CERTAIN IMPROVEMENTS IN AIR ENGINES FOR THE MOVING OF MACHINERY
Year: 1827

page_text: R. AND J. STIRLING'S SPECIFICATION.
TO ALL TO WHOM THESE PRESENTS SHALL COME, ROBERT
STIRLING, Clerk, Minister of Galston, in the County of Ayr, North Britain,
and JAMES STIRLING; Engineer, 'in Glasgow, in the County of Lanark, North
Britain, send greeting.
WHEREAS His most Excellent Majesty King George the Fourth, by
Letters Patent under the Great Seal of the United Kingdom of Great Britain
and Ireland, bearing date the First day of February, in the eighth year of
His reign, gave and granted unto the said Robert Stirling and James Stirling,
their exors, admors, and assigns, His Majesty's special licence, full power, sole
privilege and authority, that they, the said Robert Stirling and James Stirling,
their exors, admors, and assigns, and every of them; by himself and themselves,
and by his and their deputy and deputies, servants, and agents, or such other
as they, the said Robert Stirling and James Stirling, their exors, adiñiors, and
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 their Invention of "CERTAIN IMPROVEMENTS
IN AIR ENGINES FOR THE MOVING OF MACHINERY," within that part of the
United Kingdom of Great-Britain and Ireland called England, the Dominion
of Wales, and the Town of Berwick-on-Tweed, 'and also within all His
Majesty's Colonies and Plantations abroad, in such manner as to them, the
said Robert Stirling and James Stirling, their exors, admors, and assigns, or

page_text: any of them, should, in his or their discretion, seem meet; in which Letters
Patent is contained a proviso, that if the said Robert Stirling and James
Stirling should not particularly describe and ascertain the nature of their said
Invention, and in what manner the same is to be performed, by an instrument
in writing under their hands and seals, and cause the same to be inrolled in
His Majesty's High Court of Chancery within six calendar months next and
immediately after the date of the said Letters Patent, that then the said
Letters Patent, and all liberties and advantages whatsoever thereby granted,
should utterly cease, determine, and become void, anything therein contained
to the contrary thereof in anywise notwithstanding.
NOW KNOW YE, that the said Robert Stirling and James Stirling, do,
by this instrument in writing under their hands and seals duly executed,
describe and ascertain the nature of their Invention, and the method in which
the same is to be performed (that is to say):-
--
A, A, B, B, Figure First, is a vertical section (passing through the axis) of
the under part of the air vessel, which part consists of one piece of cast iron,
having the bottom B, B, B, of a spherical form, and the sides A, B, A, B,
cylindrical; the flanch A, A, serves for bolting this vessel to its cover or
lid, and the flanch C, C, for supporting it upon the building of the furnace.
The part of the side which lies between the two flanches A and C is turned
correctly on the inside, into a form which approaches so nearly to a true
cylinder that its diameter at A, the mouth of the vessel, is, about one-thousandth
part greater than its diameter at the flanch C. Into this vessel is introduced
and accurately fitted the plunger D, D, E, E, which consists of the following
parts F, G, H, is a vertical section of a horizontal ring of cast iron, which is
supported by four arms, similar to G, I, placed at equal distances round its
circumference, and united at the centre to a rod of malleable iron F, K, truly
turned and polished, and called the plunger rod. Each of the arms G, I, has
a part H, L, projecting perpendicularly from its junction with the ring F, G, H,
and having its opposite sides formed into planes parallel to the plunger rod,
and to that diameter of the circular ring above mentioned which passes through
said projecting parts respectively. The parallel sides of these projecting parts
or guides are polished, and work upon pieces of brass M, fixed in the cover
of the air vessel to keep the plunger steady in its perpendicular motion.
Figure Sixth is a birds-eye view, upon a reduced scale, of the framework of
the plunger. R, R, R, R, is the cast-iron ring; A, A, A, A, the arms by which
it is supported; G, G, G, G, the guides; b, b, the brasses upon which the
guides work; and P, the plunger rod. The ring F, G, H, Figure First, the
arms G, I, and the guides H, L, are all cast in one piece, and serve for

