CERTAIN IMPROVEMENTS IN THE STEAM ENGINE
Year: 1854

page_text: LETTERS PATENT to Thomas Craddock, of Portway Foundry, Potter's
Lane, Wednesbury, Staffordshire, Engineer, for the Invention of "CERTAIN
IMPROVEMENTS IN THE STEAM ENGINE."
Sealed the 29th December 1854, and dated the 2nd September 1854.
PROVISIONAL SPECIFICATION left by the said Thomas Craddock at
the Office of the Commissioners of Patents, with his Petition, on the
2nd September 1854.
I, THOMAS CRADDOCK, of Portway Foundry, Potter's Lane, Wednesbury,
Staffordshire, Engineer, do hereby declare the nature of the said Invention
for "CERTAIN IMPROVEMENTS IN THE STEAM ENGINE" to be as follows:-
The Invention consists in an improvement whereby the expansive valve is
made to alter the cut-off of the steam on its entering the cylinder, so as to
apportion the quantity of steam admitted on to the piston in proportion to
the resistance the engine has to encounter, by which means great economy in
the use of steam and regularity in the motion of the engine is obtained. This
is accomplish by a simple yet novel application of the worm and worm wheel
acting in connection with the governor, the resistance of the expansive and
steam valve being reduced to a minimum amount by causing the pressure of
the steam to act on the back of the valve through the intervention of vul-
canized india-rubber tube, or it may be vulcanized sheet india-rubber. .The.

page_text: fluid in contact with the india-rubber, being cold water, is in contact with the
steam that enters the engine. In this way the most complete equilibrium is
established between the pressure of the steam on the face of the valve and
the force on the back of it, so that the motion which alters the cut-off is
imparted to the valve with ease; the ware is much less, and the object is
attained efficiently.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Thomas Craddock in the Great Seal Patent Office on the
2nd March 1855.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
CRADDOCK, of Portway Foundry; Potter's Lane, Wednesbury, Staffordshire,
Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Second day of September, in the year of our Lord
One thousand eight hundred and fifty-four, in the eighteenth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Thomas Craddock, Her special licence that I, the said Thomas
Craddock, my executors, administrators, and assigns, or such others as I, the
said Thomas Craddock, my executors, administrators, and assigns, should at
any time agree with, and no others, from time to time and at all times there-
after during the term therein expressed, should and lawfully might make, use,
exercise, and vend, within the United Kingdom of Great Britain and Ireland,
the Channel Islands, and Isle of Man, an Invention for "CERTAIN IMPROVE-
MENTS IN THE STEAM ENGINE," upon the condition (amongst others) that I, the
said Thomas Craddock, by an instrument in writing under my hand and seal,
should particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause the same to
be filed in the Great Seal Patent Office within six calendar months next and
immediately after the date of the said Letters Patent..
NOW KNOW YE, that I, the said Thomas Craddock, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement (that is to say), having reference to the accompanying Drawing (see
Drawing):
The nature of this my Invention consists in arrangements whereby I balance
the pressure of the steam acting against the face of the steam and expansive

page_text: valves by a corresponding and self-adjusting pressure, which, by the means
described below, is made to act on the back of the valves, and by which the
wear and resistance to motion in the valves are reduced to a minimum amount,
so that the second part of my Invention, which consists in arrangements for
regulating the supply of steam to the engine, in accordance with the resistance
it has to encounter, is rendered effective.
Before proceeding to explain this Invention in detail by the aid of the
accompanying Drawing, I remark, that whenever a repetition of the same
letters or numbers occur on the same Figure, in all such cases, unless there be
a dot' thus, in connection with the letter, it always indicates one continuous
part, as at 19, 19, &c., see Fig. 3, which is the foundation of the expansive
motion and its four bearings, all cast in one piece. The same letters and
numbers on all the eight Figures, from 1 to 8, indicate the same parts in all
those views.
Fig. 5 is a section at A, B, C, D (see Fig. 3); Fig. 7 is a section at E, F,
G, H; Fig. 8 is a section at I, J; and Fig. 4 is a section at K, L.
Fig. 1, it will be seen, is a sectional elevation, shewing the two parts of my
Invention conjoined. 1 represents the piston; 2, the face of the cylinder (the
cylinder is not shewn as it is not required for the proper explanation); 3 is the
steam valve; 4 is the expansive valve; 5, the friction rollers, fitted into bearings
cast on to the valves. These rollers will be seen bearing against the part 6,
which part 6 receives the pressure from the part 7, which has the pressure
communicated to it from the india-rubber tube 8. This tube is enclosed on all
sides except that bearing on (what I will call) the moveable piston 7, by the
pressure box 9.
When the valves are in motion the friction rollers 5 move up and down on
the face of the part 6; this part 6 is prevented from moving in the direction
of the stroke of the valves by projecting pieces cast on to the pressure box
9, and seen in dotted lines at 1, Fig. 2. The pieces 6 are free to press on
the valve through the friction rollers 5. In the cross section, Fig. 11, is seen
another view of the piston 7, which is there represented as made of mahogany,
with iron th thick on the side next the india-rubber tube and on its opposite
side. The piston is made thus for lightness, and to keep the heat away from
the india-rubber tube 8.
The india-rubber tube is filled with cold water, and the tube x is also partly
filled with cold water; the tube x is then connected with the steam pipe that
conveys the steam to the engine, so that, by the steam pressing on the water,
a pressure is thrown on every part of the india-rubber tube, corresponding to
the pressure of that of the steam itself. In the section, Fig. 11, the pressure

