Improvements in Automatic Variable Expansion Gear for Central Valve Engines.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in Automatic Variable Expansion Gear for Central
Valve Engines.
I, WILLIAM CAMERON, of Maryport, in the County of Cumberland, Mechanical
Engineer, do hereby declare the nature of this invention to be as follows:-
In automatic expansion gear according to my invention the engine governor
operates the valve of a relay cylinder whose piston in turn operates through suit-
able mechanism the cut off sleeve which controls the admission of steam to the
engine cylinder means are also provided whereby the governor when altering the
cut off or expansion sleeve by the means referred to above arrives at a predeter-
mined point it operates the throttle valve so as to lower the steam pressure in the
engine steam chest when the load is reduced on the engine.
According to my invention I operate the expansion or cut off sleeve by means of
the governor through a relay cylinder which receives its working fluid from any
convenient source preferredly from the boiler side of the engine stop valve. The
valve of the relay cylinder which controls the supply of the working fluid to and
the exhaust from the relay cylinder is by means of suitable mechanism operated by
the governor through a lever so hung that the movement of the relay cylinder
piston due to the movement of the relay cylinder valve which is assumed to have
received a movement from the governor acts upon the before mentioned lever in
such a manner as to bring the valve back into its neutral position and prevent
further movement of the relay cylinder piston until a further movement of the
governor takes place.
The relay cylinder piston has therefore a movement exactly corresponding to
that of the governor balls but greater in extent, and consequently the cut off
sleeve being connected to the piston of the relay cylinder receives a similar move-
ment.
In
In engines of this type the dead space between the cylinder piston and cut off
sleeve is necessarily large and at the earlier points of cut off the amount of steam
contained therein is a large percentage of that required to fill the volume swept
by piston up to cut off and would interfere with the close regulation of speed
required for many purposes besides causing a waste of the working fluid.
order to prevent this fluctuation of speed and waste I cause the movement received
from the governor balls to operate the throttle valve after the cut off has reached
a predetermined point. For instance when the normal load is on the engine the
throttle valve is full open and the cut off is arranged to close the port in the
tubular piston rod at 30 of the stroke. Assume that part of the load is removed
the governor balls will now run in a greater plane due to the increase speed and
the cut off will now take place earlier say at of the stroke, the throttle valve
at that point would still be wide open but if the load be further reduced the
governor would act on the throttle valve reducing the amount of opening at the
same time the cut off would be carlier but not so early as it would have been
had the throttle valve not curtailed the opening between the boiler and steam
chest and so reduced the steam pressure in the steam chest. I arrange the move-

page_text: ment of the throttle so that it shall have completely closed the opening between
the boiler and steam chest before the cut off sleeve has reached the position for
zero cut off.
In this way I ensure that the cut off shall never take place at zero no matter
how lightly the engine be loaded. On the load increasing the governor allows the
throttle valve to open and moves the cut off sleeve back to cut off later.
Dalad this 014
T1900
Improvement in Automatic Variable Expansion Gear for Central
Valve Engines.
I, WILLIAM CAMERON, of Maryport, in the County of Cumberland, Mechanical
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:-
In automatic expansion gear according to my invention the engine governor
operates the valve of a relay cylinder whose piston in turn operates through suit-
able mechanism the cut off sleeve which controls the admission of steam to the
engine cylinder. Means are provided whereby the governor when altering the
cut off or expansion sleeve by the means referred to above arrives at a predeter-
mined point it operates the throttle valve so as to lower the steam pressure in the
engine steam chest when the load is reduced on the engine.
According to my invention I operate the expansion or cut off sleeve by means of
the governor through a relay cylinder which receives its working fluid from any
convenient source preferredly from the boiler side of the engine stop valve. The
valve of the relay cylinder which controls the supply of the working fluid to and
the exhaust from the relay cylinder is by suitable mechanism operated by
the governor through a lever so hung that the movement of the relay cylinder
piston, due to the movement of the relay cylinder valve, which is assumed to have
received a movement from the governor, acts upon the beforementioned lever in
such a manner as to bring the valve back to its neutral position and prevent
further movement of the relay cylinder piston until a further movement of the
governor takes place.
The relay cylinder piston has therefore a movement exactly corresponding to
that of the governor balls, but greater in extent, and consequently the cut off
sleeve being connected to the piston of the relay cylinder receives a similar move-
ment.
In engines of this type the dead space between the cylinder piston and cut off
sleeve is necessarily large, and at the earlier points of cut off the amount of steam
contained therein is a large percentage of that required to fill the volume swept
by the piston up to cut off and would interfere with the close regulation of speed
required for many purposes besides causing a waste of the working fluid.
