IMPROVEMENTS IN FUSIBLE PLUGS FOR STEAM BOILERS
Year: 1884

page_text: I JOHN DEWRANCE of 158 Great Dover Street Lambeth in the county of Surrey
Engineer do hereby declare the nature of my said invention for IMPROVEMENTS IN
FUSIBLE PLUGS FOR STEAM BOILERS, to be as follows:-
In fusible plugs as at present made there is always a certain thickness of fusible
metal which may partially melt out & allow the steam to leak. The effect of this
leakage of steam is to cool the remainder of the fusible metal & prevent any
further fusion.
Under such circumstances the intended large orifice for the escape of steam is
not obtained & the plate becomes overheated.
To obviate this I screw into the crown of the fire box or part of the plate
exposed to the fire a metal bush; on this bush rests a brass ring having a conical
hole through it into which a metal plug is fitted & held in by tinning with fusible
metal both the inside surface of the brass ring & the outside of the metal plug
& while the tin or fusible metal is fluid the plug is placed into the ring. The
lower end of the plug by preference is made pointed to guide it into the hole in the
bush; when the firebox plate becomes sufficiently heated to melt the fusible metal
no leakage can occur until the plug is blown right out. In order that the ring
& plug may be replaced with the least possible delay it has two ears cast upon it
which are bent over two corresponding projections formed at the end of a rod so as
to be loosely attached to it. This rod is of sufficient length to reach from the fire
box plate to a short distance outside the boiler shell so that it can be conveniently
taken hold of. In the shell of the boiler immediately opposite the bush in the
firebox plate there is a hole through which the rod passes; a cover is provided to
close this hole around the rod.
Inside of this cover or bonnet there is a coiled spring which presses on the end
of the rod which in turn forces down the brass ring against the bush; the joint
between these two surfaces is made tight by an asbestos washer & in order that
this washer may readily leave the surface of the bush it is encased with very thin
brass which is secured to the ring. When it is required to examine or to renew.
the plug when blown out it is only necessary to remove the cover, draw out the
rod having the ring attached to it, the ring is then disconnected from the rod by
bending out the ears & a new one substituted & placed into position in the bush
without either getting inside the boiler or firebox at all.
The part of this invention that refers to the fixing of the plug may be applied to
any form of fusible plug.

page_text: I JOHN DEWRANCE of 158 Great Dover Street, Lambeth in the county of Surrey,
Engineer, do hereby declare the nature of my invention for IMPROVEMENTS IN
FUSIBLE PLUGS FOR STEAM BOILERS, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
In Fusible Plugs as at present made there is always a certain thickness of
fusible metal which may partially melt out and allow the steam to leak out.
The effect of this leakage of steam is to cool the remainder of the fusible metal
and prevent any further fusion.
Under such circumstances the intended large orifice, for the escape of steam is
not obtained, and the plate becomes overheated. To obviate this I screw into the
crown of the firebox or part of the plate exposed to the fire a metal bush; on this
bush rests a brass ring having a conical hole through it into which a metal plug is
fitted and held in by tinning both the inside surface of the brass ring and the
outside of the metal plug and placing the plug in place while both are immersed
in molten tin or any other fusible metal. The lower end of the plug is by
preference made pointed to guide it into the hole in the bush; when the firebox
plate becomes sufficiently heated to melt the fusible metal no leakage can occur
until the plug is blown right out. In order that the ring and plug may be
replaced with the least possible delay, it has two ears cast upon it which are bent
over two corresponding projections formed at the end of a rod so as to be loosely
attached to it. This rod is of sufficient length to reach from the firebox plate to a
short distance outside the boiler shell, so that it can be conveniently taken hold of.
In the shell of the boiler immediately opposite the bush in the fire-box plate, there
is a hole through which the rod passes; a cover is provided to close this hole,
around the rod.'
"4
Inside of this cover or bonnet there is a coiled spring, which presses on the end
of the rod which in turn forces down the brass ring against the bush; the joint
between these two surfaces is made tight by an asbestos washer or any convenient
means. When it is required to examine or to renew the plug it is only necessary
to remove the cover or bonnet; draw out the rod having the ring attached to it,
the ring is then disconnected from the rod by bending out the ears and a new one
substituted and placed into position in the bush without getting inside the boiler
or fire box.
تو
The part of this invention that refers to the fixing of the plug may be applied to
any form of fusible plug.
On the accompanying sheet of drawings Fig. 1. represents a sectional elevation,
and Fig. 2. a side elevation. Fig. 3 a sectional plan taken at the line A A, and
Fig 4 represents an ordinary fusible plug to which has been applied a part of my
invention. a, a, represents a portion of the crown of the firebox, b, the metal bush
screwed into it, c the renewable ring which rests upon the bush b, a steam tight
joint being made by an asbestos washer or other convenient means, & is the conical
plug which as well as the ring c, is tinned and is put in its place while both are
immersed in. molten tin, e, e, are the ears which attach the ring c loosely to two
projections on the cap f, which is attached by a piu to the rod g. in such a way as
to form a universal joint so that the ring c, may accomodate itself to the position of
the bush b, in case it is not quite in a line with the rod g.
h, h, represent the outer shell of the boiler, j, being a bush on which the cover k,
forms a tight joint; inside the cover is a spring 8, which presses on the end of the
rod g and keeps the ring c, tight up against the bush b.

page_text: In Fig. 4. b is the bush which is screwed into the firebox plate, and d the conical
plug, both of these are tinned in a bath of tin or any fusible metal and the plug is
placed in its position while both are immersed in the molten metal.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
Firstly:-The construction of a Fusible plug in which an inner plug is united to
a bush by tinning their surfaces and placing them together while the tin is in a
molten state substantially as described.
Secondly The arrangement by which the Fusible plug can be renewed without
entering the boiler substantially as described.