page_text: box 9 is seen in the other direction. The piston may be of any shape, but is
shewn as extending the whole length of the valve; so also may sheet india-
rubber be substituted for the tube, and it, like the piston 7, may have any shape
given to it, which circumstances may render desirable. The same pressure per
square inch is communicated to the interior of the india-rubber tube as that on
the face of the valves, and it instantly participates of every variation which the
steam itself is subject to, so that by contracting or enlarging the surface of the
india-rubber, which acts on the moveable piston 7, the exact force requisite to
retain the valves to their faces is obtained. I shew the india-rubber tube in
the Drawing, and also that form of pressure box, as one of the simplest, and at
the same time one of the most adjustable modes of application, as in that
arrangement a large or small force may be thrown at pleasure upon the rollers,
and through them on to the back of the valves; as, by inserting a fixed piece
above the piston in the middle portion of the pressure box 9 of any given length,
the remaining portions of the two ends of of the india-rubber tube would alone
press on the moveable piston, and through it on to the rollers, and thence to
the valves. The top end of the india-rubber tube is connected to the pipe
communicating with the steam, entering the engine by means of a union joint,
which renders it tight against any pressure; the other end of the india-rubber
tube is closed by being firmly pressed together by screw pressure, or it may
be made closed at the one end, as it will be seen on inspection that no
strain can exist on the india-rubber tube, as all the strain is borne by the
surrounding metal of the pressure box 9 and the top of the piston 7; or in
case of a fixed piece being introduced above a part of the piston, as above
referred to, then this fixed piece sustains pressure corresponding to its length
and breadth, which is so much taken off the piston, and as a consequence
off the back of the valves. One, two, or three of these tubes may be made
the means of distributing the pressure in the most desirable way over the
back of the valves, and thus reduce the friction to the smallest amount by
the friction rollers sustaining the whole pressure of the steam, so that the valves
move almost in equilibrium.
At this point the second part of my Invention comes to our aid, and by
its causing a self-adjusting of the eccentric, which drives the expansive
valve, the quantity of steam admitted on to the piston is apportioned to the
wants of the engine.
On referring again to Fig. 1, a is the port leading from the boiler to the
engine, from whence the steam passes through e, e, into the circular passage
d, d, in the expansive valve 4, and from thence through the ports c, c, in
the steam valve 3 to the passage b, leading to the under side of the piston 1.

page_text: With the valves and eccentrics, as shown at Fig. 1, the steam valve is sup-
posed to be coming down and the expansive valve going up; it will therefore
be readily understood that when the ports leading to the circular passage d, d,
have passed those of c and e in the steam valve 3, that the communication
from the boiler to the under side of the piston will be shut off; bearing this in
mind in conjunction with the fact that the steam will be shut off sooner or
later, according to the position which the eccentric which drives the expansive
valve is in, relative to the eccentric that drives the steam valve, so that thereby
is determined the time that the steam can continue to flow into the cylinder
during the stroke of the piston, which may be throughout its whole stroke, or
be stopped off before the piston has made th part of its stroke; such being
the case, it is easy to see how the speed of the engine must be governed.
I now proceed to describe the means by which I adjust the eccentric, so as
to cut the steam off sooner or later, and thus economize steam and produce
uniformity in the motion of the engine. On referring to Fig. 3, which shews
a plan of the expansive motion with that portion of the main shaft 15 of the
engine which is necessary for explanation, it is there shewn that by two
equal sized wheels 17 and 16, the motion is communicated from 17, which is
on the engine shaft 15, to 16, which is on the shaft 20, of the expansive
motion. I should here remark, that it is not absolutely necessary to introduce
the second motion by the wheel 16 and shaft 20, as the various parts might be
applied direct on to the main shaft 15 of the engine; but that in such case
they would become larger in proportion to the size of the engine shaft 15, as
compared with the shaft 20 of the expansive motion. All we have to note
further in connection with the engine shaft 15 is, that the steam eccentric is
seen at 121, and the standard that carries the governors is seen at v; the wheels
that drive it are seen at w¹, and w, w, being the wheel on the engine shaft 15,
and w' the wheel on the governor spindle. The motion from the governor is
conveyed to the expansive motion by the levers s and s¹; t, t, and t', are the
supports which carry the little shaft and levers s", s', and s; t and t grow out of
the governor standard v; and t¹, from the foundation plate 19 of the expansive
motion.
On referring again to Fig. 1 and Fig. 2, which shew a sectional and a per-
spective elevation of the two parts of this Invention conjoined, it will be seen
that the shaft 20, which is put in motion by the wheel 16 gearing into the
wheel 17 (as before described), is supported by four bearings and foundation
plate 19; on to this shaft 20 the worm i, i, i, is placed, as seen in Fig. 1, it
being held concentric with the shaft by the bearing on 19, so as not to occasion
friction. To the right of this bearing is the worm, and to the left a ratchet, all