In order to prevent this fluctuation of speed and waste I cause the movement
received from the governor balls to operate the throttle valve after the cut off has
reached a predetermined point. For instance when the normal load is on the
engine the throttle valve is in its normal full open position and the cut off is
arranged to close the port in the tubular piston rod at approximately 36 of the
stroke. Assume that part of the load is removed the governor balls will now run
in a greater plane due to the increased speed and the cut off will now take place
earlier say at 1 of the stroke, the throttle valve at that point would still be in

page_text: its normal full open position, but if the load be further reduced the governor
would act on the throttle valve reducing the amount of opening. By properly
setting stops so as to limit the travel of the relay cylinder valve the cut off can
be rendered inoperative at or any desired fraction of the stroke but at whatever
point they are set I arrange that the throttle valve is completely closed before
zero cut off.
In order that my invention may be clearly understood I will now proceed to
explain the annexed drawings.
Fig. 1. Shews the gear applied to a single acting central valve engine.
Fig. 2. Is a part sectional elevation on a larger scale.
Fig. 3. Shews the cut off sleeve surrounding the tubular piston rod.
Fig. 4. Is a plan of the differential levers connected to the throttle valve and
governor.
Referring to the figs. in which similar parts are indicated by the same letters,
The engine governor acting through the rod a and lever b, which is fulcrumied
at Coperates the lever d, the levers being secured to a common spindle. The
movement is transmitted from lever d through the linkage and lever E which is
fulcrumed on the peice f and operates the valve g of the relay cylinder H. The
motive fluid enters the valve chest of the relay cylinder through an opening or
port in connection with the space I which is in communication with the source of
supply, from whence it is admitted to and exhausted from the relay cylinder by
one or other of the passages K, K 1 according to the movement of the valve g.
The fluid acting on the piston / moves the cut off spindle m by means of the linkage
shewn in Fig. 1 partially rotating the same and through it moves the cut off
sleeve N Figs. 2 & 3 altering the relative positions of the slot o in the sleeve and
the port pin the tubular rod Fig. 3. In the position shewn the slot is placed for
the latest cut off. At the other end of the relay cylinder piston rod there is
secured a coarse threaded screw which gears into a sleeve r, the movement of
the relay cylinder piston causes the sleeve r to rotate. That portion of the
sleeve on which the peice f is hung is screwed with a fine thread of a suitable
pitch, and on the sleever rotating the peice f receives a longitudinal movement
in the same diriction as that of the relay cylinder piston / but much less in magni-
tude, this movement alters the position of the fulcrum of the lever E placing the
valve in its normal position closing both ports K and K 1 thus bringing the
piston 7 to rest and fixing the position of the cut off sleeve until a further move-
ment of the governor takes place.
The differential movement given to the valve g from the movements of the
governor and relay cylinder piston can be communicated through a system of
levers, I however consider the method shewn preferable.
It will be seen that the movement of the governor balls is not directly trans-
mitted to the throttle valve, but is conveyed through the floating levers which is
hung on the lever b, one end of the lever s being connected to the throttle valve
spindle whilst the other end is connected to the peice f by means of the levers and
linkage shewn. The peice f, as has been already stated, receives a movement from
the relay cylinder piston, so that the throttle valve receives a movement from both
governor and relay cylinder piston, the actual displacement at any instant being
the difference of the two movements until the stops t, tl come into action.
The movement of the peice f is almost simultaneous with that of the governor
balls and the mechanism is so arranged that the movement given to the throttle
valve by the governor balls is conteracted by the movement given by the peice f
so that when the governor balls cease to give a movement to the rod a, the throttle
valve is always brought back to its normal full open position, unless the movement
of the governor balls has been in excess of that required to bring one or other of
the stops t, t1 against the abutment U, which prevents further movement of the
peice f, then that portion of the movement over that required to bring the stop
against the abutment acts directly on the throttle valve closing it or placing it
further open according to whether the load has been reduced or increased.

page_text: The stop limits the point of early cut off, that is, if the point at which the
earliest cut off occurs is at 1 of the stroke, the stop t would be set to come into
action at that point, that is, into contact with the abutment U, then if the load
be further reduced the governor would act on the throttle valve closing it reducing
the pressure in the steam chest X. The stop 1 limits the cut off in the other
direction, and is preferably kept beyond the latest cut off for which the slot o
in the sleeve n is arranged riz. about 6 of the stroke. When one or other of the
stops 1 are against the abutment U further movement of the lever d is per-
mitted by the compression of one or other of the springs w w 1 which are adjusted
to have equal initial compressions when the governor balls are running in their
normal plane of revolution.
