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

page_text: Date of Application, 16th Feb., 1894
Complete Specification Left, 15th Nov., 1894-Accepted, 29th Dec.,
"
1894
PROVISIONAL
SPECIFICATION.
Improvements in Automatic Variable Expansion Gear for Steam and
other Fluid Pressure Engines.
I, MARK HEATON ROBINSON, of Ferry Works, Thames Ditton in the County
of Surrey, Engineer, 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 is greatest on
the side next to the steam chest; the effective area of the other side being reduced
by a trunk or tail rod, or equivalent device. 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 consequent
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
Bufficiently 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 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 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. Owing to
the difference in the effective areas of the two sides of the piston, the latter will not
move towards the steam chest, unless there is a substantial preponderance of
pressure on the boiler side of it. The same difference of area ensures that the
piston shall move away from the steam chest though the preponderance of pressure
per square inch is still on the other side, if that preponderance is only small.
There is of course a difference of pressure, (extending through a range of a few-
pounds per square inch) which fails to overcome the friction of the piston and cut
off gear. Hence when the preponderance of the boiler pressure over that of the
steam chest exceeds a certain amount, the cut off is made earlier; when it falls

page_text: below a certain other (and lower) amount the cut off is made later. It is obvious
that the necessary tendency to move away from the steam chest may be given by
other means than by a difference of effective area between the two sides of the
piston, as by the action of a spring or weight.
3. Suppose the engine to be running with a light load and with an early cut off,
the difference of pressure upon the two sides of the piston being, such that it moves
in neither direction. Imagine now an increase of load to take place; the consequent
closing of the governor balls opens the throttle valve wider and the pressure in the
steam chest is increased; as soon as it becomes nearly the same as that on the
further side of the piston, the latter is driven away from the steam chest and
the cut off is made later. The cut off may now be 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
late as is consistent with the throttle valve returning to an approximately full open
position.
In a single acting engine of the central valve type such as is 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 a hollow sleeve in the
steam chest the sleeve may be made free to rotate. 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 herein before mentioned which is moved to and fro by the
variations of pressure in the steam chest.
In other engines the tail rod may 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.
Dated this 15th day of February 1894
Improvements in Automatic Variable Expansion Gear for Steam and
other Fluid Pressure Engines.
I, MARK HEATON ROBINSON, of Ferry Works, Thames Ditton, in the County
of Surrey, 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 :-
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
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 is greatest on
the side next to the steam chest; the effective area of the other side being reduced
by a trunk or tail rod, or equivalent device. 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

page_text: 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 governer 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
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 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. Owing to the difference in the effective areas of
the two sides of the piston, the latter will not move towards the steam chest, unless
there is a substantial preponderance of pressure on the boiler side of it. The same
difference of area ensures that the piston shall move away from the steam chest
though the preponderance of pressure per square inch is still on the boiler side, if
that preponderance is ouly small. There is of course a difference of pressure,
(extending through a range of a few pounds per square inch) which fails to
overcome the friction of the piston and cut-off gear. Hence when the preponderance
of the boiler pressure over that of the steam chest exceeds a certain amount the
cut-off is made earlier, when such preponderance falls below a certain other (and
smaller) amount the cut off is made later. It is obvious that the necessary
tendency to move away from the steam chest when the pressure on the two sides of
the piston are nearly equal may be given by other means than by a difference of
effective area of the two sides of the piston, as by the action of a spring or weight.
3. Suppose the engine to be running with a light load and with an early cut off,
the difference of pressure upon the two sides of this piston being such that it moves
in neither direction. Imagine now an increase of load to take place; the consequent
closing of the governor balls opens the throttle valve wider and the pressure in the
steam chest. is increased; as soon as it becomes nearly the same as that on the
further side of the piston, the latter is driven away from the steam chest and
the cut off is made later. The cut off may now be too late, but this
not a source
of serious irregularity in speed, because the engine is controlled by the throttle
valve, which, by reducing the pressure in the steam chest as the speed rises,
gradually brings the cut off to a point which, though earlier, is as late as is
consistent with the throttle valve returning to an approximately full open
position.
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
herein before mentioned which is moved to and fro by the variations of pressure in
the steam chest.
In other engines the tail rod may be connected in any suitable manner with the
shifting link which operates an ordinary expansion valve acting upon the back of a
slide valve, or with the moving part of any other form of expansion gear, the same

page_text: 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.
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 Patent.
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
and Figure 3 is a horizontal section of the same.
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 El; corresponding oblique ports
are also cut in the hollow piston rod.
Fis 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 Ę 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 N' 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 valve through which steam can pass freely from the steam chest to the
inner end of the cylinder M but which stops all passage of steam in the reverse
direction.
O¹ is a small passage which allows steam to pass slowly from the cylinder M to
the steam chest when the pressure in the steam chest is lower than in the cylinder.
This passage may be given by the hole through which the rod N¹ passes, instead of
by a separate bole O.
P is a pipe admitting steam from the steam supply pipe I to the outer end of the
cylinder M.
Qis a trunk or tail rod from the piston N passing through the cylinder cover,
it is made of such a diameter as to diminish to the required extent the area of this
side of the piston N, which can be acted on by the pressure of boiler steam admitted
through the pipe P, so that when there is full pressure of steam in the valve chest
this pressure acting on the larger area of the inner side of the piston may overcome
the pressure on the outer side and the piston N be consequently moved outwards.
When the oblique ports in a 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 above 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 E, either
earlier or later in the stroke according as the sleeve is rotated one way or the other.
When the piston N moves towards the steam chest the sleeve is thereby turned in
a direction to make the cut off become earlier, and as it moves away to become
later. The outward movement to make the cut-off later can take place quickly as
steam can pass quickly from the steam chest to the inner end of the cylinder M
through the valve. An inward movement to make the cut off earlier takes place
slowly as the steam in the inner end of the cylinder M can only pass from it into
the steam chest through the small passage O', or by the clearance past the rod N'.
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 P, or by other equivalent means.
Any other equivalent device such as an oil cylinder for controlling the motion of

page_text: the piston N, so that the outward movement of the piston may be quick and the
inward movement slow, may be used instead of the above arrangement.
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 I 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
with the boiler, such movement resulting from the variation of pressure in the
steam chest caused by the action of a throttle valve controlled by the governor.
2. The combination of a piston acting as and for the purpose described, with
rotating cut off sleeves surrounding the hollow piston rods of central-valve engines
substantially as described.
3. The construction of automatic variable expansion gear for steam and other
engines substantially as herein before described and illustrated in the drawings
annexed.
Dated this 14th day of November 1894.
MARK H. ROBINSON.