How Do Steam Locomotives Work?

Steam locomotives are one of the oldest forms of mass transportation, and these trains had a huge historical impact on how America was shaped during its formative years. But how exactly do steam locomotives work?

This overview of steam locomotives will give you a complete breakdown of the parts and mechanics that drive them. We’ll also learn a little bit about the history behind steam engines and their impact on society. Read on to learn more about how steam locomotives work and how operators control them.

The Mechanics of Steam Locomotion

Even though steam locomotives are complex machines, the mechanics that drive steam locomotion are relatively simple. All steam locomotives operate on the same basic principles of thermal energy transfer.

How Do Steam Locomotives Work?

In steam locomotives, water is heated by a fuel such as coal or oil until it transforms into steam. As water turns into steam, the volume of the water expands. As air pressure builds from the rising steam, it pushes pistons that connect to the driving wheels. (Source: Mid-Continent Railway Museum)

Steam locomotives are somewhat rare these days with the advent of newer and more environmentally-friendly technologies. However, there are still some steam locomotives in service across the world.

steam locomotive work
Jeff Hampton

How Do Steam Engines Make Steam?

Steam locomotives generate steam when fuel is placed in a firebox and ignited. The heat from the firebox is used to heat water to the point of boiling. As the water boils, it is converted to the steam that drives the locomotive’s engine.

What Powers a Steam Engine?

Steam engines are powered by thermal energy that is converted to mechanical energy. The mechanical energy generated by a steam engine is used to power its engine cylinders and wheels.

The Parts of a Steam Locomotive

Steam locomotives are made up of many different parts that can be controlled with a small crew of operators. Here are some of the main parts that make up a steam locomotive:


  • Boiler: The boiler is the part of the steam locomotive that is designed to transform water into steam via thermal energy transfer. This is created by using fuel to heat water until it is boiling, causing it to evaporate into the air. Most steam locomotives operate with a horizontal straight tube fire tube boiler.
  • Steam pistons: The steam pistons are the part of the steam locomotive that drives the locomotive’s movement forward with rotary power. Steam pistons are manipulated by pushing the steam into the pistons through the piston valves. These valves then direct the motion of the locomotive cylinders.
  • Firebox: The firebox is the part of the steam locomotive where fuel is deposited and ignited. The heat from this fire is used to boil water into steam to drive the steam engine. Fireboxes are usually fed with either coal or flammable oil like kerosene. In many cases, the firebox is attached directly to the locomotive’s boiler.
  • Headlight: The headlight is situated at the front of the steam locomotive and is designed to help the train conductor see in low light. These headlights must put off a minimum of 200,000 candelas of light. (Source: Cornell Law School) Headlights significantly increased the amount of time that trains could safely operate by allowing them to run all night.
  • Pilot: The pilot is the guard on the front of the locomotive that helps deflect any obstacles on the rails which might derail the train. This piece of equipment is also commonly known as a cowcatcher. In snowy weather conditions, the pilot can also act as a snow plow to push snow off the rails before the wheels reach them.
  • Cab lights: The cab lights are the lights on the interior of the train cabin that illuminate the switches, gauges, and levers that the conductor uses to control the train’s movement. In older trains, the illumination of the cab was usually performed by a hanging oil lamp situated near the train’s control panel.
  • Marker and class lights: Marker and class lights are additional lighting on the exterior of the steam locomotive that helps designate the class of the train as it stands on the train schedule. These lights also help illuminate the train at night.
  • Whistle: The whistle on a steam locomotive is used as an audible signal that the conductor can use to communicate with other railroad workers. The train whistle is also used as a safety warning to anyone on the tracks that a train is approaching. Modern locomotives often use an air horn to signal rather than a whistle.
  • Bell ringers: Before the incorporation of whistles into the steam locomotive’s design, a common audible signal used on steam locomotives was hand-rung metal bells. Locomotive bells are a popular collector’s item for railway enthusiasts, since they are often one of the only items salvaged from a scrapped train.


