The Balancing Act of Firing a Steam Engine

A Look at What it Takes to be a Fireman on a Coal Burning Locomotive

Sep 24, 2009

Firing a steam engine is more than just throwing coal on a fire. It is a fine balancing act between maintaining steam pressure and water levels.

When most people think of the fireman, the grimy labourer whose job it is to throw coal into the fire of a steam engine, they think that that’s all there is to his job.

How easy is that? Well, as it turns out, it’s not that easy. Firing a coal-burning steamengine is all about balance and timing; the balance between steam pressure and water level and the timing of when and where to throw the coal in.

The first part of the job is what people think it is, throw coal on the fire so the fire will keep burning. But they can’t just throw coal in willy-nilly, otherwise it will pile up in places, in effect smothering the fire you’re trying to keep alive.

Other places may not get any coal at all, and parts of the fire will go out for lack of fuel. This doesn’t make for a good fire. What the fireman does is spread the coal out evenly over the entire fire. This is made difficult by the sheer size of the fire box and the fact that the train is usually moving when he is trying to work, shaking him from side to side. It takes practice and a good sense of balance to make an even fire.

This is where another type of balancing act comes into play. Steam makes the engine run. The steam is created by water in the boiler being heated by the coal in the fire. The water boils into steam and this makes pressure.

As the pressure increases, water is used up in the process and the water level goes down. If the boiler runs out of water, it runs the risk of blowing up the engine and the crew. So as can be seen, it’s important to keep water in the boiler.

But, as the fireman adds water, the pressure goes down because of cooling. If the pressure goes down too much, there won’t be enough pressure to run the engine and the train stops, making the engineer blow up at the fireman.

Keeping Everything in Balance

First, the fireman will add coal to the fire, making the fire hotter, and the steam pressure goes up. Say the pressure gets to 170 PSI before the safety valve goes off (this makes sure the pressure in the boiler is never more than the boiler can handle).

Now he will add water to bring the pressure down. When the needle on the pressure gauge gets to around 150 PSI, the fireman will turn off the water. At this point, the fireman will have to shovel on more coal to get the pressure up again, so that he can add more water and repeat the process. This way, there is always pressure and water in the boiler.

If the fireman slacks off, and lets the pressure drop bellow 150 PSI, he may have to shovel on two fires before he can add water. This means that his water level will drop to a dangerous level. If he adds water before he’s gotten the pressure back up to 170 PSI, the pressure will drop to a point where the train will have to stop. This is why the fireman must keep everything in balance.

The copyright of the article The Balancing Act of Firing a Steam Engine in Steam Trains is owned by J. Jeff Riddell. Permission to republish The Balancing Act of Firing a Steam Engine in print or online must be granted by the author in writing.