Steve Bentley wrote:

> Not to dwell on the subject too much, regardless of the fuel used,
> but in the area of _safety_ for boiler operation, unscrew the
> safety valve and with an appropriate tool, work the valve off
> its seat a few times to be sure it will work at the given steam
> pressure, especially if the boiler hasn't been used for a while.
> You have a potential bomb when steaming a boiler!

He is not kidding.  I was going to send much the same message.  Even
a small steam boiler can be a serious hazard, and when you're using it
to power a steam engine, there's always the temptation to try to get
higher performance by letting the pressure increase.

As Marine Engineer Bentley points out, old safety valves tend to seize.
I might add that old boilers tend to corrode.  If a seam gives way or
a small crack develops, the superheated water inside (water that is
'superheated' is heated higher than its boiling point) will be released
and instantly flash into steam.  Besides the scalding, there is a
substantial blast effect on nearby structures and people.

One wise fellow who displays his old steam engine at local fairs
here in Southeast Ohio uses a loose-fitting cork for a boiler plug.
The engine barely runs, but it runs, and the apparatus is safe.
Conversely, we had a steam tractor blow up at an Ohio county fair
several years ago; it killed the father and son who had failed to
properly maintain the machine.

As a result of that incident, Ohio has (finally) required that
energized steam boilers be inspected before they're exhibited.   You
may find that your miniature steam engine falls under just such rules
in your locale.  Pretty much the same requirement would apply if you're
going to run high-pressure compressed air, I believe.

I love steam engines, but that boiler scares me.  The danger of
a hot boiler was perhaps the major impetus for the development of
the internal combustion engine.

Mark Kinsler