IMPROVEMENTS IN THE CONSTRUCTION OF PISTONS
Year: 1875

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane,
in the County of Middlesex, Patent Agent, for the Invention
of "IMPROVEMENTS IN THE CONSTRUCTION OF PISTONS." -A communi-
cation from abroad by Joseph Maric Agnellet and Frédéric
Rothmeyer, both of Paris, France.
PROVISIONAL SPECIFICATION left by the said Alexander Melville
Clark at the Office of the Commissioners of Patents, with his
Petition, on the 9th June 1875.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN THE CONSTRUCTION OF PISTONS,"
to be as follows:-
This Invention relates to improvements in metallic packings for
pistons, whereby a perfectly tight joint is obtained under all pressures.
The packing is composed of metallic disks or annular plates of dished
form so applied as to be capable of yielding and becoming slightly

page_text: flattened under the influence of the pressure, whereby they are caused
to expand at their circumference and press closely against the sides
of the steam or other cylinder or pump barrel in which the piston
works.
In some cases this flexibility and the consequent capability of exten-
sion is due to the thinness and elasticity of the metal of which the
packing is made, and in other cases it is obtained by the aid of radial
slits made in the disks or annular plates, thereby forming as many
flexible segments around the circumference of the same.
This improved packing may be applied to the piston in various ways,
of which I will proceed to indicate a few examples, premising that in
single-acting pistons the flexible discs are applied to that side of the
piston which sustains the pressure, whilst in double-acting pistons both
faces of the piston are fitted alike. It will therefore be sufficient to
describe the packing on one face only.
According to one arrangement the packing is composed of a pair of
discs of dished or concavo-convex form fitted together with the convex
surface of the one against the concave surface of the other, both discs
having radial slits around their circumference, the slits extending to
within a certain distance of the centre, and the two disks being so :
disposed that their slits shall not coincide. The pair of discs is applied
to the piston with the convex side next the body of the piston, and the
concave side outwards, and exposed to the pressure of the fluid in the
cylinder or barrel. The discs have a central flanged opening for the
passage of the piston rod, and they are flanged around the circumference
so as to present a cylindrical contact surface of sufficient extent to make
a tight joint. These flexible discs are enclosed by a flat cover or disc,
which bears exactly against their flanged periphery, and the whole is
secured by the screwed extremity of the piston rod passing through the
piston in the usual way.
The concave and convex surfaces of the pair of flexible discs being in
very close contact, and both discs being similarly flattened and expanded
under the steam or other pressure leakages are prevented by the slits in
the two discs breaking joint; but for greater security I may interpose
between the two discs of the pair a thin sheet of metal, of leather, 3
india-rubber, or other suitable fabric. It will be understood that the

page_text: number of flexible discs may be varied, and that three, four, or more
may be employed, fitting exactly the one in the other.
According to another arrangement I employ but one flexible disc on
each face of the piston. In this case the disc is dished, but without
slits. The face of the body of the piston is made concave to receive it;
the dished disc is retained by a covering plate having one side convex,
this convexity not being quite concentric with the concavity of the body
of the piston, so as to allow a certain amount of play for the flexible disc
at the circumference.
Instead of a single disc the packing may consist of a number of
similar discs with dished washers or plates interposed between them. In
this arrangement the various flexible discs are made of different thick-
nesses, the thickest being outermost, and the thinnest innermost, so as to
proportion their expansibility to the variations of pressure in the cylinder
or pump barrel. Thus the outer and more rigid disc will be expanded
by the highest pressure and make a tight joint, and when the pressure
diminishes the disc will return to its primitive form, and the reduced
pressure will then act on and expand the second flexible disc, which in
turn makes the joint, and so on successively as the pressure diminishes.
For pistons of large diameter the flexible discs, instead of covering the
whole face of the piston, would be of annular form by preference, and
clamped to the body of the piston by flat plates bolted thereto.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Alexander Melville Clark in the Great Seal Patent
Office on the 25th November 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Ninth day of June, 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 Alexander Melville Clark, Her special

