Improvements in and connected with the Fire Bridges of Steam Boiler and other Furnaces.
Year: 1893

page_text: COMPLETE SPECIFICATION.
Improvements in and connected with the Fire Bridges of Steam
Boiler and other Furnaces.
I, ROBERT BROWN of 8 Albert Drive, Crosshill in the City of Glasgow
Engineer do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
This invention relates to that class of steam boiler fire bridges which have
openings through them for the supply of air to the combustion chamber the said
air being heated by passing through the ash pit below the fire bars and commingling
with the fire gases effects more perfect combustion and lessens or prevents the
emission of smoke. The invention has for its object to provide means whereby the
air is retained and further heated in the bridge, and made to commingle more
perfectly with the products of combustion thereby obtaining greater efficiency and
economy.
On the accompanying drawings
Figures 1 and 2 are longitudinal vertical sections of a flue of a steam boiler
shewing one means of carrying the invention into effect; Figure 1 shewing the air
supply to the bridge cut off whilst Figure 2 shews it open.
Figure 3 is a plan of the hollow bridge with the cover removed and
Figure 4 is a plan of the covering plate shewing one method of forming the aper-
tures therein through which the heated air issues into the combustion chamber,
Figure 5 being a cross section of the cover on the line x Figure 4.
Figure 6 is a part longitudinal vertical section of a flue of a steam boiler similar
to Figure 1 and shewing the hollow part of the fire bridge inclined backwards
instead of being vertical.
The bridge which is composed of firebrick is made in two parts a a' the upper
part a resting on the plate b which is itself supported at the front end by the back
fire-bar support c and at the back end by the part a¹ of the bridge. This plate b
has a hollow vertical chamber d formed on it which is provided at its lower part
with a valve e hinged at its rear end to the plate and which valve is for the purpose
of regulating the supply of air to the combustion chamber f. The plate is also
made with an opening d¹ to allow for expansion and contraction. The valve e has
a horn formed on its underside and connected to a rod g which passes along under
the fire bars to the front of the boiler and terminates in a handle by which the
valve is operated. The rod g has a series of notches formed in it which engage
with a catch on a bracket fixed to the dead plate of the furnace so as to maintain
the valve in the position to which it has been adjusted. Over the backwardly
inclined top of the hollow chamber d a perforated plate i is placed the perforations j
of which are by preference made as shewn in Figures 4 and 5 and are collectively
of lesser superficial area than the superficial area of the mouth of the chamber d so
as to retain below it a quantity of air and ensure its being more highly heated
thereby rendering it more efficient for the purpose of smoke consumption.
Having now particularly described and ascertained the nature of my said inven
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The combination of parts constituting the steam boiler fire bridge substantially
as hereinbefore set forth with reference to the accompanying drawings.
2. In conjunction with a hollow bridge the employment of the plate i perforated
with a series of holes the superficial area of which collectively is less than the

page_text: superficial area of the hollow chamber d for the purposes hereinbefore set forth
with reference to the accompanying drawings.
Dated this 12th day of May 1893.
CRUIKSHANK & FAIRWEATHER,
62, St. Vincent Street, Glasgow, Agents.