page_text: supporting and moving the following parts of the plunger, which are of sheet
iron. D, F, is a conical ring of sheet iron, of the thickness of one-tenth of an
inch, rivetted at F to the cast-iron ring above mentioned, and also rivetted
at D to a cylindrical ring of sheet iron D, E, of the thickness of one-twelfth
of an inch; D, E, is again rivetted, as represented at E, to the spherical part
E, E, E, which is also composed of plates of sheet iron of the thickness of one-
eighth of an inch, rivetted together and hammered so as to apply exactly to the
upper surface of the spherical bottom. B, B, B, a similar compound spherical
part of sheet iron, one-sixteenth of an inch in thickness. F, F, F, is rivetted to
the cast-iron ring G, G, H, and so adjusted as to be everywhere about three
and one-half or four inches distant from the spherical plate E, E, E; both of
these spherical plates are pierced with a multitude of holes about one-fourth
of an inch in diameter, and not more than one inch distant from one another.
Before the sheet-iron box now described is finally rivetted together at D, the
space E, F, E, is filled up with successive layers of plates of the thinnest,
sheet iron in use, pierced with holes, as already described, stamped or
hammered into a spherical form, and kept at the distance of two or three
times their own thickness from one another by small indentations formed in
the imperforated parts by a proper punch or die. Figure Second, which is a
vertical section of a small portion of these plates, represents the nature of the
said indentations, and also the holes already described. a, a, are the inden-
tations, and b, b, b, the holes. The holes which are made in these thin plates
are arranged in rows at equal distances from one another, and each successive
layer is so placed that its holes shall not be opposite to those of the layer
beneath it. The object of this arrangement is to spread the air more
completely over the plates in passing upwards and downwards, and to heat
and cool it more effectually. The space between the conical part D, F,
Figure First, and the cylindrical part D, E, is in like manner filled up with
plates of the thinnest sheet iron without holes, and kept at a small distance
from, one another by indentations as already described. Instead of filling the
space or cavity E, F, E, with plates of iron or other metal, we sometimes fill
it with small pieces of stone, burnt clay, glass, stoneware, or any similar bodies
as small as possible, provided they do not pass through the holes of the sheet-
iron box. At present, however, we prefer filling the cavity with plates, as
above mentioned. The outer plate of the plunger D, E, is kept on all sides
distant from the interior surface of the air vessel about the three-hundredth
part of its diameter, and in order as much as possible to prevent the air from
passing between them, a thin plate D, N, which is partly slit into narrow
shreads, as represented at Figure Third, is rivetted or screwed to the plunger

page_text: :
at D, Figure First, extending round-its whole circumference, and its narrow
stripes are bent outwards, so as. to touch slightly the turned part of the air
vessel round_its_whole_circumference. The cover of the air vessel O, P, P, O,
is of cast iron, and of such a form, that when its flanch O is applied to the
flanch A, and the plunger drawn upwards till the point D touch the flanch O,
the remaining part of the cover shall apply as closely as possible to the upper
surface of the plunger. This cover is bolted to the lower part of the air
vessel by the bolts Q, Q; and the joining is rendered air-tight by a stripe of
sheet lead interposed between the flanches A and O. In the centre of this
cover is a perpendicular tube R, R, for receiving the plunger rod F, K, and
upon the top of this, tube a stuffing box packed with hemp and oiled to prevent
the passage. of air, and at the same, time, to permit the plunger to, be moved.
Near the circumference of the cover, there are. four projecting cavities S, S,
which receive the guides of the plunger, and the brasses upon which, they slide
or work. These cavities are provided with air-tight covers, which upon being
removed permit the brasses to be drawn upwards, for, the purpose of being
adjusted so as to keep the plunger in its proper position; and in the centre of
three covers there are stopcocks T and U, so constructed. as to admit oil at
any time for lubricating the guides and not to permit the escape of air. The
moveable part of these stopcocks is turned in the manner represented at U,
the oil is then poured in from above, and by turning it into the position
represented at T the oil is permitted to descend. In like manner oil is
introduced to lubricate, the. piston and other parts which require it. Lastly,
there is an aperture made in the cover of the air vessel, represented by the
dotted lines at V, by which the air in the air. vessel is permitted to commu-
nicate with, that in the cylinder, and at all other points, said air. vessel is made
air-tight. The whole of Figure First is drawn, to a scale of two inches to a
foot, except where the dimensions have been expressly specified in words.
Figure Fourth is an elevation, and Figure Fifth a birds-eye view, of the
manner in which we apply the part of our Invention above described, and
combine it with others for producing: a. greater power in air engines than
has been hitherto attained.. .These Figures are drawn to a scale of three-
fourths of an inch to a foot; the same parts are in both Figures when visible
marked with the same letters, and, the following. description refers to both :-
A, A, and B, B, are two' air vessels, such as we have. specified.above, in which,
however, the guides of the, plungers are omitted in Figure Fourth to prevent
confusion. The air vessel A, A, is connected with the. lower part of the
cylinder C, C, by the pipe or nozzle D; and the air vessel B, B, is connected
by the pipe E, E, with the upper part of the cylinder, which has an air-tight

