Improvements in Valve Gear for Steam and other Fluid Pressure
Year: 1887

page_text: Date of Application, 2nd May, 1887.
Specification Accepted, 19th July, 1887.
[Communicated from abroad by JESSE FAIRFIELD CARPENTER, of No. 19, Leipziger
Platz, Berlin, in the Empire of Germany, Engineer.]
Improvements in Valve Gear for Steam and other Fluid Pressure
I, HENRY HARINGTON LEIGH, practising as Phillips & Leigh, at No. 22, Southampton
Buildings, Chancery Lane in the County of Middlesex, Engineer & Patent Agent,
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:
My invention relates to an improved construction of differential valve gear for
that class of reciprocating piston engines driven by steam or other fluid pressure in
which the alternate increase and decrease of the respective pressures of two bodies
of motor fluid is the proximate agent for the actuation of the slide valve.
It has hitherto been the practice to use a balanced starting valve with a differential
valve gear, and this has involved the use of an extra stuffing box exposed to as much
risk of leakage as that of the piston rod.
Now, according to my invention, I fix one or two pistons (each having its own
cylinder) upon the valve rod to which the valve is loosely connected. This valve
rod is actuated by the piston directly or indirectly and a differentiation of pressure
established in the piston cylinders within the valve chest alternately, causes the valve
rod to move the valve from one of its terminal positions to the other.
I attain the objects of my invention by means of the mechanisms illustrated in the
accompanying sheet of drawings in which
Fig. 1 is a longitudinal sectional elevation of an engine cylinder fitted with my
invention.

page_text: Fig. 2 is a longitudinal sectional elevation illustrating a modification of my
invention.
Fig. 3 is a longitudinal sectional elevation of an engine cylinder fitted with a
second modification of my invention.
In Fig. 1, A is the cylinder; B, the piston; and B', the hollow piston rod into
which projects the head c of the valve rod C. A plate b is fixed upon the face of the
piston, which engages alternately with the head c and a shoulder c¹ of the valve rod.
The shoulder may be dispensed with and its function discharged by the closed
inner end of the bore of the piston rod.
D is the valve chest axially aligned with the cylinder. Its ends d, d¹ form guides
for the valve rod C and are extended inwards into cylinders E, E¹, the latter of a
larger diameter than the former. Each of these cylinders has a piston e, el fast upon
the valve rod, and ports e², e³ maintaining a communication between the chest and the
respective chamber of the cylinders.
F, F are two collars fast on the valve rod and 9, 9' are two depressions in the
rod, which, at certain moments, establish communication between the respective
cylinders E, E and the exhaust h³ by means of ports g³, g³.
H is the slide valve through which the valve rod reciprocates; h and h³ the ports
to the cylinder, and the exhaust.
The figure represents the relative positions of the several parts when the piston has
made about a third of its stroke from left to right. The valve chest and both
cylinders E, E are full of live steam which is flowing along the port h¹ into the
cylinder.
The operation of the invention is as follows. As the piston B approaches the end
of its left-to-right-stroke the plate b engages with the shoulder c', the valve rod is
pushed to the right taking the piston e past the port e, the collar F up to the valve H
and the piston e a corresponding distance into its cylinder. Steam flows through the
porte into the cylinder E behind the piston e which has therefore equal pressure on
both sides of it. But it is not so with the second piston e¹, for the depression g' has
opened into the subsidiary exhaust port g³. The pressure in the cylinder E¹ therefore
falls, and that on the left hand faces of the pistons e e¹ moves the valve H over to the
right, closing the port h' and opening the port h.
b
with
Steam then flows along the latter port into the cylinder, and the piston starts on its
right-to-left stroke. As it approaches the end of the stroke, the plate 6 engages
the head c of the valve rod, closes the port g³, moves the collar F¹ up to the valve, and
moves both pistons e and e¹ to the left. The pressures on the two faces of the latter
are equal. But it is not so with the piston e, for the depression g has opened into the
subsidiary exhaust port g³. The pressure in the cylinder E therefore falls, and that
on the right hand faces of the two pistons e e¹ moves the valve H over to the left
closing the port h and opening the port h¹; that is, bringing the parts in the valve
chest back into the position illustrated in the figure.
In the modification illustrated in Fig. 2 there is only one valve cylinder inside the
valve chest, but it is closed at both ends from each of which a subsidiary exhaust is
provided to the main exhaust. Those parts of Fig. 2 which are duplicates, in
respect of function, of parts in Fig. 1 are marked respectively with the same reference
letters.
h
According to the figure, the piston B is making its left-to-right stroke, the valve H
being kept in its terminal position over the port % by pressure passing from the valve
chest D into the cylinder through the ports and bearing upon the right face of the
valve piston I.
The engagement of the plate b with the shoulder c¹ moves the piston I past the
ports, and pressure is established upon the left face of said piston, while the
correspondence of the depression ; with the subsidiary exhaust j¹ reduces the pressure
upon its right face. At this moment the collar F is in contact with the valve H and
as the pressure on the left face of the piston I moves it to the right, the valve is
moved into its right hand terminal position opening the port and closing the port h¹.

