Improvements in Automatic Variable Expansion Gear for Steam and other Fluid Pressure Engines.
Year: 1894

page_text: Date of Application, 17th Feb., 1894
Complete Specification Left, 16th Nov., 1894-Accepted, 5th Jan., 1895
Improvements in Automatic Variable Expansion Gear for Steam and
other Fluid Pressure Engines.
I, MATTHEW HENRY PHINEAS RIALL SANKEY, Captain R.E. (retired) of
Ferry Works, Thames Ditton, in the County of Surrey, do hereby declare the
nature of this invention to be as follows :-
1. In automatic variable expansion gear constructed according to this invention
the governor acts by any ordinary mechanism upon a throttle valve, and the
point of cut off is varied consequentially by the change in the steam chest pressure
The rod which
following upon the closing or opening of the throttle valve.
controls the cut off gear is attached to a piston working in a cylinder; one end of
the cylinder is open to the steam chest, the other is normally exposed to the boiler
pressure; in fact the two ends of the cylinder are normally in communication with
the two sides of the throttle valve. The effective area of the piston may be approxi-
mately the same upon its two sides. The cut off gear is so arranged that cut off
is made earlier by the piston moving towards the steam chest ; later when it moves
in the contrary direction.
2. In making the cut off earlier the action is as follows: Suppose the engine to
be loaded to normal full load, the passage through the throttle valve being fully
or approximately fully open, and the cut off gear in the desired position for normal
full load. On a reduction of load taking place, the increase of speed and conse-
quent opening of the governor balls, closes the throttle valve and thereby controls
the engine; the pressure in the steam chest falls at the same time, and if the
change is sufficiently great the piston above referred to, being exposed to boiler
pressure on one side, and to the now reduced steam chest pressure on the other, is
moved towards the steam chest and by suitable mechanism makes the cut off earlier;
this motion by well understood means, which need not be here described, may, if
desired, be caused to take place slowly. As the cut off becomes earlier, the speed
tends to diminish, and the governor then opens the throttle valve wider, thus
increasing the steam chest pressure and again making the cut off later, and when
the alteration in the cut off ceases, owing to comparative equalisation of pressure
upon the two sides of the piston, the throttle valve and the governor balls will be
nearly in their original positions; the only change being that the throttle valve
bas to be a little more closed than before, on account of the smaller quantity of
steam required by the engine per unit of time. The action under a reducing load
is of course similar to the above in all cases, whatever be the load from which it
commences.
3. In making the cut off later the spindle which moves the throttle valve, also
actuates two small valves; one for cutting off the supply of steam from the boiler
to the space behind the piston already referred to; i.e. the end of the cylinder
furthest from the steam chest ; the other for opening the same space to the exhaust
or other place of lower pressure, such as the receiver in a compound engine. The
connection is such that no movement of the valves takes place when the throttle
valve moves in the direction of closing, but they are moved when the throttle valve
passes as it is free to do, beyond the position in which the steam way through it is
fully open.
4. Suppose an increase of load to take place while the engine is lightly loaded,
the throttle valve being approximately fully open and the cut-off of course early.
The action of the governor first moves the throttle valve, not only to, but beyond

page_text: the full open position; simultaneously the throttle valve spindle also moves the
valves described in the last paragraph, and the space behind the piston is both cut
off from communication with the boiler and is opened to the exhaust or other
place of lower pressure. The pressure on the other side of the piston, which is in
permanent communication with. the steam chest, now preponderates largely and
drives the piston rapidly away from the steam chest, making the cut off later,
probably too late, but this is not a source of irregularity because the engine is
controlled by the throttle valve, which, by reducing the pressure in the steam
chest, gradually brings the cut off to a point as early as is consistent with the
throttle valve returning to an approximately full open position.
With this arrangement a slow inward movement of the piston may be obtained
by making the opening between the inner end of the cylinder and the steam chest
small so that the steam in the inner end of the cylinder may form a cushion to prevent
too quick a movement of the piston towards the steam chest. When the piston
moves in the opposite direction the smallness of the opening through, which a
further supply of steam can enter the cylinder from the steam chest does not
prevent rapid movement of the piston as the steam already in the inner end of the
cylinder will act expansively.
