Improvements in Flued Steam Boilers.
Year: 1895

page_text: Date of Application, 23rd May, 1895
Complete Specification Left, 24th Feb., 1896-Accepted, 28th Mar., 1896
PROVISIONAL SPECIFICATION.
Improvements in Flued Steam Boilers.
We, DAVID DAVY, of Broom Croft, Parkhead, Sheffield, in the County of
York, Engineer, and DAVY BROTHERS LIMITED, of Park Iron Works,
Sheffield, in the County of York, Engineers, do hereby declare the nature of this
invention to be as follows:-
This invention relates to an improvement in the construction of the flues of
steam boilers, and has for its objects to increase the efficiency of the heating
surface and consequently the generative power of the boiler; to enable the flue to
accommodate itself more readily to difference of longitudinal expansion and con-
traction between the flue and the boiler shell than is possible when the flue is
constructed of plain plates in the ordinary way and to diminish the liability to
leakage at the joints consequent on such inequality of expansion and contraction;
and, further, without altering the axial distance apart of the flues in a double-flued'
boiler, to provide such an increase of space between the flues at certain points as to
enable more easy access to be had to the lower part of the boiler and greatly
facilitate the operation of cleaning or sealing.
The flue is constructed of short tubes or rings with external end flanges by
which they are united, these rings being alternately of different diameters, that is
to say every alternate ring throughout the whole length of the flue (except the part
enclosing the furnace) is of lesser diameter than the furnace and intermediate rings,
the flanges of the smaller rings being, however, of equal diameter to those of the
larger rings, so as to le adapted to be rivetted thereto. The flanges of the
smaller rings are, moreover, formed or turned up from the cylindrical part of
The effect of
the ring by a gradual sweep or curve of comparatively large radius.
this difference of diameter of alternate rings is that the direct course of the flames
through the flue is somewhat impeded so that the flames are caused to strike
against the sides of the flue in such a way as to act with greater efficiency on the
heating surface whilst the easy sweep of the flanges of the smaller tubes enables
them to accommodate themselves to differences of longitudinal expansion and
contraction.
In a two-flued boiler the rings of smaller diameter in the one flue would be more
or less opposite those of smaller diameter in the other flue so as to provide
between the flues at these points spaces of increased width for the purpose above
referred to.
Doted thie 23rd day of May 1805
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
COMPLETE SPECIFICATION.
Improvements in Flued Steam Boilers.
We, DAVID DAVY of Broom Croft, Parkhead, Sheffield, in the County of
York, Engineer, and DAVY BROTHERS LIMITED, of Park Iron Works,
Sheffield, in the County of York, Engineers, 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 an improvement in the construction of the flues of

page_text: steam boilers and has for its objects to enable the Alue to accommodate itself more
readily to any difference of longitudinal expansion and contraction between the
flue and the boiler shell; to increase the efficiency of the heating surface and
consequently the generative power of the boiler; and without altering the axial
distance apart of the flues in a double-flued boiler to increase the space between
the flues at certain points so as to enable more easy access to be had to the lower
part of the boiler and greatly facilitate the operation of cleaning or scaling.
The invention is illustrated in the accompanying drawing wherein
Figures 1 and 2 are longitudinal vertical and horizontal sections of a two-flued
hoiler, (partly broken away) and Figures 3 and 4 are cross sections thereof on
lines 3-3, 4-4, Figure 2, respectively.
Figure 5 is a detail view of one of the joints.
Each flue is constructed of short tubular lengths of flue sections A B alternately
of different diameters, that is to say every alternate section B of the flue is of
lesser diameter than the intermediate sections A, this alternation of diameter
preferably extending throughout the flue except the part enclosing the furnace
which is of sections A of uniform diameter. These flue sections A B are united
by external flange joints the flanges of the smaller sections B being of
substantially equal diameter to those a of the larger sections A. so that the flunged
ends of the large and small sections may be rivetted together either directly or
preferably with a joint ring c between them as shewn. The flue sections A B
therefore differ in diameter throughout the length of their cylindrical portions but
their flanges are of substantially equal external diameter. The flanges 6 of the
smaller sections B are therefore broader than those a of the larger sections A and
they are formed or turned up from the cylindrical part of the section preferably
to a gradual sweep or curve having a radius considerably greater than that of
the flanges a of the larger sections A so as to form a flange of trumpet-mouth
form. This difference in the relative diameters of the sections A B in the areas
and the curvatures of their flanged ends is well exemplified in Figure 5 which is a
section of such a joint full size being the radius of curvature of the flange'a and r¹
that of the flange b.
The consequence of this difference of diameter is that every such joint in the
length of the flue becomes an expansion joint and this without any increase in the
external diameter at the flanges or any such general decrease in the diameter of
the flue as would cause a diminution of generative power. The capability to yield
to expansion and contraction in the longitudinal direction of the flue is owing to
the greater area of the larger flange which lies in or approximates to a plane
transverse to the length of the flue and is therefore in the most favourable position
to yield to longitudinal stress. This increased area of the flanges of the smaller
sections and consequently the increased capability of yielding to longitudinal
expansion and contraction are obtained without loss of generative power because
the decrease in the area of the heating surface consequent on the decreased
diameter of the alternate tubes B is more than compensated for by the fact that
the flames instead of passing directly through the flue and so escaping contact with
its sides are diverted and more or less impeded in their course so that they are
caused to strike against the sides of the flue and to act with greater effi iency on the
heating surface than would be the case were the flue of uniform diameter.
It is to be understood however that the invention is not limited to the trumpet
form of flange illustrated as the same effect as regards facility for expansion and
contraction would be obtained in a greater or less degree by other forms of curvature,
for instance were the radius of curvature of flange b the same as that of flange a
(or even less) as indicated in dotted lines in Figure 4.
The construction of the flue of a single-flued horizontal boiler would be the same
as that of one of the flues herein described and in applying the invention to a
vertical boiler with a long flue for example a furnace boiler of the kind which is
commonly used in iron & steel works and elsewhere the construction of the flue
would also be similar.

page_text: .
In a two-flued boiler the joints of the one flue would preferably be so arranged
as not to come exactly opposite those of the other flue but the smaller sections B
of the two flues would for the most part be opposite each other so as to afford
spaces of increased width between the flues at these points for giving access to the
lower part of the boiler.
In conclusion we would observe that we are aware that the alternation of large
and small diameters of the flue sections and also the external flange joint are not
new considered separately, but the invention consists in the combination of the two
known forms so as to combine and increase the advantages of both.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
The herein described improvement in the construction of boiler flues, which
consists in the combination of flue lengths or sections of different diameters but
having external joint flanges of substantially equal diameter united substantially
as specified.
Dated this 22nd day of Feb 1906
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.