page_text: licence that I, the said Alexander Melville Clark, my executors, adminis-
trators, and assigns, or such others as I, the said Alexander Melville
Clark, 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, usc,
exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN THE CONSTRUCTION OF PISTONS," a communication to me
from abroad by Joseph Marie Agnellet and Frédéric Rothmeyer, both
of Paris, France, upon the condition (amongst others) that I, the said
Alexander Melville Clark, 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.
NOW KNOW YE, that I, the said Alexander Melville Clark, 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, reference being had to the accompanying
Sheet of Drawings, and to the letters and figures marked thereon,
that is to say :-
This Invention relates to improvements in the pistons of steam or
other engines and pumps, and consists more particularly in improved.
metallic packings therefor, whereby the pistons are maintained perfectly
tight under all pressures. The packing is composed of metallic discs or
annular plates of cupped or dished form, so applied as to be capable of
yielding and becoming slightly flattened under the influence of the
pressure upon them, whereby they are caused to expand at their circum-
ference, and press closely against the sides of the cylinder or barrel in
which the piston works.
In some cases this flexibility and consequent extensibility are due to
the thinness and elasticity of the metal of which the packing is composed,
and in other cases the same result is obtained by the aid of radial slits
made in the discs forming as many flexible segments around the circum-
ference of the same.

page_text: This improved construction of piston will be readily understood with
the aid of the accompanying Drawings, in which Figures 1, 2, and 3
show respectively a section, face, and edge views of a piston fitted with
metallic disc packings of concavo-convex form, and having radial slits to
impart the desired flexibility and extensibility.
Figures 4, 5, and 6 show similar views of a piston constructed with
cupped metallic discs, possessing a certain amount of flexibility and
extensibility. In this case the discs are flat at the centre, and of
conical form near the circumference, with radial slits, as before, to
impart the desired extensibility. The pistons represented in these
Figures are intended to receive the pressure of the fluids (steam, air,
water, or other fluid) on both faces, and are what are termed double-
acting, but in single-acting pistons the flexible discs are applied in that
side of the piston only which sustains the pressure.
In the arrangement shown in Figures 1, 2, and 3 the body of the
piston A is of solid metal of suitable thickness, and upon both sides a
set of expanding packing discs C, C', is applied, as shown. Each set
consists of two (or more) cupped discs with their concave surfaces
outwards, and fitting closely together, the convex surface of the one
against the concave surface of the other, both discs being provided with
radial slits around their circumference, extending to within a certain
distance of the centre, and so arranged that the slits c of discs C shall
break joint with slits c¹ of disc C¹ (see Figure 2), that is to say, that the
slits in the one disc shall come opposite a solid part of the other disc.
A flat disc or cap D without slits is applied against the flanged or
cylindrical edge of the outermost disc C, as shown, so as to entirely
cover the same. The discs have openings at the centre, by which they
are fitted on the piston rod, as illustrated.
Figures 4, 5, and 6 show another arrangement of the piston similar to
the foregoing, except that the form of the discs C, C', is different, and
the covers D and the body A of the piston are dispensed with.
.
In these arrangements the pressure of the fluid exerted on one of the
faces of the piston causes the discs on that side to expand or spread until
they press closely against the interior of the cylinder or barrel. Owing
to the intimate contact between the superposed discs C, C', they are
both expanded to an equal extent under the pressure, and any leakage

page_text: which might take place at the radial slits is prevented by making those
of the one break joint with those of the other, but for further security a
thin sheet metal, leather, india-rubber, or other disc f may be interposed
between each pair of packing discs C, C', as shown in Figures 1 and 3.
The edges of the discs C, C¹, are so formed as to present a cylindrical
surface of contact with the cylinder or barrel of such a width as will
ensure a perfect joint. The number of discs may vary from two as a
minimum to three, four, or more, all fitting accurately the one in the
other. It will be seen that the body A of the piston, and the covers D
may be dispensed with, as in the arrangement, Figures 4, 5, and 6, without
affecting the working of the piston.
The construction of piston and packings represented in Figures 1 to 6
is preferably that which would be adopted for pistons of small diameter,
but for those of large diameter it is preferable to make the expanding
packings (whether slit or not) of annular form, as shown in Figure 7,
and attach them to cast-iron plates P forming the body of the piston
mounted on the piston rod T. In this manner the packing rings C, C¹,
may be readily renewed as they become worn or injured, the piston itself
not being subject to wear.
In conclusion I would remark that the discs may be dished of various
forms, whether spherical or conical, as shown, or parabolical or of other
suitable form.
Having described the nature of the Invention, and the manner of
performing the same, I declare that what I claim as the Invention to be
protected by the herein-before in part recited Letters Patent is, the
improved construction of piston with expanding metallic discs or
packings of dished or cupped form (provided or not with radial slits, as
described), the said discs or packings being applied and operating sub-
stantially as herein shown and described.
In witness whereof, I, the said Alexander Melville Clark, have
hereunto set my hand and seal, this Twenty-fifth day of November,
in the year of our Lord One thousand eight hundred and seventy-five.
A M CLARK