CERTAIN IMPROVEMENTS IN STEAM ENGINES
Year: 1838

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
CHAPMAN, of Whitby, in the County of York, Engineer, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Thirteenth day of January, One thousand eight hundred and
thirty-eight, in the first year of Her reign, did, for Herself, Her heirs and
successors, give and grant unto me, the said George Chapman, Her especial
licence, full power, sole privilege and authority, that I, the said George
Chapman, my exors, admiors, and assigns, or such others as I, the said George
Chapman, my exors, adñiors, 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 lawfully might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed, and also within all
Her Majesty's Colonies and Plantations abroad, my Invention of "CERTAIN
IMPROVEMENTS IN STEAM ENGINES;" in which said Letters Patent is contained a
proviso that I, the said George Chapman, shall cause a particular description
of the nature of my said Invention, and in what manner the same is to be
performed, to be inrolled in Her said Majesty's High Court of Chancery
within six calendar months next and immediately after the 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, I, the said
George Chapman, do hereby declare the nature of my said invented im-
provements, and the manner in which the same are to be performed, are

page_text: particularly shewn in and by the following description thereof, and in the
Drawings hereunto annexed and referred to, that is to say:-
My said invented improvements are twofold, consisting, first, of an improved
boiler or method of generating steam; and, secondly, of an improved means of
regulating the supply of steam to the working cylinder.
And first, with respect to my improved boiler, I declare, that whereas it has
been hitherto the practice, more especially in marine boilers, to enclose the
furnace and boiler in one chamber or case of the same strength, and subject to
the same pressure in every part, instead of this I make the furnace and
boiler two separate and distinct vessels, which have no communication with
each other (except by means of a force pump, as herein-after mentioned), and
are adapted to sustain different pressures.
Figure 1 of the Drawings annexed is a cross section of a small steam ship
provided with furnaces and boilers on this improved plan. A, A, are the
furnaces; B, B, outer casings to the furnaces, which are kept filled with water
at a temperature always below the boiling point. As these casings are not
required to sustain any great pressure, they may be made externally of any
shape best suited to the place where the furnaces are fixed. C, C, are the
boilers, which I make of a cylindrical shape, as being the strongest, and place
directly over the furnace. D, D, return flues within the boilers, but which
may be dispensed with if desired. The furnace casings B, B, are supplied
with water from the hot well of the engine, which being at a higher level, the
water descends from it by its own gravity; and after the water in these
casings has been heated to near the boiling point, it is forced by a pump or
pumps, or other equivalent means, into the boilers C, C, to be there converted
into steam. The casings B, B, may be either provided at top with several
outlets, covered by light valves, to admit of the escape of any excess of water
which may flow into them from the hot well, or they may be left together
open. The furnace may be lined on the inside with fire bricks, fire clay,
or other fire-resisting material; but in many cases it will be found sufficient
to line those parts only which are more directly exposed to the action of
the fire.
And now, to describe more particularly the second part of my said invented
improvements, 1 declare that my object in these improvements is, to stop the
steam from entering the working cylinder at any fractional part of the stroke
of the piston, according to the elasticity of the steam in the boiler, or the duty
to be performed, while the steam previously admitted is allowed to expand
and effect the remaining part of the stroke. The mechanical arrangements
by which this object is accomplished are shewn in Figures 2, 3, and 4 of

page_text: the Drawings annexed. A is a cam or wiper which I fix on the principal axle
of the engine, or any other axle which is already fixed or which I may fix for the
purpose, having a rotary motion. On the circumference of this cam there are
as many teeth or cogs as that one tooth will pass any fixed point during either
one descent or ascent of the piston; for instance, if the shaft on which the cam
is fixed revolve once during the time that the piston is making a double stroke,
the cam must have two teeth; if the shaft revolves twice round in the above
time, the cam must only have one tooth. Or, to put the matter otherwise,
suppose the cam revolves once in the time the engine is making two double
strokes, then the cam must have four teeth, and so on in proportion. A good
shape for the teeth of the cam is formed in the following manner; that is to
say, suppose the engine is constructed with a cross head on the top of the
piston rod above the cylinder, from each end of which cross head descends a
connecting rod, the bottom ends of which connecting rods are attached to two
cranks, one on each end of a shaft or axle passing through from side to side
under the bottom of the cylinder, and suppose the connecting rods are three
times the length of the stroke of the piston, then I draw a circle whose
diameter is the length of the stroke upon a scale which is the full size of the
diameter of the cam at the bottom of the teeth, as shewn in Figure 3, and
through the centre of this circle I draw a perpendicular line, extending it
upwards to more than three times the diameter of the circle; I then d ide
so much of this line as falls within the circle into any number of equal parts,
say eight, which parts I number from 1 to 8 downwards. I next take a
pair of compasses, set to the length of the connecting rods (which in this case
is three times the length of the stroke), and set one point in the circle at No. 1'
division, the other point in the perpendicular line above the circle, where it
may fall and carry the points from the division No. 1 to the division No. 1 in
the circumference of the circle, where I make the dot 1, which is the point the
crank pin of the engine would have arrived at when the piston had descended
one eighth part of the stroke; I then shift the lower point of the compasses to
division No. 2, placing the other point above the circle on the line as before, and
removing the lower to the circumference as before. I make the dot 2, and so
on through all the remaining points from 1 to 8, which is the place where the
crank pin of the engine would be at when the piston had performed the cor-
responding part of its stroke. I next draw lines from the centre of the circle
through each dot in the circumference considerably beyond the circle, and
upon the perpendicular line above the circle I prick off a part (say, two inches,
a little more or less, according to the size of the engine) to form the fore part
of the tooth of the cam, which part I divide into eight equal parts, and

