Improvements in Expanding Pistons for Steam Engines, Pumps, or the like.
Year: 1887

page_text: Date of Application, 7th Sept., 1887
Complete Left, 7th June, 1888
Complete Accepted, 13th July, 1888
Improvements in Expanding Pistons for Steam Engines, Pumps, or
the like.
We, TOM THOMPSON of Raymond Street Shelton, Stoke-on-Trent, Engineer and
THOMAS MILNES FAVELL of Etruria Iron Works, near Stoke-on-Trent, Mechanical
Engineer, do hereby declare the nature of this invention to be as follows:-
The object of the present Invention is to construct a piston in such a manner that
it shall automatically expand according to the variation in the internal diameter of a
steam engine cylinder, and the bore of pump barrels, or the like, and at the same
time, preserve an equal radial pressure; thus obviating the tendency of the bore of
the cylinder or barrel to wear elliptically, or irregularly, which occurs in the cases of
expansive pistons as usually constructed.
In the Specification of the Invention of Dixon & Thompson No. 6,22788, is described
a device, comprising an inner ring, coned upon its external periphery, and pressed
outwards by means of plunger studs and spiral springs, the coned exterior surface of
which inner ring, engages in a reverse cone, formed by a chamfer upon the inner
edges of the outer rings. Now, if the outer ring aforesaid, be formed of rings of
metal, and cut or divided in one place, any equal expansive force that is applied to the
inner surface of said rings, in a radial direction, will be converted into irregular
pressure, by reason of the tendency of the material forming the outer rings, to spring
apart with greater force, at right angles to the cut or division, than it does in a
direction parallel to said division.
Therefore, while employing the inner coned ring, plunger studs, and spiral springs,
as described in the specification No. 6,22788 above referred to, it is proposed in
accordance with the present Invention, to divide the outer rings into segments, so that
the irregular direction of the force of expansion, due to the elasticity of the material
composing the outer rings, cannot, in the slightest degree, neutralise the equal radial
tension of the inner ring, plunger studs, and spiral springs. In arranging these
segments, to form the outer or bearing surface of a piston, said segments may, in the
case of using two or more rings, be arranged, so that the solid portions of one ring,
cover the slits or divisions in the adjacent ring, and thus prevent the leakage of steam,

page_text: water or other fluid past said piston; or, with a view to secure the requisite gas or
fluid tight condition, slots may, in certain cases, be cut through the ring at right
angles, or diagonally to the slits or divisions above mentioned, and metal tongues of
suitable form and size be fitted therein.
By the arrangement above described, which, it will be seen, constitutes an improve-
ment upon the Invention No. 6,2278* herein-before referred to, a piston is produced
such as will not only expand equally in a radial direction, and so ensure, and preserve
a true circular bore within the cylinder or barrel, to which said improved piston is
adapted, but, at the same time, it will readily fit a cylinder or barrel that has already
become worn to an irregular shape, also ensuring the additional advantage, that it
preserves an equal and regular lateral pressure, between the flange of the piston body,
and that of the junk ring, thus preventing leakage and "knocking," even when
moving at a high rate of speed, and also enables the junk ring to be dispensed with ;
and, as both the inner and outer rings may be formed in segments, tho piston can be
fitted together without possessing a moveable junk ring, such as is generally required
in other cases, and thus avoiding the risks of the bolts, which secure said junk ring to
the body of the piston, getting loose, and causing damage to the cylinder and other
parts, as is frequently the case in the arrangements hitherto adopted.
Dated this fith day of Santambor 1887
JAMES STEVENSON,
Gray's Inn Chambers,
20, High Holborn, London, W.C.,
Agent for Applicants.

page_text: COMPLETE SPECIFICATION.
Improvements in Expanding Pistons for Steam Engines, Pumps, or
the like.
We, TOM THOMPSON, of Raymond Street, Shelton, Stoke-on-Trent, Engineer, and
THOMAS MILNES FAVELL, of Etruria Iron Works, near Stoke-on-Trent, Mechanical
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
The object of the present Invention is to construct a piston in such a manner that
it shall automatically expand according to the variation in the internal diameter of a
steam engine cylinder, and the bore of pump barrels or the like; and, at the same
time preserve an equal radial pressure, thus obviating the tendency of the bore of the
cylinder or barrel to wear elliptically or irregularly, which occurs in the cases of
expansive pistons as usually constructed.
Said Invention consists of means which we have devised with a view to constitute
improvements upon the device described and shewn in the Specification and drawings
of the Invention of Dixon and Thompson No. 6227 of 1886 wherein is described a
piston comprising an inner ring coned upon its external periphery, and pressed
outwards by means of plunger pins and spiral springs working or being received in
recesses formed in the body of the piston extending round its external surface; the
coned exterior surface of which inner ring engages in a reverse cone formed by a
chamfer upon the inner edges of the outer rings.
Now, in accordance with our present Invention, the piston can be fitted together
without necessitating the employment of the usual junk ring and fastenings.
The arrangement of parts which we employ in carrying out our Invention is
shewn in the accompanying sheet of drawings in which Figure 1 is a half sectional
elevational view, and Figure 2 is a plan, one half of which is in section, on reference
to which it will be seen that whilst we employ the inner coned ring f, plungers d',
plunger pins d, and springs c received in the recesses & disposed round the body of
the piston, said plungers d being pressed outwards and against the inner coned ring f
which in turn expands the outer rings e, as described and shewn in the Specification
of Dixon and Thompson No. 6227 of 1886, hereinbefore referred to; we, in
accordance with this our present Invention,-instead of forming the outer rings e in
one piece with only one cut or slit as is the case in the Invention of prior date above
referred to, divide said outer rings e, forming the bearing surface of the piston, into
a number of segments, so that the irregular direction of the force of expansion due
to the elasticity of the material composing the outer rings e, cannot in the slightest
degree neutralise the equal radial tension of the inner coned ring f, plungers d¹,
plunger pins d, and springs c. In arranging these segments, to form the outer or
bearing surface of a piston, said segments may in the case of using two or more rings,

page_text: be arranged so that the solid portions of one ring, covers the slits or divisions in the
adjacent ring, and thus prevent the leakage of steam, water or other fluid past said
piston; or, with a view to secure the requisite steam or fluid tight condition, slots
may in certain cases be cut through the ring at right angles or diagonally to the slits
or divisions above mentioned, and metal tongues of suitable form and size be fitted
therein.
By the arrangement above described we are enabled not only to produce a piston
such as will expand equally in a radial direction, thus preserving a true circular bore
within the cylinder or barrel to which same is adapted, and at the same time readily
fitting a cylinder or barrel that has already become worn to an irregular shape; but,
by means of a piston constructed in accordance with our present Invention we are
enabled to ensure the additional advantage, as will be readily seen on reference to the
accompanying sheet of explanatory drawings, of dispensing with the usual movable
junk ring such as is generally required with pistons as heretofore usually constructed,
thereby avoiding the risk of the bolts which secure said junk ring to the body of the
piston, getting loose, and causing damage to the cylinder and other parts, as is
frequently the case in the arrangements hitherto adopted.
Having now particularly described and ascertained the nature of our said
Invention, and in what manner the same is to be performed, we declare that what we
claim is :
In piston for steam engines, pumps, and the like, the means which we employ
whereby we are enabled to render unnecessary the use of the ordinary adjustable
junk ring and fastenings for same, substantially as and for the purposes herein set
forth.
JAMES
STEVENSON,
Gray's Inn Chambers,
20, High Holborn, London, W.C.,
Agent for Applicants.