IMPROVEMENTS IN STEAM BOILERS
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Graham Stovenson at the Office of
the Commissioners of Patents on the 14th October 1881.
GRAHAM STEVENSON, of Airdrie, in the County of Lanark, North Britain,
Engineer. "IMPROVEMENTS IN STEAM BOILERS."
This Invention has for its object by improved modes of combining tubes having
the water inside of them with other parts to form boilers which have extensive
heating surfaces of a very efficient character, which are of comparatively small sizo
and cost for their steam generating power and which are extremely safe.
Wrought-iron or steel tubes of from three to six inches in diameter are employed
in modifications suitable for large powers to form the lower portions of the boiler
and are connected to an upper horizontal cylindrical shell, the upper portion of
which forms the steam space. In one modification a number of vertical A-shaped
frames, each formed by a combination of inclined and horizontal tubes, are placed
close together in a long series under the upper cylindrical shell, to which shell the
upper ends of the inclined side tubos are connected. The side tubes enclose a space
which is divided by the transverse horizontal tubes forming a longitudinal main
horizontal tube partition into an upper flue space immediately beneath the upper
cylindrical shell and a lower space, the front end of which lower space may form a
single furnace space. The lower space is however by preference divided to form
two furnace spaces by a longitudinal vertical middle partition formed by short
vertical tubes or by longitudinal tubes. Transverse horizontal tubes which are in
this case by preference of triangular section, are connected to the lower ends of
the inclined side tubes to form fire bars, and at the inner end of the furnace spaces
round tubes are arranged to form the bottoms of two flues extending longitudinally
under the main tube partition, these flues uniting at the back end. Immediately
over each furnace space openings are formed in the main tube partition and are
furnished with valves or dampers, which may be either fireclay slabs or hollow
iron casings through which water passes. These valves are opened and closed
alternately and the furnaces are alternately supplied with fresh fuel. The valve
over the furnace freshly supplied with fuel is closed, and the gases therefrom pass
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page_text: backwards along one lower flue and forwards along the other to the other furnace,
the greater heat and incandescent fuel of which insures their more complete com-
bustion. The gases from the two furnaces then pass together into the flue above
the main tube partition from the back end of which they may go directly to the
chimney; or in the case of some kinds of fuel they may be led along flues formed
outside of the inclined side tubes before going to the chimney. In the bottom of
one or both legs of each A-frame it is proposed to fit a small valve for blowing off
sediment, such valve being held by a lever loaded to a weight somewhat in excess
of that on the main safety valve. The several blow-off valves will act as additional
safety valves in the event of the main safety valves not acting properly. Each of
these blow-off valves may'bo connected by an internal rod to a valve at the upper
end of the side tube to shut off communication with the upper cylindrical shell in
the event of any of the A-frames giving way.
Instead of the inclined tubes at the sides vertical tubes may be employed, and
these may at their upper ends be connected by castiron union pieces to inclined
tubes connected to the horizontal cylindrical shell above; or curved tubes may be
used to form both the sides and the upper connecting parts.
In another modification the top shell instead of being cylindrical is of a saddle-
like or semi-elliptical shape in cross section, and the vertical tubes forming the
enclosing sides or walls have their upper ends connected directly to it, so that it
forms a roof or dome to the space between the sides; or instead of the enclosing
sides or walls being formed of tubes they may be made as downwardly extended
lateral parts of the upper shell itself.
In boilers of the so-called vertical class usually adopted for small or moderate
Bizes the increased heating surface, which by this Invention is obtained by using
tubes in contact with each other, as hereinbefore described, is applied by
arranging such tubes vertically or horizontally outside of the main vertical
cylindrical shell of the boiler in a manner to enclose an annular cylindrical space.
The furnace is arranged within an inner shell in the ordinary way, and the uptake
or chimney by which the fire gases finally pass off proceeds upwards from the top.
of this inner shell, but the space within the inner shell is divided into upper and
lower parts by a partition of fireclay or of tubes, or the like, and the fire gases
pass from the bottom or furnace space through lower tubes into the cylindrical
annular space and return thence by upper tubes into the upper space communi-
cating directly with the uptake. In a similar way existing cylindrical boilers,
whether vertical or horizontal, may be provided with additional heating surface by
enclosing flue spaces for the fire gases with tubes placed in contact, such tubes
being formed with kneed ends by which they are connected to the main boiler
shell.
The connections of the tubes with the other parts or with each other may be
made in various ways, but it is preferred in most cases to secure tightness at the
joints by applying rings of small copper wire between the joint surfaces, the parts
being drawn forcibly together so as to compress the copper wire by scrow bolts or
screwed tie rods, or by means of screw threads formed on the parts themselves.
In order that the tubes may be laterally in contact or nearly so with each other,
their ends are cressed-in or contracted, and rings are welded or brazed on for
forming the joint connections. At the joints between the horizontal and inclined
tubes of the A-frames, and in other cases in which the tubes are connected to each
other at right or other angles, there is in each case a ring formed with a flat surface
for the joint and with a concave surface to fit on one of the tubes to which it is
brazed, and when the tubes form an acute angle with each other the connecting
bolt is placed at right angles to one of the tubes and passes through the side of
the other tube which has an angular piece brazed on it to form a proper seat for
the bolt head or nut. Where the tubes are connected to the cylindrical or other
main boiler shell, cross bows or bars or cups are placed inside of such shell to hold
the heads of bolts or rods which are passed through the tube and have nuts
screwed up on their outer ends. In some cases the tube ends are cressed-in or have

page_text: rings brazed to them so as to present elongated openings into which T-headed
bolts can be inserted to be turned a quarter round or otherwise shifted so as to
hold when the nuts on them are screwed up. The tubes forming the fire bars are
fixed to the bottoms of the side casings or tubes by bolts passing up into recesses
provided for screw nuts or wedge keys, and such recesses are closed by screw plugs
after the parts are fixed together, and where convenient any others of the tubes
may be fixed in the same way.