Improvements in Piston Valves and Ports for Steam Engines.
Year: 1887

page_text: Date of Application, 16th Aug., 1887
Specification Accepted, 21st Oct., 1887
Improvements in Piston Valves and Ports for Steam Engines.
I, CHARLES TALBOT PORTER, of No. 51 W. 37th Street, New York City, County of
New York, in the State of New York, United States of America, 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 improvement relates to that form of steam engine valve which is known as the
hollow piston valve. This valve has heretofore usually been made as a single hollow
casting, closed at the ends and with an opening or openings in the middle of its
length for the passage of steam from the steam pipe or to the exhaust pipe according
as it is arranged in this respect, and with openings near each end for the passage
through it of steam either to or from the ports of the engine. It is important that
the end openings be opposite the cylinder ports, requiring the valve to be nearly as
long as the cylinder. It is not practicable under ordinary conditions to employ
packing. The valve must closely fill the long seat.
The seat is liable to slight distortion of its form by curving through unequal
expansion, especially while the engine is being warmed up in starting, due to the
unequal heating of its opposite sides. This distortion tends to cause a seizure of the
valve requiring the exertion of much force to overcome it, while the friction abrades
the surfaces, and may involve the breaking of a valve connection or some other
important part, and the crippling of the engine. Such liability to seizure increases
with each increase in the length of the cylinder.
I have discovered means of avoiding this difficulty while still enjoying all the
advantages of the piston-valve and retaining substantially the present length of
bearing so as to maintain the tightness.
I will use the term "diaphragm" to denote the web of metal extending across
the valve near each outer end. I divide the present long hollow piston-valve into
two separate valves omitting the middle portion by which the ends have heretofore
been commonly united, and connecting these instead by a central stem extending
the whole length and attached to the diaphragm of each valve in the following
manner:
The stem is provided with collars on opposite sides of the diaphragms, one of which

page_text: forms with each diaphragm a steam-tight joint, yet allowing liberty for the slight
changes of alignment required.
The pressure of the steam either within or without the valves forces each valve
firmly against one or the other of these collars. In this manner, while the pressure is
on, the position of each valve is determined, the line of draft is made truly central,
lost time or lost motion, or reversal of the movement is impossible, and a close fit
being made leakage around the stem is prevented. The corresponding collar on the
opposite side of the diaphragm is nearly in contact with it, and thus prevents the
valve from getting much out of place when the steam pressure has been shut off and
the engine is coming to rest, or even if conditions obtain which induco a momentary 1
reversal of the pressure.
"
The pressure of steam on the two valves being in opposite directions and on equal
areas is always in equilibrium, and the valves move together precisely as they would
do if they were united in one casting.
I have also devised an improved form of the ports by which the steam is caused to
flow more easily and rapidly to and from the piston valves.
The accompanying drawings form a part of this specification and represent what I
consider the best means of carrying out the invention.
Figure 1 is a longitudinal section through a cylinder and valve chest.
Fig. 2 is an end view of the same.
Fig. 3 is on a larger scale, and is a longitudinal section through the lower end of
the valve-stem, showing the plug screwed up firmly to the end of the stem, and the
adjacent portion of a valve.
Fig. 4 is also on a larger scale, and is a cross-section through a portion.
The remaining figures show a modification.
Fig. 5 is a longitudinal section, and
Fig. 6 is a cross-section on the line x x in fig. 5.
Similar letters of reference indicate corresponding parts in all the figures where
they occur.
A A represent the two valves. The vacant space, b, between these valves
corresponds in function to the ordinary apertures at this point, for the admission or
discharge, through a suitable passage provided in the cylinder casting, of the steam
passing through the valves to or from the cylinder.
Referring to figures 1 to 4 inclusive, the openings c c communicate with the ports
of the cylinder, when the motion of the valve brings them into the required positions.
the same as the corresponding openings in an ordinary hollow piston-valve.
The form of the port m immediately exterior to each valve A, is shown in dotted
lines in figure 2, and will be described further on.
The opening through the centre of each diaphragm, a, for the valve-stem is made
large, so that in preparing the mould for the valve the parts of the core on opposite
sides of the diaphragm a may be properly united through it.
E is the valve stem, made hollow so as to combine stiffness with lightness and
also without unnecessary weight to fill the large openings. The interiors of the ends
are threaded to receive the screw-plugs F, F, one of which is prolonged to constitute
part of the valve-stem, by which the valve receives motion from valve-gear, not
shown. The heads of these plugs form the collars outside of the diaphragms a a.
Each collar has a spherical face f. Those plugs are screwed up firmly against the
ends of the stem E. Each diaphragmn a is finished with a spherical concave matching
to f. The surfaces of each being nicely finished, a steam-tight contact of the metals is
obtained.
Collars E¹ E are formed on the hollow valve-stem E at or near each end, which
constitute the collars to lie inside of and nearly touching the diaphragms.
The construction while insuring a strong and reliable connection of the parts
allows all the freedom which is ever required for the slight obliquity of position of
the valves A A.
The strong pressure of the steam from within holds the valves A A outward in
steam tight contact with the spherical surfaces f of the collars of the respective plugs F.

