IMPROVE- MENTS IN FUSIBLE BOILER PLUGS FOR PREVENTING EXPLOSIONS OF OR OTHER INJURY TO BOLLERS THROUGH A DEFICIENCY OF WATER
Year: 1875

page_text: LETTERS PATENT to Thomas Joseph Smith, of North Bow, in the
County of Middlesex, Engineer, for the Invention of "IMPROVE-
MENTS IN FUSIBLE BOILER PLUGS FOR PREVENTING EXPLOSIONS OF OR OTHER
INJURY TO BOLLERS THROUGH A DEFICIENCY OF WATER
"
Sealed the 2nd November 1875, and dated the 5th May 1875.
PROVISIONAL SPECIFICATION left by the said Thomas Joseph
Smith at the Office of the Commissioners of Patents, with his
Petition, on the 5th May 1875.
I, THOMAS JOSEPH SMITH, of North Bow, in the County of Middlesex,
Engineer, do hereby declare the nature of the said Invention for "IM-
PROVEMENTS IN FUSIBLE BOILER PLUGS FOR PREVENTING EXPLOSIONS OF OR OTHER
INJURY TO BOILErs through a DEFICIENCY OF WATER," to be as follows:-
:-
This Invention relates to improvements in fusible boiler plugs for
preventing explosions of or other injury to boilers through a deficiency
of water.

page_text: According to my Invention one form of plug I construct of a bulb
(by preference spherical and of gun metal) having at its lower side an
opening forming a short tube, which has a screw thread cut on it
exteriorly for the purpose of enabling the plug to be screwed into the
top or other suitable part of the fire tube. Through the said bulb I pass
and fix a tube at an angle with the horizontal plane, and larger at the
upper
than at the lower end. This tube I may form either in a piece with
the bulb or separate therefrom, and fix it by any suitable means. I
prefer however to screw it into the front or larger opening, its further
end being thus screwed up to a seating formed around the inner side of
the opposite or smaller opening. The inner area of the bulb and the
outer area of the tube which passes through it are thus in communica-
tion with the interior of the fire-tube and subject to the heat therefrom,
whilst the exterior of the bulb and the interior of the tube passing through
it are surrounded by and in contact with the water in the boiler; the
slanting direction of the tube and the increased area of the upper end
thereof combining to cause a constant and rapid circulation of water
therethrough. The said tube is perforated with slots or holes of any
convenient number, size, and form, filled in with a soft fusible metal,
which so long as the tube is full of water is thereby kept from melting,
but should the water in the boiler get below the level of the tube then
the heat from the fire-box, acting within the bulb and around the tube,
will melt the said soft fusible metal, and thus form apertures through
which the steam will rush and put out the fire. The constant circula-
tion of water through the tube as described, effectually prevents the
formation of any incrustation therein.
Another form of plug I construct (by preference of gun metal) with
a dome-shaped top perforated with holes or slots of any convenient
number, size, and form, but by preference radial slots. These slots are
filled with a soft fusible metal, which metal is also made to cover the
whole dome-shaped top as a cap. The plug is screwed into the top of
the fire-tube; as with the one above described the heat from the fire-
tube acting within the plug.
The object of covering the whole of the dome-shaped top, with the
soft fusible metal, as well as filling up the apertures. is as follows:-
Should incrustation have formed on the top of the plug when the plug
is called into action by reason of the water having sunk to too low a
level the heat imparted to the soft metal in the slots will be imme-

page_text: diately transmitted to the continuous surface of metal on the exterior
surface, which will thereby be caused to expand, cracking the incrusta-
tion, which will then fall away or at least be prevented from forming
any sufficient impediment to the passage of the steam through the
apertures to the fire when the soft metal has been melted.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Joseph Smith in the Great Seal Patent'
Office on the 5th November 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
JOSEPH SMITH, of North Bow, in the County of Middlesex, Engineer,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fifth day of May, in the year of
our Lord One thousand cight hundred and seventy-five, in the thirty-
eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Thomas Joseph Smith, Her special
license that I, the said Thomas Joseph Smith, my executors, admini-
strators, and assigns, or such others as I, the said Thomas Joseph Smith,
my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during
the term therein expressed, should and lawfully might make, use,
exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for "Im-
PROVEMENTS IN FUSIBLE BOILER PLUGS FOR PREVENTING EXPLOSIONS OF OR OTHER
INJURY TO BOILERS THROUGH A DEFICIENCY OF WATER," upon the condition
(amongst others) that I, the said Thomas Joseph Smith, my executors or
administrators, by an instrument in writing under my, or their, or one
of their hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to be
performed, and cause the same to be filed in the Great Seal Patent
Office within six calendar months next and immediately after the date of
the said Letters Patent.

