Improvements in or relating to Piston Packing.
Year: 1899

page_text: Date of Application, 14th Nov., 1899-Accepted, 16th Dec., 1899
COMPLETE SPECIFICATION.
Improvements in or relating to Piston Packing.
I, ARNOLD GOODWIN, of 56, Sumner Street, Southwark, in the County of
London, 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:-
Engine, pump and other pistons have heretofore usually been provided with
split packing rings that are at all times forced outward into close contact with the
inner surface of the cylinder in which they work by imparting to them an initial
spring action produced (a) by turning each ring to a larger diameter than the
internal diameter of the cylinder in which it is to work, then cutting a segment
out of it, compressing the cut ring to bring its ends together, and then returning
it to the exact bore of the cylinder thus imparting to it what is generally known
as an initial spring, or (b) by first turuing each ring to the same diameter as the
bore of the cylinder and then imparting an initial expanding force to it by the
aid of internal springs or spring rings; or both of these means of expansion may
be used, the said piston rings being subjected to an additional expanding force
when in use by reason of the pressure on their inner surfaces of the steam or other
fluid under pressure the escape of which past the piston the rings are designed to
prevent. It will be seen that with these arrangements, which it would seem
are designed to prevent any tendency of the rings to be compressed onto the
piston body, the fluid tight joint between the piston and cylinder is produced
mainly if not wholly by direct outward radial pressure of the packing ring
against the inner surface of the cylinder, this pressure acting at all times and
whether there is any tendency of fluid under pressure to escape between the
piston and cylinder or not. The above mentioned mode of packing a piston is
open to the serious practical disadvantage that great friction is produced between
the piston rings and cylinder wall when the piston is in motion whereby con-
siderable loss of power takes place and the cylinder is subjected to rapid wear,
the cylinder being often so worn as to assume in some cases a bell-mouthed shape,
that is to say, larger in diameter at each end than at the central portion, and
in other cases a bellied"
or barrel shaped, that is to say larger in diameter at
the central portion than at the ends.
"
Furthermore it has been a common practice to secure the piston rings to the
piston body in such a way that they could not rotate, the result being that owing
to the non-rotatability of the rings, to the unequal initial expansive force put
upon them, and also to the rings being of a slightly oval or other non-circular
shape when in place on a piston, the rings have become scored and have caused
rapid and very unequal wear of the cylinder, necessitating either costly repairs, or
loss in the efficiency of the engine or other apparatus of which the piston forms
part.
Now this invention has reference to an improved construction and arrangement
of piston packing whereby the above mentioned evils are obviated and a fluid

page_text: tight joint of great durability and efficiency is obtained with a very much smaller
friction than has heretofore been usual.
According thereto instead of producing a fluid tight joint between the piston and
cylinder mainly or wholly by direct outward radial pressure of the packing ring
against the cylinder wall brought about by the combined initial spring action of
the ring and the action of steam or other fluid under pressure on the inner
surface of the ring, such a joint is produced mainly or wholly by the steam or
other fluid under pressure which expands the ring outward into close but light
contact with the wall of the cylinder when the piston body and cylinder fit each
other, and also tends to force the packing ring endways in a longitudinal direction
between the piston body and cylinder wall when there is sufficient wear between
the piston body and cylinder wall to set up an unbalanced endways pressure on
the ring, scoring of the ring and unequal wear of the cylinder being presented
by leaving the ring free to rotate and adjust itself on the piston body. For this
purpose the piston rings are constructed and arranged as I shall now describe
with reference to the accompanying illustrative drawings wherein Fig. 1 shows
a packing ring according to this invention in end view. Fig. 2 is a cross section
of the ring on the line AA of Fig. 1. Fig. 3 is a face view of part of the ring
with a tongue plate, and Fig. 4 is a section thereof on the line BB of Fig. 3.
Figs. 5, 6, 7 and 8 show partly in side elevation and, partly in longitudinal
section, various forms of pistons fitted with rings according to this invention.
The several figures are drawn to different scales.
The piston ring 1 is slit at 2, the opening between the adjacent ends of the
ring being closed by a flat plate or tongue piece 3 that is fixed in a recess 4 in
one end of the split ring and slides in a recess 4* in the other end thereof. The
ring is turned to a slightly larger diameter than the bore of the cylinder and
then has a short length or segment cut therefrom and is then ready for use, the
slight increase of diameter being provided merely for the purpose of overcoming
the mechanical defects due to machining the cylinder and ring. After being in
use for a time, the ring and cylinder will become so worn that the former will
be of less diameter than the cylinder and will require the expenditure of force
to expand it to the wall of the cylinder. By the construction described it will be
seen that the ring when not subjected to the action of fluid pressure will excrt
very little initial spring pressure against the cylinder wall, when new, and no
pressure at all after being in use for some time. Furthermore the ring is made
of such a light and delicate section that when fluid pressure is applied thereto, it will
open out and be expanded truly all-round to the wall of the cylinder. The section
of ring which I adopt for this purpose is shown in Fig. 2 which provides a large
outer peripheral wearing surface 1, a smaller inner peripheral surface 1b, B
flat annular surface 1° at one side of the ring, and at the other side an annular
surface the inner portion 1d of which is flat and parallel to the side 1º, the inter-
mediate portion 1° of which is of hollow conical or bevelled shape, and the outer
portion 1 of which is narrow and parallel to the side 1°. The ring thus con-
structed is so applied to a piston 5 having a circumferential groove 6 therein that
the inner parallel portion of the ring comprised between the surfaces 1b, 1, 1ª
fits into the circumferential groove 6 after the manner of a piston; that the flat
side 1º bears against a flat annular surface 5° on the piston body 5; and that the
conical or bevel surface 1 and flat surfaces 14 and 1 face to one end of the
cylinder so as to be subjected to the pressure of fluid within that end of the
cylinder, the outer circumferential surface 1" of the ring being flush or nearly 'so
with the outer circumferential surface of the portion 5b of the piston. For a
double acting piston two packing rings of the kind described are used, the conical
or bevel surface on the two rings facing in opposite directions. In the case of a
solid or hollow piston 5 (see Figs. 5 and 6) the two packing rings are sprung over
the ends of the piston which, to enable this to be easily done and to expose the
surfaces 1 and 1' to fluid pressure, are reduced in diameter as shown at 5º. In
Fig. 7, the two packing rings † are fitted in a similar manner to a
ring 7 held

