IMPROVED MEANS FOR AUTOMATICALLY VARYING THE CUT-OFF IN STEAM AND OTHER ENGINES
Year: 1885

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COMPLETE SPECIFICATION. ·
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1.
I, HENRY GEORGE HOLBOROW, of Dudbridge Iron Works, Dudbridge, in the
County of Gloucester, Mechanical Engineer, do hereby declare the nature of my
Invention for. "IMPROVED MEANS FOR AUTOMATICALLY VARYING THE CUT-OFF IN
STEAM AND OTHER ENGINES" 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 improved means for automatically varying the degree of
admission of steam or other aëriform fluid to the cylinders of motor engines, and
thereby regulating the supply of the said fluid relatively to the power required to
be developed.
1
With the object of adınitting steam to the cylinder fully and at the proper
inoment and subsequently of cutting off that supply suddenly, it is a common
practice to employ a supplementary slide-valve, usually working on the back of the
main valve and termed an "expansion" valve. In some instances, the expansion-
valve, like the main valve, is worked direct from an accentric and has a constant
travel. Under such circumstances, both the admission and the cut-off of the steam
may be well defined, but the proportion of the stroke during which the steam
supply is continued does not vary. In other cases, mechanism of a complicated
character is employed for controlling the movements of the expansion valve and
varying the period during which the steam supply to the cylinder is maintained.
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My invention consists of improved means for actuating an expansion valve of
the kind before referred to; the period during which steam is admitted by it being
automatically varied in relation to the amount of power required to be developed
by the engine. The means I employ are at the same time of a simple description
mechanically, and are not readily liable to derangement.
".
And in order that my Invention and the mode of carrying it into effect may be
fully understood, I will now proceed more particularly to describe the same, and
for that purpose shall refer to the accompanying drawings; of which Figure 1 is a
side elevation of my improved apparatus, Figure 2 a horizontal section on the
line A B (Figure 1), and Figure 3 a vertical transverse section on the line Û D
(Figure 1). Similar letters of reference indicate corresponding parts in all the
Figures. a is a portion of a steam-engine-cylinder provided with slide-jacket, of
which the parts marked a¹ are walls, and furnished with the usual inletiports.a² a³
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page_text: and exhaust port a³, leading to and from the interior of the cylinder. Against the
face wherein these ports are formed, the main slide-valve b works. In this valve
suitable passages are provided for the transmission of steam to the ports a² a and
for conducting the exhaust steam alternately from these to the port a³. On the
back of the main valve b, an expansion-valve c works; the latter being provided
with long narrow openings c¹ suitably disposed in relation to similar inlet orifices
in the main valve. For steam to reach either of the ports a², it is necessary for the
valves b and c to be in such positions that communication is established through one
series of openings c¹ in the expansion-valve cand through the corresponding passage
in the main valve b. In the position of the valves shown in the drawing, steam is
just able to find its way to the right-hand port a². The main valve b is connected
by means of a rod 6¹ to a block 6ª mounted in guides 63. The block 6s is attached
to the main eccentric-rod b' whence the block derives a reciprocative motion, which
latter is also imparted to the main valve b. The expansion-valve c is connected by
means of a rod c² to a block c³; this block being formed with a vertical slot c and
being mounted to slide in the block b. On the sliding block 63 is also mounted a
vibrating lever c³ pivotted at of and attached at its outer end c to the expansion-
eccentric-rod (not shown in the drawing). The lever c is slotted similarly to the
block c3; and both slots are fitted with suitable sliding pieces, through which a
pin passes, forming a pivot for the said sliding pieces to turn upon. The pin c³
08
is also in connection with the governor rod d, which, for the purpose of the present
illustration, may be understood to work vertically; falling when the speed of the
engine decreases and rising again when an acceleration takes place.
The action of the apparatus is as follows:-The main valve b, being in direct
communication with its eccentric, partakes of a regular reciprocative motion. The
nature of the connection between the expansion-valve-eccentric and the expansion-
valve c is not, however, of the same rigid character; inasmuch as one element in
the connection between these parts consists of the pin c with its two blocks
working respectively in the slot c* and slotted lever c³, the position of the pin c8 in
the said slots being regulated by the action of the governor. When the pin c³
approaches the lower end of the slots and consequently the centre from which the
lever c³ vibrates, there is but little differential motion as between the main and
expansion valves. When, however, the pin c³, owing to the action of the governor
rod d, rises to the upper ends of the slots, thereby establishing a connection between
the blocks c³ and lever c³ at a point further removed from the centre co, the actual
motion of the expansion-valve is diminished; the movements of the eccentric-rods
and consequently of the centres c and c being timed in suitable relation to one
another. In the result, the period during which communication is open between
the expansion-valve and main valve passages is shortened; or in other words, the
steam supply is cut off at an earlier point in the stroke of the piston, this effect
being produced by the action of the governor, which in turn depends on the speed
of the engine and ultimately on the load or resistance to be overcome.
The slotted lever c being operated at its opposite extremities c and c' by the
main and expansion eccentric rods respectively, it results that the pin o³, communi-
cating between that lever and the block c³, may be moved longitudinally in the
slots with great facility; the sensitiveness of the controlling effect exerted by the
governor being correspondingly increased and steadiness of working secured.
Although I have described my improved apparatus as applied to an engine where
the main elide face, the governor spindle and the slotted lever care all vertical,
it will be obvious that, with slight modifications, the invention is capable of being
adapted for use with an engine having either or any of the parts alluded to
horizontally or otherwise disposed.
Having now particularly described and ascertained the nature of my invention
and in what manner the same is to be performed, I declare that what I claim is
First-In motor engines, the improved means whereby the working of the
expansion-valve is rendered subject to the action of the governor and the steam

page_text: adinission automatically varied in relation to the resistance to be overcome, arranged
and operating substantially as herein described.
Secondly: The combination of the slotted lever c³ mounted on a pivot moving
simultaneously with the main valve, the slot c', and the governor-moved pin c8, the
last named sliding in the two slots and actuating the expansion-valve from a point
at a greater or less radius from the pivot of the vibrating lever co, substantially as
and for the purposes herein specified.