The automatic variable expansion gear above described may be used for giving
a turning movement to a cut off sleeve in single acting engines of the central
valve type such as are described in the Specification of a prior Patent No. 1852
of 1885 in which the valves work within a hollow piston rod which itself moves
up and down within the sleeve. If oblique ports be cut in the sleeve and corre-
sponding ports in the hollow piston rod of the engine the admission of steam from
the steam chest to the hollow piston rod can be cut off earlier or later by turning
the sleeve and this turning movement may be given to the sleeve by coupling it
to the rod hereinbefore mentioned which is moved to and fro by the variations of
pressure in the steam chest and by the action of the two small valves as
described.
It is also evident that the piston described may be connected equally well to the
moving part of many other forms of variable cut off gear, which need not be
described. For instance a tail rod may be added and be connected in any suitable
manner with the shifting link which operates an ordinary expansion valve acting
upon the back of a slide valve, the same rule being observed that as the piston
moves towards the end of the cylinder which is connected with the steam chest
the cut off becomes earlier, and vice versa. Or it may be used to control the
position of a plate with oblique ports in it lying on the back of an ordinary slide
valve. In the latter case corresponding oblique ports or oblique edges in the valve
would be employed. The motion of the plate would be perpendicular to that of
the valve and cut off would be made earlier or later according as it is moved in
one direction or the other.
Dated this 15th day of February 1894.
Improvements in Automatic Variable Expansion Gear for Steam and
other Fluid Pressure Engines.
I, MATTHEW HENRY PHINEAS RIALL SANKEY, late Captain R.E. (retired) of
Ferry Works, Thames Ditton, 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 :-
1. In automatic variable expansion gear constructed according to this invention

page_text: the governor acts by any ordinary mechanism upon a throttle valve, and the
point of cut off is varied consequentially by the change in the steam chest
pressure following upon the closing or opening of the throttle valve. The rod which
controls the cut off gear is attached to a piston working in a cylinder; one
end of the cylinder is open to the steam chest, the other is normally exposed
to the boiler pressure; in fact the two ends of the cylinder are normally in
communication with the two sides of the throttle valve. The effective area of
the piston may be approximately the same upon its two sides. The cut off
gear is so arranged that cut off is made earlier by the piston moving towards
the steam chest; later when it moves in the contrary direction.
2. In making the cut off earlier the action is as follows; Suppose the engine to
be loaded to normal full load, the passage through the throttle valve being fully
or approximately fully open and the cut off gear in the desired position for normal
full load. On a reduction of load taking place there is an increase of speed and
the consequent opening of the governor balls wholly or partly closes the throttle
valve, and thereby controls the engine; the pressure in the steam chest falls at the
same time, and if the change of pressure is sufficiently great the piston above
referred to, being exposed to boiler pressure on one side, and to the now reduced
steam chest pressure on the other, is moved towards the steam chest and by suitable
mechanism makes the cut off earlier; this motion by well understood means, which
need not be here described, may if desired, be caused to take place slowly. As
the cut off becomes earlier, the speed tends to diminish, and the governor then
opens the throttle valve wider, thus increasing the steam chest pressure and again.
making the cut off later and when the alteration in the cut off ceases owing to
comparative equalization of pressure upon the two sides of the piston, the throttle
valve and the governor balls will be nearly in their original positions, the only
change being that the throttle valve has to be a little more closed than before, on
account of the smaller quantity of steam required by the engine per unit of time.,
The action under a reducing load is of course similar to the above in all cases,
whatever be the load from which it commences.
3. In making the cut off later the spindle which moves the throttle valve or some
other suitable part of the governor mechanism also actuates two small valves; one
for cutting off the supply of steam from the boiler to the space behind the piston
already referred to, i.e. the end of the cylinder furthest from the steam chest; the
other for opening the same space to the exhaust or some other place of lower
pressure, such as the receiver in a compound engine. The connection is such
that no movement of the valves takes place when the throttle valve moves in
the direction of closing, but they are moved when the throttle valve passes,
as it is free to do, beyond the position in which the steam way through it is fully
open.
