IMPROVEMENTS IN THE MODE OF WORKING CUT-OFF SLIDE VALVES FOR ENGINES WORKED BY STEAM OR OTHER FLUID PRESSURE
Year: 1875

page_text: LETTERS PATENT to William Haslett Mitchel, of Newry, in the
County of Armagh, Ireland, for the Invention of "IMPROVEMENTS
IN THE MODE OF WORKING CUT-OFF SLIDE VALVES FOR ENGINES WORKED BY
STEAM OR OTHER FLUID PRESSURE."
Sealed the 25th March 1875, and dated the 27th January 1875.
PROVISIONAL SPECIFICATION left by the said William Haslett
Mitchel at the Office of the Commissioners of Patents, with his
Petition, on the 27th January 1875.
I, WILLIAM HASLETT MITCHEL, of Newry, in the County of Armagh,
5 Ireland, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN THE MODE OF WORKING CUT-OFF SLIDE VALVES FOR ENGINES WORKED BY
STEAM OR OTHER FLUID PRESSURE," to be as follows:-
?
The present Invention relates to that class of combination steam
engine valves in which a cut-off valve actuated by steam pressure is
mounted on the back of the ordinary slide valve, the action of such
cut-off being placed under the control of the governor, so as to
.

page_text: produce a sen-acting albic Cu-on
by fixing a small travelling cylinder on the back of the slide valve
carrying a piston, to the rods of which the cut-off plates were attached,
the time of action of such piston being regulated by small slide valves
actuated or controlled by the governor.
The object of the present Invention is to effect the same purpose by
means of a simple and compact arrangement comprising few moving
parts.
In proceeding to state the nature of the said improvements, I premise
that for the purposes of this description, the slide valve referred to is of
that variety through which the steam passes by ports passing through
the valve from back to face, enabling the supply of steam to be cut off
by a second slide valve mounted on the back.
In the back of the main slide valve according to my Invention I form
a cavity which may be semi-cylindrical or of other convenient form, and
I form the cut-off valve as a plate extending from one steam port to the
other of the main valve, and of such length as to cover one or other of
such ports, according as it is at one end or other of its traverse. On the
under side of such plate I form or fix a boss or projection fitted to work
in the cavity in the main slide valve as a plunger, approximately steam
tight, and in a direction parallel to the motion of the main valve, the
cavity being so much longer than the boss or plunger as to admit of the
necessary amount of traverse in the cut-off valve. Near to cach end of
the cavity are two small ports, one to supply, the other to exhaust
steam, which ports pass downwards through the main valve to its face,
and correspond, the former to two depressions in the main valvo seat
adapted to admit steam from the steam chest at suitable times to the
small ports, the latter to a single port in the valve seat communicating
with the exhaust.
In the passage by which the last-mentioned port communicates with
the exhaust I place a cock or valve which is connected with the
governor, so that an increase of speed may give a wider, and a decrease
of speed a more contracted passage to the escaping steam.
On the under side of the cut-off valve where it works steam tight on
the edges or lips of the cavity and close to the ends of the boss or
plunger I form two depressions rather wider than the said lips, so that

page_text: as the plunger approaches the end of its traverse steam is admitted by
the depressions to pass over the said lips in front of the advancing
plunger.
The manner of acting is as follows:-As the main valve advances
from right to left, the cut-off valve and its plunger are at the left-hand
end of their traverse, leaving the right-hand steam port of the main
valve uncovered; the right-hand end of the cavity is charged with steam
from the last stroke, and the left-hand end is by the depression on the
under side of the cut-off valve in communication with the steam
chest; the small ports are for the present all closed. The main valve
advancing in this manner and carrying the cut-off valve with it (both
retaining the same positions relatively to one another), uncovers the
right-hand steam port of the engine and admits steam in the usual
manner ; but very soon after steam has thus been admitted, the exhaust
port of the right-hand end of the cavity arrives over the port or passage
in the valve seat leading to exhaust, the equilibrium of pressure
existing between the two sides of the plunger is destroyed, and the cut-
off valve moves to the right; for the first part of its traverse steam
enters as described over the lip of the cavity, but this source of supply
being soon cut off, the steam to complete the traverse passes through the
small admission port of the left-hand end of the cavity, which has now
arrived over one of the depressions in the main valve seat; the cut-off
valve thus moving towards the right cuts off the supply of steam from
the engine, and at the same time the plunger also closes, the exhaust
port of the right-hand end of the valve cavity, while by the depression
on the under side of the cut-off valve, steam is allowed to flow over the
lip of the cavity in front of the advancing plunger, thus restoring the
equilibrium and destroying the moving force; the remainder of its
traverse therefore is accomplished by its momentum only, which is in a
great measure overcome by friction before it reaches the end, thus pre-
venting too violent a slamming of the plunger against the end of the
cavity; the valve and cut-off valve are now in their proper position to
begin their advance from left to right, when a similar series of operations
takes place.
The desired variation in the point of cut-off is obtained by means of
the partial opening or closing, by the action of the governor of the cock
or valvė through which the steam passes on its way from the valve
cavity to the exhaust. as already described. When this cock is widely

