IMPROVEMENTS IN OR CONNECTED WITH THE EXPANSION VALVE GEAR OF STEAM ENGINES
Year: 1878

page_text: LETTERS PATENT to Bristow Hunt, of Serle Street, Lincoln's Inn, in the
County of Middlesex, Gentleman, for the Invention of. "IMPROVEMENTS IN OR
CONNECTED WITH THE EXPANSION VALVE GEAR OF STEAM ENGINES." A
communication from abroad by Carl Rudolf August Virck, of Mecklenburg, in
the Empire of Germany.
Sealed the 6th August 1878, and dated the 12th February 1878.
PROVISIONAL SPECIFICATION left by the said Bristow Hunt at the Office
of the Commissioners of Patents on the 12th February 1878.
BRISTOW HUNT, of Serle Street, Lincoln's Inn, in the County of Middlesex,
Gentleman. " IMPROVEMENTS IN OR CONNECTED WITH THE EXPANSION VALVE
GEAR OF STEAM ENGINES." (A communication from abroad by Carl Rudolf August
Virck, of Mecklenburg, in the Empire of Germany.)
This Invention relates to certain improvements in or connected with the
expansion valve gear of steam engines, and the characteristic features thereof are as
follows:-
The main steam cylinder is provided with separate admission and eduction slide
valves at each end. The steam valves work at the top of the cylinder in an
ordinary steam chest, but the exhaust valves are placed at the ends of the cylinder,
and work on the insides of the covers thereof, access to them being obtained by
means of a small cover.
The exhaust valves having no chest to themselves, and there not being even a
port to fill with steam, there is practically no dead space to be filled at each stroke
of the engine.
The steam and exhaust valves derive their alternate movements from a shaft
revolving alongside the cylinder, and which is driven direct from the crank shaft by
bevil gearing. The governor also receives motion by bevil gearing from the said
revolving shaft.

page_text: The exhaust valves are worked by two cams arranged one in advance of the other
on the said shaft, and the "motion frames" of these cams being formed with slots
the most advantageous amount of compression can be obtained by choosing the
proper lead. The steam valves are also worked so far as their opening is concerned
by cams arranged on the said shaft, but their closing is effected at the proper
instant by a small steam expansion cylinder (the piston of which is suitably
connected to them) placed above the steam chest, and the ends of which are
connected with the ends of the main steam cylinder by two steam pipes provided
at their inner ends with circular slide valves, which are worked from a spiral cam
on the sleeve of the governor, and thus sooner or later according to the height of
the governor balls the main steam valves are shut, and a correct steam admission
varying from a minimum per-centage to about 9° per cent. of the stroke can be easily
obtained.
The steam which has worked at full pressure in the expansion cylinder, expands
down into the main cylinder through the same valve through which it entered, and
this valve only closes if the opposite valve, that is, the valve at the other end of
the cylinder, opens for the return stroke to shut off the steam at the corresponding
end of the main cylinder.
If by any chance sufficient steam should remain on the exhaust side of the
expansion cylinder to oppose the return stroke, the valve will lift off its seat, and
restore the communication with the main exhaust. With this arrangement, as there
is no one sided pressure resting on the main steam valves when they close, very little
power will be required to move them, and a small expansion cylinder will effect a
prompt cut off of the steam.
To prevent a shock at each end of the stroke two air cylinders are provided in.
connection with the expansion cylinder. There will also be comparatively little
power required for opening the steam valves, and even an excessive wear of the
cams and the ends of their respective operating levers will not materially affect
the distribution of the steam, and can at any time. be easily allowed for and
adjusted by means of lock.nuts with which the valve spindles are provided.
The expansion cylinder may be replaced by a spring contrivance wound up for
each stroke, and released by the governor when expansion has to begin; this
arrangement being similar to that now in use for the Corliss type of engine.
The governor may also shut the steam valves direct without the intermediation
or use of any special contrivances therefor.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Bristow Hunt in the Great Seal Patent Office on the 10th August
1878.
