IMPROVEMENTS IN AUTOMATIC CUT-OFF VALVES
Year: 1880

page_text: LETTERS PATENT to George Fletcher, of Derby, in the County of Derby,
Engineer, for an Invention of "IMPROVEMENTS IN AUTOMATIC CUT-OFF
VALVES." Partly a communication from abroad by James Henry Man, of
Demerara, British Guiana.
PROVISIONAL SPECIFICATION left by the said George Fletcher at the
Office of the Commissioners of Patents on the 6th July 1880.
GEORGE FLETCHER, of Derby, in the County of Derby, Engineer. "IMPROVE-
MENTS IN AUTOMATIC CUT-OFF VALVES." [Partly a communication from abroad
by James Henry Man, of Demerara, British Guiana.]
This Invention relates to improvements in automatic cut-off valves for steam,
air, and gas engines.
The ordinary method of throttling steam by means of a governor and throttle
valve causes the admission line on the indicator diagram to slope down before the
actual cut-off occurs, the degree of slope increasing with the amount of throttling
now this Invention consists in the application or utilization of this reduction of
pressure for obtaining a nearly perfect automatic cut-off and utilization of steam to
the utmost economy.
The following is a suitable arrangement for carrying out the Invention:-
The cut-off valve on the back of the slide may consist of two inverted disc.
valves resting on levers actuated by an ordinary governor, so that the said disc
valves form the throttle valves, one for each end of the cylinder. The said disc valves
should be well fitted and connected with cushion pistons, the cylinders into which
these pistons are thrust each having a small hole for the admission of steam from "
the slide case. A suitable method is adopted to prevent any jarring from the
return of the valves upon their levers. Now it is evident that so long as the piston
does not run away from the steam, and there be maximum pressure in the cylinder,
the cut-off valve will remain resting on its lever, but the instant there is a slight
difference between the pressure in the cylinder and that in the slide case the cut-off
valve will rise and remain closed until equilibrium is again established about the
cut-off valve.
"

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said George Fletcher in the Great Seal Patent Office on the 6th
January 1881.
GEORGE FLETCHER, of Derby, in the County of Derby, Engineer. " IMPROVE-
MENTS IN AUTOMATIC CUT-OFF VALVES." Partly a communication. from abroad
by James Henry Man, of Demerara, British Guiana,
This Invention relates to improvements in automatic cut-off valves for steam, air,
and gas engines.
The ordinary method of throttling steam by means of a governor and throttle
valve causes the admission line on the indicator diagram to slope down before the
actual cut-off occurs, the degree of slope increasing with the amount of throttling;
there are also other causes producing a sloping steam admission line, but they do
not affect the independent action of the improved cut off valve; now this Invention
consists in the application or utilization of this reduction of pressure for obtaining
a nearly perfect automatic cut-off and utilization of steam to the utmost economy
and extent.
The following is a suitable arrangement for carrying out the Invention :—
The cut-off valve on the back of the slide may consist of two inverted disc-
valves resting on levers actuated by an ordinary governor, so that the said disc-
valves form the throttle valves, one for each end of the cylinder. The said disc-valves
should be well fitted and connected with cushion pistons, the cylinders into which
these pistons are thrust each having a small hole for the admission of steam from
the slide case. A suitable method is adopted to prevent any jarring from the
return of the valves upon their levers.
same
But to make the Invention better understood. I will proceed to describe the
by reference to the accompanying Drawings, in which Figures 1,2,3, and 4, Sheet 1,
represent views of a suitable arrangement of the improved automatic cut-off valve
or apparatus fixed on the back of the slide valve of an ordinary steam cylinder,, A
being the slide valve, and B, B, B, the steam passages of the cylinder.
In these Figures the cut-off valves on the back of the slide are constructed of
two disc-valves C, which may be inverted or horizontal, according to the type of
engine. These said valves C work in cylindrical cases D, and are in contact with
the levers E, which are actuated by an ordinary governor moving the spindle F,
so that the said disc-valves act as throttle valves, one for each end of the cylinder.
The disc-valves are accurately fitted to their cylindrical cases D, in which they
move, the back ends of the cases being closed by means of: the cover G, through
which a small hole H is drilled, allowing the steam in the slide case to obtain access
to the back of the disc-valve, thus forming a steam cushion for the valve to work
against, and preventing a too sudden closing of the valves when actuated by the
engine governor.
A suitable arrangement is adopted to prevent jarring or shock from the return of
the valves upon their levers.
From the herein before described arrangement it will be evident that so long as
the piston does not run 'away from the steam, or that the engine is not too lightly
loaded, and that there is a maximum pressure in the cylinder, the cut-off valve will
remain in contact with its lever E, but the moment 'there is a slight difference
between the pressure in the cylinder and that in the slide case the cut-off valve will
close, and, remain closed until equilibrium is again established about it.
The slide case D of the cut-off valves is so arranged that it is stationary or fixed
while the slide valve moves under it, or it may have a sliding motion between two
adjustable stops equal to a little more than the "lead" of the slide valve.
With either arrangement it will be seen that there will be a space for the

page_text: admission of "lead" steam to each end of the cylinder, thus maintaining the
required equilibrium about the cut-off valves until the piston has commenced its
forward or backward stroke, when the space immediately closes and the cut-off
valve is left to act by itself. This space in the return stroke of the slide valve
performs also another duty, videlicet, that of producing equilibrium about the cut
off valve immediately after the ordinary slide valve has cut off its steam, thereby
enabling the cut off valve to return to its lever E before it is again required for use,
and therefore being automatic in its action.
'
Although I have described disc-valves as being the most suitable for carrying out
my Invention, other forms of valves may be employed, as will be well understood,
and the automatic cut off valve may be adapted to serve both ends of the cylinder
with one cut-off valve.
Figures 1, 2, and 3, Sheet 2, represent views shewing the Invention applied to a
slide valve of the kind known as Howe's straight through equilibrium slide valve,
similar letters of reference to those used in Sheet 1 being used to represent similar
parts in Sheet 2.
Having now described the nature of the said Invention, and the best means with
which I am acquainted for carrying the same into effect, I wish it to be understood
that I do not confine myself to the precise details shewn and described, as they may
be varied without departing from the principle of the Invention, and the Invention
may be applied to other classes of valves than those herein described and shewn,
but what I do claim is,-
•
Firstly. An automatic cut-off valve for steam, air, and gas engines actuated by
the difference of steam or other pressures on either side of such valve, and inde-
pendent of any difference between the pressures on either side of the steam or other
port, as herein before described.
Secondly. The general arrangement and construction of automatic cut-off valves,
as hereinbefore described and represented in the accompanying Drawings.
Thirdly. The combination of a throttle valve actuated by the engine governor
and an automatic cut-off valve, substantially as hereinbefore described.
In witness whereof, I, the said George Fletcher, have hereto set my hand
and seal, this Sixth day of January, in the year of our Lord One thousand
eight hundred and eighty one.
Witness,
G. F. REDFERN,
4, South St.,
Finsbury,
London.
GEORGE FLETCHER. (L.S.)