page_text: ⋅
in one piece. At h, k, is seen a part which is keyed fast on to the shaft 20, the
bush part that is keyed on being covered by the worm i; this part k will be
seen to carry a small worm wheel w, which gears into the worm i, and on
referring to Fig. 7, it will be seen that the small worm wheel w has a worm
also cut on its face, which takes into the teeth of the larger worm wheel m, as
seen at Fig. 7 and Fig. 1; with this larger. worm wheel all the parts are cast
in one piece that are marked m, so that it will be seen that the catches n' and
n (see Fig. 1) are carried round with the large worn wheel. The part p is
cast on to the eccentric that drives the expansive valve, and q is a separate
plate with a boss bored out to fit the shaft 20, on to which it is also keyed,
and the expansive eccentric is made to move freely on this boss, as seen in
Fig. 1. The expansive eccentric is set to some fixed point by the plate q,
which has a circular slot in it, which in conjunction with the screw bolt, which
is made fast into the expansive eccentric, and does not allow the expansive
eccentric to move back beyond the point intended; but the circular slot allows
it to be moved forward by the worms and worm wheels, so as, if required, to
cut off the steam from entering the cylinder through the expansive valve; it will
do so at its most advanced position almost as soon as the piston commences
its stroke, and so long as the engine be at the full speed to which the governors
are set.
I now come to the explanation how the worms and worm wheels cause the
expansive: eccentric to be moved in advance when the engine is advancing
beyond the desired speed and the governor balls open, as seen in Fig. 2.
When the governor balls are down, as seen in Fig. 1 and Fig. 5, then all
things go on without alteration, as the worms and worm wheels go round
with the shaft, and the relative position of all of them remain the same;
but when the governor balls are open, as in Fig. 2, then the lever s (sec
Fig. 5), which is pressed by the spring y, is forced into the ratchet i, which it
will be remembered is one with the worm i; the worm i then becomes fixed,
and the part, which is keyed on to the shaft 20, carries the small worm
wheel w round with it, and in so doing the large worm wheel and all that is
marked m, n, and p; but from the moment the worm wheel i stands still and
the parts , w, and m go round it, the small worm wheel w has a motion given
to it by the worm i. This motion again by the worm on the face of w, as before
explained, gives a slow but distinct motion to the larger worm wheel m, and,
in consequence, to all the parts marked m, n, and p, so long as the governor
remains open, as seen in Fig. 2. so that the expansive eccentric will be slowly
advancing and the steam be cut off carlier, as before explained. But on the
engine being barely supplied with steam sufficient to keep it to its speed, the

page_text: governor balls fall a little, and then the levers (see Fig. 5) is forced out of
the ratchet and the expansive eccentric remains fixed until the speed of the
engine varies again; if it should do so, by again increasing its speed, by work
being thrown off or the steam getting up, the lever s is again brought into the
ratchet and the expansive eccentric is moved still further forward. But should
the engine get below its fixed speed, and the governor balls fall farther than in
the first instance, then the part o, o, is brought to act upon the catches n' and
n, which, as will be seen, push forward and hold the expansive cccentric in con-
nection with the worms and worm wheels; but when these catches are lifted by
the part o, o, which is pushed into contact with them by the continued falling
of the governor balls, as seen at Fig. 4, Fig. 1, and Fig. 3, the expansive
eccentric p gradually goes back to its fixed point, unless the governors are first
caused to rise by the engine again increasing in speed; in such case the first
thing that takes place is to remove o, o, out of the circle described by the tail
of the catches n' and n; this is done, as is seen at Fig. 4, by o, o, being drawn
up by the governor acting through the lever s¹ and rod r¹, so as to cause o, v,
to approach the position seen in Fig. 2. I have said that the expansive
eccentric p gradually gets back to its fixed position; it is so by the catch n
being in the ratchet when the catch n¹ is out, so that by giving this ratchet a
finer or coarser pitch it will go back faster or slower, as may be desired; the
same holds good as to the threads and pitch of the worms and worm wheels in
advancing it faster or slower, as may be desired.
In applying this expansive motion to my double cylinder engines, I set
the expansive eccentric so that the permanent cut-off shall not be less
than half stroke in the high pressure or small cylinder. This is effected
by means of the part q, q, and the screw bolt, seen at Fig. 1, as screwed
into the expansive eccentric; and from this point, as before explained,
the worms and worm wheels in conjunction with the governors carries
the expansive eccentric further forward, so as to regulate the speed of the
engine, and extend the economy of the expansive action of the steam!
But, as before remarked, the cut-off may be left entirely to the expansive
motion, so as to return at slow speeds of the engine to full pressure
throughout the whole stroke, and consequently it is adapted to any engine
and any degree or no degree of fixed cut-off. It is almost needless to
remark that what is done by the governors can be done by hand, or by.
any other means that will clevate and depress the levers s and s' at the
proper time. g and h (see Fig. 1) are the ports in the steam valve that
convey the steam on the completion of its duty in the high pressure cylinder
into the low pressure or large cylinder; it will be seen that q'is just opening

