Contra's Steam Boiler

[contrahead]

I like the look and shape of your heat exchanger and the stainless pot; but for different reasons than you might expect.

I'm midway into the process of converting an old 6 HP Tecumseh roto-tiller engine, into a functional steam engine. It will look something like this.

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Now I need to fabricate a convenient and efficient stem boiler (for education and display purposes).
It would probably be easier to build a simple “fire-tube” boiler than a “water -tube” boiler. But water tube designs are safer and handle more pressure.
Historically fire tube boilers have been heavy, ugly, boiler plate or cast iron things, that needed pressure relief valves to keep from running amuck and exploding. Fire tube boilers like those found in old steam locomotives began working at pressures around 20 to 50 psi, and graduated up to pressures of 200 psi or more by the 20th century. An exception to this was in the Stanley auto's firetube boiler, pictured below.

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This was a vertical fire-tube boiler with a vaporizing burner underneath. The boiler was reinforced by several layers of piano wire wound around it, which made it strong and lightweight at the same time. Working pressures could reached and controlled anywhere between 400 and 600 psi. Initially the vertical fire-tubes were all made of copper.... ..

Water tube designs are safer (mainly because they contain less heated water) and work at even higher pressures - which improves efficiency and the amount of work that can be done. A 1/2" copper pipe can typically withstand a maximum working pressure of around 613 psi when annealed and 1206 psi when drawn, depending on the specific type of copper tube used. (1/2" Type L copper pipe rated at 1200 psi at 200°F).

The Dobel steam car boiler (a water tube design) used a highly efficient monotube steam generator to heat a much smaller quantity of water. (In 1923 a Doble steam car could be started from cold, with the turn of a key. And then the heavy, stately, luxury car could driven away in 40 seconds).

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Autos like the Stanley, White and Dobel, all used a fuel like kerosene to heat the water. I want to design a water tube boiler (1/2” copper tubed) that is portable, heated by firewood and easy enough for most back yard mechanics to construct. It does not need to work at high pressure. An off the shelf 'temperature & pressure relief valve” that typically opens when the pressure exceeds 150 PSI or the temperature exceeds 210 degrees, should be adequate for safety.

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