BOILERS AND FIRE-BOXES.
CARE OF LOCOMOTIVE BOILERS.
THE present tendency of steam engineering, in the effort
to increase the work performed in return for every pound of fuel
consumed, is to employ steam of very high pressure. The greater
the initial pressure of the steam, the greater are the advantages
to be derived from its expansive principle. To resist successfully
the enormous aggregate of pressure to which locomotive boilers
are subjected, a well-constructed strong boiler is absolutely
necessary; and the various railroad companies throughout the country
meet the required conditions in an admirable manner, as is evidenced
by the remarkable exemption of such boilers from serious accidents.
Although the locomotive is the most intensely pressed boiler in
common use, that supreme disaster, an explosion, is of rare occurrence,
considering the vast number of boilers doing service all over
the States. This result is due to constant care in the construction,
in the maintenance, and in the management, of the locomotive boiler.
Like the conservation of liberty, eternal vigilance is the price
FACTOR OF SAFETY.
There is perfect safety in using a boiler so long as
a good margin of resisting power is maintained above the tendency
within to tear the sheets asunder. This margin is very low for
locomotive boilers generally, hence the greater necessity for
care in maintenance and management. Years ago the mechanical world
established by practice a rule making one-fifth of the ultimate
strength of a boiler its safe working-pressure. That is, a boiler
carrying 140 pounds working-pressure should be capable of withstanding
a tension of 700 pounds to the square inch before rupture ensues.
Locomotive practice in this country does not provide much more
than half of that margin of safety. When deterioration or accident
reduces this margin, danger begins.
Certain mechanical empirics and impractical quasi-scientists
have at various times attempted to surround the cause of boiler
explosions with a halo of mystery. But our most accomplished scientists
who have made the subject a special study, and our best mechanical
experts who have devoted years of patient experiment and research
to the investigation of boiler explosion, attribute the terrible
phenomenon to intelligible causes alone. The conclusions of the
practical part of the mechanical world are well summed in one
sentence in one of the annual reports of the Master Mechanics'
Association. It says, "Explosions originate from over-pressure:
it matters not whether the whole boiler, or a portion of it, is
too weak to resist the pressure."
PRESERVATION OF BOILERS.
The preservation of a boiler depends very much upon
the care and attention bestowed upon it by the engineer, and no
other person is so much interested in its safety. To prevent undue
strains from being put upon the boiler, the engineer should see
that the safety-valves and the steam-gauge are kept in proper
order. To secure this, the steam-gauge should be tested at least
once a month. The rule established on well-conducted roads, prohibiting
engineers from interfering with safety-valves, is a very judicious
one; and no persons are more interested in its strict observance
than the engineers themselves.
CAUSING INJURY TO BOILERS.
Some men are idiotic enough to habitually screw down
safety-valves, that the engine may be able to overcome heavy grades
without doubling. This is criminal recklessness, and all train
men are interested in its suppression. Low water has often been
blamed falsely as the cause of disaster to boilers; a theory having
prevailed, that permitting the water to become low led to the
generation of an explosive gas which no sheet could withstand.
That theory was exploded long ago; but, nevertheless, it is certain
that low water paves the way for explosions by deteriorating the
fire-box sheets, and destroying stay-bolts. A careful engineer
watches to prevent his engine from getting "scorched"
even slightly; for the smallest scorching may yield a harvest
of trouble, even after many days. The danger of scorching is most
imminent when an engine is foaming badly from the effects of impurities
in the feed-water or in the boiler. At such a time the water rises
so lavishly with the steam, that the gauges are no indication
of the true water-level. The steam must be shut off to find the
true level of the water. Where this trouble is experienced, the
engineer should err on the safe side, ever, though untold patience
is needed to work the engine along with the boiler full of water.
DANGERS OF MUD AND SCALE.
Mud within the boiler, and scales adhering to the heating
surface, are dangerous enemies to the preservation of boilers;
and engineers should strive to prevent their evil effects by rooting
them out so far as practicable. Much can be banished by washing
out frequently; and scales can, to some extent, be prevented by
selecting the softest water on the road. If water in a tank is
so hard that it makes soap curdle instead of lather when a man
attempts to wash with it, that tank should be avoided as far as
BLOWING OFF BOILERS.
