An Improved Piston for Steam Engines.
Year: 1890

page_text: Date of Application, 11th Oct., 1890
Complete Specification Left, 3rd Dec., 1890-Accepted, 3rd Jan., 1891
PROVISIONAL SPECIFICATION.
An Improved Piston for Steam Engines.
1, GEORGE TWIGDEN, of 34 Mount Stuart Square. Cardiff, in the County of
Glamorgan, Consulting Engineer, do hereby declare the nature of this invention
to be as follows:-
:-
This invention consists in an improved piston in which is fitted a packing ring
having flanges at top and bottom so arranged that when the piston is applied to a
cylinder the peripheries of the flanges only bear against the cylinder wall, and the space
intervening between the top and bottom flanges constitutes a recess extending all
round the piston and closed outside by the wall of the cylinder. In the body of
the packing ring, at suitable distances apart, are apertures which afford a means of
communication between the hollow part of the interior of the piston and the recess
aforesaid. The junk ring or end disc of the piston does not bear on the packing
ring and hence a space is provided all round the piston whereby steam has access to
to the interior. The steam thus admitted acts both on the internal face of the
packing ring, tending to expand it, and on the external face, tending to contract
the ring.
The area of the internal face is sufficiently in excess of that of the
external face as to maintain the piston steam tight without causing undue friction
between the peripheries of the flanges of the packing ring and the wall of the
cylinder..
The packing ring is split and is closed at the split or division by a tongue-
piece or key in the usual way.
Date: 10
NICHOLAS WATTS,
Bristol Bank Buildings, Bristol, Agent.
COMPLETE SPECIFICATION.
An Improved Piston for Steam Engines.
I, GEORGE TWIGDEN. of 34 Mount Stuart Square, Cardiff, in the County of
Glamorgan, Consulting 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:-
This invention, which relates to pistons for steam engines, consists, in applying to
such pistons, and adapting the same to receive, a special packing ring. The said
packing ring, which is split, as usual, is flanged outwards at top and bottom so that
when a piston to which the ring is applied is inserted in the cylinder of an engine the
flanges only of the ring are in contact with the cylinder, and an annular space is
formed extending around the body of the ring and closed above and below by the
flanges. By an aperture or apertures made through the body of the ring communi-
cation is provided from the exterior thereof to the space existing behind it, between it
and the periphery of the piston body or head which the ring surrounds. The ring
has play between the inner faces of the junk ring and the flange of the piston, and
hence steam is free to pass into the space existing, as aforesaid, between the back of
the ring and the periphery of the piston body or head. When the piston is moving ir
one direction the steam passes into the said space below the junk ring. On the reverse
stroke, the steam passes in behind the piston flange. Accordingly, steam pressure is
obtained to act inside the ring and expand it against the interior of the cylinder. To
this pressure is opposed that of the steam which having passed through the aperture or
apertures in the body of the ring acts inwardly thereon and tends to contract it.
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page_text: The area at the back of the ring exposed to steam pressure is sufficiently in excess
of the external area acted upon as to keep the piston steam-tight in the cylinder
without causing undue friction between the exterior of the ring and the wall of the
cylinder.
Referring to the accompanying drawings,
Fig. 1 represents a plan, partially sectional, of a piston arranged and fitted in
accordance with this invention.
Fig. 2 is a part elevation and part section. In this view is shown a portion of a
cylinder.
Fig. 3 is a section of the piston ring.
The piston packing ring a which, as is usual, is split diagonally at a' and provided
thereat with tongue pieces b. is contained between the junk ring c and the flange d of
the piston. The ring a, which has play between the junk ring c and the piston flange d
in the line of the axis of the piston rod e, is flanged at top and bottom.
The flanges bear against the interior of the cylinder wall w, as seen at Fig. 2, and
an annular space f, closed at top and bottom by the flanges. is thus obtained between
the body of the ring and the cylinder. Communication between the space and the
space g existing between the body h of the piston and the internal face or back of the
packing ring a is established by an aperture or apertures in the body of the ring a.
The ring a being free to move axially, as aforesaid, it follows that when the piston is
moving in the direction indicated by the arrow shown on the piston rod e, Fig. 2, the
ring is, by the pressure of the steam behind the piston, kept away from the junk ring
and, consequently, an opening is left all around between the junk ring and the packing
ring, by which opening steam has access to the space g.
Thence by the aperture or apertures in the ring a the steam is admitted to the
space. On the reverse stroke of the piston the ring a is forced against the junk ring
and thereby, an opening for the steam is presented between the ring a an the piston
flange d. Thus it will be seen that the ring a is acted upon at all times by steam
pressure from within and without, the steam in the space g tending to expand
it, and the steam in the space f tending to contract it. The internal area
of the ring a acted upon by the steam within is in excess of the external area acted
upon by the steam without, and the respective areas are regulated by the thickness
of the ring and the depth of the flanges, so that the said ring is kept steam-tight
by the preponderance of the outwardly acting or ring-expanding pressure over the
inward contracting pressure, without causing undue friction between the ring and the
cylinder wall.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is
In a piston for steam engines, a packing ring flanged, outwardly at top and bottom
so that when in place in the cylinder of an engine the flanges only of the packing ring
bear against the cylinder (the body of the ring being kept off by the flanges), the said
packing ring being free to move axially between the junk ring and the piston flange,
thus admitting steam behind the packing ring and, through an aperture or apertures
in the body of the packing ring, to the periphery of the latter, so that the steam
pressure acts both inwardly and outwardly on the packing ring, the area internally of
which is in excess of the area externally, substantially as hereinbefore described with
reference to the accompanying drawings.
Dated this 2nd day of December 1890
NICHOLAS WATTS.
Bristol Bank Buildings, Bristol, Agent.