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How a Steam Locomotive Works

The design of all steam locomotives is based on the same principles that governed the building of the very first steam locomotives.
  1. A fire in the firebox heats up the water in the boiler, producing steam.
  2. This steam is used to move a piston back and forth.
  3. The movement of the piston turns the wheels via a connecting rod and crank.
Steam locomotive

There are different classes of steam locomotives and they are often described by their wheel arrangements. For example, a locomotive that has a 4-6-2 wheel arrangement means it has four leading wheels (4-6-2), six driving wheels (4-6-2), and two trailing wheels (4-6-2). The MCRR's Number 6, shown above is a 2-6-0, also known as a "Mogul."

To create steam, hot gases created by burning oil, coal, or wood in the firebox pass through the boiler inside approximately 150-180 tubes known as flue pipes, heating the water. The gases leave the locomotive via the smokebox and smokestack.

The "wet" steam passes from the dome on top of the boiler through the throttle valve. In some locomotives, it is then dried in superheater tubes before being led to the cylinders. The superheater tubes are located inside the flue pipes, absorbing more heat from the fire's hot exhaust gasses.

Steam is admitted alternately to either side of a piston in the cylinder, pushing the piston back and forth. The piston is connected to the driving rod and crank. The "back and forth" motion of the piston turns the driving wheel. Each time the cylinder piston moves back and forth, the driving wheel completes a full rotation.

After leaving the cylinder, the spent steam escapes from the locomotive via the exhaust pipe which is routed through the smokestack in the smokebox. Depending on the state of the fire, the steam exhaust action may be visible as the smoke leaves the smokestack in the form of puffs and a familliar chuff chuff chuff sound will be heard. The movement of the steam exiting through the smokebox helps to draw fresh air into the firebox enhancing the fire and generating more steam.

- Taken from "Train" by Eyewitness Books



 Midwest Central Railroad  Mount Pleasant, Iowa 52641 319−385−2912 (updated 01Aug16)