The national Republican., 1866-12-10

Common-Sense Explanasion or the
n Last steam.Deiler Explosisn.
cit Is surprising that so much ignorance
should prevail Is to he csnse Of 50 souznon
IN accident as the explosion OF stsem
boiler, especially one Of the class Usually on
steamboats, supplied with Z steam chimAey
which rises from ten to twenty feet above
the height at which the water is generally
carried into the boiler. A steam chimney d
an sppendase to boiler having for its pur.
pose the drying Of the steam, and d, essen-
tally, two strong iron tubes Of large dimen.
sions, one inside Of the other, with an annu-
lar spsce between, them, occupied by the
steam. These are firmly fixed together at
tho ends, and by stays intermediately. The
stays, however, have only the purpose Of pre-
serving the relative circular form, upon which
the strength OF the inner tube depends. II is
doubtful whether stays or socket bolts are
best for this purpose; either is good enough.
The innss tube Is called the "sptsks Jjaus," I"
and conducts the hot gases from the I'm mp
ward through the steam TO the smoke ptpe.
During Its passage part Of its heat IL com
municated to the steam lin the annular space
between the tubes) to dry ii, which function
1t performs admirably while the engine is
running. q .. ..-' ..... rr- ......-.... -
But it sometimes happens that when the
engine Is at rest, or when, in case there be
two boilers, one is generating steam faster
than the other, that the uptake Hue and the
steam in contact with II become highly su-
perheated, (the uptake aue has at all times
. higher temperature than the shell of the
steam chimney, or the outside one Of the
two tubes,) while the outside Of the steam
chimney, being exposed to the atmosphere,
radiates away its heat more rapidly o. the
temperature 10 increased. The result b the
uptake Jaue has its length increased by ex-
pansion, as its temperature exceeds that Of
the shell outside, and il lifts up with great
force, (sometimes one hundred times ~ great
as the pressure Of the steam and pulls the
steam chimney away from its fastenings to
the toagon part Of the boiler, ruptures the
plate somewhere in its length, or sheers of
the rivets in the seams Of the uptake flue.
The steam then presses the sheet Of iron out
wards, and, escaping, performs the work Of
destruction that ensues. .r..
The opening Of me safety valve would not
relieve the boiler Of this strain Of UNEQUAL
expansion. T 10 -. : I'd
Making the boiler stronger would not pre-
vent the accident, for the force Of expansion
is exactly proportioned to the strength Of
the plate, and greater irregulsrity Of expan-
sion would occur in the thick than in the
thin plate. .. - I.
The inspectors test by cold water pressure
only shows the ability Of the boiler to with
stand the pressure Of the steam, and Is NO
indication Of the ability Of the boiler to with
stand unequal expansion Of the iron plates.
Our whole system Of testing and inspecting
boilers is farce, and should be amended by
Congress, for at present il only lsgslises
ignorance and error. There Is no possible
way by which to correct the evil except by
equalizing the temperature in all parts Of
the boiler by some means, or to construct
boilers so that elasticity shall be provided in
parts liable to unequal expansion.
The danger Of an explosion Of the boiler
on this steamer was pointed out to the off,
GERS on board few months since by gen.
tlemen of our acquaintance, and the exact
place Of the rupture was indicated.
1t is well known to engineers that the
place Of fastening Of the steam chimney upon
boilers is q place where leaks IRE continually
occurring, always cause entirely beyond the
control Of the engineer.