IMPROVEMENTS IN VALVES FOR STEAM ENGINES
Year: 1875

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane,
in the County of Middlesex, Patent Agent, for the Invention of
"IMPROVEMENTS IN VALVES FOR STEAM ENGINES."-A communication
from abroad by Gustave Arnoux, of Marseilles, France.
Sealed the 4th April 1876, and dated the 15th November 1875.
PROVISIONAL SPECIFICATION left by the said Alexander Melville
Clark at the Office of the Commissioners of Patents, with his
Petition, on the 15th November 1875.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, do hereby declare the nature
of the said Invention for "IMPROVEMENTS IN VALVES FOR STEAM ENGINES,"
to be as follows:-
This Invention relates to improved rotary slide valves having movable
seats, which the Inventor terms distributors. The Invention is applicable
to all kinds of steam engines, and by it an improved steam distribution
and reversing motion are obtained.

page_text: The Invention is illustrated in the accompanying Drawings; Figures
1, 2, 3, 4, 5, and 6, of which show the valve as applied to small engines;
Figures 7, 8, 9, 10, and 11, show its application to large engines.
The improved valve is circular, and in the case of the distribution
valve receives continuous rotary motion from the engine shaft by means
of gearing as shown or otherwise. In the smaller class of engine its
axis is perpendicular to the longitudinal axis of the steam cylinder, as
seen in Figures 1 to 6. It has two ports, the steam port q, r, s, t, which
is made as large as will ever be required, and the exhaust port u, v, x, Y.
The two are separated by the construction of the valve as shown.
The valve rotates upon a circular plate (termed by the Inventor the
distributor) which forms a seat for the valve, and is placed between the
valve and the cylinder as shown. The valve is kept up to the plate
by the pressure of the steam or of springs R, R. This distributor has
two ports m, n, o, p, and m", n", o", p", placed diametrically opposite
cach other, by which the steam is admitted or exhausted according to
the position of the valve ports relatively thereto.
By means of this distributor the engine is reversed in the following
manner: If the distributor be rotated (by means of worm or toothed
gearing, or by a hand lever according to the power of the engine) so
that the port m, n, o, p, occupies the position m³, n², o¹, p¹, indicated in
dotted lines instead of the small angle of lead m, z, t, q, z', p¹, will be
the angle of lead at the opposite edge of the valve steam port, and
thereupon the engine will be reversed or the steam port will be closed
and the engine will be stopped.
The expansion valves are also of circular form, and receive continuous
rotary motion. They are also provided with movable seats called
distributors for reversing their motion, and also for varying the cut off
both when the engine is running forward and backward.
J
The distributor of the main or distribution valve is fast on a shaft,
which is operated by a hand lever outside the valve chest. This shaft
also serves as an axis for the main valve, for the expansion valve and
its distributor. The main valve and the expansion valve both run loose
on said shaft, and are connected together by the boss of the main valve
fitting within that of the expansion valve with a key on the one
received in a longitudinal key way in the other, whereby the valves are

page_text: caused to turn together whilst admitting of their moveing away from
one another, and being pressed against their distributors by the force
of the springs or the pressure of the steam, thereby compensating for
the wear of their surfaces.
For engines of small or moderate size a single slide valve with its
distributor may be employed, having its axis perpendicular to the
longitudinal axis of the steam cylinder as above described.
In this case
the distributing valve makes the same number of revolutions as the
engine; but in large engines it is preferable, in order to avoid using
valves of large size and therefore having great circumferential speed,
to employ two valves with distributors, one for each end of the cylinder,
and making one revolution for every two revolutions of the engine. In
this case the common axis of the slide valves is parallel with the longi-
tudinal axis of the steam cylinder, as shown in Figures 7 to 11, and
each valve has two steam ports diametrically opposite to one another,
which at each half revolution of the valves admit steam to the same end
of the cylinder.
In order to still further reduce the circumferential speed of the valves
they may each have three or four steam ports, and thus make but one
revolution for every three or four revolutions of the engine.
In large engines the shaft on which the main and expansion valves
are mounted has keys or feathers by which the valves are rotated, the
shaft turning loose in the distributors.
The slide valves are free to slide along the shaft, and are held up
against their respective distributors by the pressure of the steam or of
springs so as to compensate for wear.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Fifteenth day of November, in the
year of our Lord One thousand eight hundred and seventy-five, in
the thirty-ninth year of Her reign, did, for Herself, Her heirs and
successors, give and grant unto me, the said Alexander Melville Clark,
Her special license that I, the said Alexander Melville Clark, my
executors, administrators, and assigns, or such others as I, the said
Alexander Melville Clark, my executors, administrators, and assigns,
should at any time agree with, and no others, from time to time
and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within
the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN VALVES
FOR STEAM ENGINES," a communication to me from abroad by Gustave
Arnoux, of Marseilles, France, upon the condition (amongst others)
that I, the said Alexander Melville Clark, my executors or admini-
strators, by an instrument in writing under my, or their, or one of
their hands and seals, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to
be performed, and cause the same to be filed in the Great Seal Patent
Office within six calendar months next and immediately after the
date of the said Letters Patent.
NOW KNOW YE, that I, the said Alexander Melville Clark, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the two accompanying
Sheets of Drawings, and to the letters and figures marked thereon, that
is to say:-
This Invention relates to improved rotary slide valves having movable
seats, which the Inventor terms distributors. The Invention is applicable
to all kinds of steam engines, and by it an improved steam distribution
and reversing motion are obtained.
The Invention is illustrated in the accompanying Drawings, Figures
1, 2, 3, 4, 5, and 6, of which show the valve as applied to small engines,
Figures 7, 8, 9, 10, and 11, show its application to large engines.
The improved slide valve is circular, and receives continuous rotary
motion from the engine shaft by means of gearing, as shown or