page_text: number them from one to eight downwards. From the division No. 1, with a
pair of compasses set to the centre of the circle, I describe part of a circle
towards the left until it cuts the radial line No. 1, and no further. I likewise
draw lines from the other divisions till they cut the radial lines bearing the
same numbers. A regular curve, drawn through the points where the circular
and radial lines intersect each other, will then be the proper shape for the
tooth of the cam that has to open the steam valve to admit steam to the top of
the cylinder. The shape of the tooth to admit the steam to the bottom of the
cylinder requires to be rather different, and must be obtained as follows:-The
perpendicular line before described must be continued downwards, and the same
space (say, about two inches) pricked off on it, and divided into eight divisions,
as before, but marked from 8 to 1 downwards. With the compasses set to
the length of the connecting rods, you must then set one point in division No. 1
at the bottom of the perpendicular line, and the other point in the same line
where it may fall. The lowermost point must then be removed to the circum-
ference of the circle to the right hand, at which place you must make the dot 1.
Then shift the lowermost point of the compasses to the line at No. 2, and by
repeating the same process transfer the division to the circumference at 2.
After all the other divisions to 8 have been thus gone through, draw radial
lines as herein-before directed, and segments to intersect them at their proper
numbers. A curve drawn through the points of contact will be found to be
somewhat different from the curve obtained in the former case, and presents
the form which ought to be given to the tooth that is to admit the steam to
the bottom of the cylinder. And there is good reason for this difference in the
forms of the teeth, inasmuch as the piston travels the upper half of the cylinder
at a greater speed than it travels the lower half, and of course requires the
valve to remain open longer on the piston's ascent during the first half. If,
however, the engine have a beam to which the top end of the connecting rod
is attached, then, instead of the compasses being set in the straight line in
transferring the divisions from the diameter to the circumference of the circle,
the upper point must be set in a curve from the centre of the beam, as shewn
in Figure 4. The cam teeth A, A, (see Figure 2,) I make to act on the
end B of a lever B, C, the other end of which, C, is connected with the steam
admission or throttle valve of the engine by a connecting rod and lever. The
centre D of the lever B, C, is fixed ou a pin projecting at right angles from
the end of the bent lever E, F, which bent lever is supported on a standard
bolted to the floor of the engine house or to the framing of the engine, or any
other fixture which may be found most convenient. The end E, of the bent lever
E, F, is connected to the governor of the engine (where a governor is used), by

page_text: connecting rods; but where no governor is used the lever may be clamped to a
fixed support placed for the purpose in any position which the engineer may think
best suited to the elasticity of the steam in the boiler, or the duty the engine
has to perform. If there is a governor, the manner of action of the apparatus
is as follows:-The steam being up, and the engine being ready to start, the
engineer lifts the lever C by the handle, which opens the steam admission
valve, and keeps it open till the engine gets sufficient motion and the governor
balls have expanded to the proper degree, when he lets go the handle. (The
engineer will have previously clamped the lever to the connecting rods of the
governor at a point, as H, which he knows from practice to be nearly suitable
for the duty required). The engine continues its motion till the cam tooth comes
in contact with the end of the lever B, which it depresses, and raises the opposite
end C, which, by its connecting rod and levers I, K, turns the spindle L on
its centre ninety degrees, more or less, at every ascent and descent of the
piston. The reason that it should be turned as near ninety degrees as
possible is this, that on the spindle L is fixed the steam admission valve, which
is a thin disk or diaphragm, and when in its quiescent state this valve occupies
the full width of the steam pipe and shuts off the steam from the cylinder,
while, by turning the spindle on its centre ninety degrees, the thin edge of the
valve presents itself to the steam, which has a free passage to the cylinder.
The lever B, C, is so proportioned that a very small portion of the tooth of
the cam A touching the lever B will open the valve to the full extent required.
Were the lever B advanced, therefore, towards the cam A, so as to hold the
valve open till the piston performed the full length of the stroke, or even much
less than that, the connecting rod I would carry the lever K and spindle L, and
consequently the valve, further than to the proper point, that is, at right angles
where the valve is closed; to prevent which, I make the lever of the valve,
and the connecting rod of the lever that acts on it, in the following manner :-
To the centre spindle of the valve, when the valve is closed, I attach a
lever K, which lever extends from its centro at an angle of 45 degrees with the
horizon for a space of about two inches, more or less, according to the lift of
the lever B, C, after which it is bent until it becomes parallel to the horizon
for the space of about four inches more. In this lever, from about two inches
of its centre, there is a straight groove cut through it to where it is bent, after
which it continues in a curve, or part of a circle, whose centre is the length
of a lever M, one end of which is fixed to any suitable support, and the other
end attached to the connecting rod I of the levers K, M, by a round steel pin,
which projects from behind at right angles, and enters the groove in the valve
lever K. When, therefore, the end B of the lever B, C, is pressed down, the