The sudden cooling down of boilers, by blowing them
off while hot, is a most pernicious practice, which is responsible
for many cracked sheets and broken, stay-bolts. It also tends
to make a boiler scale the heating surfaces rapidly. Every time
a boiler is blown out hot, if the water contains calcareous solution,
a coat of mud is left on the heating surfaces, which dries hard
while the steel is hot. If a piece of scale taken from a boiler
periodically subjected to this blowing-out process be closely
examined, it will be found to consist of thin layers, every one
representing a period of blowing off, just as plainly as the laminae
of our rocks indicate the method of their formation. When a boiler
must be cooled down quickly for washing out or other purposes,
the steam should be blown off, and the boiler gradually filled
up with water. Then open the blow-off cock, and keep water running
in about as fast as it runs out until the temperature gets even
with the atmosphere. The boiler may now be emptied without injury.
Or another good plan is to blow off about two gauges of water
under a pressure of forty or fifty pounds of steam, then cool
down the boiler gradually, to prepare for washing.
Although the dangers of blowing off hot boilers, and then rushing
in cold water to wash out, are well known and acknowledged, yet
the practice is still followed on many roads where more intelligent
action might be expected.
Should it happen from any cause that the safety-valves
fail to relieve the boiler, and the steam runs up beyond a safe
tension, the situation is critical; but the engineer should not
resort to any method of giving sudden relief. To jerk the safety-valve
wide open at such a time is a most dangerous proceeding. A disastrous
explosion lately occurred to a locomotive boiler from this cause.
The safety-valves had been working badly; and, while the engine
was standing on a side track, they allowed the steam to rise considerably
above the working-pressure. When the engineer perceived this,
he threw open the safety-valve by means of a relief lever, and
the boiler instantly went into fragments. Cases have occurred
where the quick opening of a throttle-valve has produced a similar
result. The proximate cause of such an accident was the violent
motion of water a within the boiler, induced by the sudden diminution
of pressure at one point; but the real cause of the disaster was
a weak boiler, a boiler with insufficient margin of resisting
power. The weakest part of a boiler is its strongest point. This
may seem paradoxical, but a moment's reflection will show that
the highest strength of a boiler merely reaches to the point where
it will give out. Hence engineers should see that a boiler is
properly examined for unseen defects so soon as signs of distress
appear. Leaky throat-sheets or seams, stay-heads dripping, or
incipient cracks, are indications of weakness; and their call
should be attended to without delay.
When an engineer finds the steam rising beyond a safe
pressure, he should reduce it by opening the heaters, starting
the injector, dampening the fire, or even by blowing the whistle.
The whistle offers a convenient means of getting rid of superfluous
steam, and its noise can be stopped by tying a rag between the
bell and the valve opening.
Should any boiler attachment, such as a check-valve
or blow-off cock, blow out or break off, no time should be lost
in quenching the fire. That is the first consideration. A bursted
flue will generally save an engineer the labor of extinguishing
the fire. In this case an engineer's efforts should be directed
to reducing the pressure of steam as quickly as possible, so that
he may be able to plug the flue before the water gets out of the
boiler. Flue-plugs and a rod for holding them are very requisite
articles; but, in driving flue-plugs, care must be exercised not
to hammer too hard, or a broken flue-sheet may result. Plugs are
often at hand without a rod to hold them. In such an emergency,
a hard wooden rail can be used; the plug being fastened to the
end by means of nails and, wire, or even wet cord. Where no iron
plug is available, a wooden plug driven well in, away from the
reach of the fire, may prevent a bursted flue from leaking, and
enable the engine to go along; but wooden plugs are very unreliable
for such a purpose. They may hold if the rupture in the flue should
be some distance inside; but, should the cause of leaking be close
to the flue-sheet, a wooden plug will burn out in a few minutes.
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