4. Suppose an increase of load to take place while the engine is lightly loaded,
the throttle valve being approximately fully open and the cut off early. The
action of the governor first moves the throttle valve, not only to, but beyond the
full open position; simultaneously the throttle valve spindle (or other part of the
governor mechanism) also moves the valves described in the last paragraph, and
the space behind the piston is both cut off from communication with the boiler and
is opened to the exhaust or other place of lower pressure. The pressure on the
side of the piston which is in permanent communication with the steam chest, now
preponderates largely and drives the piston rapidly away from the steam chest,
making the cut off later, probably too late. But this is not a source of irregularity
in speed, because the engine is controlled by the throttle valve, which by reducing
the pressure in the steam chest, gradually brings the cut off to a point which,
though earlier, is as early as is consistent with the throttle valve returning to an
approximately full open position.
With this arrangement a slow inward movement of the piston may be obtained
by making the opening between the inner end of the cylinder and the steam chest

page_text: small so that the steam in the inner end of the cylinder may form a cushion to
prevent too quick a movement of the piston towards the steam chest. When the
piston moves in the opposite direction the smallness of the opening through which a
further supply of steam can enter the cylinder from the steam chest does not
prevent rapid movement of the piston, as the steam already in the inner end of the
cylinder will act expansively.
The automatic variable expansion gear above described may be used for giving
a turning movement to a cut off sleeve in single acting engines of the central valve
type, such as are described in the Specification of a prior Patent No. 1852 of 1885,
in which the valves work within a hollow piston rod which itself moves up and
down within the sleeve. If oblique ports be cut in the sleeve and corresponding
ports in the hollow piston rod of the engine, the admission of steam from the steam
chest to the hollow piston rod can be cut off earlier or later by turning the sleeve,
and this turning movement may be given to the sleeve by coupling it to the rod
hereinbefore mentioned which is moved to and fro by the variations of pressure in
the steam chest and by the action of the two small valves as described.
It is also evident that the piston described may be connected equally well to the
moving part of many other forms of variable cut off gear, which need not be
described. For instance a tail rod may be added and be connected in any suitable
manner with the shifting link which operates an ordinary expansion valve acting
upon the back of a slide valve, the same rule being observed that as the piston
moves towards the end of the cylinder which is connected with the steam chest the
cut off becomes earlier, and vice versa. Or it may be used to control the position
of a plate with oblique ports in it lying on the back of an ordinary slide valve.
In the latter case corresponding oblique ports or oblique edges in the valve would
be employed. The motion of the plate would be perpendicular to that of the valve
and cut off would be made earlier or later according as it is moved in one direction
or the other..
The drawings annexed show the invention applied to a single acting engine of
the central valve type such as is described in the above mentioned Pateut.
Figure 1 is a front elevation of the engine.
Figure 2 is an elevation partly in section and on a larger scale of the steam
chest. Figure 3 is a horizontal section of the same, and
Figure 4 is a vertical section on a still larger scale of the valve used for
controlling the admission of steam to the outer end of the cylinder used for
controlling the cut off.
A is the crank shaft of the engine.
B B are two sets of cylinders, the cylinders in each set being one above
the other.
C (see Figure 2) is the upper end of the hollow piston rod of one set which as
described in the above mentioned Patent, rises up into the steam chest D.
E is a sleeve surrounding the upper end of the piston rod, it is free to turn but
not to move up or down. In it are oblique ports E' corresponding oblique ports
are also cut in the hollow piston rod.
F is a governor which may be of any ordinary_construction, acting on a rod G,
which at its upper end carries the throttle valve H.
I is the steam supply pipe.
KK (see Figure 3) are links connecting arms on the sleeves E to a crank
lever L which can be rocked on its fulcrum L.
M is a cylinder extending outward from the steam chest. N is a piston working
therein, the piston rod N¹ of this piston has projections standing out from it, which
enter radial slots in one of the arms of the lever L.