page_text: otherwise. In the smaller class of engines the axis of the valve is
perpendicular to the longitudinal axis of the steam cylinder, as seen in
Figures 1 to 6. It has two ports, the steam port q, r, s, t, which is
made as large as will ever be required, and the exhaust port u, v, x, y.
The two ports are separated from one another by the two rims and
the back of the valve as shown.
The valve rotates upon a circular plate (termed by the Inventor the
distributor) which is placed between the valve and the cylinder as
shown. The valve is kept up to the plate by the pressure of the steam
or of springs R, R. The distributor has two ports m, n, o, p, and
m, n, o", p, placed diametrically opposite each other, by which the
steam is admitted or exhausted according to which orifice of the valve
coincides therewith.
By means of this distributor the engine is reversed in the following
manner-When the engine is on a dead point the valve has a certain
angle of lead relatively to the piston, and by the motion of the engine
through the medium of the shaft and gearing from main shaft the steam
port of the valve is gradually opened more and more. Now if the
distributor be rotated by means of worm toothed gear or hand lever
according to the power of the engine, so that the angle of lead when
the engine is on a dead centre instead of being at one edge of the
port is at the opposite one, the engine will necessarily be reversed, since
if it continues to move in the same direction it shuts the steam port
instead of opening it. In other words, if the distributor (Figures
1, 2, 3, 4, 5, 6) be rotated until the port m, n, o, p, occupies the position
m¹, n', o', p', indicated in dotted lines instead of m, z, t, q, 21, p³ will be
the angle of lead at the opposite edge of the steam port of the valve, .
and thereupon the engine will be reversed or the steam port will be
closed and the engine will be arrested.
The expansion valves are also of circular form, and receive con-
tinuous rotary motion from the main valve or its spindle as the case
may be. They are also provided with distributors for reversing their
motion and varying the cut off, both when the engine is running forward
and backward.
In Figures 1 to 6 the distributor of the main or distribution valvo
is fast on a shaft upon which as an axis the main valve runs loose, said
shaft also serving as an axis for the expansion valve and its distributor.

page_text: This shaft is operated by a hand lever outside the valve chest. The hub
of the main valve fits within that of the expansion valve, and the two
arc connected together by a key fixed on the hub of main valve and
received in a longitudinal key way in the hub of the expansion valve
whereby the two valves are made to turn together, yet are free to move
away from one another when pressed against their distributors by the
force of the springs or the pressure of the steam, thereby compensating
for the wear of their surfaces.
For engines of small or moderate size a single valve with its
distributor may be employed, having its axis perpendicular to the
longitudinal axis of the steam cylinder as above described. In this case
the valve makes the same number of revolutions as the engine; but in
large engines it is preferable, in order to avoid using valves of large size
and therefore having great circumferential speed, to employ two valves,
cach with a distributor as above described, onc valve and distributor
for each end of the cylinder, making one revolution for every two
revolutions of the engine. In this case the common axis of the slide
valve is parallel with the longitudinal axis of the steam cylinder, as
shown in Figures 7 to 11, and cach valve has two steam ports
diametrically opposite to one another, which at each half revolution
of the valves admit steam to the same end of the cylinder.
In order to still further reduce the circumferential speed of the valves
they may each have three or four steam ports, and make but one
revolution for every three or four revolutions of the engine.
In large engines the shaft on which the main and expansion valves
are mounted has keys or feathers fixed on it by which the valves are
rotated, the shaft turning loose in the distributors.
The slide valves are free to slide along the shaft, and are held up
against their respective distributors by the pressure of the steam or of
springs, so as to compensate for wear.
The improved continuous rotary valves enable link motions to be
dispensed with, which is a great advantage in the case of large marine
engines and locomotives. They also dispense with distribution and
expansion eccentrics, and sometimes with a shaft and its bearings in
large marine engines, and to substitute therefor a small shaft and gear
for driving the valve from the main shaft. They have also the

page_text: advantage of the same regulation when running either in forward or
backward gear, and obviate the objections to the link motion and the
obliquity of the valve rods.
Having described the nature of the Invention and the manner of
performing the same, I declare that what I claim as the Invention to
be protected by the herein-before in part recited Letters Patent is, the
improved circular slide valve having continuous rotary motion, and
provided with a distributor whereby an improved steam distribution and
reversing motion are obtained, as herein shown and described.
In witness whereof, I, the said Alexander Melville Clark, have
hereunto set my hand and seal, this Twenty-eighth day of April,
in the year of our Lord One thousand eight hundred and seventy-
six.