IMPROVEMENTS IN THE CONSTRUCTION OF METALLIC PISTONS
Year: 1857

page_text: LETTERS PATENT to Thomas Forsyth, of the City of Manchester, Engineer,
for the Invention of "IMPROVEMENTS IN THE CONSTRUCTION OF METALLIC
PISTONS."
Sealed the 23rd March 1858, and dated the 8th October 1857.
PROVISIONAL SPECIFICATION left by the said Thomas Forsyth at the
Office of the Commissioners of Patents, with his Petition, on the 8th
October 1857.
I, THOMAS FORSYTH, of the City of Manchester, Engineer, do hereby declare
the nature of the said Invention for "IMPROVEMENTS IN THE CONSTRUCTION OF
METALLIC PISTONS," to be as follows:-
The nature of my Invention consists in casting, forging, or otherwise
attaching to the body or block of the piston a projection which answers the
purpose of the separate stop piece hitherto employed to close the joint of the
packing or wearing ring.
The packing or wearing ring of my improved piston is made with an
internal groove fitting on the circumference of the body or block, and it is
opened to pass on on each side of the fixed projection, and in resuming its form
encloses the said projecting piece in recesses formed in the ring for that

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Forsyth in the Great Seal Patent Office on the
7th April 1858.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
FORSYTH, of the City of Manchester, Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eighth day of October, in the year of our Lord
One thousand eight hundred and fifty-seven, in the twenty-first year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Thomas Forsyth, Her special licence that I, the said Thomas
Forsyth, my executors, administrators, and assigns, or such others as
I, the said Thomas Forsyth, 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 THE CONSTRUCTION OF METALLIC PISTONS,"
upon the condition (amongst others) that I, the said Thomas Forsyth, 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 Thomas Forsyth, do hereby declare
the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement (that is to say) :-
:-
The nature of my Invention consists in casting, forging, or otherwise
attaching to the body or block of the piston a projection which answers the
purpose of the separate stop piece hitherto employed to close the joint of the
packing or wearing ring; as described in the Specification of Letters Patent
granted to me on the Fifth day of January, One thousand eight hundred and

page_text: fifty-seven; and in order that my Invention may be fully understood and
readily carried into effect, I will proceed to describe the accompanying Sheet
of Drawings, reference being had to the figures and letters marked thereon.
Figure 1 is a front view of a piston, constructed according to my present
improvements, which are particularly beneficial when applied to locomotive or
other steam engines having horizontal cylinders. Figure 2 is a transverse
section; and Figure 3 a side view of the same; a is part of the piston rod;
b, the body or block, which is here shewn as screwed to the piston rod, but
which may be forged therewith or otherwise attached thereto; the body or
block is furnished with a projection c, which answers the purpose of the
separate stop piece described in the Specification of the Letters Patent above
referred to, to close the joint of the packing or wearing ring d, and also to
prevent the ring turning on the body or block; this stop piece should be at
the lower part of the piston to insure its contact with the cylinder; the ring d
is made with an internal groove fitting on the circumference of the body or
block b. In making these packing or wearing rings, I prefer to adopt the
process described in the Specification above referred to, with this exception,
that I find it more beneficial to turn them of rather larger diameters than the
cylinders in which they are to work, to increase their elasticity and facilitate
the putting together of the parts; a portion of the ring is then cut away, and
the proper recesses are cut in the ring to fit the projection c, as shewn best in
Figure 3. When the packing or wearing ring d is to be put on the body or
block b, it is sprung open to pass on each side of the projection c, and when on,
the elasticity of the ring permits it to resume its circular form, thereby
bringing the recesses on each side of the projection c, and the circular groove
on to the circumference of the body or block b; it is desirable to leave a little
space between the ring d and the body or block b, as shewn in Figure 2, to
allow for the irregularities in the diameters of the cylinders in which the piston
works.
Figure 4 represents part of a piston constructed according to a modification
of my Invention; in this instance two packing rings d, d, are employed, and
the body or block 6 is furnished with two projecting flanges 61, 61, on which
the rings d, d, fit, as described in reference to the preceding Figures.
The object of my Invention is to reduce the cost, weight, number of parts
and consequent liability' to derangement of metallic pistons.
Having thus stated the nature of my Invention, and described the manner
of performing the same, I wish it to be understood that I do not limit
myself to the details herein set forth; but what I claim is casting, forging, or

page_text: otherwise attaching a projection to the body or block of a piston for the
purposes described.
In witness whereof, I, the said Thomas Forsyth, have hereunto set
my hand and seal, this Sixth day of April, in the year of our Lord
One thousand eight hundred and fifty-eight.
THOMAS FORSYTH. (L.S.)