IMPROVEMENTS IN STEAM ENGINES
Year: 1850

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, we, WILLIAM
POLE, of Great George Street, Westminster, Engineer, and DAVID THOMSON,
of Belgrave Road, Pimlico, Engineer, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Eleventh day of June,
One thousand eight hundred and fifty, in the thirteenth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto us, the said
William Pole and David Thomson, our exors, admors, and assigns, Her
especial licence, full power, sole privilege and authority, that we, the said
William Pole and David Thomson, our exors, adñors, and assigns, or such
others as we, the said William Pole and David Thomson, our exors, admors,
or assigns, should at any time agree with and no others, from time to time
and at all times during the term of years therein expressed, should and law-
fully might make, use, exercise, and vend, within England, Wales, and the
Town of Berwick-upon-Tweed, our Invention of "IMPROVEMENTS IN STEAM
ENGINES;" in which said Letters Patent is contained a proviso that we, the
said William Pole and David Thomson, or one of us, shall cause a particular
description of the nature of our said Invention, and in what manner the same
is to be performed, by an instrument in writing under our hands and seals,
or under the hand and seal of one of us, to be enrolled in Her Majesty's High
Court of Chancery within six calendar months next and immediately after the

page_text: date of the said in part recited Letters Patent, as in and by the same,
reference being thereunto had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, we, the said
William Pole and David Thomson, do hereby declare that the nature of our
said Invention, and the manner in which the same is to be performed, are
particularly described and ascertained in and by the following statement
thereof, reference being had to the Drawings hereunto annexed, and to the
figures and letters marked thereon, that is to say :-
Our Invention consists in an improved arrangement of valves, and apparatus
for moving the same, applicable to that description of steam engine commonly
known as the double combined or compound cylinder steam engine (some-
times also called Woolf's engine) having two cylinders of unequal capacities,
the steam being first admitted at high pressure into the smaller cylinder, and
then being allowed to expand into the larger: The object usually sought in
the use of this kind of engine is, so to apply the principle of expansion that
the moving force shall be less unequal during the stroke than when a similar
degree of expansion is used in a single cylinder. For example, if the steam
be expanded to six times its volume in a single cylinder (by cutting it off
after 1/6th of the stroke is passed over) the moving force acting on the piston
will be about six times as great at the commencement as at the end of the
stroke; this irregularity tending to produce violent and destructive concussions
to the machinery, and requiring all its parts to be made proportionably
stronger than would be otherwise necessary, as well as producing other incon-
veniences in the working of the engine. But by expanding the steam to the
same extent in a double cylinder engine, the irregularity may be made much
less, by which the evils above mentioned may be considerably diminished,
while the full economical benefit of the expansion is retained. Now we have
found, in the course of our experiments and investigations on this form of
engine, that it is advisable not to allow the steam to enter the small cylinder
during the whole of its stroke (as is most commonly done), but to cut it off
after a certain portion of the stroke has been passed over, and to allow
the expansion to commence at that point. And we have moreover discovered
that there is a certain part of the stroke (depending, as will be hereafter
explained, on the degree of expansion to be made use of) at which it is more
advantageous to cut off the steam than at any other, by reason that the
irregularity in the moving force before mentioned is then reduced to a
minimum.
The following example (which we have put in the form of a tabular state-
ment for the sake of distinctness) will illustrate the foregoing remarks:-

page_text: COMPARATIVE STATEMENT of the Inequality of the Moving Force in a single
and double cylinder Engine, supposing the Steam to be expanded at the
end of the Stroke to six times its Original Volume :-
This example shows that the case in which the steam is cut off from the
small cylinder at one half the stroke produces less inequality, and is, there-
fore, more advantageous than either of the others with which it is compared.
For higher degrees of expansion than six times, the steam must be cut off
earlier; for example, for eight times expansion it should be cut off at about
four tenths of the stroke of the small cylinder; for 10 or 12 times at about
1/3rd, and so on. Having therefore determined on the degree of expansion to
be used, and the point of the stroke at which the steam is to be cut off from
the small cylinder, the dimensions of the two cylinders may be proportioned
to each other by the ordinary rules. We would explain that in order to
render the foregoing calculations and statements as simple as possible, we
have made no allowance for the effect of loss of steam in the passages or other
slight disturbing causes, as these do not materially affect the principles we
have laid down. Moreover we find that by the use of certain kinds of valves
of simple construction, such as we shall hereafter describe, these losses and
irregularities may be reduced to a much lower amount than has been here-
tofore done with this kind of engine. We have also further to remark that it
is very essential to the beneficial and economical working of the double
cylinder engine that the valves (meaning by this term the entire apparatus
used for admitting steam to the small cylinder, for forming a passage between
the two cylinders, and for exhausting the steam from the large cylinder)
should be of the simplest possible character, and so arranged as to cause. the

