_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 of safety.
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.
BOILER EXPLOSIONS.
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, even 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 possible.
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
laminæ 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.
OVER-PRESSURE.
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 and steam 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.
RELIEVING OVER-PRESSURE.
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.
BURSTED FLUES.
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.