O is a small passage which allows steam to pass slowly from the steam chest to
the inner end of the cylinder M, or from the inner end of this cylinder to the
steam chest.
P is the shell of a double valve P. It has three pipes leading from it.

page_text: No. 1 going to some portion of the steam pipe between the throttle valve and the
boiler. No. 2 going to the outer end of the cylinder M, and No. 3 to the exhaust
or to some place of low pressure.
R is a lever one arm of which is acted on by the rod G; the other acts on the
stem of the valve P, to draw it downward when the rod G moves upward to open
the throttle valve H.
In the ordinary running of the engine, when the throttle valve is in the full open
or nearly full open position, and the valves are in the position shown in Figures 2
and 4, pipes Nos. 1 and 2 are in communication with one another, and No. 3 is
closed, so that there is free communication between the boiler and the outer end of
the cylinder M; but when under the influence of an increased load, the speed of
the engine has commenced to diminish, and a later cut off is required, the governor
spindle rises and carries the throttle valve beyond the full open position, and in so
doing depresses the valve P, and thereby opens the outer end of the cylinder M, to
the exhaust or other place of low pressure; at the same time closes the
communication between the outer end of the cylinder M, and the boiler. The
pressure in the outer end of the cylinder M, being in this way relieved the piston N
moves away from the steam chest and the cut off is made later. When the oblique
ports in sleeve E and hollow piston rod C are opposite to one another steam is
admitted to the interior of the piston rod, and thence by other ports in the rod to
the cylinders B of the engine as described in the before mentioned Patent, but
when through the descent of the piston rod, the ports in it have passed below the
ports E in the sleeve steam is cut off. It is obvious that the point of cut off may
be varied by rotating the sleeve upon its axis, thus causing the ports in the
hollow piston rod to pass below the oblique lower edges of the ports E¹ either
earlier or later in the stroke according as the sleeve is rotated one way or the
other. When the piston N moves toward the steam chest, the sleeve is thereby
rotated in a direction to make the cut off become earlier and as it moves away, to
become later. When the piston moves towards the steam chest the movement is
slow as the steam in the inuer end of the cylinder can only pass slowly from it
into the steam chest, through the small opening O'. When the piston moves
outward consequently upon the outer end of the cylinder having been put in
communication with the exhaust, the steam in the inner end of the cylinder acts
expansively and the movement of the piston takes place quickly, the smallness of
the opening O¹ through which steam can enter the cylinder M from the steam
chest is therefore no hinderance to the piston making a quick outward movement.
The piston may be cushioned at the outer end of its stroke by causing it to pass
over and close the opening leading into the pipe No. 2 or by other equivalent
means. It is obvious that the cylinder may be detached from the steam chest, and
be only connected with it by a pipe, the piston acting on the sleeves by mechanism
external to the steam chest.
A stop may be attached to any convenient part of the mechanism to limit the
travel of the rotating sleeves (or other cut off gear) in the direction of early cut
off, so that the engine may be governed by varying the cut off down to a certain
load, and by throttling only below that load. The same effect may be obtained
by altering the shape of the ports in the sleeve and in the trunk.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed 1 declare that what I
claim is :-
1. The herein described method of automatically shifting the variable expansion
gear in steam or other fluid pressure engines, namely by the movement of a piston
in a cylinder communicating at one end with the steam chest and at the other end
through a valve or valves either with the boiler or with the exhaust (or other
place of relatively low pressure) such movement resulting as regards the travel of
the piston in one direction from the fall of pressure in the steam chest caused by
the closing of a throttle valve, controlled by the governor; and as regards the

page_text: travel of the piston in the other direction, from the preponderance of pressure on
the steam chest side of the said piston caused by the opening of the other end of
the cylinder to the exhaust (or other place of lower pressure) by the direct action
of the governor, substantially as described.
2. The construction of automatic variable expansion gear for steam and other
fluid pressure engines, substantially as hereinbefore described and illustrated in the
drawings annexed.
Th