page_text: to f, which allows the steam to pass from the top of the high pressure cylinder
to the top of the low pressure cylinder. At 18 (see Fig. 1 and Fig. 2) is
seen a part, the only object of which is to facilitate the setting of the expan-
sive eccentric, as by unscrewing the two bolts which bolt the wheel 16 to it,
the wheel 16 turns upon the boss, as will be seen by inspecting the Drawings.
Fig. 6 is an end view; 13 is the weigh shaft; and 13' is the lever, to which the
eccentric rod 12 connects, that drives the steam valve; and 121 is the steam
valve eccentric. At Fig. 9, Fig. 10, and Fig. 12 is scen a mode of constructing
one of these valves, to be placed in the steam pipe as a substitute for the ordi-
nary throttle valve; the part to be attached to the steam pipe will be seen to be
divided by a bridge of metal, forming the ports a and c. These ports are covered
by the hollow of the moving part of the valve b, and the governors are sup-
posed to be connected to the rod o, and to open and close it in the same way
as it does the ordinary throttle valve. The advantage of this valve over the
ordinary throttle valve is, that in no case can it fail to check the speed of
the engine, as when closed it acts as a complete stop valve, as will be seen.
As none of the other details relating to this valve differ from those I have
given, it is useless to go over them again.
The two worms and we, two worm wheels w and m, and the ratchet on
the plate p, which is attached to the expansive eccentric, are arranged for an
engine with a two-feet stroke, and making 60 strokes per minute; and if we
suppose, as in this case, that the expansive eccentric has what I have called
its fixed cut-off set at half stroke, then the expansive eccentric will, when
the levers is in the ratchet i, advance, so as to cut the steam off at on tho
engine, making 12 strokes; and on its making 19 strokes it will cut off at ;
by the time it has made 30 strokes it will cut off at ; at 44 strokes,; and
at 65 strokes, or in little more than a minute, it will cut off at 3. On the
governors falling, and o, o, being brought to act on the tail of the catches n¹
and n, the eccentric returns at 5 strokes of the engine, so as to bring the cut-
off from to; and at 74 strokes from 3 to; at 94 strokes from 3 to;
at 11 strokes from to; and at 14 strokes of the engine the expansive valve
will have returned from cutting the steam off' atto, which is that to which
it is set. It is arranged to come, back so much faster than it advances to
meet the case of work being thrown heavily and suddenly on.
Having by the Drawing clearly illustrated and by this Specification fully
explained this my Invention in detail, I claim,
Firstly, the peculiar method by which I balance and hold the valves to their
faces, as explained in this Specification, so that the steam is made to act on
the back of the valve with all the advantages of the old closed valve box, but

page_text: without its disadvantages, whether such end be obtained in the identical
manner here described or the form of its parts be changed; and whether the
substance that retains the fluid be india-rubber, as in this case, or some other
yielding body merely as a substitute for it.
Secondly, I claim the combination of the worms and worm wheels, as
described in this Specification, for the purpose of giving motion to the eccen-
tric or a substitute for the eccentric, when such substitute for the eccentric
be used in combination with the worms and worm wheels; and whether the
arrangements be identically such as shewn in the Drawing, or some modifi-
cation of those shewn, and whether the same be put in motion by mechanism
acted on by the engine, as in the case of the governors, or by hand.
Thirdly, I claim these two parts of my Invention, whether acting conjoined
or separate, and to whatever kind of steam engine they may be applied;
whether to the steam pipe, as a substitute for the throttle valve, or to the
working valves of the engine.
In witness whereof, I, the said Thomas Craddock, have hereunto set
my hand and seal, this Second day of March, One thousand eight
hundred and fifty-five.
THOMAS CRADDOCK. (L.S.)