IMPROVE- MENTS IN STEAM GENERATORS
Year: 1867

page_text: PROVISIONAL SPECIFICATION left by Alexander Melville Clark at the
Office of the Commissioners of Patents, with his Petition, on the
26th October 1867. - A communication from abroad by S. Lloyd
Wiegand, of Philadelphia, in the State of Pennsylvania, United States
of America.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of
Middlesex, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN STEAM GENERATORS," to be as follows:-
The nature of this Invention consists in forming a steam generator of a
series of vessels connected together and having tubes descending therefrom
into a fire chamber, and providing each tube with an arrangement which
insures an active circulation of water in it, and at the same time avoiding such
joints as are difficult to make or repair by ordinary labour. By this means I
am enabled to make a boiler which can be readily put together or transported
in parts or sections and erected without difficulty, and at the same time a
boiler that is compact and therefore requiring an inexpensive setting, and
which by reason of containing at any time but a small volume of water in any
one compartment or vessel is not liable to destructive explosion.
I will now proceed to describe more particularly the construction and
operation of this Invention. In a furnace chamber is placed a number of
vertical or inclined tubes which are closed at the lower end, and at the upper
end are inserted into rectangular iron vessels with which they have free com-
munication. Within the tubes are placed other smaller tubes, which extend

page_text: from near the bottom of the external tube to a short space above the bottom of
tl:e vessels or tanks placed above them, passing through a perforated plate placed
parallel with the bottom of said vessels. These vessels or tanks are connected
with a steam drum or main steam pipe by means of pipes, and are supplied
with water and emptied by means of other pipes connecting them with water
supply pipes, on which are placed the feed cock or valve and the blow-off
cock or valve. Upon water being supplied to the boiler to about the level of
the perforated plates before mentioned, and heat being applied in the furnace
an ascending current is formed in the annular spaces between the outer and
inner tubes, and a descending current in the inner tube, and this circulating
action becomes more and more active as the temperature is increased, by
reason of the heated column of water containing bubbles of steam between
the outer and inner tubes being lighter than the less heated column of water
in the inner tubes. The functions of the perforated plate are to support the
inner tubes, and also to facilitate the separation of the steam from the currents
of water rising from-the annular spaces between the outer and inner tubes.
The inner tubes are kept in position at the lower ends by means of projections
cast in the caps which close the lower end of the outer tubes; these caps are
screwed upon the outer tubes, and said, tubes are attached to the vessel or
tank before mentioned, being screwed in the bottom thereof. The ends of this
vessel are made with apertures closed with plates secured to bridge bars by
bolts and nuts, and afford facilities for the introduction of the perforated plates
and the removal of the core used in casting them, and also for inspecting and
cleaning when necessary. The internal tubes may be made of different
material from the external tubes, and thus galvanic action produced to promote
>the cleanliness and durability of the boiler.
A steam generator thus constructed possesses the following advantages not
-common to others:-It is more cheaply constructed than others; all of the parts
are of such form and dimensions as not to require any great thickness of metal to
impart the strength requisite for safe use; none of the parts are of such size or
form as to be inconvenient for transportation; it requires but little skill to erect
the boiler; all of the tubes are free to expand or contract independently of
each other, and thus avoid straining and liability to leakage. There is never
at any one time a large volume of water contained in the boiler, so that in
the event of a rupture of any portion of the boiler a destructive explosion
cannot ensue. Any of the tubes may be removed without disturbing the
efficiency of the others. The circulation of the water in the boiler when in
use is so active as to preclude the deposit of sediment. in the tubes, and the
heating surface is thus preserved in a condition of the greatest efficiency

page_text: The boiler can be enlarged by the addition of other vessels with the tubes
connected therewith, without incurring expensive alterations of the portions
already erected.
A modification of this Invention, which is found in practice to be advan-
tageous in point of economy, consists as follows:-In the pipes leading from
the several sections of the generator to the main steam pipe or drum I place
valves opening upward or outward from the tanks before mentioned, that
while steam can readily pass from the several sections to the steam drum or
main steam pipe it cannot return therefrom; I also insert in the several
branches of the water supply pipe valves opening toward the several tanks,
and arranged so that water cannot return from any of the tanks to the main
water supply pipe. The functions of these valves are to admit the water to
the several tanks and allow the steam to pass to the steam pipe, and in the
event of the rupture of any of the outer tubes of the generator or caps of any
section to prevent the contents of the other sections from being discharged
through the break thus made.
The arrangement of the furnace is another point of peculiar advantage in
this Invention. It is constructed either partially or entirely projecting from
the generator, the front wall being made oblique so as to leave between itself
and the grates a space in which the gases are formed from the fuel, and is in
such a position as to radiate and reflect the heat upon the tubes of the
generator, and retains enough of heat in it to ignite the mixture of air and
combustible gases formed from the fuel. The front wall may sometimes
advantageously be made in a curved form, and provided with a door to feed in
fuel when burning shavings. The combustion of fuel placed upon the grate is
regulated by means of a valve or register admitting air to the ash-pit, which
in other respects is air-tight. The air is admitted above the fire in regulable
quantities, distributed and heated by passing through channels in the walls of
the furnace, so that it is presented in a hot state to mingle with the gas in the
furnace chamber, and thus effectually secure thorough combustion. The tubes
in the furnace are arranged in such a manner that the tubes of the second
row from the front are opposite the interstices between the tubes in the first
row, and the tubes of the third row opposite the interstices between the tubes
of the second row, and so on throughout the entire series of tubes, the flame
and products of combustion are thus compelled to impinge against the surfaces
of all the tubes in passing back to the flue, thus thoroughly intermixing the
air and gas and promoting combustion, and also securing the most effectual
extraction of heat from the flame and gas by the steam generating surfaces.
The perforated plate before mentioned is made with depressions around the

page_text: aperture for the insertion of the tubes shaped like the flared mouth of a
trumpet, which form facilitates the flow of fluid into the internal tubes and
out of the external tubes into the tanks, which flow is still further promoted
by beveling or chamfering out the ends of the tubes, so as to make lines con-
tinuous or nearly so with the lines of the depression in the perforated plate
and tank bottom. Above said perforated plate I sometimes place one or more
other perforated plates, which I sometimes make with small tubulures on the
upper surface around the apertures, which arrangement affords a space for the
collection and removal of the foreign matter that may be precipitated by
the evaporation of the water, and deposited therein by the circulation of the
currents from the tubes of the generator; and these plates also participate in
the function of the lower perforated plates in facilitating the disengagement of
the steam from the water.