page_text: The pressure in the cylinder I cannot escape by the exhaust, because the depression jª
is to the right of it. The valve rod will therefore remain stationary until the right-
The
to-left stroke of the piston B brings the plate b into contact with the head c.
piston I will be moved back to the left of the ports, the exhaust closed, pressure
established on the right face of the piston I, the exhaust opened, and the collar F¹
brought up to the valve H now over the port . The piston I then moves to the left,
and pushes the valve into its left terminal position.
According to the second modification of my invention illustrated in Fig. 3, the
valve chamber K is placed upon the side of the cylinder A and the valve rod L moved
indirectly by the piston B through levers having their fulcra in chambers in the
ends of the cylinder A.
The remaining parts are substantially duplicates of those illustrated in Fig. 1 and
described therewith.
M is the valve; m, m³, and m³, the ports to cylinder and exhaust therefrom.
N, N' are two collars fast upon the rod C; O and O³, the pair of pistons; and o, 0²,
their cylinders. In the latter I form ports p, p¹ to admit pressure to the cavities of
the cylinders behind their respective pistons; and subsidiary exhausts g' which
2 by a pair
are alternately placed in communication with their respective cylinders o,
of depressions, upon the valve rod C.
According to the figure, the piston has made two thirds of its right-to-left stroke,
the valve M being held in its left terminal position by the pressure upon the right
faces of the pistons 0,0¹.
As the piston reaches the end of its stroke it will trip the lever and move the
rod C to the right, bringing the collar N up to the valve M, the piston O past the
port p, stopping the communication between the cylinder o and the subsidiary
exhaust q, moving the piston O' past the port p³, making communication between
the cylinder o¹ and the exhaust q', and making the lever project into the
cylinder A.
There is now pressure on both sides of the piston O, but on only the left face of the
piston O'. The valve M is consequently moved by the collar N over to its right
terminal position, closing the port m² and opening the port m, at which moment the
piston will commence its left-to-right stroke, the excess pressure on the left of
the piston O' holding the valve in its new position until the piston contacts with the
lever and trips it, when the rod C will be moved to the left again until the collar N'
bears against the valve M. At the same time, the exhaust g is opened, the port p
covered by the piston O, and pressure admitted into the cylinder o¹ to the right of
the piston O' through the port p', the effect of which is to move the valve over to its
left terminal position, that is to say, into the position it is shewn as occupying in the
figure.
I wish to point out that I can, according to my invention, adapt the single-cylinder-
and-piston valve-gear illustrated in Fig. 2 to a valve chest on the side of the cylinder,
and provide for the valve rod being moved by the piston in the manner illustrated in
Figure 3. Neither do I confine myself to the device of levers projecting into the
cylinder to be there engaged by the piston for the purpose of actuating the valve rod
inasmuch as the rod itself may be extended in either direction and its ends returned
so as to alternately project into the cylinder as far as would be necessary for the
piston to engage them in turn. It would of course be necessary with this last
described modification to reverse the relative positions of the valve chest mouths of
the steam ports m and m¹.
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 :—
1. The combination with the reciprocating piston of an engine operated by steam
or other fluid pressure, of a valve rod loosely connected to the slide valve, and which
rod is moved in alternate directions by the stroke of the piston and thereby caused
to bear against alternate sides of said valve; a pair of pistons upon said valve

page_text: rod, each moved therewith in its respective cylinder; and supply ports and exhaust
ports admitting an excess pressure to one of said pistons while pressure exhausts
from the cylinder of the other, substantially as described with reference to the
accompanying figures 1 and 3.
2. The combination with the reciprocating piston of an engine operated by steam
or other fluid pressure, of a valve rod loosely connected to the slide valve and moved
in alternate directions by the strokes of the piston, said rod contacting in alternate
directions with the valve; a cylinder in the valve cheque in which a piston fast upon
the valve rod works, and into which cylinder pressure is admitted on alterate sides
of its piston from the valve chest and exhausted therefrom by the said piston
alterately opening and closing the ports in said cylinder, substantially as described
with reference to Figure 2.