding high pressure for long periods of time. But at the beginning of the 19th century — ironically, just as Watt's patents were expiring — Trevithick discovered that modern boilers could now withstand higher pressures. At the same time, American inventor Oliver Evans experienced similar achievements.

Trevithick's new Cornish Engine was cheaper, lighter and smaller than the Boulton and Watt engine. Arthur Woolf further improved the use of high-pressure steam in 1804. The London brewery engineer realized the idea of compounding — a method where excess steam from one piston fires a second piston and then a third. This method results in less heat loss.


The Steam Locomotive

Cornish inventor and engineer Richard Trevithick's steam locomotive successfully hauled 25 tons of cargo and 36 passengers at Pen-y-Darren, Wales in 1804.
Hulton Archive/Getty Images

Inventors were working on designs for steam-powered cars even as the first steam pumps were fine-tuned in the late 1600s. While some believe Ferdinand Verbiest created a working steam car in 1672, more evidence suggests French inventor Nicolas-Joseph Cugnot made the first steam-powered vehicle in 1769. But while the research and development of steam-powered cars continued for some time, the idea was most successful in the form of the rail-mounted steam locomotive.

The man behind the Cornish Engine, Richard Trevithick, was also a key individual in the development of the steam locomotive. It's important to note that train tracks already existed in the 1770s in various industrial areas of England. Iron-enforced wooden rails called tramways had been built for horses to pull carts of coal. In 1804, Trevithick unveiled a steam-powered engine capable of hauling 10 tons of iron for 10 miles. In 1808, Trevithick's Portable Steam Engine was displayed on a circular track in central London.


Earliest Locomotives

Another British engineer, George Stephenson, picked up two decades later where Trevithick left off. Stephenson's work in developing increasingly efficient steam engines for transporting coal led to the decision to create a rail link between Durham Coalfields and a shipping port in Stockton. Stephenson suggested that the plan also permit the engines to carry passengers. In 1825, Stephenson conducted Locomotion No. 1 on its first journey — carrying cargo and an estimated 600 passengers.

Robert Stephenson also played a pivotal role in this era. He helped construct the Rocket locomotive, which won the Rainhill Trials in 1829, proving the feasibility of steam locomotives for public transportation.


The Tom Thumb is another notable early locomotive. In the United States, this train, built by Peter Cooper in 1830, became the first successful steam locomotive. The Tom Thumb, named as such because of its compact size, featured a small vertical boiler and a single-cylinder engine and made its debut on the Baltimore and Ohio Railroad.

Shortly after, the Baldwin Locomotive Works, founded by Matthias Baldwin in Philadelphia, emerged as a dominant force in the manufacturing of American locomotives. Baldwin Locomotive became synonymous with the United States’ railway development and played a crucial role in expanding rail networks across the nation.


Steam Locomotive Components and Operation

Steam locomotives create steam in the boiler through the combustion of fuel, typically coal or wood. Early locomotives used a fire-tube boiler, which featured a network of tubes carrying hot gases to heat the water. The valve gear controls the admission and release of steam into the cylinders.

When this high-pressure steam is directed into the cylinders, it pushes against pistons to create mechanical motion. As the steam expands and does its work, it loses pressure and energy. The boiler pressure directly affects the performance and efficiency of the steam locomotive.


After the steam has performed its worked in the cylinders, it is exhausted or released from the cylinders into the smokestack or chimney of the locomotive as exhaust steam. The exhaust steam carries away the energy and waste heat from the steam engine, releasing it into the atmosphere.

The expulsion of exhaust steam helps maintain the pressure balance within the locomotives cylinders and allows for the continuous cycle of steam generation, expansion and exhaust.


Steam Locomotives and World War II

Steam locomotives played a crucial role during World War II. They were used to transport troops and military equipment to various locations, as well as to main supply lines by getting food, ammunition, fuel and raw materials to soldiers. They were a lifeline during the war, but they also delayed the conversion from steam to diesel locomotives.

The Steam Locomotive transformed the way people thought about distance.
Frans Lemmens/Iconica/Getty Images


Advancements in Technology

While the development of steam cars remained a mere scientific curiosity for the next 100 years, the steam-powered locomotive took off. The engine operated on a system of wheels rotated by a steam-driven piston. Engineers worked continuously to improve the system by increasing steam pressure, applying compounding and adding additional wheels.

The railway proved a vital part of the­ Industrial Revolution, changing the way in which cargo was transported across land and tying together distant populations. Steam powered the railways until diesel engines and electric power came to the forefront in the 20th century.


The Dangers of Steam Power

Given the high pressures and temperatures of steam engines, it's not surprising that explosive accidents have peppered the technology's development. For this reason, boilers — ranging from simple pressure cookers to power plants — are equipped with some manner of safety valve.

When the pressure inside the boiler becomes too great, excess steam is released through the valve to prevent an explosion. These devises are typically weight- or spring -powered and require a set level of pressure to open the valve. However, accidents still occur.

Explosions due to the intentional or accidental deactivation of safety valves were fairly common in the 19th century. The bad press from such incidents proved a hurdle to steam pioneers and inventors of the day.

One of the more notable steam-related accidents of the 20th century occurred at the Three Mile Island Nuclear Generating Station. The accident began when pumps feeding cool water to the steam generators stopped running, resulting in increased steam pressure. This triggered the plant's release valve, but when the valve failed to close, the reactor core itself overheated.


Lots More Information

Related How Stuff Works Articles

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This article was created in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.