page_text: NOW KNOW YE, that I, the said Thomas Joseph Smith, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in
and by the following statement thereof (that is to say) :-
This Invention relates to improvements in fusible boiler plugs for
.preventing explosions of or other injury to boilers through a deficiency
of water.
And in order that my Invention may be clearly understood and
readily carried into effect, I will proceed to describe the same with the
aid of the accompanying Drawings, reference being had to the letters
and figures marked thereon. The same letter of reference wherever it
occurs indicates the same or corresponding part.
One form of plug constructed according to my Invention is illustrated
at Figures 1 to 5, Figure 1 being a side elevation; Figure 2, a front
elevation; Figure 3, a sectional view taken at the line a, b, Figure 2;
Figure 4, a sectional view taken at the line c, d, Figure 3; and Figure 5,
a sectional view of a modification.
I construct the plug of a bulb A (by preference spherical and of gun
.metal), having at its lower side an opening and terminating there in a
short tube B with a screw thread on its exterior surface formed to enable
the plug to be screwed into the top or other suitable part of the fire-tube
or box in proximity to the fire; the screw terminating at its upper end
in an ordinary rectilineal bolt head formation 6¹, to enable a spanner to
be used to fix the plug. Through the bulb A. I pass and fix a tube C
at an angle with the horizontal plane and, by preference, larger at the
upper than at the lower end. This tube I form either in a piece with
the bulb or separate therefrom, and fix it in any suitable manner. I
.prefer however to screw it into the front or larger opening in the
bulb A; its further end being thus screwed up to a seating formed
around the inner side of the opposite or smaller opening in the bulb.
The inner area of the bulb A and the outer area of the tube C are
thus in communication with the interior of the fire-tube or box,
and subject the heat of the fire therein, whilst the exterior of the
bulb A and the interior of the tube C are surrounded by and in
contact with the water in the boiler, the slanting direction of the
tube and the increased area of the upper end thereof combining to
cause a constant and rapid circulation of water therethrough. The
.

page_text: tube C is perforated with slot or holes of any convenient number,
size, and form; which slots or holes are filled in with a soft fusible
metal D. This soft metal so long as the tube is full of water is
kept by the water from melting; but should the water in the boiler fall
below the level of the tube, then the heat from the fire acting within
the bulb and around the tube will melt the soft metal, and thus form
apertures through which steam will rush, and so relieve the boiler of
the excess of pressure, at the same time putting out the fire. The
constant circulation of water through the tube C, as described, effectually
prevents the formation of any incrustation therein.
At Figure 5 is illustrated a modification of the above form of plug. In
this arrangement the tube C is formed partly in a piece with the bulb A,
as shewn the other part of the tube screwing in from the front as in
the previous case. The tube thus formed instead of being perforated
with holes to be filled in with soft metal has a ring E thereof at the
junction of the ends of the two parts of the tube, and between the
same, as shewn, which ring is fixed and kept in position by the screwing
in of the front part of the tube.
Another form of plug constructed according to my Invention is illus-
trated at Figures 6 to 10 of the accompanying Drawings, Figures 6
and 7 being elevations; Figure 8, a vertical section at the centre line;
Figure 9, a plan partly in section; and Figure 10, a sectional view of a
detached portion. As in the form of plug above described the material
I prefer is gun metal. This plug has a dome-shaped top G perforated
with holes or slots of any convenient number, size, and form, but by
preference radial slots (see Figures 8 and 9). These slots are filled in
with a soft fusible metal H, which is also made to cover the whole dome-
shaped top of the plug as a cap. This form of plug is like the other, also
screwed into the top of the fire-tube or box, the heat from the fire thus
acting on the inner surface of the plug.
The object of covering the whole of the dome-shaped top of the plug
with the cap of soft metal as described, as well as filling in the slots or
holes is as follows:-Should incrustation have formed on the top of the
plug when it is called into action by reason of the water in the boiler
having sunk to too low a level, the heat of the fire imparted to the soft
metal in the slots or holes will be immediately transmitted to the con-
tinuous surface of the same metal on the exterior surface of the plug

page_text: which will thereby be caused to expand and crack; the incrustation
which will then either fall away, or at least be prevented from forming
any sufficient obstacle to prevent the passage of the steam through the
apertures to the fire when the soft metal has been melted. Figure 6
shews the plug formed to screw into the fire-tube or box from the
inside, whilst Figure 7 illustrates a form to screw in from the outside.
When this form of plug has been once called into action I sometimes,
to save the loss of time in removing the plug and replacing it by.a fresh
one, simply place over the top of the plug a cap of soft metal to fit the
top of the same. This cap is illustrated at Figure 10 in section, and has
been found quite effective.
Having thus particularly described and ascertained the nature of my
said Invention, and the manner in which the same is to or may be
performed, I claim as my Invention to be secured by the herein-before
in part recited Letters Patent, the improvements in fusible boiler plugs
substantially as and for the purpose or purposes herein-before set
.forth and described and illustrated in the accompanying Drawings.
In witness whereof, I, the said Thomas Joseph Smith, have here-
unto set my hand and seal, this Fifth day of November, in the
year of our Lord One thousand eight hundred and seventy-five.
T. J. SMITH.
(L.S.)