IMPROVED MEANS FOR INCREASING THE DRAUGHT IN STEAM BOILER AND OTHER FURNACES OR FIRE-PLACES
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the
Office of the Commissioners of Patents, with his Petition, on
the 6th May 1868.-A communication from abroad by Jearum
Atkins, of the City of Washington, D.O. in the United States of
America.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County
of Middlesex, Gentleman, do hereby declare the nature of the said
Invention for "IMPROVED MEANS FOR INCREASING THE DRAUGHT IN STEAM
BOILER AND OTHER FURNACES OR FIRE-PLACES," a communication to me
from abroad by Jearum Atkins, of the City of Washington, D.C. in
the United States of America, to be as follows:-
This Invention relates to certain means for increasing the draught
in steam boiler and other furnaces or fire-places, and consists of peculiar
combinations and arrangements of tapered or expanded smoke tubes or
passages, the diameter of which increases towards the discharging mouth.
According to one combination or arrangement, intended to be applied
to a locomotive or multitubular boiler, the boiler tubes in lieu of ter-
minating in the smoke box tube plate as heretofore are made to enter
or project some distance through the tube plate into the smoke box,

page_text: that portion of the tubes which projects inside the smoke box being
expanded or enlarged conically towards the extremity. The tubes in
the lower tier are made the longest and extend nearly to the front of
the smoke box, whilst each successive tier from the bottom is shorter
than the tier next below in order to afford more space for the free exit
of the products of combustion in their passage to the chimney. The
prolonged and expanded part of each tube in the smoke box may
either form a part of the boiler tube itself or it may consist of a
separate expanded mouth piece fitted onto the end of each of the ordinary
tubes. In combination or not with these expanding tubes it is further
proposed to employ a group of expanding tubes situate in the lower
portion of the chimney just above the smoke box, the larger ends of
the said tubes being at the top. In the centre of this group of expanded
or taper tubes which are supported at the top and bottom by tube
plates there is situate the ordinary steam blast pipe, but in some cases
the group of expanded tubes at the lower part of the chimney may
be used alone without the blast pipe and expanded boiler tubes herein-
before referred to.
It is sometimes proposed to employ in the lower part of the chimney
a series of concentric tapered or expanded tubes in lieu of a group of
separate tubes placed side by side, the blast pipe when used passing
up the middle of the centre tube. The principle on which these expanded
tubes act is as follows:-The smoke and gases in their passage through
the tubes in the direction of their increasing diameter must in order
to fill the tubes have their velocity retarded in a ratio corresponding
to the increasing area of the tubes, and thus their momentum has to
be overcome by the resistance of the atmospheric pressure at the larger
end of the tubes. The force with which the gases in the tubes act
against the resisting atmosphere tends to produce a vacuum in the
smaller portion of the tube, and into this partial vacuum the gases from
the fire rush with increased force, any diminution in the pressure
in the tubes being equivalent to a corresponding increase of pressure
in the fire-box or furnace.
The axes or centre lines of the several expanded tubes forming the
group herein-before referred to in the lower part of the chimney may
either be parallel to each other or they may converge downwards, and
they may extend some distance into the smoke box, being made to
project below the top thereof. The blast pipe, which is in the centre

page_text: of this group, is sometimes expanded or trumpet-shaped at the top, at
which part it is provided with a number of smaller pipes or nozzles
corresponding in number and in the direction of their axes with another
set or group of expanded pipes fitted inside the upper part of the
chimney. The axes or centre lines of the pipes in this second group
also converge downwards and coincide exactly with the axes of the
steam blast pipes or nozzles which terminate a little below the lower
contracted mouth of each of the pipes in the group above. Some-
times the upper group only is used in combination with the divided
blast pipe or nozzles, in which case the pipes in the group will extend
down the whole length of the chimney or to a level with the top of
the boiler.