page_text: cover; as in the best steam engines. By means of the plunger, rods, the cross
heads, and the side, rods, as represented in the Figures, the plungers are con-
nected to the opposite ends of the balance beam F, G, which moves upon the
fixed centre H. The interior diameter, of the pipes or nozzles is one-fifth of
the diameter of the cylinder, and one-fifteenth of that of the air vessels, and
the stroke, of each plunger' is one-fourth of the stroke of the piston. The
cylinder C, C, the air pump I, I, one end of the crank shaft K, K, and, the
pillar which supports the working beam are supported upon the frame L, L, L,
the greater part of which is formed into an air-tight vessel or magazine for
containing a supply of condensed air or gas. For the purpose of procuring
and maintaining this supply, the air pump I, I, whose diameter, and stroke
are each half of those of the cylinder, and which has a solid piston and air-
tight cover, is made to communicate to the magizine both from above and
below the piston by proper pipes with self-acting valves, so constructed as to
throw air continually into the magazine while the engine is at work. From
the magazine, (which has a safety valve for the escape of the surplus air) a
communication is made with the nozzles D and E by means of the small pipes
M and N; and these latter pipes are provided with self-acting valves, which
permit the air to pass from the magazine, into the nozzles and cylinder, but
prevent it from returning into the magazine. The piston rods of the cylinder
and air pump are connected with the crank K, K, by a parrallel joint, working
beam, and connecting rod, or by any of the means commonly employed in
steam engines. The crank shaft K, K, carries a fly wheel O, P, Q, and an
eccentric wheel or secondary crank, which last ought to be so adjusted that
the stroke of the plungers is exactly half completed when the piston is on the
point of having its motion reversed. The eccentric wheel communicates
motion to the balance beam, and plungers in the following manner:-The
eccentric rod R, R, communicates a reciprocating motion to the levers S, T,
and S, U, which move upon the fixed centre or shaft S. The moveable end
of the lever S, U, is connected by the rod U, V, to the rod V, W, which in
like manner moves upon the fixed point W, and the point V being thus made
to rise and fall alternately, communicates a reciprocating vertical motion to the
balance beam and plungers through the rod V, X. The operation of the
whole engine is after this manner:-We make a fire beneath each of the air
vessels A, A, and B, B, at such a distance that its heat may be equally diffused
over the spherical bottoms, and at the same time we keep the upper part or
cover of the said air vessels as cold as possible, either by their own power of
dispersing heat into the atmosphere, or by directing upon them a stream of
air or water. When it is seen through a small aperture in the furnace that

page_text: the smoke of the coals is burnt off from the bottoms of the air vessels by the
heat_of_the_fire_the_apparatus_is_ready_for_working,_and_we_keep_the_bottoms
as near as possible to this temperature while the engine is at work. Suppose
now, therefore, the crank to be in the position represented in the Figures
Fourth and Fifth, and that by the revolution of the crank shaft and eccentric
wheel or by moving the handle Y the plunger in the air vessel B, B, has been
brought to the top and the plunger in A, A, to the bottom, the air which
was formerly above the plunger in the air vessel B, B, has now been made to
descend through the holes, in the thin plates of which the plunger is composed,
and has been heated in its passage, and consequently its elasticity has been
increased, as also its pressure upon the interior of the air vessel and upon the
upper side of the piston in the cylinder with which it communicates; in like
manner the air which was formerly beneath the plunger in the air vessel A, A,
by passing upwards through the plates of said plunger has been cooled, and
its elasticity and its pressure upon the lower side of the piston is diminished.
The pressure upon the upper side of the piston therefore being greater than
that upon the lower side, the piston is forced downwards, the crank is drawn
upwards, and an impulse is communicated to the fly wheel, which moves round
in the order of the letters O, P, Q, carrying along with it the eccentric wheel,
which, drawing the eccentric rod towards the crank shaft, depressed the point V,
and thus reverses the piston of the plungers and the pressure upon the piston,
which again is forced upwards and gives another impulse to the fly, and so on
continually. The engine is at first started or set in motion by detaching the
eccentric rod from the lever S, T, and moving the plungers with the hand, like
the valves in a steam engine; and when the fly has acquired a sufficient
momentum, the connection is restored also in order to start at first with greater
power. We sometimes employ the condensing power of the plungers as a
substitute for the air pump to throw a supply of air into the magazine; and
though we generally work the engine with common asmopheric, yet whenever
a supply can be conveniently obtained of nitrogen, carbonic acid, or any per-
manent gas which does not readily corrode iron nor cause explosion, we use it
with equal and in some respects greater advantage.
Know ye also, that we, the said Robert Stirling and James Stirling, do
not profess to be the first and sole Inventors of all the parts which compose
the engines now described, such as cylinders, pistons, valves, parallel joints,
cranks, fly wheels, and such other things which have been long in common
use, nor of the principle of giving motion by means of the alternate expansion
and contraction of air; but we have applied for and obtained His Majesty's
Letters Patent as the true Inventors of such applications or combinations of

page_text: those elementary parts described above as enable us to produce a new
manufacture of improved air engines.
In particular, our first improvement upon air engines consists in giving
to the air vessel and plunger the form and structure represented in Figures
First, Second, Third, and Sixth, and the description referring to them, by
which we are enabled to make the thin plates or other bodies filling the
plunger, which are necessary to retard the passage of heat upwards, serve also
for heating and cooling the air.
Our second improvement upon air engines consists in the application of two
or more such air vessels and plungers to one cylinder, so as to act alternately
and equally upon opposite sides of the same piston.
Our third improvement upon air engines consists in admitting air by means
of valves into the cylinder or air vessels, so as to keep up a greater pressure
upon the piston when we do not wish to employ an air pump.
And our fourth improvement consists in forcing through the said valves by
means of an air pump a greater quantity of air than could be introduced by
the simple pressure of the atmosphere. It is for the Invention of these four
improvements only that we have applied for and obtained His Majesty's
Letters Patent.
In witness whereof, we, the said Robert Stirling and James Stirling,
have hereunto set our hands and seals, this Twentieth day of July, in
the year of our Lord One thousand eight hundred and twenty coron