At 06:50 PM 1/25/07 +0000, you wrote:
>After the water falls below the flues they are
>forced to radiate their heat to the air (or
>conduct their heat into surrounding metal
>structures) so the water cools and pressure drops,
>slowing the engine. But by this point the engine
>is 'running dry' and may have suffered some damage.
Perhaps, but as long as there is steam within the boiler you will
not be running dry, or completely so. Remember, in a historical sense
"running dry" meant that the crown sheet was uncovered, not that the boiler
was empty of water or steam. Anyone who has tried to soft solder a joint
in a copper plumbing line where water remains in the line can attest that
the heat absorbing and conducting qualities of steam under certain
conditions can carry heat away faster than it can be applied by a small
flame or torch. Such is the case with our boilers. If, however, you run
the boiler truly dry and don't douse the fire the result for us is
generally fried O-rings, seals, gaskets, and paint. (You want fries with
that?)
I have a Pannier which exhibits visibly livelier behavior when the
water level is very low. I have attributed this to drier/hotter steam, and
the subsequent increase in expansion within the cylinders, the result of
some superheating of the remaining steam taking place at the upper flues,
which are by that time uncovered. This is not IMHO due to an increase in
pressure for if that were the case the safety would lift constantly or at
least more frequently, but it doesn't.
I have never in my life seen and meths fired locomotive which was in
any way self-regulating, or self-extinguishing, in the way described, nor
would I want one. For many of us one of the pleasures of live steam is the
challenge of driving the locomotive, learning its behavior, balancing the
load, fuel, water, blower, throttle, and reverse to make it out and back.
Regards,
Harry Wade
Nashville Tennessee
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