page_text: open the cut-off valve will act almost immediately after the valve cavity
is placed in communication with the exhaust, but if the cock be partially
closed and the passage thereby contracted, a somewhat longer time will
clapse before the escape of steam has created the degree of inequality of
pressure necessary to overcome friction and to move the cut-off. Thus,
the more nearly closed the cock may be the longer time will be allowed
for the admission of steam to the main cylinder. A somewhat similar
device and for a somewhat similar purpose has heretofore been used in
connection with a passage leading steam from the main cylinder to
actuate the cut-off valve, but I prefer to place it on the passage to the
exhaust. I also place the cock or valve introduced for the purpose as
described under the control of the governor which has not hitherto been
donc.
A modification of the above arrangement for varying the time of
cut-off consists in elongating the exhaust ports of the valve cavity where
they open on the valve face, and in making them diagonal to the motion
´of the valve a small slider may be fitted in a recess in the valve seat over
the entrance of the passage to the exhaust, and having a hole passing
through it by which steam may pass from the diagonal ports to the
exhaust; attached to this slider is a rod or spindle which passes out
through a stuffing box, and is so connected with the governor that the
action of the latter may move the slider slightly in a transverso
direction.
It is is evident that the position of the slider will determine the point
at which one or other of the diagonal ports will arrive over the hole in it
which opens a passage to the exhaust, and will thus determine the point
at which the cut-off valve will act.
·
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Haslett Mitchel in the Great Seal Patent
Office on the 27th July 1875.
.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
HASLETT MITCHEL, of Newry, in the County of Armagh; Ireland, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-seventh day of January, in the

page_text: year of our Lord One thousand eight hundred and seventy-five, in the
thirty-eighth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said William Haslett Mitchel, Her
special license that I, the said William Haslett Mitchel, my executors,
administrators, and assigns, or such others as I, the said William
Haslett Mitchel, 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 THE MODE OF WORKING CUT-
OFF SLIDE VALVES FOR ENGINES WORKED BY STEAM OR OTHER FLUID PRESSURE,"
upon the condition (amongst others) that I, the said William Haslett
Mitchel, my executors or administrators, by an instrument in writing
under my, or their, or one of their hands and seals, should par-
ticularly 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 William Haslett Mitchel, 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 thereof, reference being had to the
Drawings hereunto annexed, and to the figures and letters marked
thereon, similar parts being marked with similar letters of reference in
all the Figures.
The present Invention relates to that class of combinations of steam
engine valves in which a cut-off valve, actuated by steam pressure, is
mounted on the back of the ordinary slide valve; the action of such
cut-off valve. being placed under the control of the governor so as to
produce a self-acting variable cut off. With this view I form the cut-off
valve as a plate, having on its under side a boss or projection, and in the
upper side of the main valve I form a cavity or plunger box, in which
the said boss is fitted to work as a plunger, approximately steam tight
and in a direction parallèl to the motion of the main valve, the cavity or
plunger box being so much longer than the boss or plunger as to admit
of the necessary movement of the cut-off valve or plate. Steam is

