IMPROVEMENTS IN THE In steam engines having their valves worked by differential gear
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by the said Henry Davey at the Office
of the Commissioners of Patents on the 26th July 1880.
HENRY DAVEY, of Leeds, in the County of York.
DIFFERENTIAL VALVE GEAR OF STEAM ENGINES."
"IMPROVEMENTS IN THE
In steam engines having their valves worked by differential gear, as described
in the Specifications of Patents previously granted to me, the subsidiary piston
which conspires with the main piston to work the differential lever connected
to the main slide or valves is controlled in its movement by a cataract.
According to my present Invention I apply stops to one of the fulcra of this
differential lever, so that it is capable of a limited amount of movement. By this
means I am enabled to arrest the motion of the cataract piston at any point
of its stroke, so that it can have only a definite lead depending on the adjustment
of the stops in advance of the engine motion. The stops for this purpose may be
simply nuts on a sliding rod, which can be separately screwed more or less along
the rod on each side of a stationary boss through which the rod slides. Or the nuts
may work together on right and left threads, or may be connected by gearing to a
handle so that they can both be adjusted simultaneously. When a compound
engine having differential valve gear is unequally loaded, having more duty to
perform in the one stroke than in the other, I dispense with the balance weights
usually employed for the purpose of equalising the load by adapting to the low
pressure slide an adjustable plate or shutter, which I set so as to throttle more
or less one of the steam ports. Thus, when the engine is making its easier stroke
its low pressure cylinder gets a smaller supply of steam than when it is making
the stroke that requires more power, and the surplus of steam discharged from the
high pressure cylinder during the light stroke of the engine is thus made available
for acting in the low pressure cylinder during the succeeding heavy stroke. When,
instead of a slide, lift valves are employed to admit steam to the cylinder, I use for
the purpose of equalising the action levers for working the supply valves of the low

page_text: pressure cylinder, these levers having adjustable fulcra, which can be shifted nearer
to or farther from the valve stems. The inlet valves at the two ends of the low
pressure cylinder can thus be made to have different strokes, so that the one end
gets a greater and the other a less supply of steam to suit the inequality of the
load. In order to avoid the long pause which occurs at the end of a stroke in
a differential engine when it is worked with an early cut off, I arrange the supply
valves so that they are opened for each stroke by the differential gear, but are
closed independently of the differential gear by a motion derived from the engine.
For this purpose I work from a lever which moves with the main piston recipro-
cating cams that act on arms of levers, the opposite arms of which are also acted on
by reciprocating cams worked 'by the differential gear. These levers have their
fulcra on the stems of the supply valves, so that the movement of these valves
is made to depend on the relative positions of the two cams that act on the
lever, while the eduction valves are worked by the differentially moved cams
alone, the levers for the eduction valves being acted on by these cams at their one
end, and moving on fixed fulcra at their other end.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry Davey in the Great Seal Patent Office on the 24th January
1881.
HENRY DAVEY, of Leeds, in the County of York.
DIFFERENTIAL VALVE GEAR OF STEAM ENGINES."
"IMPROVEMENTS IN THE
In steam engines having their valves worked by differential gear, as described
in the Specifications of Patents previously granted to me, the subsidiary piston
which conspires with the main piston to work the differential lever connected to
the main slide or valves is controlled in its movement by a cataract.