Hundreds of years after their invention, the basic operation of steam locomotives remains largely unchanged despite the upgrade of certain technologies and technical designs on them.

steam locomotive
Brad Joyce

What Supplies Does a Steam Locomotive Need?

Along with the right parts, steam locomotives also require some consumable supplies to remain operating.

The main supplies needed to run a steam engine are fuel and water. The fuel is used to create thermal energy that is transformed into steam-powered rotary motion. On a steam locomotive, these supplies are carried in their own train car, known as a tender.

Water in Steam Locomotives

When steam locomotives were first invented, the necessity for water stops to replenish the water on the train negatively impacted the locomotive’s efficiency. Before tender cars were invented, steam locomotives had to stop approximately every 7-10 miles to replenish their water supplies.

After the tender was attached to steam locomotives, train engineers could extend train operations to 100-150 miles before needing to stop and restock water. This had a massive impact on the steam locomotive’s efficiency and contributed to it becoming a major mode of long-distance transportation in the 1800s.

What Fuel Is Used in Steam Locomotives?

The fuel used in steam locomotives is one of the most essential parts of the machine. Without fuel, the steam engine wouldn’t be able to generate the air pressure needed to drive its engine pistons.

Historically, kerosene oil or coal were the main fuels used to power steam locomotives. Modern steam engines can also operate on diesel, wood, biomass, or electricity in contemporary steam engines.

In recent years, steam locomotives have largely fallen out of favor in mass transportation because of their large carbon emissions and low power ratio. However, green steam locomotives that run on electricity or biomass are helping to keep this old technology relevant in the modern age.

steam locomotive night
Jonathan Lee

Sand in Steam Locomotives

Another material that is used in steam locomotives is silica sand. Silica sand is used in locomotives to help create extra friction on the rails and prevent trains from derailing.

Sand on a steam locomotive is stored in a sand dome container and then sprinkled through pipes to hit the rails right before the train wheels hit them. Sand is especially useful in helping the wheels grip in wet conditions that might cause hydroplaning otherwise. (Source: USGS)

Operating a Steam Locomotive

So we’ve gone over the basic mechanics that allow a steam locomotive to function. But there are several parts and processes that go into the locomotive’s operations.

How Does Airflow Factor into Steam Locomotives?

In steam locomotion, the expanded hot air caused by boiling water is what generates motion in the driving wheels. This air pressure is responsible for generating the forward motion of the steam locomotive.

Airflow also affects how fuel is burned on the locomotive. When exhaust steam is released through the locomotive’s smokestack, this causes a backdraft of fresh air that is swept down into the firebox. This fresh air gives the fire in the firebox the additional oxygen it needs to keep burning consistently.

Airflow in the steam engine can be manipulated by using the throttle or the Johnson bar. These levers control the amount of steam that the steam engine has access to, controlling the locomotive’s torque, speed, and direction.

classic steam locomotive
Todd and Jack Humphrey

How Does the Throttle Work in Steam Locomotives?

Another aspect of how steam locomotives work is the control of their forward rotary motion. This is done through the train’s throttling system. The throttle in a steam locomotive controls the amount of steam pressure being sent to the locomotive’s cylinders. The throttle is also known as a regulator.

By controlling the amount of steam delivered to the steam locomotive driving wheels, the conductor can control both the speed and the direction of the train.

What Is the “Johnson Bar” on a Steam Locomotive?

If you read about steam locomotives, you may eventually read about the Johnson bar. Also known as the reversing lever, the steam engine control is responsible for allowing the locomotive to reverse direction on the tracks and back up.

To reverse the locomotive, the Johnson bar cuts off the airflow of steam into the locomotive’s cylinders.

Another aspect of the operation that the Johnson bar is responsible for controlling is known as steam cut-off. This is the point where new boiler steam is admitted to the cylinders, and this ratio can be set as high as 90% or as low as 10%. Using the Johnson bar to adjust speed and steam power on the locomotive can help save on wasted fuel while the train runs.

milw 261
Jeff Hampton

How Does a Steam Locomotive Exhaust Work?