"
BRISTOW HUNT, of Serle Street, Lincoln's Inn, in the County of Middlesex,
5 Gentleman. IMPROVEMENTS IN OR CONNECTED WITH THE EXPANSION VALVE
GEAR OF STEAM ENGINES." (A communication from abroad by Carl Rudolf August
Virck, of Mecklenburg, in the Empire of Germany.)
This Invention; which relates to certain improvements in or connected with the
valve gear of steam engines, is illustrated on the accompanying Sheet of Drawings
in Figures 1 to 12, of which Figure 1 represents a sectional elevation of sufficient
of a steam engine to illustrate the application of my improvements thereto,
Figure 2 being a plan view thereof also partly in section, the governor being
removed; Figure 3 is a longitudinal section through the line A-B, Figure 2;
Figure 4 is a transverse section through the line C-D, Figures 1 to 3; Figure 5
is a horizontal section through the line E-F, Figures 1 to 3; Figure 6 is a similar
view through the line G-H, Figures 1 and 3.
Figure 7 is an elevation of the expansion cylinder; Figure 8 is a transverse section
thereof.
.
Figures 9 to 11 are detailed views of the governor; and Figure 12 is a section
through the slide bar.
In carrying out the Invention in practice the steam cylinder 1 is provided with
separate admission and eduction ports 2, 3, at each end, each port having a separate
steam or exhaust valve 4, 5. The steam valves 4 (which are flat side valves) work
on the top of the cylinder 1 in an ordinary steam chest 6, but the exhaust valves 5
which are of an annular configuration are placed at the ends of the cylinder, and
work inside and at the bottom of the cylinder 1 and adjacent to its covers 7.
The governor 9 which is erected beside the centre of the cylinder 1, and is con-
structed on "Proell's" system, makes the same number of revolutions as the engine
itself, it being actuated from the crank shaft 10 by the gearing 11, and the inter-
mediate shaft 12. This system of governor has the great advantage of working
well, even at a very small number of revolutions, without necessitating a large
size; but any other suitable governor may be used.
The valves 5 are worked from the governor spindle 8 by a cam 14 arranged on
and near its bottom end, and working in a motion frame 15 connected by rods 16
to levers 17, which engage with the valve spindles 18 in the manner shewn most,
clearly in Figure 6. By choosing the proper shape for this cam and its frame a
correct compression and timely release can be easily obtained. This cam arrange-
Inent also allows the piston 19 to come at the end of the stroke in contact with the
valve; thus reducing the waste steam space required for the exhaust valve to nil;,
and the valves are only moved at the end of the stroke when the pressure on them.
is very little. An ordinary excentric motion might be substituted for the cam
motion, but would not have the above named advantages. The valves 4 are also.
worked; so far as their opening is concerned, from the spindle 8 by a cam 20, rods 21,
and levers 22, engaging with their spindles 23, in the manner shewn most clearly
in Figure 5, but their closing is effected at the proper instant from a small steam
cylinder 24, called the "expansion cylinder," the piston 25 of which by means of the
rods 26 and levers 27 acts upon the spindles 23 of the valves in the manner shewn
most clearly in Figure 3.
The cylinder 24 is placed on the top of the chest 6; and its ends are connected
with the corresponding ends of the cylinder 1 by two steam pipes 28 provided at:
their ends in the cylinder 24 with any suitable kind of valves 29 which are worked
from the governor 9 by means of a spiral cam 30 on its sleeve and the connections 31
in such a way that if the one opens the other shuts, as most clearly shewn in Figures 2,
4, 7, 8, and 10, and. thus sooner or later, according to the height of the governor.
balls, the valves 4 are shut by the piston of the expansion cylinder and a correct

page_text: and quick cut off varying from about 0·03 to 0.8 of the stroke can be easily obtained,
but when the engine starts and the governor balls are down, the valves 4 are shut
as well as opened by the main gear, and the steam is admitted almost throughout
the whole of the stroke, but the cut-off is then much slower.
