Randall Hess Wrote:
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> Since no one responded to my first request, I'll
> try a simpler version:
>
> Please, someone, explain to the rest of us how one
> of these works.
A regular locomotive boiler is a fire tube boiler - basically a tank filled with water with a firebox at one end, and a smokebox at the other end. The two are connected with tiny tubes called fire tubes. These tend to get thinner on the fire side, and covered with scale on the other. Should they, or any other part of the boiler develop a hole, all of the water inside the boiler will try to rush out of that hole. When the pressure outside the boiler suddenly drops to atmospheric pressure, the water instantly turns to the steam in a BELVE, or steam explosion. The usual result is destruction of the engine, and/or death or serious injury to the crew. To prevent this calls for routine maintenance of the boiler, careful training of the crew, and proper operation of the engine.
This little engine has a water tube boiler. In this case, the "tank" contains the fire, or is a firebox. There is a single coiled tube that runs around the inside of the tank; as water travels through it, it picks up heat until it leaves the boiler as steam, because the water flashes to steam very quickly, they are called "flash" boilers.
Water tube boilers are considered safer than fire tube boilers because (a) they contain less water, (b) in much larger (utility) boilers, a tube leak will only result in the loss of water from that tube; rather than a steam explosion. That is probably why the museum decided to go with a water tube boiler; the alternative insurance-wise and other reasons may have been no steam at all.
Yes, Stanley steam cars had vertical fire tube boilers. But Doble steam cars had flash boilers. The main disadvantage with water tube boilers is that because there is not a tank full of hot water, they cannot take large swings in demand. In a fire tube boiler, taking a large amount of steam will result in a pressure drop; causing some of the liquid water in the boiler to convert to steam, and raising pressure again, with a drop in the water level in the boiler.
Most package boilers you see in industrial and commercial service nowdays are water tube boilers. Regular utility boilers are also water tube boilers with a big firebox, but have tubes running in the sides of the box; a steam drum at the top of the unit is used to hold the water and let the steam escape; much like a locomotive boiler. However, "flash" boilers like the one used on this engine, in steam cleaners, and Doble steam cars also scale all the way up to utility (power plant) boilers. In those instances, the pressure and temperature inside the boiler are way far away from the vapor curve on a steam chart, and up in the supercritical region (where, it is my understanding, water behaves like a critical fluid, or water and vapor at the same time.) So they, are called supercritical, or once-through boilers. All of the units in the world like the one at Eddystone that have set world records for steam pressure and temperature are supercritical boilers. Had a chance to test one such unit; it was the first of it's kind to return to service after being in reserve storage for several years. Made me think twice as I was straddling the main steam line to put some temperature probes in the belly of the steam turbine; you can't see a steam leak at that temperature and pressure because it turns immediately to a gas.
Anyway, getting back to the subject matter; it is at least working steam, and not a C.P. Huntington park train with a gasoline engine in the tender, or a steam locomotive with it's guts ripped out, and powered by a diesel engine (as found at another museum and many theme parks.) I would also guess it either runs off of natural gas, or a light fuel like kerosene. Thus the reason why it doesn't smoke (another advantage to some folks); but it is probably also set up for one man operation with automatic controls; no need for extensive training and careful operation like you would need with a regular fire tube locomotive.
Hope this helps.
-James Hefner
Hebrews 10:20a
Surviving World Steam Project- New Address!
International Stationary Steam Engine Society
