IMPROVEMENTS IN FUSIBLE PLUGS FOR STEAM BOILERS AND OTHER LIKE VESSELS."
Year: 1881

page_text: LETTERS PATENT to Harry Jones Harman, of Manchester, in the County of
Lancaster, Mechanical Engineer, for an Invention of "IMPROVEMENTS IN
FUSIBLE PLUGS FOR STEAM BOILERS AND OTHER LIKE VESSELS."
PROVISIONAL SPECIFICATION left by the said Harry Jones Harman at
the Office of the Commissioners of Patents on the 2nd December 1881.
HARRY JONES HARMAN, of Manchester, in the County of Lancaster, Mechanical
Engineer. "IMPROVEMENTS IN 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 one form of my improved plug as
follows:-I make the casing of the plug in two parts, viz., an upper removable
part and a lower permanent 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, which end is also provided with a
small flat internal projection or flange. The male screw is for the purpose of
attaching the casing to the top of the boiler flue or firebox, 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 the upper removable part of a cylindrical
form externally, and with a male screw formed thereon, and internally, of a
hexagonal or other suitable shape. The male screw terminates at its upper
extremity with a flat shoulder, upon which I place a ring of asbestos, lead, or other
suitable material, for the purpose of making a joint against the small flat pro
jection or flange, hereinbefore described as being formed on the lower or permanent
part of the casing.

page_text: I form the upper portion internally of a hollow circular form for about half the
depth, and the other or upper half of a hollow, conical, cylindrical, or other suitable
form, the major diameter if conical being uppermost. In the interior I fit a metal
plug and ring or wad of packing formed as follows:-This metal plug I make of a
conical or other suitable form in the upper portion, and the lower portion of a
cylindrical form, a collar or projection being formed between the upper and lower
portion. The lower portion terminates in a collar or washer, which may be either
screwed or rivetted to the cylindrical portion. Between the centro collar or pro-
jection and the lower collar or washer I place a ring or wad of packing of any
suitable metal or material, such as are hereinafter described, so formed as to fit
with sufficient accuracy the lower cylindrical internal portion of the hereinbefore
immediately preceding described upper removable part of the casing.
A modification of the construction of the interior of the upper removable part
of the herein before described plug I make as follows:-The upper portion of this
upper part I make externally of a circular forin, and internally a hollow circular
form for about half the depth, and the other half or upper portion of a hollow,
conical, cylindrical, or other suitable form, the major diameter if conical being
uppermost. The lower internal portion of this part is recessed for the purpose of
receiving a ring of packing hereinafter described, terminating immediately below
the said recess in a stoppered end, the said end having a cylindrical opening
formed therein. In the interior of the preceding described upper part I fit a metal
plug formed as follows:-This metal plug 1 make of a cylindrical form, the upper
half being so shaped as to be held fast by any metal or material when cold with
which it may be surrounded when such material is in a molten or pliable state.
I prefer to make it conical, or to form grooves or recesses therein. The lower end
of this metal plug may be formed with a suitable projecting flange for the purpose
of protecting the packing ring from any accumulation of dirt and deposit, but it is
not absolutely necessary to the carrying out of my Invention.
In the internal recess in the lower portion of the upper portion of the upper
removable part of the casing hereinbefore described, I place a ring of packing made
of any suitable metal or material so formed ns to fill the recess, and accurately fit
around the lower cylindrical portion of the interior metal plug.
In putting the parts together, the packing having been inserted in its place, the
metal plug is placed in position. in the interior of the upper portion of the upper
part of the casing herein before described, and the space around the upper part of
the metal plug is surrounded by a fusible alloy so composed as to melt by the heat
of the furnace when not kept sufficiently cool or covered by any fluid.
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 part. This operation
may usually be performed from the interior of the tubo or furnace, thus avoiding
the delay generally incurred in removing the manhole cover and waiting while the
boiler or other vessel is cooled down.
Another form of my improved plug, wherein the packing is placed above the
fusible alloy instead of below, as in tho herein before described forms, I make as
follows:-
I make 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 half of the lower part of the casing in the form of a hollow vertical
cylinder which is provided with a male screw and octagonal portion similar to
the lower part of the casing previously herein before described for the preceding
form.
