Improvements in Piston Slide Valves and their Packings.
Year: 1898

page_text: Date of Application, 22nd Apr., 1898-Accepted, 28th May, 1898
COMPLETE SPECIFICATION.
Improvements in Piston Slide Valves and their Packings.
I, WALTER PAYTON, of No. 138, Sheen Road, Richmond, in the County of Surrey,
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 relates to certain modifications of parts of the piston valve
described in my Specification No. 14082 of 1896, as I shall describe with reference
to the accompanying drawings.
Figure 1 is a sectional plan of the piston on the line 1, 1 of Fig. 3. Figure 1A
is a sectional plan on the line 1* 1ª, Fig. 3; Figure 2 is a plan of the exhaust side
with part broken away to show the spring tongue K. Figure 2A is a part
plan and part section on the line 2" 2, Fig. 3, of the steam side; Figure 3
is a section on the line 3, 3 of Figure 1; Figure 4 is a section on the line 4, 4
of Figures 1 and 2; Figure 5 is an elevation looking at the left side of
Figures 1, 1 and 2, 24.
Figure 6 are internal and external elevations of the packing segments C.
Figure 7 are similar views of the packing segments D.
Figure 8 shows a front view, a longitudinal section, and a back view of one of the
spring tongues K which cover the meetings of the packing segments.
A is the cylinder in which the piston valve reciprocates, the ports through
which the working fluid passes.
B is the body of the valve, which on the one side H is subject to the high
pressure of the working fluid, and on the other side L is subject to the lower
pressure of the exhaust.
The body of the piston is made circular and has two flanges 6 and b¹ between
which is held the packing ring hereinafter described.
The flanges bb are somewhat less in diameter that the cylinder A and their
outer edges are chamfered off to allow the working fluid to have easy access to the
ports a.
The packing is formed as a ring of equal diameter with the cylinder A, and it is
provided with a flange at one of its ends and short projections at its other end. It
is fitted so as to move freely between the flanges b 6' and when in position its flanged
end is towards the exhaust side L.
The packing ring is divided into the two larger and two smaller segments C, D,
by lines parallel to one another in plan as shewn by Figs. 1 and 1^, but in elevation
the divisions are made oblique as illustrated by Fig. 5, and the bridges between the
ports are so arranged that the divisions of the segments lie about the
middle of the bridges. Each of the segments is provided at its middle with
a rib e made hollow at e¹ to contain a helical spring and projecting a short

page_text: distance beyond its high pressure end so as to form when the segments are in place
the narrow spaces c¹ between the segments and the inner side of the flange b,
through these spaces the high pressure fluid has access to the space between the
flanges b b¹.
The flanged ends of the segments are formed with shallow depressions as shewn
by dotted lines on Fig. 1 so as to provide between them and the inner side of the
flange b¹ narrow spaces c² into which the exhaust fluid has access from the exhaust
side L.
The escape of high pressure fluid through the spaces where the segments meet
each other is prevented by the sliding tongues K fitted to move freely within the
sockets 62 which are made as part of the piston body B. In order that the tongues K
may be easily and accurately made the inner sides of the flanges b¹ are cast
with lumps corresponding with the sockets b² so that entire holes can be bored in
the lumps.
The tongues are then turned cylindrically so as to be a working fit in the holes
and are secured in their places by temporary set screws.
In this condition the space between the flanges b b¹ and the circumference of
the piston body are turned to their proper dimensions and when this is completed,
the tongues K are accurately shaped for covering the spaces between the
segments.
The tongues K are recessed in the manner shewn at k¹ Fig. 8, to receive helical
springs, which press them outwards against the cylinder A, and the shoulders k²
are provided with adjusting screws k³, to prevent the tongues from moving too far
out.
The upper part of the outer ends of the tongues is inclined at to prevent the
piston from being locked in the cylinder A should the tongues by accident get into
its ports. Should this at any time occur the inclines enable the piston to be released,
by drawing it into its middle position and then turning it till the tongues coincide
with the bridges between the cylinder ports.
The segments CD are prevented from turning within the piston, or moving too
far out of it, by the adjusting screws e² engaging in slots e³ formed in ribs e of the
segments.
The inner ends of the slots are inclined at e to enable the segments to move more
or less out of the piston when the screws e² are turned. The heads of the screws
are placed inside the flangeb to prevent them from being shaken out of place when
the piston is in motion and by turning the screws e² entirely out of the slots the
segments may be inserted or withdrawn from the piston without entirely removing
the screws from the flange.
When the segments are in their places in the piston and the side H of the piston
is subject to the high pressure fluid, and the side L to the exhaust fluid, the high
pressure fluid not only presses the segments outwards and keeps them in contact
with the cylinder A, but at the same time it presses the flanged ends of the
segments against the flange b¹ of the piston, with a force the amount of which is
determined by the difference between the pressures of the fluids upon the two
sides of the piston and the areas on which these pressures act.
By making the above described depressions in the flanges of the segments of
sufficient area the force thus obtained can be made to exceed the friction caused by
the movement of the segments over the ports in the cylinder A and to compel the
segments to keep in close and continuous contact with the flange 1 and thereby
preventing side motion of the segments between the flanges and also preventing
escape of working fluid through the piston. To effect this the area of the depression
in the flange of any one segment should be about one half the area of the port over
which the segment has to move. The segments are also pressed outwards by the
helical springs to keep them in contact with the cylinder A as shewn in Figs. 1 and 3
when the working fluid is absent.
Having now particularly described and ascertained the nature of this invention

page_text: and in what manner the same is to be performed, I declare that what I
claim is:-
The construction of a piston slide valve and its packing, substantially as described
with reference to the accompanying drawings.
Dated this 22nd day of April 1898
ABEL & IMRAY,
Agents for the Applicant.