IMPROVEMENTS IN OR CONNECTED WITH THE FIRE BRIDGES OF STEAM BOILER AND OTHER FURNACES
Year: 1879

page_text: LETTERS PATENT to William Anderson, of Dundee, in the County of Forfar,
North Britain, Furnace Builder, for the Invention of "IMPROVEMENTS IN
OR CONNECTED WITH THE FIRE BRIDGES OF STEAM BOILER AND OTHER
FURNACES."
Sealed the 6th April 1880 in pursuance of an Order of the Lord Chancellor, and
dated the 3rd June 1879.
PROVISIONAL SPECIFICATION left by the said William Anderson at the
Office of the Commissioners of Patents on the 3rd June 1879.
"
WILLIAM ANDERSON, of Dundee, in the County of Forfar, North Britain, Furnace
Builder. IMPROVEMENTS IN OR CONNECTED WITH THE FIRE-BRIDGES OF STEAM
BOILER AND OTHER FURNACES."
The said Invention relates to those bridges which are formed hollow for the
supply of heated air to the products of combustion at the bridge; and has for its
object so to construct the said bridges that they are kept comparatively cool,
especially at the parts presented towards the fire, and at the sametime the air is
delivered at the bridge in a condition better calculated to consume the smoke than
is the case with hollow bridges at present in use.
According to one part of the said Invention the hollow fire bridge is protected
by a water casing, the water to which is supplied from a water tank independent
of the boiler and situated in any convenient place, from which tank a supply pipe
leads to the lower part of the casing, the water escaping by a pipe at the upper
part of the casing, leading it back to the tank, so that a constant circulation of the
water is kept up in the hollow casing; or the water may in some cases by a similar
arrangement be supplied from the boilers instead of from the said tank. The bridge
is hollow and is perforated at its upper part, the perforations continuing through
the water casing by short tubes or passages. Air is admitted from the ashpit to
the bridge by a valve, the opening of which may be regulated from the front of the
furnace.
In applying this part of the Invention to locomotive fire boxes the bridge is
formed double, the front part being the water casing and the back part being the

page_text: duct for the admission of heated air to the products of combustion. Passages will
be formed through the water casing and air duct, through which passages the
products of combustion pass to the combustion chamber. The heated air from the
air duct escapes to meet with the products of combustion at perforations at the back
of the air duct, or in the passages for the products of combustion through the air
duct.
Another part of the Invention relates also to those bridges wherein air is admitted
from the ash pit to a hollow bridge, escapaping to meet the products of combustion
as they pass over its top. According to this said part of the Invention the bridge
is made of less capacity at its lower part than at its upper part, so as to cause a
rapid current of cool air to pass there-through and come into contact with and tend
to keep cool the lower front part of the bridge, which is the part most exposed to
the heat of the furnace.
The valve by which air is admitted to the hollow bridge is hinged on the side
nearest the front of the furnace, so that the air enters the bridge from the back
towards the front thereof so as to impinge on the front part and assist in keeping
it cool, the lower part of the back of the bridge being inclined, if desired, to assist
the direction of the air.
To prevent the burning of the bridge through the carelessness of the furnace-man
in leaving the air valve entirely closed a small passage is cut through the valve so
that a small supply of air will be admitted to the bridge should the valve be
entirely closed.
The improvements herein-described are applicable to steam boiler furnaces
generally, and to other furnaces, such as those which heat brewers' boilers and
bakers' ovens.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, and of
an Order of the Lord Chancellor, filed by the said William Anderson in the
Great Seal Patent Office on the 6th April 1880.
WILLIAM ANDERSON, of Dundee, in the County of Forfar, North Britain, Furnace
Builder. "IMPROVEMENTS IN OR CONNECTED WITH THE FIRE BRIDGES OF STEAM
BOILER AND OTHER FURNACES."
My said Invention relates to those bridges which are formed hollow for the
supply of heated air to the products of combustion at the bridge, and has for its
object so to construct the said bridges that they are kept comparatively cool,
especially at the parts presented towards the fire, and at the same time the air is
delivered at the bridge in a condition better calculated to consume the smoke than
is the case with hollow bridges at present in use.
And in order that my said Invention may be properly understood I now pro-
coed more particularly to set forth the system, mode, or manner in or under which
the same is or may be used or practically carried into effect, reference being had
to the accompanying Drawings, and to the letters and figures marked thereon, that
is to say:-
Figuro 1 of the accompanying Drawings represents in longitudinal vertical
section a part of a Cornish boiler and its flue; and Figure 2 represents in trans-
verse section the flue alone of the said boiler, to which a bridge A, constructed
according to my Invention, is applied. The said bridge is formed hollow, and is
protected at the sido presented to the fire by a water casing B. To the interior of
the said protecting casing of the bridge water is supplied from a tank C indepen-
dent of the boiler, and situated in any convenient place, a supply pipe & leading
from this tank to the lower part of the protecting casing of the bridges, as shewn,
the water escaping from the said casing by a pipe à at the upper part thereof,
which piped conveys the said water back to the tank C, so that a constant circula-
tion of the water is kept up in the hollow casing of the bridge. The bridge A is
hollow, its back plate E forming a chamber F within it, to which air is admitted
from the ash-pit. The bridge is perforated at its upper part, the perforations
continuing through the water casing by short tubes or passages a, a When there-
fore the furnace is in operation air is admitted to the chamber F (and thence by
the passages a, a, to the products of combustion at the bridge) by the valve G, the
degree of opening of which may be regulated from the front of the furnace by the
rod g.
Figure 3 represents in longitudinal section a Cornish boiler, to the bridge A. of
which my Invention is applied; Figure 4 is a transverse section of the flue taken
on the line 1, 2, Figure 3. The water space is marked B and the air passages «.
In this modification however communication is established between the water space
of the boiler and the water casing of the bridge, so that water is supplied to the
casing from the boiler (either directly by the pipes c and d², or through the
pipe c and through the bridges H and the pipe d, as hereinafter described), instead
of from an independent tank, as in the arrangement first described. Other parts
which correspond with the said arrangement first described are marked with corre-
sponding letters of reference. In these Figures 3 and 4 I have shewn a series of
auxiliary bridges H, having ducts h for the passage of the products of combustion
and air therethrough, the spaces around these ducts being water spaces which
communicate, the water space of one bridge with those of another and with
the water casing B of the first bridge by means of pipes i leading from the
upper part of one bridge to the lower part of the bridge next before it, the last
bridge communicating with the water space of the boiler by the pipe d. One of
the bridges H is shewn in section in Figure 3, the others being in elevation; in

