They’re more of a novelty now, but steam locomotives (we call them steam engines) had a huge role in our country’s development, taking part in the Industrial Revolution, spurring the growth of countless towns along the tracks and assisting in the transformation of the west.
Despite its large size, the mechanics of a steam locomotive are fairly straightforward. Coal burning in the firebox, which is a lot like an oven, provides the heat. Thin metal tubes run from the firebox to the chimney. Hot smoke exhaust from the burning coal travels through the pipes, which pass through a boiler containing water. Water for the boiler tank is provided either by side tanks or the tender, which is a separate car that also holds the coal. Steam from the boiling water is directed out of the tank and into a cylinder ahead of the wheels that contains a piston. An inlet valve lets the steam in. The steam then pushes the piston, powering the wheels. As the wheels complete a full revolution, they push the piston back. The inlet valve closes and the outlet valve opens, allowing the steam to exit into the chimney. The locomotive has cylinders on both sides that fire slightly out of phase so that there’s a constant power supply. This type of steam engine is called a single-acting steam engine. Double acting-steam engines are more complex and allow the steam to push on the piston in both directions instead of relying on momentum to complete the cycle.
Being an engineer (the type that drives trains) was a pretty dangerous job back in the day. It was imperative that the water level in the boiler be kept in a defined, safe range. Too much water in the boiler at one time causes the production of steam to decrease and lowered the efficiency of the engine. An unchecked, rising water level would eventually cause the cylinders to flood as well.
Since the firebox sits against the boiler, the liquid water helps to manage the temperature of the firebox walls. Too little water in the boiler would lead to the walls of the firebox overheating and softening. This runs the risk of the firebox experiencing rupture caused by the high-pressure steam in the boiler, meaning that the engineer would be sprayed forcefully by hot steam.
The use of steam engines declined in the United States in the 1930s, but you can still find them running recreationally across the country today. Many railway museums (we have one nearby in Monticello) will run steam engines seasonally. These train rides are often called heritage rides. In Colorado, you can take a ride on the Durango & Silverton narrow gauge railroad, which runs between (you guessed it) the towns of Durango and Silverton.