IMPROVEMENTS IN AND RELATING TO SLIDE VALVES FOR STEAM ENGINES
Year: 1883

page_text: LETTERS PATENT to .John Thom of Barrow in Furness in the County of
Lancaster Engineer for an Invention of IMPROVEMENTS IN AND RELATING
TO SLIDE VALVES FOR STEAM ENGINES
PROVISIONAL SPECIFICATION left by the said John Thom at the Office of
the Commissioners of Patents on the 23rd August 1883.
JOHN THOM, of Barrow in Furness, in the County of Lancaster, Engineer.
"IMPROVEMENTS IN AND RELATING TO SLIDE VALVES FOR STEAM ENGINES"
My Invention has for its object to so construct slide valves for steam engines
that I obtain a large opening for the exhaust, with a short travel of valve, and to
provide a means for utilizing the steam from one side of the piston at the end of
the stroke, for use at the other side of the piston.
My Invention consists in constructing a slide valve with all the exhaust ports
(which may be of any desired number so as to reduce the travel) separated from
the steam inlets by the back of the valve, that is to say, so that the steam enters
only from the outside of the valve whilst the inside of the valve is entirely devoted
to the exhaust. For example, a slide valve of the
type may be constructed
as a single ported steam and double ported exhaust slide valve by having two
exhaust openings from the cylinder at each end of the cylinder valve face, which
openings are covered by the valve at the requisite part of the stroke, the end ports
only being used for steam. In like manner I construct a double ported steam and
exhaust slide valve by having three openings from the cylinder at each end of the
cylinder valve face, the inside openings being for exhaust only, the centre openings
being for exhaust and steam and the outside openings being for steam only. In
this case a port is provided in the valve flange at each end so that the steam passes
through such port and also over the end of the valve. In like manner I construct
a double ported steam and treble ported exhaust valve. In this case I provide
four openings at each end of the cylinder valve face, three being available for
exhaust and two being available for steam.

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My Invention further consists in forming a longitudinal passage through the
back of the valve which I use as a passage for steam and to form a communication
between the ends of the cylinder just before exhausting to the condenser so that a
portion of the steam from one side of the piston at teriniual pressure is transferred
from one end of the cylinder to the other and used over again on the return stroke.
For example this valve may partake of the nature of what is known as a
" trick
valve, but I so form the passages that a communication is opened through the
passage of the valve, from one end of the cylinder to the other so that the steam
flows through the passage just before communication to the condenser is opened to
one end of the cylinder, and before new steam is admitted, to the other end of the
cylinder.

page_text: ..
"
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Thom in the Patent Office on the 21st February 1884. .
JOHN THOM, of Barrow-in-Furness in the County of Lancaster, Engineer
IMPROVEMENTS IN AND RELATING TO SLIDE VALVES FOR STEAM ENGINES
My Invention has for its object to so construct, slide valves for steam engines
that I obtain a large opening for the exhaust with a short travel of valve and to
provide a means for utilizing a portion of the steam from one side of the piston
at the end of the stroke for use at the other side of the piston.
My Invention consists in constructing a slide valve with all the exhaust ports
(which may be of any desired number so as to reduce the travel) separated from
the steam inlets by the back of the valve, that is to say, so that the steam enters
only from the outside of the valve, whilst the inside of the valve is entirely
devoted to the exhaust. For example a slide valve of the
type.may be
constructed as a single ported steam and double ported exhaust slide valve by
having two exhaust openings from the cylinder at each end of the cylinder valve
face, which openings are covered by the valve at the requisite part of the stroke,
the end ports only being used for steam. In like manner I construct a double
ported steam and exhaust slide valve by having three openings from the cylinder
at each end of the cylinder valve face, the inside openings being for exhaust only,"
the centre openings being for exhaust and steam and the outside openings being
for steam only. In this case a port is provided in the valve flange at each end, so
that the steam passes through such port and also over the end of the valve.
In'
like manner I construct a double ported steam and treble ported exhaust valve?
In this case I provide four openings at each end of the cylinder valve face, three
being available for exhaust and two being available for steam.
My Invention further consists in forming a longitudinal passage through the
back of the valve, the said passage being so arranged as to form a communication
between the ends of the cylinder, so that a portion of the steam from one side of
the piston at terminal pressure is transferred from one end of the cylinder to the
other and used over again on the return stroke. For example this valve may
partake of the nature of what is known as a "Trick" valve, but I so form the
passages that a communication is opened through the passage of the valve from one
end of the cylinder to the other, so that the steam flows through the passage just
before communication to the condenser is opened to one end of the cylinder, and
before new steam is admitted to the other end of the cylinder.
The beforegoing being the nature, object and purposes of my Invention, I will
now proceed to describe more in detail how the same may be carried out into
practical effect, and for that purpose I have hereunto attached two sheets of
Drawings illustrative of my Invention, which are marked with letters and figures
of reference corresponding with those used in the following description, like letters
and figures being used to denote the same, or corresponding parts throughout the
various views.
In the Drawings.
Figures 1. 2. 3. 4. 5. 6. 7 and 8 are sectional elevations of a single ported steam
and double ported exhaust slide valve and valve face also showing the means which
I employ for conveying and utilizing the steam from one side of the piston to the
other. These figures show the position of the slide valve in relation to the piston.
Upon reference to these figures A is the slide valve. B the cylinder valve face;
Ca portion of the cylinder. D is a portion of the piston.-The arrow E shows the
direction of the pistons travel, a.are the exhaust ports of the valve A. separated