I make the upper half of the lower part of a cylindrical form externally and
internally, the lower portion of a hollow conical form, the major diameter being
uppermost, and the upper portion of a hollow cylindrical form having a female
screw formed thereon.
I make the upper part of the casing of an octagonal or other suitable form in

page_text: the upper portion and the lower portion of a cylindrical form having a male
screw formed thereon. Between the upper and lower portions I form a shoulder
or projection for the purpose of making a joint with the lower part of the casing
herein immediately before described.
Internally I form this upper part of the casing of a hollow vertical cylinder,
terminating at its upper extremity with a small suitably shaped projection for the
purpose of making a joint with a part hereinafter described.
In the interior of the preceding described lower part of the casing I fit a metal
plug formed as follows:-This metal plug I make of a cylindrical form externally
with grooves or recesses formed thereon, and internally of a hollow cylindrical
form terminating at its upper extremity with a stoppered end. Around the
external portion I place a coating of fusible metal or alloy so formed as to fit
accurately the conical portion of the interior of the upper portion of the lower
part of the outer casing herein before described.
In the interior of the upper part of the outer casing I place a ring or wad of
packing of any suitable metal or material as hereinafter described, so formed as to
accurately fit it and prevent any passage of steam. On the top of this wad or
ring of packing I place a cover of lead or other suitable metal or material so
formed as to fit against the internal shoulder or projection and make a steam
tight joint.
In putting the parts together, the packing wad or ring and metal cover having
been inserted in the upper part of the casing and the metal plug with the alloy
cover having been placed in the interior of the lower part of the casing, the upper
part is screwed into the lower part until a joint is made between the two parts
and also between the metal cover and packing wad, thereby rendering the wholo
steam tight.
The packing ring or wad I make of iron, steel, brass, cotton, hemp, jute, asbestos,
carbon, caoutchouc, mica, plumbago, or a combination of any of these motals,
minerals, or materials, but I prefer to use asbestos either pure or in combination
with any suitable admixture.
The action of my improved fusible plug is as follows:→
When the water becomes sufficiently low to leave the portion containing the
fusible metal or alloys unsurrounded by water the heat from the furnace is com-
municated rapidly to the fusible metal or alloy which, as the water or other fluid
recedes, becomes sufficiently melted to allow of the interior metal plug being forced
out by the pressure of steam within.the boiler or other vessel, 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 ring or wad of packing herein before described when placed below the fusible
metal or alloy serves to prevent any escape of the fusible metal or alloy until it is
sufficiently melted to permit of the plug being blown out freely. When the ring
or wad of packing is placed above the fusible metal or alloy it serves to prevent
any escape of steam until the fusible metal or alloy is sufficiently melted to allow
of the wad and metal plug being forced out. Partial fusion of the metal or
alloy and escape of steam thereby is entirely overcome, it being well known
that the flow of steam through the fusible metal or alloy instantly arrests all
further fusion.
By the construction of portions of my improved fusible plug the furnace gases
are prevented from deteriorating the fusible metal or alloy.
That portion of my Invention relating to the interposing of a ring or wad of
packing between the fusible metal or alloy and the furnace is applicable to many
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.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Harry Jones Harman in the Great Seal Patent Office on the
24th May 1882.
HARRY JONES HARMAN, of Manchester, in the County of Lancaster, Mechanical
Engineer. "IMPROVEMENTS IN FUSIBLE PLUGS FOR STEAM BOILERS AND OTHER
LIKE VESSELS."
My Invention relates to improvements in the construction of fusible plugs for
steain boilers and other like vessels, whereby the said plugs are rendered more
efficient and reliable in their action, and other advantages are obtained.
In the accompanying Drawing Figures 1, 2, and 3 show one form of my improved
plugs. Figure 1 is a vertical section, Figure 2 is a plan, and Figure 3 is an
inverted plan. Like letters denote like parts in these three Figures.
