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What Is the Anatomy of a Steam Locomotive? By Danielle Abram Print

What Is the Anatomy of a Steam Locomotive?

What are the different parts of a train?

When looking at the anatomy of a train, there are many different components to look for and too many answers for one broad question. You first have to identify the type of train you are looking at in order to know what you are looking for. For example, if you are looking at a locomotive, a hopper car, or a trolley car, they all have different key parts that make up their construction. 

Now, model trains can look quite similar to the original model they are replicating. Depending on which brand, which materials, and your price range, there can be more or less trim pieces and details included. Also, some people have their own freedom of creating and replicating certain items if they choose to custom paint or build their own train. 

Let’s try and break it down and start with a classic...

What are the main parts of a steam locomotive train?

As you can see, there are many different components that make up a steam locomotive. Here is a quick breakdown as to why each piece is important or even worth mentioning.

  • Headlamp – Projects light at the front of the locomotive.

  • Marker Jewel –  Also called classification lights, they are typically green, red, or amber and indicate the schedule of the train. 

  • Smoke Stack – The place where the smoke leaves the boiler.

  • Bell – Mostly used when a train is approaching a railroad crossing, grade crossing, or a level crossing. They may also ring if they are approaching a station or moving at a slow speed. 

  • Sand Dome – Sand is stored here, at the top of the engine, to help provide traction on the rails.

  • Steam Dome – This is at the top of the engine and contains the main steam pipe, which should be kept above the water level in the boiler. 

  • Whistle – This signaling device is used to communicate with rail workers or warn others if a train is approaching. 

  • Cab – This is the crew and driver’s compartment which has the controls for the locomotive to operate.

  • Struts – On the window as a separation piece. 

  • Ashpan – An ashpan is mounted underneath the firebox on a steam locomotive to catch hot embers, ashes, or any other solid combustion waste that may fall through the grates. 

  • Trailing Truck – This truck helps support the weight of the cab and the firebox. 

  • Drive Rod – This steel arm converts the horizontal motion into a rotary motion of the driver wheels. 

  • Eccentric Crank and Rod – The rod that is in front of the wheels is connected to the crank on the back part of the wheels. The crank is connected to the pin of the driver to help operate the valve gear. When in motion, it moves in an elliptical path. 

  • Driver – The drivers are the wheels that move the locomotive and are balanced with weights to help reduce unwanted motion the engine may experience. 

  • Valve Gear - Controls the running direction and power of the locomotive with the system of rods and linkages synchronizing the valves that release and exhaust steam from the cylinders.

  • Steam Chest – This valve chamber contains a passageway to help distribute steam to the cylinders with the pistons, which it is adjacent to. 

  • Pilot Truck – This truck takes some of the load of the front of the locomotive and helps guide the locomotive when going into a curve or to help deliver a smoother transition altogether.

  • Pilot/Cow Catcher – Mounted on the front of the locomotive, the purpose of the pilot is to help deflect obstacles on the track that may derail the train otherwise.

What about the tender?

A lot of times you will see a tender attached to a locomotive. A tender is the container that holds water for the boiler as well as fuel, such as wood, coal, or oil for the firebox. There is a coupler on the back of the tender to connect other cars, such as a tank car, passenger car, and eventually a caboose. 

How Are Steam Locomotives Named?

Depending on where you are located, steam locomotives can be named differently, but often follow the Whyte notion. The Whyte notion classifies steam engines, as well as some internal combustion engines, by their wheel arrangements.

In order to follow the Whyte notion, you have to count the number of leading wheels, then the number of driving wheels, and finish with the number of trailing wheels. 


This engine has four leading wheels, six driving wheels, and finishes with two trailing wheels creating: 4-6-2.

This method has been used since the early 20th century after being devised by Frederick Methvan Whyte, though other classification schemes, such as the UIC classification, count the number of axles instead of the number of wheels. To each their own, as countries in continental Europe trend toward UIC, but refer to the Whyte notation for most steam locomotives. 

Do the Number Of Wheels Change How the Engine Runs?

As a matter of fact, yes. There are different wheel combinations that can alter how a train operates based on speed, turn radius, or holding the weight of a locomotive. The leading wheels help to guide the locomotive during high speed and the trailing wheels support the firebox. The driver wheels transmit the engine’s power to the rails and as a general rule of thumb the bigger the driver wheel, the faster the engine.

Some of the more popular types of locomotives are: 

  • 4-6-2 Pacific

  • 4-6-4 Hudson locomotive, famous on the New York Central

  • 2-8-0 Consolidation would be an early freight locomotive

  • 2-8-2 Mikado was a later improvement with a bigger firebox for more power

  • 2-8-4 Berkshire was a fast freight

  • 4-8-4 Could be a passenger, freight, or mixed traffic engine

  • 4-2-2 Single Driver or Jumbo

Do Articulated Locomotives Follow the Same Rules?

Articulated locomotives are two locos that have been efficiently joined by a common boiler. They do follow the same rules as a normal locomotive, but they would use a plus sign, +, in order to separate the two locomotives. The plus symbol represents the bond that links the two engines together; carrying the boiler. 


Double Pacific by Garratt: 4-6-2+2-6-4

Union Pacific Big Boy: 4-8+8-4

What Are the Suffixes for the Whyte notation?

Most times, when a locomotive has a suffix, it is easier to identify the purpose or difference in each engine. Here are some examples:

  • VB or VBT = vertical boilered locomotive

  • F = fireless locomotive

  • R = rack locomotive

  • G = geared steam locomotive 

  • C = crane tank 

  • No suffix = tender locomotive

  • T = a tank locomotive, which can possibly indicate the type to tank locomotive as well. For example: 

    • T = side tank

    • PT = pannier tank

    • ST = saddle tank

    • IST = inverted saddle tank

    • WT = well tank

    • T+T = tank locomotive that also has a tender

As you can see, there are many different components that go into the anatomy of a steam locomotive and its naming process. Did you learn anything new? We hope so! Make sure to stay tuned on more train anatomy lessons ahead!


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Anything You Want To Add?

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