page_text: from the steam inlets at the back of the valve A, that is to say the steam enters
only from outside of the valve A, whilst the inside is entirely devoted to the
exhaust. a' is a passage through the back of the valve similar to the passago in
what is known as the "Trick" valve, but the ports a² a³ of the passage a¹ are so
arranged in reference to the ports of the cylinder valve face that the passage al
serves to supply steam to the cylinder in similar manner to a "Trick" valve and
also to form a communication between the opposite ends of the cylinder C so that
a portion of the steam from one side of the piston nt terminal pressure is transferred
from one end of the cylinder to the other and used over again on the return stroke.
bbb are the ports in the cylinder valve face, the ports b serving for both steam
and exhaust and the ports bi serving for exhaust only, the port 6" being the main
exhaust.
The working of the valve will be understood upon reference to Figures 1 to 8
inclusive, in which Figure 1 shows the valve at the " top lead" steam being
supplied in the direction shown by the arrows from the outside of the valve A and
through the passage a similar to a "Trick" valve. Figure 2 shows the valvo with
greatest steam opening. Figure 3 shows the steam cut off. Figure 4 shows the
point at which communication opens between the ends of the cylinder C so that
the steam passes through the port a passage al and port a³ to the other end of the
cylinder. Figure 5 shows the communication full open between the ends of the
cylinder C. Figure 6 shows the commencement of compression of the steam which
has passed from one end of the cylinder to the other end of the cylinder. Figure 7
shows the point at which the exhaust opens. Figure-8 shows the valve at the
bottom "lead."
Figure 9 shows a slide valve for a single ported cylinder with "Trick"
arrangement and having negative lap on inside edge of the passage a¹ forming
communication between the ends of the cylinder C. Figuro 10 shows a slide valve.
for a double ported cylinder with "Trick" arrangement and having negative lap
on inside edge of the passage a¹ forming communication between the ends of the
cylinder C.
Figure 11 shows a slide valve for a double ported cylinder with bars over the
exhaust ports and having about "nore positive lap than the exhaust edges of
the steam ports have of negative lap. This Figure shows how communication
between the ends of the cylinder C can be arranged by putting bars at on tho
exhaust passage of the valve and a bar 63 on the exhaust passage b' with a little
more positive lap than there is negativo exhaust lap on the steam ports. This
arrangement lengthens the valve to a certain extent, but at the same time it
increases the area of communication between the ends of the cylinder three fold,
which is advantageous in quick running engines.
"
Figuro 12 shows a slide valve constructed without the "Trick" passage a' and
illustrates how communication between the ends of the cylinder can be applied to
an ordinary slide valve by having bars at over the exhaust ports with about more
positive-lap than the steam ports have negative exhaust lap. This arrangement can
be applied to single, double, or treble ported cylinders.
Figure 13. shows my Invention as applied to an ordinary double ported slido
valve with the "Trick" passage also arranged as to have negative lap on the
insido edges of the ports a² 3. The outside edges of the exhaust ports a.are made.
with a little larger positive lap so as to prevent the steam from passing from the
ports a³ or a direct to the exhaust a
On reference to the beforegoing description it will be seen that a valve according
to my Invention contains the "Trick"" arrangement applied to a valve having
positive exhaust lap at the top and bottom of the cylinder on the port edges in
connection with tlie condenser and negative exhaust lap between the top and bottom
of cylinder on the passago through the valve; contained in one valve thereby
forming a communication between the ends of the cylinder just before exhausting
to the condenser, so that steam at terminal pressure is transferred from one side of
the piston to the other, then compressed nearly up, to initial pressure and used.

page_text: over again on the return stroke: it can be arranged to suit single, double and
treble ported cylinders.
A valve constructed according to my Invention saves in each revolution of the
crank an amount of steam at terminal pressure equivalent to the capacity of the
ports and clearance between the ends of the cylinder and piston which in many
cases is fully 15 per cent of the total capacity of the cylinder.
As there is little to compress in the low pressure cylinder with the ordinary slide
valve, if the vacuum is good and the ports large enough, the work stored in the
piston and other parts moving vertically is thrown away against the steam
admitted by the lead; but in this arrangement the steam is taken from the other
end of the cylinder after performing its ordinary work and is compressed nearly,
or quite up to initial pressure using the work stored in the piston and other moving
parts, for this purpose so that there is no loss of power from changing the direction
of the motion of the piston and a greater number of revolutions can be got out of
the engines with the same I H P.
The change of pressure from the one side of the piston to the other side being
divided into four stages
a release by communication.opening
6 compressing steam transferred.
c exhaust opens to condenser.
d initial steam enters, causes the engines to turn the centres without shock even
though the brasses are slack.
The friction of the valve is reduced to a great extent through. one port being
always exposed to the pressure in the cylinder, thus tending to reduce the pressure
on valve face
Having now described the nature object and purposes of my Invention and
shown how the same may be carried into practical effect, what I claim is
First Constructing and arranging slide valves for steam engines as herein
described, whereby I obtain a large opening for the exhaust with a short travel of
valve substantially as set forth and shown in the Drawings hereto annexed..
Second The mode substantially herein described of conveying steam from one
side of the piston of the cylinder, for re use at the other side of the piston, which
mode consists of leading the steam through the slide valve by arranging the ports,
so that a communication is opened between the ends of the cylinder at the end of
the stroke substantially as herein described and shown in the Drawings hereto
annexed.
Third Constructing and arranging slide valves of the "Trick" type so that the
inside edges of the ports of the Trick " passage have a negative lap, and thereby
effecting a communication between the ends of the cylinder at the end of the
stroke of the piston substantially as herein described for the purposes set forth and
as shown in the Drawings here to annexed.
In Witness whereof, I, the said John Thom have hereunto set my hand and seal
this Fifteenth day of February, in the year of our Lord one thousand eight
hundred and eighty four.