page_text: aumitted to and exhausted from the cavity or plunger box by small ports
passing through the main slide valve to its face and acting in connection
with a port and depressions in the valve seat. The cut-off valve or plate
is caused to move at the proper times by creating a partial vacuum in
the cavity or plunger box in front of the boss or plunger, and the
formation of the requisite degree of vacuum is retarded or accelerated
by the partial closing or opening of a cock placed in the passage leading
steam from the cavity or plunger box to the exhaust, which cock is
connected with the governor.
In some cases I use a modification of the above in which the cock is
'dispensed with.
In the accompanying Drawings Figure 1 is a longitudinal section of
the main and cut-off slide valves, with the valve casing or steam chest,
the steam ways, and a portion of the cylinder. y is a part of the cylinder
of the engine; S, S, are the steam ways, and the exhaust port and
pipe V is the main slide valve with its steam ports S1, S2, which arc
formed as mortices to admit steam through the valve instead of over the
end; f is the cut-off valve or plate, and P the boss or plunger on its
under side; C is a cavity or plunger box formed in the back of the
main slide valve in which the plunger P works approximately steam
tight; u is a stud on the back of the main valve carrying a washer plate
and pin to keep the cut-off valve in its place.
-
Figure 2 is an enlarged view of the back of the main valve with the
cut-off valve removed, so as to shew the plunger box with its ports. The
direction taken by said ports in passing through the main valve, as well
as the several ports and depressions of the valve seat, are shewn in
dotted lines. a, a², are small admission ports, and e, e³, are small
exhaust ports leading from the bottom of the plunger box to the valve
face and opening thereon at h and g, and at m and n respectively; d, d²,
arc depressions in the valve seat corresponding to h and 9 respectively,
and adapted to admit steam thereto at suitable times from the steam
chest; E is a small port situated in the valve seat, and communicating
by a passage through the valve casing with the exhaust. The steam
ports S, S, and the exhaust port t of the valve scat in this Figure are
shown by dotted lines.
Figure 3 is a vertical section on the line x, q, of Figure 1, showing
the valve casing and the main and cut-off valves. i, i, arc strips of metal

page_text: rivetted or otherwise fixed to the side of the main valve which close tho
ends of the cavity or plunger box C and serve as guides for the cut-off
valve. The dotted lines a, h, indicate the position of the admission
ports of the plunger box, and d the depressions in the valve scat by
means of which steam is admitted thereto at proper times. The dotted
lines e, n, in like manner indicate the position of the exhaust ports of
the plunger box, and E the passage to the exhaust with which they
communicate alternately. k is a cock placed in the said passage, having
a spindle and lever I, by means of which it is connected with the
governor.
The mode of action is as follows:-Referring to Figures 1, 2, and 3,
in which the main valve V is shown at the middle point of its motion, it
will be seen that as the main slide valve moves in the direction of the
arrow steam will be admitted to the cylinder through the port S¹ and
the steam way S, while at the same time the end of the small admission
port a (see Figure 2) opens into the depression d adapted to admit steam
thereto from the steam chest, and the end m of the small exhaust port e
opens into the passage E communicating with the exhaust. A partial
vacuum is thus produced in the cavity or plunger box C in front of the
plunger P, and steam being at the same time admitted behind it by the
small port a it is caused to move in the direction of the port S¹, which it
closes by means of the cut-off plate f, and so shuts off steam from the
cylinder. The main slide valve V having now completed its motion
returns in the opposite direction when, by means of exactly corres-
ponding ports, a similar series of operations takes place. Were the
passage E at all times widely open there would be no variation in the
time of cut-off, which would take place almost immediately after the
admission of steam to the cylinder, but by means of a cock k (see
Figure 3) placed in the said passage I retard, as required, the formation
of the requisite degree of vacuum in the plunger box, and until such
degree of vacuum is reached the cut-off valve does not move, and thus
steam continues to be admitted to the cylinder for a longer time. In
order that such retardation of the action of the cut-off valve may
correspond with the actual requirements of the engine I connect the
cock with the governor by means of the spindle ; and lever I in such
a manner that a lowering of the speed of the engine causes the passage
to be contracted.

page_text: time of cut-off is shewn in Figure 4, in which modification the cock / is
dispensed with, the device now to be described being substituted therefor.
The small exhaust ports e, e², are made to terminate on the valve face in
triangular recesses and w, having one side placed obliquely or
diagonally to the motion of the main slide valve. The small port E in
the valve seat is covered steam-tight by a small slider or sliding piece N,
which is fitted in a recess of the valve seat, and so that its surface is
level with that of the valve seat. Through the slider passes a hole T,
which opens into the port E beneath. A transverse motion, as required,
is given to the slider by means of the spindle D, which passes out
through a stuffing box in the valve casing, and is connected with the
governor in such a manner that a lowering of the speed of the engine
causes the slider to move in the direction of the arrow. It will be
evident from the Drawing that such outward movement of the slider
will cause the triangular recesses and wo to communicate with the
exhaust by means of the hole T somewhat later, and will thus delay the
formation of the vacuum in the cavity or plunger box C, and will
therefore cause steam to be admitted to the cylinder during a longer
time.
A somewhat different arrangement is shewn in Figure 6, in which the
passage E is formed as a notch in the valve seat leading directly into
the exhaust port t. The sliding piece N serves as a cover for the notch
or passage E, and the steam in the plunger box C is retained until some
part of one of the diagonal recesses 1, w, passes over the notch or
passage E clear of the end of the sliding piece N, which will be carlier
or later, according to the position of the latter. In this arrangement
the obliquity of the recesses and wis reversed, and the plunger box is
placed centrally on the main valve instead of near the end, as shown in
the other Figures.
In some cases, with a view to prevent too violent a slamming of the
plunger against the end of its box, I admit steam in front of it, a little
before the completion of its stroke, by means of cavities L, L, (Figure 5)
in the under side of the cut-off valve or plate f, which permit, steam to
flow over the lip of the cavity or plunger box C, a little before the boss
or plunger P reaches the end of it, thus impairing the vacuum, and
allowing the plunger to complete its stroke by momentum chiefly.
It is obvious that the above-described arrangement of main valve and
cut-off valve may be modified in various ways, the mode of action

