The evening telegraph. [volume] (Philadelphia [Pa.]) 1864-1918, 1869-11-03

Il
heating surface is q vertical one, so that the
steam on rising forms a separate film between
it and the water. Two explosions resulting
from this cause may be referred to. One of
these occurred at an iron works on the 9th of
February, 1865, to an externally fired boiler
of the upright furnace class. heated by the
flames passing off from two pudding furnaces,
as well as from large fre-grate. Another
explosion of q similar character occurred on
the 7th of February, 1866, to plain cylindri-
cal egg-ended boiler, heated by the flames
passing off from a mill furnace at a works
employed in the manufacture of angle iron.
1t is desired, however, on the present occa-
sion, to call attention more especially to those
cases in which pverheating of the plates,
whether in externally or internally heated
boilers, has occurred simply through the char
acter of the feed-water, and not from any pc
cuiarity in the mode of firing. The feed
water which is found to be more particularly
productive of overheating is highly impreg-
mated with carbonate of lime. 1t forms but
little scale, and that seldom thicker than an
egg shell, though perhaps in some cases it
may be nearly equal to one-eighth of an inch.
1t deposits, however, a good deal of fine
flour or dust, which is generally of a
lightish color, AS this dust is quite
loose, q good deal of it is foated
away with the water when the boiler is
emptied, while the remainder is readily
washed out, so that on account of the ease
with which it is removed, and the light
character of the scale, it frequently escapes
attention. If grease be introduced into
boilers in which this deposit is formed, the
furnace crowns are found to give way, the
plates to bulge downwards, and leakage to
take place at the seams of rivets. The dis
tortion of the furnace plates, however, does
not as q rule, take place suddenly; on the
contrary, the crowns come down very gradu-
ally, progressing little by little, day after
day, though hard firing, in many cases, has
an immediate influence. Grease is intro
duced into boilers in various ways The
feed-water is frequently heated by blowing
the exhaust steam from the engines upon it,
| so that the grease in the cylinders is carried
with the feed-water into the boiler, while, in
addition, the discharge taps from the cylinders
sometimes blow into the cistern from which
the feed-pump draws, so that the boiler gets
all the engine sewage. Blowing the exhaust
| steam from the feed-water has another effect
| beside the Introduction of grease. 1t is some
| times lost sight of how much of the deposit
formed within boilers is lifted out of the
water by the steam and carried through to the
engines, and thus disposed of either through
the exhaust pipe in high-pressure engines, or
| in the hot well in low-pressure ones. When,
therefore, the exhaust is blown upon the feed
! water this deposit is returned to the boilers
and constant accumulation takes place. more
| especially if blowing out be neglected. That
the steam lifts the deposit, and carries
it along with it, is clear from the fact that
it is frequently manifested at the glands
and other parts of the engines, and also is
heaped up in the steam dome when there is
a shelf on which it eau accumulate. These
shelves are formed when the shell plate at the
base of the dome is not cut away tc
its full size. This forms an eddy in the
| current of the steam, and leads to the de.
posit being dropped on the shelf plate, as
last stated.
With regard to the manner in which this
| floury deposit affects the plates over the fire
and leads to their injury, it does not appear
to be necessary to suppose that this deposit
| becomes heaped upon the plates in order tc
lead to their overheating. 1t is doubtful
whether it settles at all as long as the
boiler remains in active work; while, were
it to do so, it would settle where the ebulli
tion was the least violent, and thus not on
the furnace crowns of internally fired boil
ers. Possibly this fine fioury deposit, by
thickening the water, interferes with the due
escape of the globules of steam, so that they
are kept longer in contact with the plates
over the fire than they should be, and thus
the intimate contact of the water with tn,
plates becomes interrupted, and overheatine
is produced. This may perhaps be illustrated
in the following way:--Clear water placed il
clean saucepan may be briskly boiled owe
fire without foaming over, but if littl
meal be dropped into ut, or the water ex
changed for milk, the globules of steam ar
no longer able to escape freely, and in thei
struggle they upheaye the whole mass, ant
vomit portion of it into the fire. Such i
thought to be somewhat the action that take
place within boiler charged with this fin
floury deposit. The globules of steam i'm
prisoned in the water lift it from the plate
in their struggle to escape, and thus gradua
overheating takes place in proportion to tn
character of the water and the intensity o
the fire. r M ..-,-. .a .. r
am not desirous, however, of entering to-
infinitely upon the precise manner in whic
this foury deposit leads to the overheatinI
of the plates; suffice to say that the result
are indisputable, that numlers of boiler
have been injured by it, and whatever ma
be the precise mOduS Operdndt, it appears t
have the power of preventing that intimat
contact of the water with the plates whicl
is essential for carrying off the heat wit
sufficient rapidity, so that although they ma
not be made red hot, yet they become sutfici
emily overheated to lose portion OF thei
tenacity, when bulging under pressure ensuet
Numerous instances of this have come befor
! |