page_text: least possible loss in the passages; and our experiments and investigations
have led us to consider that a single sliding valve of suitable construction
(examples of which we shall hereafter more particularly describe and shew)
is the best adapted for this purpose. And we also consider it very important
that this single valve and its apparatus should be so constructed as to cut off
the steam from the small cylinder at any required point of the stroke without
the addition of any separate expansion valve. And although there is, as we
have before stated, a certain part of the stroke at which it is more advan-
tageous to cut off the steam than at any other, yet, whereas it frequently
happens that one and the same engine is required to work up to variable
degrees of power, and since it is desirable, for the sake of economizing fuel,
to produce this variation of power by varying the degree of expansion, it
becomes necessary that the said valve and apparatus for moving it should
be capable of easy adjustment, by which the point of the stroke, at which
the steam is cut off from the small cylinder, may be varied at pleasure.
Now having explained the objects which we consider it desirable to effect,
we declare our Invention to consist of an improved arrangement of valves and.
apparatus for moving the same, applicable to double cylinder steam engines,
according to which arrangement a single sliding valve is made to answer the
purpose of opening the requisite passages to and from both cylinders in the
most advantageous manner, and also to cut off the steam from the small
cylinder at any required point of the stroke within reasonable limits, without
the addition of a separate expansion valve.
We now proceed to describe how our Invention is to be carried into effect.
Figure 1, on the Drawings hereunto annexed, is a plan of a portion of a
double cylinder engine to which our Invention is shewn as applied, and
Figure 2 is a section taken on the red dotted lines on the plan; Figures 3,
4, 5, are also similar sections, but shewing the valve in different positions.
The same letters refer to the same parts in all the Figures; and we would
premise that we shall only describe those parts which are essential to the
understanding of our Invention, the other details shewn on the Drawings being
such as are usual and commonly understood by engineers. A is the smaller
cylinder with its piston B, and C the larger one with its piston D, both these
pistons being connected to the same end of the engine beam in the usual
way; E is a cylindrical valve box or nozzle, the upper and lower portions of
which are connected by the exhaustion pipes F and F¹ respectively with the
condenser, while the middle portion is supplied with steam from the boilers
by the steam pipe G; a, b, are ports or passages from the valve box to the
top and bottom respectively of the small cylinder, and c, d, similar ports or

page_text: passages, but of larger area, to the large cylinder; H is the valve, consisting
of four pistons e, f, g, h, connected together and furnished with metallic ring
packing, so as to slide steam tight up and down in the cylindrical valve box E.
The
space between the two upper pistons e, f, has a constant communication,
by a pipe or passage i, with that between the two lower pistons g, h. The
entire valve is moved by a rod k. K is a shaft, to which is given, by wheels
or any other convenient means, a motion in the direction of the arrow exactly
corresponding in angular velocity with that of the crank shaft of the engine;
Z is a cam firmly fixed to the shaft K, and m is another or expansion cam
fixed by a bolts upon the cam l, but which, by reason of the bolt & passing
through a curved slot or groove, may be bolted or fixed in different positions
with respect to the cam l, according to the degree of expansion required in
the small cylinder. As the shaft K revolves, the cams come in contact with
rollers n, o, which, by means of levers p, q, and a connecting rod r, move the
rod k of the valve. The action of the valve is as follows:-The figures shew
the apparatus adjusted to cut off the steam at half the stroke of the small
cylinder. In Figure 2 the steam pistons B, D, are shewn at the top of the
cylinders, and are supposed to be commencing their down stroke. The steam,
coming from the boilers by the steam pipe G, enters the middle space of the
valve box E (limited by the two middle pistons of the valve f, g), and passes
through the port a into the top of the small cylinder. At the same time the
steam in the portion of the small cylinder under the piston is at liberty to pass
through the port b, up the valve pipe i, and through the port c into the top
of the large cylinder, in which it will expand as it forces the piston down.
Also the steam contained under the piston of the large cylinder escapes
through the port d into the bottom part of the valve box, and thence by the
pipe F to the condenser. The course of the high-pressure steam entering
the small cylinder is shewn in all the figures by red arrows, that. of the steam
passing from the small to the large cylinder by green arrows, and that of the
exhaustion from the large cylinder by black arrows. The steam pistons B, D,
now descending, the shaft K revolves in the direction of the arrow without
moving the valve until the pistons have made half their stroke, when the
projecting part of the expansion cam m, arriving at the bottom roller o,
thrusts it down, and by that means moves the valve into the position shewn
in Figure 3, where the piston f covers the port a, and thus prevents further
ingress of steam to the small cylinder for the remainder of the stroke, the
other ports and passages being, however, left open as before. The form of
the cam allows the valve to remain in this position as the shaft revolves, till
the steam pistons B, D, have arrived nearly at the bottom of the cylinders,