page_text: however remaining substantially the same. For example, the positions
of the plunger and plunger box might be reversed, the plunger being
placed upon the main valve and the plunger box on the cut-off valve,
the positions of the small ports being altered to suit. Or in place of the
plunger and box as described a small piston and cylinder might be sub-
stituted. Or the retarding cock might be placed in an admission instead
of an exhaust passage, so as to retard the inflow instead of the outflow
of steam from the plunger box. In such case the depressions d, d³, (see
Figures 2 and 3) instead of opening directly into the steam chest beside
the valve might lead first into a common passage, in which the retarding
cock would then be placed.
☐
Having now described the nature of my Invention, and the best mode
I am acquainted with for carrying the same into effect, I desire to state
that a cut-off valve mounted on the back of the main valvo has hereto-
fore been actuated by steam pressure applied by means of a small tra-
velling cylinder fixed to the back of the valve, and furnished with a
piston to the rods of which the cut-off valves were attached.
In the case referred to steam from the steam chest to actuate the small
cut-off piston was admitted and exhausted by means of a small slide
valve travelling back and forward with the main valve, but having an
independent transverse reciprocating motion communicated to it by the
governor in such a way as to produce a self-acting variable cut-off. It
has also been attempted to produce the required variation in the time of
cut-off by means of "screw plugs" applied in connection with small
passages leading steam from the main cylinder to actuate the piston of a
cut-off valve, the action of such plugs being to contract the passages,
and retard in any required degree the inflow of steam. The above plugs.
however being unconnected with the governor were not self-acting.
I would also state that I do not claim as novel the use of ports placed
obliquely or diagonally to the motion of the valve combind with a
transverse motion to vary the time of cut-off; but what I claim as my
Invention is,
First. The application to or combination with the cut-off and main
slide valve of a projection on the one working as a plunger in a cavity
or plunger, box formed in the other, said plunger and plunger box
serving instead of a piston and cylinder to actuate the cut-off valve in
manner substantially as herein shown and described.

page_text: Second. Admitting steam to the said travelling plunger box or to a
cylinder as its equivalent, and exhausting it therefrom by means of ports
passing through the main valve to its face, and acting in connection
with a port and depressions in the valve seat, so as to actuate the plunger
or piston of a cut-off valve at the proper times as a result of the motion
of the main valve itself, and without the use of a separate valve for the
purpose in manner substantially as hercin shown and described.
Third. Producing a self-acting variable cut-off by placing a cock or
equivalent device connected with the governor in the passage through
which the plunger box or cylinder of a steam worked cut-off valve com-
municates with the exhaust, whereby the escape of the steam may be
more or less retarded, and the formation of the degree of vacuum
required for the action of the cut-off valve correspondingly delayed, in
manner substantially as herein shown and described.
Fourth. Connecting a retarding cock or equivalent device with the
governor, so as to produce a self-acting, variable cut-off, whether said
cock or device be applied to retard the inflow or the outflow of steam into
or out of the plunger box or cylinder of a cut-off valve in manner sub-
stantially as herein shown and described.
Fifth. The use of the slider N connected with the governor as a cover
for the passage through which the plunger box or cylinder communicates
with the exhaust, and which, acting in connexion with oblique recesses
in the valve face, serves to vary the time at which the steam in the
plunger box is allowed to escape, and the required vacuum is formed
to work the cut-off valve in manner substantially as herein shown and
described.
In witness whereof, I, the said William Haslett Mitchel, have
hereunto set my hand and seal, this Nineteenth day of July, in
year of our Lord One thousand eight hundred and seventy-
the