page_text: opposite end C lifts the connecting rod I and guide lever M, and the steel
pin which projects from them, and on which they turn as a joint, lifts the
valve lever K until it comes to that part of the groove which is curved, at
which time the grooved part is in the line of its path, so that it does not carry
the valve lever K any further round with it, but traverses the groove, hower
high the cam A may lift the lever C. In like manner, on its return it holds
the valve open until the steel pin comes in contact with the straight part of the
groove in the valve lever, when it brings the lever down suddenly to its
original position, and the valve is closed. I sometimes make a guide pieco,
which I fix to the steam pipe, with a groove in it for the round steel pin to
slide in, and which it will keep perpendicular without the lever M; but, in
that case, the segmental groove in the valve lever K must be straight. Instead of
the thin disc or common throttle valve, I sometimes make use of the button
and stalk valve, in which case there is no occasion for the compensation lever,
for by making the stalk of the button valve sufficiently long it will allow for
the long and the short lifts of the communicating lever, but in general I prefer
the common throttle valve. The cam A may be dispensed with by making the
lever B to be acted on by one or more pins fixed in the side of a wheel or plate,
or between two plates, on an axle or shaft, which will, to a partial extent, answer
the purpose of the cam by advancing or withdrawing the lever to or from the
pin or pins, but I greatly prefer the employment of a cam such as I have
herein-before described. Instead of the lever B, C, being fixed on a pin at
the end of the bent lever D, it may be fixed on a centre made to slide to and
from the cam in dovetail slides. Where there is no governor I make the
centre of the lever D to advance or recede to and from the centre of the cam
or other acting apparatus by a screw or other equivalent means.
And having now fully described the nature of my said invented improve-
ments, and the manner in which the same are to be performed, I declare,-
First, as respects my improved method of generating steam, that what 1
claim as new and of my Invention is, the making of the furnace and the boiler
in two separate and distinct vessels, or at least so far separating them that the
water in the furnace casing is wholly separated from the water in the boiler
properly so called, and is pumped from the said casing before it reaches the
point of ebullition into the boiler, to be therein more highly heated and con-
verted into steam, by which arrangement a much less pressure is required to
be sustained by the furnace and its casings than by the boiler, where the
steam is ultimately produced.
And, secondly, as respects my improved method of regulating the supply of
steam to the working cylinder, I declare that what I claim as new and of my

page_text: Invention is, the employment of a cam, graduated, fixed, and adjusted in the
manner bereiu-before described, in conjunction with an advancing and receding
lever, acted on by the governor of the engine or other substitute (however
they may be altered or modelled to suit the different construction of engines
to which they may be applied), to keep open the steam admission valve for any
period of each stroke of the piston which may be desired; as also the employ-
ment of the compensation lever, herein-before described, to compensate for
either the short or long lifts of the lever B, C.
And such my Invention being, to the best of my knowledge and belief,
entirely new, and never before used within that part of Her said Majesty's
United Kingdom of Great Britain and Ireland called England, Her said
Dominion of Wales, or Town of Berwick-upon-Tweed, and also within all
Her Majesty's Colonies and Plantations abroad, I do hereby declare this
to be my Specification of the same, and that I do verily believe that this
my said Specification doth comply in all respects, fully and without reserve or
disguise, with the proviso in the said herein-before in part recited Letters
Patent contained. Wherefore I hereby claim to maintain exclusive right
and privilege to my said Invention.
In witness whereof, I, the said George Chapman, have hereunto set my
hand and seal, this Tenth day of July, One thousand eight hundred
and thirty-eight.
Inrolled the Thirteenth day of July, in the year of our Lord One thousand
eight hundred and thirty-eight.