The steam which has worked at full boiler pressure in the cylinder 24 expands
down into the cylinder 1 through the same valve 29 through which it entered, and
this valve only closes when the opposite valve (29) is opened by the governor for
the return stroke to shut off the steam at the corresponding end of the cylinder 1 ;
thus the steam necessary for working the expansion cylinder is ás completely as
possible converted into useful work, and finally exhausted through the exhaust
valve 5 of the cylinder 1.
If by any chance sufficient steam should remain on the exhaust side of the
cylinder 24 to oppose the return stroke, the valve 29 (being fitted as shewn in
Figure 8) will lift off its seat and restore the communication with the main exhaust,
thus always ensuring a prompt action of the expansion gear.
With this arrange-
iment of steam valve gear also, as there is no one sided pressure acting on the valves 4
when they close, very little power will be required to move them, and the cylinder 24
need only be made very small, as only the friction resulting from the stuffing boxes
and the dead weights have to be overcome, the cubical contents of it and of its
piping 28 will always be but a fraction of the necessary space between the piston
and cylinder cover.
+
To gradually reduce the speed of the steam valves after they have closed their
ports, and to prevent a shock at each end of the stroke, two air cylinders 32 are
provided, in which buffers 33 on the rods 26 work. There will also be comparatively
little power required for opening the valves 4, and even the excessive wear of the
cams and the ends of their respective operating devices will not materially affect
the distribution of the steam, and can at any time be easily allowed for and adjusted
by means of lock nuts with which the valve spindles are provided.
If the governor should be considered not sufficiently powerful to neutralise the
vertical force which has a tendency to lift the balls when the spiral cam 30 works
the valves of the expansion cylinder it is only necessary to effect the rotation of the
same, not direct from the spindle but by the intervention of four spiral springs 13,
as shewn in Figures 9 and 11, or any other elastic medium, and not to cast the
sleeve with the spiral cam together with the bottom boss 34 of the governor, but to
adjust it in such a way that it receives its rotation not from the governor proper,
but direct from the spindle 8 by a key 35 of the shape shown in Figures 9 and 10,
and which is set in the sleeve and allowed to slide in a slot in the spindle, then
during the short time that the spiral cam works the valves of the expansion cylinder
the friction between the key and the sides of the slot will always be sufficient to
prevent any undue lifting of the governor balls. This method of driving the
governor by the intervention of an elastic medium will at the same time prevent the
unsteady working of the same, which otherwise would be the case owing to the very
light work thrown upon it.
By the addition of a second bevil wheel (11) on the governor spindle and a clutch
with proper notches between them which connects either the one or the other of the
two bevil wheels to the spindle the engine can be made reversible, and whether
running forward or backward the cam gear will always go the same way.
The draining of the cylinder 1 is affected at each stroke when the exhaust port
is open through a small hole 36 in the centre of each exhaust valve, and a bridge in
the centre of the port prevents the escape of the steam through this hole when the
valve is closed (see Figure 4).
Having now described the nature and object of the said Invention, together with
the manner in which the same is to be or may be performed or carried into practical
effect, I would remark in conclusion that I claim as the Invention communicated to
me by the above named Carl Rudolf August Virck, the above described improvements
in or connected with the valve gear of steam engines, substantially as described, and
as illustrated on the accompanying Sheet of Drawings, and the application of the

page_text: same either with or without the "expansion cylinder" or with any other expansion
mechanism to steam engines, and also the use of the "expansion cylinder" in con-
nection with any other valve gear, and the use of exhaust slide valves inside of the
cylinder or of its covers, and the above described improvements in or connected
with the governor; but the Inventor desires it should be distinctly understood that
he does not limit bimself to any particular construction or arrangement, shape, and
relative positions of the parts, as such may be varied without departing from the
above described main features of the Invention or violating the principle involved
therein, and specially desires it should be understood that the principle of the
expansion cylinder may be carried out in various ways, and he claims such generally
whenever the expansion is effected by steam acting in one or more cylinders
provided with valves controlled by the governor.
In witness whereof, I, the said Bristow Hunt, have hereunto set my hand
and seal, this Tenth day of August, in the year of our Lord One thousand
eight hundred and seventy-eight.
BRISTOW HUNT. (L.S.)