‘THE BOILER IS LEAKING, DAD’

Rochester, New York

Few indeed are the drivers of the steam engines who have not
heard a similar statement upon firing-up a cold boiler. Luckily the
boiler was generally only ‘sweating’ not leaking, so the
only lamentable aspect was the lack of adequacy of the
explanation.

Two conditions are necessary to make a boiler ‘sweat’
when fired. There must be water vapor present in the flue gases and
the flue gases must be exposed to surfaces sufficiently cool to
cause some condensation of that vapor. The vapor may come from
moisture in the fuel or from the burning of hydrogen, and hydrogen
is present in the combustible gases given of by burning wood or
coal. In burning, the hydrogen unites directly with the oxygen of
the air to form water vapor as an end product. Water vapor is
invisible. In passing through a boiler too hot to condense it, it
escapes undetected in the stack gases . Whereas in a cold boiler,
the vapor is condensed to form liquid water. Hence, ‘The boiler
is leaking, Dad.’

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