The action of the apparatus under a reduction and increase of load is as follows
Suppose the engine to be running with its full normal load, the govenor balls
will then be running in their normal plane of revolution and the valve g and the
relay cylinder piston will be in, or approximately in the position shewn in Fig. 2,
the relative position of the port and slot o being set to give the most economical
result. Suppose a portion of the load to be removed then the speed of the engine
would increase and the govenor balls would run in a greater plane of revolution,
the governor rod would be moved downward, the movement being transmitted
through the beforementioned levers and connecting links would move the valve g
and open the passage K to steam and the passage K 1 to exhaust, at the same time
the throttle valve through the lever s would be moved downwards but almost
instantaneously the piston would be moved in the direction of the arrow rotating
the sleeve and moving the peice f also in the direction of the arrow. The result
of the movement of the peice f is that instantly the movement of the governor
balls cease the valve is placed in its normal position closing the ports K K 1
and at the same time the throttle valve is placed in its normal full open position.
The positions of the various parts now are, the valve g and the throttle valve
returned to their normal positions as shewn in Fig. 2 and the piston / would have
a position to the right of its normal position corresponding to the amount which the
governor balls are now running above their normal plane of revolution and the
cut off would be earlier. If however the load on the engine was such that the
mean effective pressure resulting from say ¼ cut off was more than sufficient to
overcome it, at the speed the engine was now running, the speed would increase
and the governor balls would open still further which would move the rod a
further downward moving the lever d and the stop t would come against the abut-
ment, the movement of the lever d now compresses the spring to 1 the spring w
being correspondingly extended. This movement is however communicated to the
levers it being hung on lever b, and as the end of levers which is connected to
the peice f is now stationary the only movement communicated to the throttle
valve is the downward movement of the governor rod a 1 which closes it, or nearly
so, reducing the pressure in the steam chest .r.
Assume that the load is increased but not sufficiently to necessitate a cut off
later than of the stroke, the speed of the engine now falls and the governor
balls close running in a lower plane of revolution, and the governor rod, a¹ is
moved upward moving the levers b and d, this movement compresses spring to
allowing 1 to extend but the stop t still remains up to the abutment until the
forces exerted by the springs w, w 1 are in equilibrium, and this does not take place
until that point is reached where their equilibrium was disturbed by the stop t
coming against the abutment which was at a point corresponding to ¼ cut off,
therefore there can be no movement given to the valve g or piston and the cut
off sleeve still remains at cut off and the end of the lever s which is coupled
to the peice f still remains stationary, so that the only movement which the
throttle valve receives is that due to the upward movement of the governor rod a
which opens it, or increases the opening raising the pressure in the steam chest r.
This continues until the load is so increased as to require a cut off later than
of the stroke. At cut off the throttle valve is in its normal full open position

page_text: and the pressure in the steam chest is at, or nearly equal to the boiler pressure,
and the forces exerted by the springs w, 1 being now in equilibrium the stop t
leaves the abutment. On a further movement of the lever taking place, and
the valve g moves placing the port 1 to steam and to exhaust, now moving the
piston towards the left which partially rotates the cut off sleeve o, making the
cut off later. The movement of the governor rod a is at the same time com-
municated to the throttle valve but as the piston 7 moves practically simul-
taneously towards the left rotating the sleeve r and moving the peice f also
towards the left, the throttle valve and the valve y are at once brought back to their
normal positions on the upward movement of the governor rod ceasing. The
closing of the ports K K 1 brings the piston to rest and fixes the position of the
cut off which remains unaltered until a further movement of the governor balls
takes place. The same series of movements occur on the loads being further
increased until a predetermined limit is reached when the stop t 1 reaches the abut-
ment u, at which point the engine would be carrying approximately its maximum
load. It will be apparant that the engine is governed by throttling, that is by
varying the steam pressure in the steam chest, from a cut off of 4 of the stroke
upwards whilst for heavier loads neccessitating a cut off later than 1% of the stroke
the engine is governed by varying the volume of the steam admitted, the pres-
sure remaining constant or nearly so.
The exhaust steam from the relay cylinder is led by suitable pipes y, y 1 to the
low pressure cylinder steam chest or other convenient place.
Water or other liquid under pressure may be employed to operate the piston of
the relay cylinder.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:
1st. The method of operating the expansion or cut off sleeve in central valve
engines in such a manner that for light loads the expansion or cut off sleeve shall
be caused to become inoperative and the engine is controlled by the throttle
valve, whilst for heavy and normal loads the cut off sleeve is allowed to act and
the engine is controlled by varying the volume of steam admitted substantially
as herein described.
2nd. In expansion gear for central valve engines the gear substantially as
shown by the annexed drawings.
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