page_text: when the projection of the fixed cam l, following the expansion cam, comes in
contact with the roller o and thrusts it down still further, carrying the valve
with it into the position shown on Figure 4. The steam above the small
piston then finds its way through the port a, the pipe i, and port d, into the
lower part of the large cylinder; the steam above the large piston passes
through the port c and the eduction pipe E into the condenser, and a fresh
supply of steam from the boilers enters the bottom of the small cylinder through
the port b. The steam pistons B, D, then ascend, the valve remaining
stationary till half the up stroke has been travelled over, when the projection
of the expansion cam m arrives at the upper roller n and lifts it, and with it
the valve, into the position shewn in Figure 5, where the piston g of the
valve stops the ingress of steam into the small cylinder without interfering
with the other passages. Finally, when the steam pistons B, D, have arrived
nearly at the top of their stroke, the fixed cam 7, still following the expansion
cam m, lifts the upper roller n still further, and brings the valve again into
the position shewn in Figure 1, herein-before described. When any other
degree of expansion is required to be made use of, the bolts (by which the
expansion cam is fastened to the fixed cam) must be loosened, and the expan-
sion cam m shifted round upon the fixed cam l either forward or backward,
and refixed so as to strike the rollers sooner or later, as may be required. In
order that the above-described action of the valve may be properly obtained,
it is necessary that the breadth of the valve pistons and the spaces between
them be properly proportioned to the size and position of the ports; and it is
also necessary that the form and position of the cams be such as to give to
the valve the proper degree of motion, and at the proper times; but these
arrangements and adjustments being of a nature to which mechanical
engineers are perfectly well accustomed, we consider. it unnecessary to explain
them further. The peculiar advantages of the valve we have above described
are, first, that the valve, being as single one, is exceedingly simple in construc-
tion and action, it has all the advantages of slide valves, and is, at the same
time, an equilibrium valve, the steam pressure having no tendency to produce
friction on the faces. Second, the passage, that forms the communication
between the two cylinders, is as direct as. possible. It is never open cither to
the boilers or to the condenser, and it is surrounded by steam of a high tem-
perature, these being the most favorable conditions as regards economy.
Third, the steam may be cut off from the small cylinder at any desired
point of the stroke, without any separate expansion valve.
Figures 6, 7, 8, 9, and 10, shew modifications in the forin of the valve by

page_text: which the same results are obtained. In Figures 6 and 7 the valve is shewn
of the D shape, packed at the back in the usual way.
Figures 8, 9, and 10 shew a valve having three sides, one of which forms a
face towards the small cylinder, another towards the large cylinder, while the
third or curved side receives suitable packing. The various parts are marked
with the same letters as the corresponding parts in Figures 1 to 5, and the
action in each case is the same as herein-before described.
When
Figures 11, 12, 13, 14, 15, shew a modification of the apparatus for
moving the valve by applying two expansion cams instead of one.
only one expansion cam is used, as already described, the obliquity of the
connecting rod of the engine causes the point, at which the steam is cut off
in the up stroke to be somewhat different from that in the down stroke of the
engine. In order to obviate this, we use two expansion cains m, z, one on
each side of the fixed cam l. One of these expansion cams m acts on the
upper roller n to cut off the steam in the up stroke, but misses the lower
roller o; the other expansion cam acts on the lower roller o to cut off the
steam in the down stroke, but misses the upper one n. A bolt y is fixed on
the cam z and passes through a slot in the cam m, and by means of this bolt
the position of the two expansion cams may be so adjusted with respect to
each other, the valve may be made to cut off the steam after exactly the
same portion of the stroke is passed over in both the up and down motions of
the engine.
Having now described the nature of our Invention and the manner in
which the same is to be performed, we wish it to be understood that we do
not claim as our Invention the application of expansion in the small cylinder
of the double cylinder engine, this having been heretofore practised, nor do we
claim any of the parts of which the apparatus we use is composed, taking
such parts separately. But we claim the application to the double cylinder
expanding engine of a single sliding valve and apparatus for moving the same
which shall not only serve to admit the steam to and allow of its passage from
both cylinders, but shall also be so constructed as to serve for cutting off the
steam from the small cylinder at any desired point of the stroke within
reasonable limits, without the addition of any separate expansion valve.
In witness whereof, I, the said William Pole, have hereunto set my
hand and seal, this Tenth day of December, in the year of our Lord
One thousand eight hundred and fifty.
WILLIAM (L.S.) POLE.

page_text: AND BE IT REMEMBERED, that on the Tenth day of December, in the
year of our Lord 1850, the aforesaid William Pole came before our said Lady
the Queen in Her Chancery, and acknowledged the Specification aforesaid,
and all and every thing therein contained and specified, in form above
written. And also the Specification aforesaid was stamped according to the
tenor of the Statute made for that purpose.
Enrolled the Eleventh day of December, in the year of our Lord One
thousand eight hundred and fifty.