The flush front is one of the earliest forms of fronts, and though it
often gives good satisfaction, yet it is liable to certain accidents.
[Illustration: Front for Water Tube Boiler.—Fig. 71.]
[Illustration: Flush Front.—Fig. 72.]
As will be seen from cut 72, the front of the smoke arch, in this form
of setting, is flush with the front of the brickwork, and the dry sheet
just outside of the front head is built into the brickwork. The heat
from the fire, striking through the brickwork, impinges on this sheet,
which is unprotected by water on the inside. So long as the furnace
walls are in proper condition the heat thus transmitted should not be
sufficient to give trouble; but after running some time bricks are very
apt to fall away from over the fire door, and thus expose portions of
the dry sheet to the direct action of the fire, causing it to be burned
or otherwise injured by the heat, and perhaps starting a leakage around
the front row of rivets when the head is attached to the shell.
In the overhanging front this tendency is entirely prevented by setting
the boiler _in such a manner that the dry sheet projects out into the
boiler room_. If the brickwork over the fire door falls away when a
boiler is set in this manner, the only effect is to slightly increase
the heating surface. No damage can be done, since the sheet against
which the heat would strike is protected by water on the inside.
[Illustration: Overhanging Front.—Fig. 73.]
The objection is sometimes raised against the projecting front, that it
is in the way of the fireman. To meet this point and yet preserve all
the advantages of this kind of front, the cutaway style has come into
use. In this form the lower portion or the front sheet is cut obliquely
away, so that at the lowest point the boiler projects but little beyond
the brickwork.
[Illustration: Cutaway Front—Fig. 74.]
It will be noticed that in the flush and overhanging fronts, the doors
open sidewise, swing about on vertical hinges; in the cutaway front
the best way to arrange the tube door is to run a hinge along the top
of it, horizontally, and to have the door open upward. But with such a
disposition of things the door is not easy to handle. For the purpose
of support a hook and chain, hanging from the roof should be provided.
[Illustration: Front for Manhole.—Fig. 75.]
Fig. 75 shows a boiler the setting of which is similar in general
design to the other three, except that in the place of a cast-iron
front it has bolted to it a sheet iron breeching that comes down over
the tubes and receives the gases of combustion from them. In Fig. 75 a
manhole is shown under the tubes. This, of course, is not an essential
feature of the breeching, but it will be seen that manholes can readily
be put below the tubes on fronts of this kind, in such a manner as to
be very convenient of access.
In addition to these more general styles of boiler fronts, there are
fronts designed particularly for patent boilers, water-front boilers,
etc., which are made, very often, in ornamental and attractive designs.
In Fig. 71 is shown a beautiful and appropriate design in use in
connection with water tubular boilers.