Improvements in or applicable to the "Cut-off Gear" of Steam Engines.
Year: 1894

page_text: Date of Application, 14th Apr., 1894-Accepted, 9th June, 1894
COMPLETE SPECIFICATION.
Improvements in or applicable to the "Cut-off Gear" of Steam
Engines.
We GEORGE SAXON, JAMES SAXON, and ALFRED SAXON all of Openshaw
Engineering Works Manchester in the County of Lancaster, Engineers, and JOHN
MITTON of the same place, Draughtsman, 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 :-
This invention relates to apparatus for actuating the "cut-off" slide or valve
applied to the main valves of steam engines with the object of working the steam
expansively and especially to such engines wherein the cut-off slide is actuated by
means of a small auxiliary piston working in a cylinder provided for that purpose,
the principal object of the invention being to work the steam admission and
exhaust of such auxiliary cylinder by means of a revolving or reciprocating
cylindrical valve, driven direct from the main shaft of the engine so as to obtain
the requisite amount of cushion both at front and back of the auxiliary piston, and
at the same time to regulate the amount of "cut-off" to the load upon the engine
for the time being, by the action of the governor.
The nature of our said invention and the manner in which the same is to be
performed will be readily understood on reference to the two sheets of drawings
hereunto annexed and the following explanation thereof.
On Sheet 1 of the drawings Fig. 1 is a longitudinal section and Fig. 2 a
transverse section of the auxiliary cylinder showing the steam and exhaust passages
and rotary cylindrical valve, Figs. 3, 4 and 5 are detached sections showing the
action of the rotary valve, and Figs. 6 and 7 are detached sections showing the
construction and action of the valve when the same is caused to reciprocate instead
of revolving.
On Sheet 2 of the drawings Fig. 8 is an elevation and Fig. 9 a horizontal section
showing the connection of the cut off gear with the cylinder, slide valve box, and
governor of a steam engine.
Referring to Sheet 1.(Figs. 1 to 5 inclusive) A is the cylinder B the piston and
C the piston rod connected to the "cut-off" slide, DD and E E' are four steam
passages, F is the cylindrical valve rotated by its shaft F. G. and G' are the
steam ports in the valve and H is the steam admission pipe. I is the exhaust
passage leading to the low pressure cylinder of a compound engine or to the
condenser or to the atmosphere as the case may be.
The arrow on Fig. 1 shows the direction in which the valve F revolves, the
figures 1, 2, 3, 4 being the edges of ports G and G¹.
In the position shown at Fig. 1 the piston B being at the back end of the
cylinder the edge 1 of the valve port G is just about giving steam by the
passage D to the back end of the cylinder, the passage E' being open to
the exhaust I.
As soon as the piston B has closed the passage E' it "cushions" on the steam
which remains in the front of the cylinder the bottom of the passage D¹ being
closed. The edge 2 of the valve port G' now commences to give steam to the
front end of the cylinder (see Fig. 3) the edge 1 of the valve port G first opening
the steam passage E to the exhaust. As soon as the piston closes the passage E,
it "cushions on the steam which remains in the back of the cylinder (see Fig. 4).
The edge 2 of the valve port G' then begins to give steam to the passage Ď and
the piston is driven forward completing the stroke as at Fig. 5 and so on alternately,
"

page_text: r
one revolution of the valve F giving four strokes of the piston B (two from each
end).
It will be evident that when exhausting into the condenser if the vacuum therein
should be excessive the steam would be caused to escape so rapidly from the
cylinder A that there would not be sufficient left, for the piston to "cushion"
against and the result would be that it would strike against the cylinder ends; and
on the other hand when exhausting into the low pressure cylinder of a compound
engine if the steam could not escape with sufficient rapidity there would be too
much "cushion" and the stroke of the piston B (and hence of the "cut-off" slide)
would be too short. In order to remedy this defect we fit at a convenient part of
the exhaust passage I (but not necessarily so near to the cylinder A as shown at
Fig. 2) a back pressure valve J held down by a coiled spring K the pressure of
which can be increased or decreased until the desired amount of "cushion
" is
obtained by turning the hand wheel L.
The valve F (see Figs. 6 and 7) is so constructed that, instead of revolving it
works by being caused to oscillate in the arc shown by the dotted lines by means
of the lever M. In Fig. 6 the steam is full on between 3 and 4 whilst the
exhaust 1 and 2 is closed by the piston and the steam in the passage D acts as a
66 cushion " and the reverse action is shown at-Fig. 7. In this case each oscillation
to and fro of the lever M gives one motion to and fro of the piston B and
consequently of the "cut-off"slide.
"
Referring to Sheet 2 (Figs. 8 and 9) N is the high pressure or main cylinder of
the engine, the valve box and P the governor. Qis a shaft driven by a pair of
bevel wheels from the main shaft of the engine, and driving by spur gearing Ra
short spindle S which by bevel gear T drives the first bevil of the sun and planet
gear U on the spindle of the revolving valve F (see Fig. 9). The stud of the
planet wheel U₁ of this gear is carried by a lever V which is connected by a rod W.
to the lever X of the governor P.
By this arrangement the action of the governor P acting through the "sun and
planet" gear
U causes the spindle F¹ of the valve F to be retarded or set on so as
to automatically accommodate the action of the cut-off" slide to the load upon the
engine for the time being.
We may here observe that although we have shown and described the above
automatic gear for the sake of illustration we do not wish to confine ourselves to
such arrangement as the same effect of automatically setting on or retarding the
revolution of the "cut-off" valve spindle F¹ may be effected by other known
automatic "cut-off" arrangements actuated by the governor, such for example as
a sliding bush fitted with a spiral groove or other equivalent devices, and that
although we have shown and described our "cut-off" notion as applied to a slide
valve, it will be evident that it is equally applicable to " Corliss or other rotary
or oscillating valves.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
laim is
The improved apparatus for actuating the "cut-off" slide or valve applied to the
main valves of steam engines substantially as hereinbefore described and illustrated
by the drawings annexed.
...
GEO. DAVIES & SON,
4, St. Ann's Square, Manchester, Agents for the Applicants.