page_text: Figure 4 is shewn a transverse section of one of the said bridges. In place of the
second bridge H communicating with the first bridge A. by the pipe i, as shewn,
it may communicate direct with the water space of the boiler by a pipe, as shewn
by the dotted lines at . The first bridge in this case will communicate with the
water space of the boiler by means of the pipe c and that shewn in dotted lines
at d. I have shewn three of these auxiliary bridges H in the Drawings, but it is
to be understood that one, two, or more than three such bridges inay be employed,
as may be convenient or desirable, and they may be furnished with sediment
removing pipes leading into one general pipe running along the length of the flue.
Figure 5 represents in longitudinal vertical section and Figure 6 in transverse
section a mode of applying this part of my Invention to the fire boxes of locomotives.
The bridge A is formed double; the front or lower part B (being the part nearest
the fire) is the water casing protecting the back part F, which is the duct for the
admission of heated air to the products of combustion. Air is admitted to the said
air-duct F from the external atmosphere by passages formed by pipes, as at k,
passing through the water casing of the fire box and opening into the said duct F,
and the said air is delivered in a heated state from the said air-duct at the
openings a into the part through which the products of combustion pass on their
way to the boiler tubes. The water casing is or may be supplied with water by
means of openings at its sides establishing communication with the water space
around the fire-box.
In Figure 6 I have shewn the bridge as being straight, but it will be evident
that my Invention may be equally well applied to a curved bridge or arch, and
although I have shewn but two rows of openings a yet one, or three, or more rows
may be employed if desired. The air casing F, Figure 5, can be placed upon
existing fire-brick bridges of locomotives if desired.
I have not shewn the means by which the bridge is attached to or supported in
the fire box, as this may be effected in any convenient and well known manner.
In hollow air supplying bridges constructed according to the herein before
described part of my Invention the water casing B tends greatly to preserve the
bridge from that injurious action of the fire which has rendered the ordinary air
supplying bridges objectionable in use by reason of their being rapidly destroyed by
the fire.
Figure 7 represents in longitudinal section a portion of the flue of a boiler with
a bridge constructed according to another part of my Invention, this said part of
my Invention also relating to those bridges whereby air is admitted from the ash-
pit, escaping to meet the products of combustion as they pass over its top. According
to this part of my Invention the bridge is constructed with a lower part or
passage of less internal capacity than the internal capacity of the upper part m of
the bridge, so as to cause a rapid current of cool, or comparatively cool, air to pass
up this passage into the said bridge and come into contact with and tend to keep
cool the lower front part 1 of the bridge, which is the part most exposed to the
heat of the fire. The valve by which air is admitted from the ash-pit to the hollow
bridge is marked n. It is hinged on the side of the bridge nearest the front of the
furnace below the level of the top of the fire bars, and the lower part of the back
of the bridge at is inclined upwards and inwards so that the air enters the bridge
from the back towards the front thereof, and impinges on the said front part l', as
shewn by the arrows, and assists in keeping it cool. The air passes from the bridge
in a heated state by the openings a. The front part and the top of the bridge
may be of iron, or of iron coated with fire clay, or of fire clay alone, or of other
suitable material.
To prevent the burning of the bridge through the carelessness of the furnaceman
in leaving the air valve entirely closed a small passage is cut through the valve so
that a small supply of air will be admitted to the bridge should the valve be
entirely closed.
The several improvements hereinbefore described are applicable to steam boiler

page_text: furnaces and to other furnaces having bridges, such as those furnaces which heat
brewers' boilers and bakers' ovens, and the like.
Having now described and particularly ascertained the nature of my said Inven-
tion, and the system, mode, or manner in or under which the same is or may be
used or practically carried into effect, I would observe in conclusion that I do not
claim as my Invention (except as hereinafter stated) bridges constructed to supply
heated air to the products of combustion in furnaces, but what I consider to be
novel and original, and therefore claim as the Invention secured to me by the
herein before in part recited Letters Patent is,-
First. The combination with hollow bridges for supplying air to the products of
combustion in the furnaces of stationary, locomotive, marine, or other boilers of a
water casing upon the side of the bridge presented towards the fire, or upon both
the said side and the top, for the purposes and essentially as hereinbefore described
and illustrated in the accompanying Drawings.
Second. The improvement in bridges which supply air to the products of com-
bustion of the furnaces of stationary, locomotive, inarine, and other boilers, described
with reference to Figure 7; that is to say, making the said bridges with a port or
passage at the lower part of less internal capacity than the internal capacity of
their upper part, for the purpose of causing a rapid current of cool air to pass in
contact with the front of the bridge for the purpose hereinbefore described.
In witness whereof, I, the said William Anderson, have hereunto set my hand
and seal, this Twenty seventh day of March, in the year of our Lord One
thousand eight hundred and eighty.
WILLIAM ANDERSON. (LS.)