IMPROVEMENTS IN THE CONSTRUCTION OF FUSIBLE PLUGS FOR STEAM BOILERS AND OTHER LIKE VESSELS
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Harry Jones Harman at the Office
of the Commissioners of Patents on the 5th July 1880.
HARRY JONES HARMAN, of Manchester, in the County of Lancaster, Mechanical
Engineer. "IMPROVEMENTS IN THE CONSTRUCTION OF FUSIBLE PLUGS FOR STEAM
BOILERS AND OTHER LIKE VESSELS."
My Invention relates to improvements in the construction of fusible plugs for
steam boilers and other like vessels, whereby they are rendered more efficient and
reliable in their action, and other advantages are obtained.
In carrying out my Invention I construct the casing of the plug in two parts,
viz, an upper part and a lower part, which are arranged and combined together in
the following manner-I make the lower part of the casing of gun metal or other
suitable material, in the form of a hollow vertical cylinder or of any other suitable
shape, the said lower part having an external or male screw at the lower end and
an internal or female screw at the upper end.
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The male screw is for the purpose of attaching the casing to the top of the boiler
flue or fire box, a portion of the exterior of the casing being made octagonal and
forming a shoulder, by means of which the casing is firmly screwed into the boiler
plate where it forms a permanent fixture.
I make the lower portion of this upper part of a cylindrical form externally,
and with a male screw formed thereon, and internally of an hexagonal shape.
The upper portion of this upper part of the casing I make of a hollow cylindrical
or circular form, terminating at the lower extremity with a stopped end, the
said end having a cylindrical opening formed therein to which is adapted a conical
plug or valve. This conical plug or valve I make with a small projection on its
upper side, so shaped as to be held fast by any metal or material when cold, with
which it may be surrounded when such metal is in a molten state. The lower side
immediately below the valve or conical shaped portion I make of a cylindrical or
other suitable form, and of any approved length, for the purpose of acting as a
conductor of heat to the portion surrounded by the fusible metal. This plug or
valve may be made of any suitable material, but I prefer to make it of copper.
In putting the parts together the conical plug or valve is placed in position in
the upper portion of the casing herein before described, and the projection on the

page_text: upper side is surrounded by a layer of fusible metal so composed as to melt by the
heat when not kept sufficiently cool or covered by any fluid. Over the top and in
contact with this first layer of fusible metal I place a second layer of fusible or
other suitable metal or substance, which is so composed that if it be not in a liquid
state when cold it is easily reduced to a liquid or molten state, at a very much
lower temperature than is required to bring the lower layer into a state of fusion.
This object can be effected at any desired temperature.
The upper portion of the casing containing the fusible metal and plug is screwed
into the internal thread of the lower portion of the casing by means of a suitable
key made to fit the hexagonal part formed in such upper portion. This operation
may usually be performed from the interior of the tube or furnace, thus avoiding
the delay generally incurred in removing the manhole cover, and waiting while the
boiler or other vessel is cooled down.
The action of this improved fusible plug is as follows:-
As soon as steam is raised in the boiler or other vessel, the upper layer of fusible
or other suitable metal or substance becomes liquid or molten, and remains in that
state during the working of the boiler or other vessel.
When the water becomes sufficiently low to leave the portion containing the
fusible metals-or-alloys uncovered therewith, -the heat from the furnace. is
communicated rapidly to the lower layer of fusible metal, which as the water or
other fluid recedes lower, becomes sufficiently melted to allow of the conical plug or
valve being forced out by the pressure of steam within the boiler or other vessel
acting upon the top layer of fusible or other suitable metal or substance, which is
itself also blown out, thus leaving a clear opening through which the steam
rushes.
Timely notice is thus given to the attendant, so as to permit of the fires being
drawn before any serious damage is done to the boiler or other vessel.
The upper layer of fusible or other suitable metal or substance hereinbefore
described serves to prevent any incrustation settling thereon by reason of its being
continually in a molten or liquid condition, or by its continual expansion and
contraction, and also-as-a-means-of-preventing-any-contact-of-steam-with the lower.
layer of fusible metal, whereby any escape of steam and consequent partial fusion
only is entirely overcome, it being well known that the flow of steam through the
fusible alloys instantly arrests all further fusion.
By the construction also of the conical plug or valve the furnace gases are
prevented from deteriorating the fusible metal.
That portion of my Invention relating to the interposing of a layer of fusible or
other suitable metal or substanco between the steain or water and the lower or
acting fusible metal, is applicable to most of the so called fusible plugs now in use,
and may be used in conjunction therewith, rendering them more certain and
reliable in their action.