The casing of my improved plug consists of two parts, viz., an upper removable
part B and a lower permanent part A, the said parts being arranged and combined
together in the following manner :-I make the lower part A of gun-metal, or other
suitable material, in the form of a hollow vertical cylinder or of any other suitable
shape, and provide the same with a male screw at its lower end and a female screw
at its upper end, the upper end being also provided with a small flat internal projection
or flange A The male screw is for the purpose of attaching the casing to the
top of the boiler, flue, or fire-box, the portion A' of the said 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 the part B of a cylindrical form externally, and form thereon a male
screw, the interior of the said portion being of an hexagonal or other suitable
shape. The said male screw terminates at its upper extremity with a flat shoulder,
upon which I place a ring B" of asbestos, lead, or other suitable material for the
purpose of making a joint against the flange A", I forin the lower half of the
part B internally of a hollow circular form, and the upper half B' of a hollow,
conical, cylindrical, or other suitable form, the greatest internal diameter, if conical,
being uppermost, as shown in Figure 1. In the part B 1 fit a metal plug C and a
ring or wad of packing C'. The upper portion of this metal plug C I make of a
conical or other suitable form, the lower portion of the said plug being of a
cylindrical form, a collar or projection being formed between the upper and lower
portions of the said plug. The lower portion terminates in a collar or washer C¹¹
which may be either screwed or rivetted to the cylindrical portion of the said
plug C. Between the centre collar and the lower collar or washer C₁ I place the
ring or wad of packing C' of any suitable metal or material such as are hereinafter
described, tho said ring or wad being so formed as to fit with sufficient accuracy
the lower cylindrical internal portion of the casing B.
Figures 4, 5, and 6 illustrate a modification of the interior of the upper removable
part of my improved plug.
Figure 4 is a vertical section, Figure 5 is a plan, and Figure 6 an inverted plan
of the same. Like letters indicate like parts in these three Figures.
The lower portion A of the casing is made precisely similar to that of the plug
shown in Figure 1, 2, and 3. The upper portion E' of the part E I make of a
circular forin externally and internally of a hollow circular form for about half its
depth, and the other half or upper portion of a hollow, conical, cylindrical, or
other suitable form, the greatest internal diameter, if conical, being uppermost, as
shown in Figure 4. A channel or groove is formed in the lower internal portion
of the part E' for the purpose of receiving a ring of packing F hereinafter described,

page_text: the said part E¹ having a cylindrical opening formed in its lower extremity, into
which is inserted the metal plug G. I make the said plug G of a cylindrical form,
the upper half being so shaped as to be securely held in position by any metal or
material when cold, with which it may be surrounded when such material is in a
molten or pliable state. I prefer to make the said plug G conical, or to form
grooves or recesses therein, as shewn in Fig. 4. The lower end of this metal plug &
may be formed with a suitable projecting flange G₁ for the purpose of protecting
the packing ring from any accumulation of dirt and deposit, but it is not absolutely
necessary to the carrying out of my Invention. In the channel or groove formed
in the part E¹ I place a ring of packing F made of any suitable metal or material
so formed as to fill the said channel or groove and accurately fit around the lower
cylindrical portion of the plug G. In putting together the parts of this and the
previously described forms of plug, the packing having been inserted in its place,
the metal plug is placed in position and the space around the upper part of the
said metal plug is filled by a fusible alloy, shown black in Figures 1 and 4, the said
alloy being so composed as to melt by the heat of the furnace when not kept
sufficiently cool or covered by fluid. The upper or removable portion of the casing
containing the fusible metal and plug is screwed into the internal thread of the
lower or permanent portion of the casing by means of a suitable key made to fit
the hexagonal part formed in such upper part. This operation may usually be
performed from the interior of the tube or furnace, thus avoiding the delay
generally incurred in removing the man-hole cover and waiting until the boiler or
other vessel is cooled down.
Figures 7, 8, 9, and 10 show another form of my improved plug wherein the
packing is placed above the fusible alloy instead of below it, as in the forms
previously described.
Figure 7 is an external elevation; Figure 8 is a vertical section; Figure 9 is
a plan; Figure 10 is an inverted plan. Like letters indicate like parts in these
four Figures.