page_text: The joint is steam tight, and the other collar E' is in position to hold the valve against
misplacement whenever the engine shall make one or more revolutions with the steam
shut off.
The invention is of service in allowing this desirable style of valve to serve reliably
with light connections and consequently with but little inertia, which is an important
point in quick engines.
This kind of valve works theoretically without resistance. My invention aids to
make it approximate such condition practically. As heretofore made there is always
a more or less serious binding of the surfaces approximating a seizure of the valve
at each starting.
A' A' are thin ribs cast in one with the valves A A, and bridging across the
passage or port e, which latter may be nicely finished by turning in a lathe. The
ribs A are sharpened on their edges so that the steam finds a free passage past them
outward and inward, and the whole area of the passage is available.
These ribs form a strong and absolutely rigid connection between the parts of the
valve on the two sides of the passage c. The "lead and lap" may be determined with
the same absolute accuracy as with other forms of valves.
These ribs perform also an important function in taking hold of and stiffening the
diaphragms a, which in large valves present considerable area, and are subjected to
great strain.
In the modification shown in figures 5 and 6 the portions corresponding to the
valves A A, are short and are without openings c, through them, the steam being
admitted to the cylinder of the engine past one edge and discharged from the cylinder
past the other edge of the valve. The same screw plugs, F F, are employed as in the
other form, and the spherical faces, f, make the same steam-tight joint with the
diaphragms of the valves.
Fig. 6 shows more clearly than the dotted lines in fig. 2, a feature to which I attach
importance and which I propose to use in any and all modifications. This is the form
of the ports which convey the steam from the valves A to the main cylinder, or in the
reverse direction from the main cylinder to the valves. It is usual to make these
ports nearly concentric to the valve-chest, thus presenting the inner surfaces, so as
to reflect the steam backward upon itself and greatly retard its flow. The steam
issuing into the port radially all around, it follows that at the back it issues in a
direction opposite to that in which it must go to reach the cylinder. If, as usual, the
back of the port is a surface concentric with the valve or nearly so, the steam is
reflected straight back where it came from. The port is thus choked so that
considerable of this part of a piston-valve is of but little use for admission of the
steam. The form shown, on the contrary, causes the steam to be reflected so as not to
choke the issuing steam in the least.
This reflection is shown at three points, 1, 2, 3.
The angle of reflection is equal to the angle of incidence. The line of incidence is
the radial line. The line of reflection is determined in this way. The angle included
between these two lines is bisected by a line perpendicular to the surface at that
point.
This form of the ports adds materially to the efficiency of the piston valves.
Further modifications may be made in the forms and proportions. I can make the
valves longer, taking care that there be sufficient space between them to allow the
steam to move out or in as the case may be. I can make the bearing surfaces and
the adjacent concaves in the diaphragms parts of larger or smaller spheres. I can
leave more or less space between the collars. It is sufficient that there shall be a
little play, or rather that it shall be an easy bearing.
The engine may be so arranged that the valve shall receive the steam from outside
and exhaust from inside of the hollow piston valve. The pressure of the steam in
such case urges the valves A, A, inward into steam-tight contact with the collars E¹.
The valve-stem may be made solid. As shown the parts are adapted to receive the
strong steam between the valves and to discharge the exhaust-steam from the end-
spaces through any suitable passages leading therefrom, not shown. If the engine is

page_text: organized to work under the opposite condition, that is to say, with the strong steam
on the ends of the valve and the exhaust steam between, it will follow that the valves
will be forced together instead of apart. In such case the spherical bearing will be
formed on the outer faces of the collars E', and the corresponding concaves in the
diaphragms will be made on the inner faces.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed, I declare that what I claim is :-
:-
1. In an engine having a cylindrical valve-seat, the two piston-valves A, A, serving
for the admission and release of the steam at the corresponding ends of the cylinder,
in combination with a central stem, and means as the collars E, F, f, for attaching
the valves thereto, compelling them to move together, but allowing them to assume
slightly oblique positions while maintaining a steam-tight connection with the stem,
substantially as herein specified.
2. In an engine having a piston valve or valves, and a corresponding cylindrical
valve seat, the ports m formed as shown so as to present deflecting surfaces aiding
the free movement of the steam between the valve chest and the cylinder, as herein
specified.