A Simple Boiler For Model Steam Engines


        First things first: I absolutely recommend that you not build this boiler. This page is being provided for informational purposes only.  During the course of my experiments with model steam engines, I did build a boiler based on these concepts. I am simply providing a review of the design and my observations of it’s operation. If you are intent on building a boiler for your model, I’d recommend that you review the plans in some of the books available through “Home Shop Machinist” or their publisher, The Village Press.

The model steam engines appearing on these pages will operate just as well, and much more safely, on compressed air. This does not imply that using compressed air is foolproof. An engine that is poorly constructed and/or run on too much pressure may “blow up” and scatter metal projectiles. When test running our motors, we always use a clear plastic Lexan scatter shield (the kind used on metal cutting lathes……available through Enco, Broadhead-Garrett, etc.). It goes without saying that we always wear safety glasses in our lab.  


1.      Use a standard size steel soup can that does not have a “pop-top” lid (do not use an aluminum soda can). Choose a can that contains a light broth (no noodles, etc) since you will have to drain all the product through two small holes.

2.    Remove the paper label

3.    Drill two small holes (about 3/16 “) in the top near the edge and about 1” apart. Drain the product and flush thoroughly.

4.    For “outlet” and “pop-off” connector, use two pieces of small metal tubing, about 3” long with about 3/16" OD. Bend gently as shown. Solder into the holes as shown. For the metal tubing, I used automotive brake line (from a junk car). Brass or copper tubing (from a hobby shop or hardware store) would also work.

5.    Cut a 2”length of rubber tubing (3/16” ID automotive fuel line hose would work well) and plug one end tightly with a machine screw. This is the “plug” for your pop-off connector……effectively, this is the safety valve. Slide the plug over the pop-off connector and apply compressed air to the outlet connector. Adjust the plug until it just pops off at about 30 PSI (by “adjusting”, I mean the distance the rubber plug is slid over the pop-off pipe) .

6.    Construct a sheet metal support (as shown)

7.    Connect a longer piece of hose to the “outlet” pipe (about 12 inches).

8.    Put about 4 ounces of water in boiler and heat gently with a propane torch (not too close to can) until water boils and steam is emitted from outlet hose……practice holding torch far enough away from can, so that it just barely produces steam. When you have mastered this, connect the steam hose up to the inlet connector on the engine and spin the motor. Don't let boiler run dry!

9.    Note: Make sure the engine you are powering with steam will already run on compressed air……otherwise, you might be troubleshooting two things at the same time.