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 20th February 1868.-A communication from abroad by
Jearum Atkins of the City of Washington, 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 of "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, 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 in the
employment of tapered or expanded smoke tubes or passages, the
diameter of which increases towards the discharging mouth, arranged
and combined together, substantially in the manner herein-after
described.
In applying this Invention to a tubular boiler, for example, the
boiler tubes in lieu of terminating in the smoke box tube. plate as

page_text: heretofore are made to enter or project some distance therein and
have their inner ends enlarged conically. The lower tier of tubes
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
prolongation or 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 picce fitted on to 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
largest 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 or expanded boiler tubes herein-before referred to. It is some-
times 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.