page_text: in an annular groove 8 formed by and between the flanged body part of the
piston 5 and a flanged plate 9 suitably secured to the piston body. In the case
of single acting pistons, a single packing of the kind described is used. Fig. 8
shows one such ring applied to an air pump piston 5 fitted with lift valves 10,
the packing ring 1 being fitted into a groove 6 formed by and between the body
of the piston and a junk ring 11. Each ring when thus placed on a piston and
before it is inserted in a cylinder, is of a truly circular shape whereas an ordinary
packing having initial pressure is, under like conditions, of an oval or non-
circular shape.
Packing rings constructed and applied to pistons according to this invention
and as herein before described, exert little or no pressure against the wall of a
cylinder containing the piston, when the latter is at rest, or also when running
free, that is to say, not under pressure.
In each case the improved packing ring, or each such ring, is left loose or free
in a circumferential direction so that it can rotate around the piston and adjust
itself to the cylinder. This is a point of considerable practical importance as it
ensures that the ring, and the cylinder in which it works, shall wear evenly,
whilst should the ring be used in a cylinder that has become worn to a non-
circular shape by the use of ordinary spring pressed packing rings, it will
gradually wear the inner surface of the cylinder to a circular section whereupon it.
practically ceases to wear the cylinder, the said ring, whilst wearing the cylinder
to a circular section, being not appreciably worn itself.
When a piston fitted with a packing ring constructed and arranged as
described is at one end of its stroke within a cylinder ready to receive fluid under
pressure, it will, as herein before stated, exert little or no initial pressure against
the cylinder wall. When, however, steam or other fluid under pressure (herein-
after referred to as steam) is admitted to the said end of the cylinder, it will
immediately act against the conical or bevel surface of the ring facing that end of
the cylinder and will slightly expand the ring evenly all round into close but
light contact with the cylinder wall, after which some of the steam will enter
the circumferential groove 6 in the piston body and by acting against the inner
surface 1ª of the part of the ring fitting the said groove, will act to maintain the
ring in close contact with the cylinder wall while the piston is travelling. the
steam acting to maintain the ring in its expanded condition against the resistance
naturally offered by the ring to such expansion. Thus it will be understood that
the ring is merely pressed against the cylinder wall by the steam pressure alone,
or by the difference between the outward pressure due to the action of the steam
on the ring and the resistance to expansion offered by the ring, and which
difference can be made as small as desired consistent with keeping the ring in
close contact with the cylinder wall, so that the friction between the ring and
evlinder can be made correspondingly small. When by wear of the body of the
piston, or of the inner surface of the cylinder, or both, the former does not fit
the latter, rart of the endways pressure on the piston ring will be unbalanced
by the body of the piston with the result that the resultant pressure of the radial
and endways pressures on the ring will act in a direction inclined to the axis of
the cylinder and tend to force the ring between the piston and cylinder and so
exert an additional expanding force evenly all round the ring but such additional
force acts against the resistance offered by the ring to additional expansion. Thus a
fluid tight joint with very little friction will still be maintained between the
piston and cylinder wall, under the altered relative conditions, as regards wear, of
the piston and cylinder.
Piston rings constructed and operating in the manner described enable many
important practical advantages to be obtained. Whilst producing an efficient
fluid tight joint between the piston body and cylinder. they do not cause undue
friction between themselves and the cylinder whereby the loss of power and the
rapid and uneven wear of the rings and cylinder that obtain with the ordinary
packing arrangements are very considerably reduced, and the small wear that

page_text: does take place is distributed evenly over the rings and cylinder which are con-
sequently maintained of a circular shape. The reduction of friction also enables
a large reduction in the consumption of cylinder lubricant to be effected.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is :-
1. A piston packing ring constructed substantially as hereinbefore described
with reference to Figs. 1 to 4 inclusive of the drawings annexed for the purposes
specified.
2. A piston having a rotary packing ring constructed arranged and operating
substantially as herein before described with reference to the drawings annexed.
3. The improved combined pistons and packing rings hereinbefore described
with reference to and shown in Fig. 5; in Fig. 6; in Fig. 7; and in Fig. 8 of the
Dated this 14th day of November 1899.
For the Applicant,
W. LLOYD WISE.
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.