Ever meet a cook that couldn't even boil water?

Many newcomers to building model steam engines don't give a second thought to boilers. When they meet some engineer and tell them they are about to build a boiler and the engineer gives them a stern warning about exploding boilers and how amateurs ought not build such dangerous things, they walk away thinking the engineer is an idiot.

She isn't. Building a boiler should be viewed more or less like building an explosive device. This is simply because a boiler is an explosive device. Most states in the United States have laws governing boilers. Model size boilers are typically exempted, but those laws are there for a reason: many people have been killed in boiler explosions.

On the other hand, if you know what you are doing, a safe boiler can be constructed.

This is a simple horizontal pot boiler. It is about as close to a pan on the stove as you can get. This illustration does not show the burner assembly - look for burners in a future post.

This illustration show some of the basic components: the tank, a safety valve and water level indicator. The water level indicator is nothing more than a clear tube in which you can see the water level. The safety valve is a simple spring type valve:

You adjust how much pressure it takes to push the spring back by how far you screw the top part of the assembly into the bottom part of the assembly. This type of safety valve should not be trusted with much pressure - the springs have a way of failing without telling you. I'll post some designs soon that do not rely on a spring.