Long and heavy boilers are best suspended from two beams or girders by
two or three bolts at each end. Boilers over 40 feet long should have
three or even four sets of hangers, as the case may require.
Side brackets resting on masonry may be used for short boilers. If used
on long boilers, side plates or expansion rollers should be used at
one end of boiler. There ought to be not more than two brackets on one
side, so divided that the distance between them is about three-fifths
of the total length of the boiler, or the distance from ends of boiler
to center of bracket is equal to one-fifth the length of boiler.
The side walls in boiler-setting should not be less than twenty inches
with a two inch air space; the rear wall may vary from 12 to 16 inches
according to the size of the boiler; the front wall 9 inches and the
bridge wall may be from 18 to 24 and perfectly straight across the rear
of the furnace. If the boilers are supported by side walls, the outside
walls should be not less than 13 inches thick and have pilasters where
the boiler is resting.
Flues touching the boiler above the water space should be emphatically
condemned.
Unless the boiler walls are very heavy, they should be stayed by cast
or wrought iron bunch stays, held together by rods at tops and bottoms.
It is dangerous to have large spaces in which gases may collect for
sudden ignition, producing the so-called “back draft.”
Connections between the rear end of the boiler and brickwork is best
made with cast-iron plates or fire-brick, suspended, when boilers are
suspended, as the expansion and contraction will destroy an arch in
a short time. If resting on mud-drum stand, this connection can be
arched, as in this case the rear end of boiler will remain stationary.
If the draughts from the different boilers come in the same direction,
or nearly so, no special provision is necessary, but if the draught
enters from directly opposite directions a centre wall should be
provided.
An advantage claimed for water in the ash pit is: by the dropping
of hot ashes and cinders from the grate into the water, steam is
generated, which, in passing through the hot coal lying on the grate,
is there divided into oxygen and hydrogen, thus helping the combustion.
A dry brick will absorb a pound of water, and it is the water in the
mortar that causes it to set, and harden. To prevent this loss of the
water of crystalization, and give it time to harden and adhere to the
brick, the brick must be well saturated with water, before they are
laid.
Whenever steam is allowed to come in contact with mortar or cement an
injurious effect is produced. The action of the steam is much more
rapid than that of air and water, or water alone, when in abundance,
as the effect of the steam in every case is to soften the mortar and
penetrate to a greater depth than water could possibly do.
The distance between the rear head of the boiler and brickwork should
not be less than 12 inches.
In setting steam boilers, allowance must be made for the expansion
and contraction of the structure and this is usually done by placing
rollers under the rear lug or side bearing of the boiler. Care should
be exercised that the boiler rests are always in good condition so that
they may move freely and not place the boiler in any danger of sticking
and buckling.