According to my present Invention I apply stops to one of the fulcra of this
differential lever, so that it is capable of a limited amount of movement. By this
means I am enabled to arrest the motion of the cataract piston at any point of its
stroke, so that it can have only a definite lead, depending on the adjustment of the
stops in advance of the engine motion. The stops for this purpose may be simply
nuts on a sliding rod, which can be separately screwed more or less along the rod
on each side of a stationary boss through which the rod slides. Or the nuts may
work together on right and left threads, or may be connected by gearing to a
handle, so that they can both be adjusted simultaneously. When a compound
engine, having differential valve gear is unequally loaded, having more duty to
perform in the one stroke than in the other, I dispense with the balance weights
usually employed for the purpose of equalising the load by adapting to the low
pressure slide an adjustable plate or shutter which I set so as to throttle more or
less one of the steam ports. Thus, when the engine is making its easier stroke, its
low pressure cylinder gets a smaller supply of steam than when it is making the
stroke that requires more power, and the surplus of steam discharged from the
high pressure cylinder during the light stroke of the engine is thus made available
for acting in the low pressure cylinder during the succeeding heavy stroke. When,
instead of a slide, lift valves are employed to admit steam to the cylinder, I use for
the purpose of equalising the action levers for working the supply valves of the
low pressure cylinder, these levers having adjustable fulcra which can be shifted
nearer to or farther from the valve stems. The inlet valves at the two ends of the
low pressure cylinder can thus be made to have different strokes, so that the one
end gets a greater and the other a less supply of steam to suit the inequality of
the load. In order to avoid the long pause which occurs at the end of a stroke in
a differential engine when it is worked with an early cut off, I arrange the supply
valves so that they are opened for each stroke by the differential gear, but are
closed independently of the differential gear by a motion derived from the
engine. For this purpose I work from a lever which moves with the main piston
reciprocating cams that act on arms of levers, the opposite arms of which are also
acted on by reciprocating cams worked by the differential gear. These levers have
their fulcra on the stems of the supply valves, so that the movement of these
valves is made to depend on the relative positions of the two cams that act on the
lever, while the eduction valves are worked by the differentially moved cams
alone, the levers for the eduction valves being acted on by these cams at their one
end, and moving on fixed fulcra at their other end.

page_text: To the end of the lever E is
linked a rod G which is connected to the valves of the main engine, and has its
movement limited by the two stops K and L, adjustable by screwing towards or
from each other. If the point F were supposed to be stationary, the movement of
the point Z of the lever E, and consequently of the pistons A and B, would be
determined by the range of the rod G between the stops K and L. In the
differential gear, as it is usually arranged, these stops do not exist, consequently,
while F is stationary the point Z can be moved by the piston B over its whole
stroke, giving a complete stroke to the valve rod G, and this may occur before the
engine begins to move the point F. By applying the stops K. and L to the rod G,
the piston B is prevented from completing its stroke until after the point F has
moved with the engine, and thus, by the adjustment of the stops, I am enabled to
give the piston B a definite lead in advance of the engine. Fig. 2 shews a similar
arrangement with fixed stops, the rod G being made with a slot of definite length,
in which the end of the lever E is free to move a certain distance to and fro.
Figs. 3 and 3 shew an arrangement by which the stops are simultaneously adjusted
by turning the handle of a worm Y. This worm gears with a worm wheel X, forming
a nut to act on two sleeves, having respectively right and left screw threads,
and prevented from turning by feathers in their bearings. As the wheel is
turned in the one direction or the other the sleeves are protruded or retracted
so as to give less or greater range between the stops K and L. Fig. 4 is a
longitudinal section of the cylinders of a compound engine and their slides,
with apparatus according to my Invention applied to the slides so as to
compensate for a difference of load in the forward and back strokes of the
pistons. One method of effecting this is to fit a sliding plate S under the
slide of the high pressure cylinder, so that by the setting of this plate the discharge
of steam from one end of the cylinder can be more or less throttled, while the full
discharge is given at the other end to effect the more heavily loaded stroke.
