IMPROVEMENTS IN PISTON PACKINGS
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 PISTON PACKINGS."-A communication from
abroad by Paul Giffard, 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 22nd May 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 PISTON PACKINGS," to be as
follows:-
This Invention relates to improvements in piston packings and com-
prises several modifications of the same idea.
'
In order that the Invention may be readily understood I have illus.
trated it in the accompanying Drawings, in which,―

page_text: Figure 1 shows a part sectional elevation and plan of one arrangement
or modification of the improved piston packing. In this case the piston is
single acting; it consists of a simple band or strip of leather or of india-
rubber, fitted as tightly as possible in a circumferential groove A around
the piston B. There is a hollow space D at the bottom of this circum-
ferential groove behind the leather packing. Apertures E admit the
gases or other fluid in the cylinder to this groove so as to press on the
back of the packing and keep it tight. The ends of the bands are joined
by a lap joint.
Figure 2 shows a section of a double-acting piston, and is the arrange-
ment before described, duplicated as shown.
Figure 3 shows a section of a second arrangement suited for steam
engines. In this case F is a metallic ring and A a band of india-rubber
at the back of the metallic part of the packing, the india-rubber ring
boing fitted very tightly in the groove which is made the same as before
and provided with apertures as shown to admit the steam to press the
india-rubber forcibly against the metallic ring. This arrangement may
be duplicated as in the former case, Figure 2.
Figure 4 shows a section of a third arrangement in which A is a thin
band or strip of leather or india-rubber wound several times round
the piston, and received in a circumferential groove as before. The
automatic tightening of the packing is the same as before.
Besides leather or india-rubber, hemp, or other gaskets, hardened
wood, or compressed paper may be used.
SPECIFICATION filed in pursuance of the conditions of the Letters 2
Patent, and of an Order of the Lord Chancellor, by the said
Alexander Melville Clark in the Great Seal Patent Office on the
1st December 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 Twenty-second day of May, in the year
of our Lord One thousand eight hundred and seventy-five, in the thirty-
•
8

page_text: •
eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Alexander Melville Clark, Her special
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, use,
-exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for
"IMPROVEMENTS IN PISTON PACKINGS," a communication to me from
abroad by Paul Giffard, 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 on or before the Eighth day of December, One thousand
eight hundred and seventy-five.
'
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 Figures on the
accompanying Sheet of Drawings, and to the letters of reference marked
thereon (that is to say) :—
5 This Invention relates to improved automatic piston packings called
"Giffard's," and comprises several modifications of the same system,
and the simplest arrangement or modification is shewn in the part
sectional elevation and plan, Fig. 1. In this case the packing is formed
of a single band or strip A of leather or caoutchouc fitted as tightly as
0 possible in a circumferential groove around the metallic piston block B.
At the bottom of the circumferential groove there is a space D behind
the band in the groove, and from the bottom of the piston there are.
several apertures or holes E, E, leading to the space D behind the band
in order to enable the gases or fluids in the barrel or cylinder to enter
5 the piston and press on the back of the packing, and thereby give
automatically the pressure required to make the packing hermetically
tight against the interior of the barrel or cylinder. The band or strip
of leather or caoutchouc is fitted into the groove so as to have no play,
"

page_text: and with the greatest possible tightness, and the ends of the band overlap,
each other by gradually thinned surfaces.
In Fig. 1 the packing is of single effect, but a piston of. double
effect is shewn in the section, Fig. 2, the packing being purely and
simply formed of two rings or bands instead of one. The holes E, E,,
E, E, formed in the top or bottom faces of the metallic piston block B
allow gases or fluids to circulate around the interiors of the packing.
bands and expand them outwards.
•
}
Fig. 3 is a section of a piston having packings suited for steam-
engines. In this case there is a metallic band or ring F and an elastic"]
band of caoutchouc A placed in the circumferential groove around:
the piston as before described, the metallic band F being in close'
contact with the elastic band A which is tightly placed in the groove."
Behind the elastic band there is a space D as in the other examples,'
communicating with the cylinder by means of holes E, E, through-1
which holes the steam enters into the circular space D, and causes the
elastic band A to press forcibly against the metallic band or ring F, and
the result of this automatic action is the double hermeticity of the
two bands and the steam cylinder, and it is evident that this arrange-
ment or system can be duplicated or made of double effect, as in Fig. 2. 2
The section Fig. 4 represents an arrangement in which a thin band
or strip of leather or caoutchouc A, A, is wound several times in the
interior of the circumferential groove around the piston block B, there
being a space D and holes E, E, to enable the packing to be auto-
matically pressed against the interior of the barrel or cylinder as
before.
Giffard's new automatic piston packing can be made of all required
dimensions, and the bands employed may be made of greased leather,"
but the ordinary strap leather is well suited for the formation of the
bands, and besides caoutchouc in thick and thin bands the packing may
be made of hemp, gasket, wood, compressed paper, and other suitable
materials, and for the metallic bands or rings various descriptions of
metals or alloys may be used.
The space D behind the leather or elastic band may be made of any
desired shape, but it is incumbent that it should be made of the
minimum capacity, and the holes E, E, should also be made no larger
than is required to allow the entrance of the gases, fluids, and steam as
quickly as required.

page_text: As this system of piston packing is essentially automatic the following
advantages are the result:-The mode of construction is entirely new,
entremely cconomical, easily adapted, and the wear compensated. It
is also infallible in its working, lasts a long time, can be easily and
quickly renewed, enables a cheap piston to be obtained, having the
minimum amount of friction, and such an absolute hermeticity or
proper tightness as to enable cent. per cent. of the volume of gases,
fluids, or steam to be utilized..
Having now described the nature and particulars of the said Invention,
as communicated to me, I desire it to be understood that I claim the
system of making the pistons before described and shewn on the accom-
panying Sheet of Drawings, and characterised by the following points :-
First. The arrangement of the piston packing of simple effect, Fig. 1.
formed of a single band, or strip A of leather or caoutchouc, tightly
encased in a circumferential groove formed in the outside of the piston
block, and also the space D communicating by holes E with the barrel
or cylinder, so that gases or fluids can enter into the piston to act
upon the band and produce by their automatic action a prossure
causing absolute hermeticity or proper tightness.