XVIII. MODEL BOILERS.
A chapter devoted to the construction of model boilers may well open with a
few cautionary words, as the dangers connected with steam-raisers are very
real; and though model-boiler explosions are fortunately rare, if they do
occur they may be extremely disastrous.
Therefore the following warnings:--
(1.) Do not use tins or thin sheet iron for boilers. One cannot tell how
far internal corrosion has gone. The scaling of 1/100 inch of metal off a
"tin" is obviously vastly more serious than the same diminution in the
thickness of, say, a 1/4-inch plate. Brass and copper are the metals to
employ, as they do not deteriorate at all provided a proper water supply be
maintained.
(2.) If in doubt, make the boiler much more solid than is needed, rather
than run any risks.
(3.) Fit a steam gauge, so that you may know what is happening.
(4.) Test your boiler under steam, and don't work it at more than half the
pressure to which it has been tested. (See p. 220.)
In the present chapter we will assume that the barrels of all the boilers
described are made out of solid-drawn seamless copper tubing, which can be
bought in all diameters up to 6 inches, and of any one of several
thicknesses.
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