Another method is to apply a sliding plate N on the back of the slide M of the low
pressure cylinder. This plate N has its movement limited by brackets which form
bearings for a screwed rod O which passes through packing in the end of the
slide jacket, and can be turned outside the jacket by a hand wheel P. By turning
this rod in the one direction or the other the slide N can be made to cover and
throttle more or less either of the supply passages to the cylinder, so as to admit
less steam for the lighter stroke of the piston. This arrangement is preferable to
the throttling of the high pressure passages, because, by the throttling of one of the
low pressure passages, a smaller quantity of the exhaust steam from the high pressure
cylinder is used for the one stroke of the low pressure piston, and consequently more
steam is left each time for effecting the other, which is the heavier stroke. Fig. 5
is a side elevation, and Fig. 6 is a plan of an engine with differential valve gear
arranged according to my Invention so as to open the supply valves whilst these
valves are closed, independently of the differential gear, by a motion derived from
the engine itself. Figs. 7, 8, 9, and 10 shew separately the action of the cams
employed, as I will now explain. E is the differential lever worked by the rods
c, c, and lever b from an arm a attached to the engine crosshead. The lever E is as
usual linked to the auxiliary piston B and controlling cataract piston A. A bevil
wheel worked from the differential lever E gears with bevil wheels on two shafts
9, g, which have on them respectively cams o, o¹, and n, n'. Another shaft h, having
on it cams m, m³, is worked by bevil gear f' through a rod s from the spindle of
the lever b. The induction valves k, k, of the high pressure cylinder V have their
stems jointed to levers, the arms of which rest each at one end on the cams o, o',
and at the other end on the cams m, m¹, respectively. The high pressure eduction
valves i, ', have likewise their stems jointed to levers which work each at one end
on a stationary fulcrum, their other ends resting on the cams o, o', respectively. The
arrangement of the cams and levers for the valves of the high pressure cylinder is
shewn in Figs. 7, 8, and 9, from which it will be seen that whilst the opening of both
the induction and the eduction high pressure valves, and the closing of these eduction
by the cataract piston A in the known manner.

page_text: valves result from the motion of the cams o, o', which are worked by the differential
gear, the closing of the induction valves results from the motion of the cams m, m³,
which are worked from the engine crosshead. The low, pressure valves, both those for
induction and eduction, as shewn in Figure 10, have the levers to which their stems
are jointed, working at their one end in each case on a stationary fulcrum, and resting
by their other ends on the cams n, n', which are worked from the differential gear.
The fulcrum of either of the low pressure induction valves may be made adjustable,
as shewn in Fig. 10, by fitting it to be slid along a bracket p by means of a screw
with handle r. According as this fulcrum is slid nearer to or farther from the
valve stem, the opening of the valve, resulting from the action of the cam n', will
be less or greater, and thus the supply to the one or the other end of the low
pressure cylinder can be more or less throttled to compensate for an inequality of
the load resisting the one or the other stroke of the piston.
Having thus described the nature of my Invention, and in what manner the same
is to be performed, I hereby declare that I make no general claim to the use of
differential valve gear for steam engines, but I claim in respect of engines having
differential valve gear,―
First. Fitting on the valve rod worked from the differential lever adjustable
stops, substantially as and for the purposes herein described with reference to
Figs. 1, 2, and 3 of the accompanying Drawings.
Second. Compensating an inequality of load on the alternate strokes of the
engine by more or less throttling one or other of the cylinder passages by means
of an adjustable slide applied to the main slide, substantially as herein described
with reference to the accompanying Drawings.
Third. The combination of cams o, o¹, worked by the differential gear, and cams
m, m², worked from the engine crosshead, or from a synchronously moving part of
the engine, with levers jointed to the stems of the induction valves, so that whilst
the opening of these valves is determined by the movement of the differential gear,
their closing is determined by the movement of the engine, substantially as herein
described with reference to Figs. 5, 6, 7, 8, and 9 of the accompanying Drawings.
Fourth. Working a supply valve by a lever jointed to its stem, the one arm of
the lever being moved by a cam, and the other arm working on a fulcrum which
can be adjusted nearer to or farther from the valve stem, so that either of the
valves may be made to receive a less or greater opening movement according as the
load on the one stroke or the other is less or greater, substantially as herein
described with reference to Fig. 10 of the accompanying Drawings.
In witness whereof, I, the said Henry Davey, have hereunto set my hand
and seal, this Twentieth day of January, in the year of our Lord One
thousand eight hundred and eighty one.