Once the steam in a steam locomotive has been used to move the steam engine’s pistons, the leftover steam is sent up the train’s smokestack to be expressed into the atmosphere as exhaust.

The color of the train’s exhaust is an indicator of how fuel-efficient the locomotive is as it runs. Dark-colored or black smoke indicates a locomotive with poor fuel economy, while more modern or efficient locomotives put off white steam that indicates less wasted fuel during combustion.

Why Do Steam Locomotives Chug?

One of the most iconic qualities of a steam locomotive is the chugging “choo-choo” noise that the train makes as it runs down the tracks. The chugging noise that steam locomotives make results from escaping exhaust steam being blown out of the smokestack. The puffs of smoke leaving the train exhaust are timed with the strokes of the train’s cylinders.

nkp 765
Jonathan Lee

How Fast Can a Steam Locomotive Move?

The fastest steam locomotive in the world was the A4 4-6-2 (aka Mallard), which could reach speeds up to 125-126 miles per hour (mph). However, the average speed of an operating steam locomotive throughout the machine’s history has been 40-50 mph.

How Many People Can A Steam Locomotive Carry?

Traditional steam locomotives in the 1800s were known to carry between 150 and 200 people. While locomotive travel used to be very popular in the 19th century, long-line passenger train travel fell off significantly in the 20th century with the invention of the modern passenger plane.

Air Pressure in Steam Locomotives

Since steam locomotives operate on steam energy, the air pressure generated inside the locomotive’s engine is a major part of its operations. Most steam locomotives operate with air pressure between 200-300 pounds per square inch (PSI).

While adequate air pressure is essential for keeping the steam locomotive running, too much steam pressure in the locomotive can be dangerous. A high pressure in the steam on a steam engine can cause it to leak into the firebox, causing a dangerous backdraft. This results in fire being blasted out of the firebox door, potentially injuring anybody standing in front of it.

Locomotive Air Pressure Failures and the LMS Fury

One of the most famous reports of this kind of locomotive accident was in the LMS No.6399 Fury of the London Midland and Scottish Railways.

While testing a new high-pressure steam engine system, the boiler tube on the locomotive exploded, causing the firebox to backdraft and kill the train engineer Lewis Schofield. This accident and associated maintenance costs of high-pressure systems diminished the popularity of high-pressure steam engines moving forward.

iais steam
Jonathan Lee

Controlling a Steam Locomotive

Even though steam locomotives are relatively complex machines, they are designed to be operated with a skeleton crew, especially if they’re only transporting cargo rather than passengers. The main operators that control a steam locomotive are the train engineer and the train conductor. (Source:

Train Engineers

A train engineer is mainly responsible for the operation of the train and driving it by controlling the amount of steam power being delivered to the driving wheels. They’re responsible for the following operations on a steam locomotive:


  • Adjusting how much steam is sent to the cylinder
  • Shutting off steam flow to the engine (when necessary)
  • Adjusting airflow and fuel levels in the firebox

Train Conductors

The train conductor is the public-facing position that deals with any passengers that might be on board, as well as organizing the train’s route and schedule. The conductor is responsible for the following operations on a steam locomotive:


  • Making sure the train moves safely and on schedule
  • Inspecting of the train’s cargo and equipment
  • Monitoring the behavior and safety of the train’s crew
  • Reporting unsafe conditions during locomotive operation


Between the two positions, locomotive conductors are the less experienced. Train engineers have to have a strong knowledge of the train’s technical systems in order to operate it, and conductors often get their certification and get promoted to the ranks of train engineers after several years of experience on the front of the train. (Source: Train Conductor HQ)

up bigboy
Jonathan Lee

History of the Steam Locomotive

Another aspect of how steam locomotives work other than their mechanics is how they work in the wider world. Steam locomotives possibly had a greater impact on society than any other mode of transportation other than the automobile. During the Manifest Destiny period in American history, steam engines helped drive the modernization of the American West.