In this form of my improved plug I make the casing in two parts, viz., an
upper part or cap I and a lower part H, which are arranged and combined together
in the following manner:-I make the lower portion H₁ of the part H in the form
of a hollow vertical cylinder, which is provided with a male screw and an octagonal
portion similar to the lower parts of the casings previously described. I make the
upper part H of the casing H of a cylindrical form externally. Internally the
lower portion of the part H" is of a hollow conical form, the greatest diameter
being uppermost, as shown in Figure 8, the upper portion of the said part H¹¹
being of a hollow cylindrical form with a female screw formed therein. I make the
upper part of the cap I of an octagonal or other suitable form, and the lower
portion of a cylindrical form having a nale screw formed thereon. Between these
upper and lower portions I form a shoulder or projection for the purpose of making
a joint with the lower part of the casing H. Internally I make this cap I in the
form of a hollow vertical cylinder, terminating at its upper extremity with a small
suitably shaped flange or projection, for the purpose of making a joint with the
part M hereinafter described. In the part H I fit a metal plug K of a cylindrical
form externally, with grooves or recesses formed thereon, and internally of a hollow
cylindrical form, terminating at its upper extremity with a stoppered end. Around
the external portion of the plug K I place a coating of fusible metal or alloy,
shown black in Figure 8, so formed as to fit accurately the conical portion of the
part H. In the interior of the cap II place a ring or wad of packing L of any
suitable material, as hereinafter described, so formed at to accurately fit it and
prevent any passage of steam. On the top of this wad or ring of packing L I place
a cover M, of lead or other suitable metal or material, so formed as to fit
against the internal shoulder or projection of the portion I and make a steam
tight-joint.
In putting together the parts shown in Figure 8 the packing wad or ring L
and metal cover M, having been inserted in the cap I, and the metal plug K with

page_text: its alloy covering having been placed in the part H", the upper part or cap I is
screwed into the portion H" until a joint is made between the said parts, and until
the packing wad L is firmly pressed against the metal cover M, thereby rendering
the whole plug steam tight. I make the packing ring or wad L of iron, steel, brass,
cotton, hemp, jute, asbestos, carbon, caoutchouc, mica, plumbago, or a combination
of any of these materials; but I prefer to use asbestos, either pure or in combi-
nation with any suitable admixture.
The action of my improved fusible plug is as follows:-When the water becomes
sufficiently low to leave the portion of the plug containing the fusible inetal or
alloys unsurrounded by water, the heat from the furnace is communicated rapidly
to the fusible metal or alloy, which as the water or other fluid recedes becomes
sufficiently melted to allow of the interior metal plug being forced out by the
pressure of steam within the boiler or other vessel, 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 serious damage is done to the boiler
or other vessel. When the plug shown in Figure 8 has operated through deficiency
of water, or when the interior requires renewing, or the fire-side of the plug requires
cleaning, all that is necessary is to remove the cap I, and the whole of the interior
can then be removed and cleaned or renewed, as required. After cleaning, the alloy
cone having been dropped into its seat, and the metal cover and wad replaced in
the cap, the latter is then screwed into its place and the plug is again ready for
The ring or wad of packing, hereinbefore described, when placed below the
fusible metal or alloy, serves to prevent any escape of the said metal or alloy until
it is sufficiently melted to permit of the plug being blown out freely. When the
ring or wad of packing is placed above the fusible metal or alloy it serves to
prevent any escape of steam until the fusible metal or alloy is sufficiently melted
to allow of the wad and metal plug being forced out. Partial fusion of the metal
or alloy and consequent escape of steam is entirely overcome, it. being well known
that the flow of steam through fusible metal or alloys instantly arrests all further
fusion. By the construction of portions of my improved fusible plug the furnace
gases are prevented from deteriorating the fusible metal or alloy. That portion of
my Invention relating to the interposing of a ring or wad of packing between tho
fusible metal or alloy and the furnace is applicable to many of the so-called fusiblo
plugs now in use, and may be used in conjunction therewith, rendering them more
certain and reliable in their action.
use.
Having thus fully described my said Invention, and shown how the same may
be conveniently and advantageously carried into practice, I claim-
First. In a fusible plug for strain boilers or other like vessels the use of a
packing ring or wad of inetal, mineral, or other suitable material above or below
the fusible alloy, for the purposes herein before set forth.
Second. Fusible plugs for steam boilers or other like vessels, constructed
substantially as herein set forth and illustrated by the accompanying Drawing.
In witness whereof, I, the said Harry Jones Harman, have hereunto set my
hand and seal, this Eighteenth day of May, in the year of our Lord Oue
thousand eight hundred and eighty two.