Who Invented the Steam Engine?

The first working steam engine as we know it in steam locomotion was invented by Thomas Savery, though it wasn’t originally designed to drive trains. In 1698, Savery invented a steam-based machine that was designed to help draw water out of flooded mine passages.

Even earlier than Savery, an ancient Greek inventor named Hero of Alexander invented the first steam-based turbine, leading to the later invention of the proper steam engine. As you can see, humanity has been working on refining the technology of steam for a long, long time.

Who Built the First Steam Locomotive?

The first steam locomotive was built by Richard Trevithick in 1804. This locomotive was deployed at Penydarren Ironworks in Wales to help move loads of ironworkers and iron, and was based on an earlier design Trevithick came up with in 1801 that he called the “Puffing Devil.”

Unfortunately, the locomotive’s weight caused it to break the train tracks during operation, and it was retired after only three round trips. This technological breakthrough, however short-lived, set the stage for other locomotives to be built and refined in its wake.

Only four years after the retirement of Trevithick’s puffer, another steam locomotive was designed to haul passengers around Torrington Square in London. This locomotive was nicknamed Catch-Me-If-You-Can. Like Trevithick’s iron mover, this novelty steam locomotive also ended up breaking its rails. (Source:

It would still be several years before the technology of steam locomotion would be refined enough to use in standard industrial transportation.

steam locomotive
Hugh Llewelyn

Why Were Steam Locomotives Known as the “Iron Horse”?

When steam locomotives were first introduced, engineers had a bit of a hard time convincing passengers to ride them. Between the dizzying speeds that locomotives ran compared to the horse-drawn carriage (20-30 mph versus 3-5 mph) and the loud noises generated by the locomotive, some would-be passengers found the machines frightening.

One way that railway marketers tried to break through the public’s resistance to using steam engines was to nickname steam locomotives the “iron horse.” Since people of the time period associated horse-drawn carriage travel with ease and luxury, it helped convince more people to accept locomotive travel as a safe, efficient, and fun alternative.

The term “iron horse” also saw growing popularity after a famous race in 1830 between a horse-drawn railroad car (the predominant technology of the day in railways) and a steam locomotive named Tom Thumb that was built and designed by Peter Cooper.

Unfortunately, the iron horse Tom Thumb lost its race against real horsepower in 1830. However, this technological breakthrough nevertheless cemented the popularity of steam locomotion moving forward. This makes the Tom Thumb race one of the turning points in the Industrial Revolution. From this point in history on, the popularity of horse-drawn railways declined sharply. (Source:

What Was the Steam Locomotive Historically Used For?

The steam engine was originally used to pump water out of coal mines, but the use of this engine type eventually spread to powering locomotives. Using steam locomotives, Americans were able to set up mass transport across the North American continent and facilitate Manifest Destiny as new colonies were established in the American West.

NW 611

Where Is the Oldest Working Steam Engine and Locomotive?

The Smethwick Engine at the Birmingham Science Museum in the United Kingdom is the oldest working steam engine in the world. The world’s oldest working steam locomotive that is still running is the Fairy Queen in India, which runs between Delphi and Alwar via Rewari.

Is Steam Locomotion a Dead Technology?

Even though steam locomotion seems like an old-fashioned mode of transportation, there are new types of fireless locomotives that are known as modern steam engines.

Modern steam technology is designed to eliminate many of the negative aspects of traditional steam locomotion. These include excess pollution, low power, and high labor investment compared to more modern modes of transit.

Steam Locomotives Are a Piece of History

Steam locomotives may not be as popular as they were back in the 1800s, but there’s no denying that this mode of transportation had serious historical impacts on modern society and the advancement of modern transport technologies.


Lifelong Rail Enthusiast and Owner of Worldwide Rails

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