IMPROVEMENTS IN HOT-AIR ENGINES
Year: 1869

page_text: LETTERS PATENT to Beauchamp Tower, of Moreton near Ongar, in
the County of Essex, for the Invention of "IMPROVEMENTS IN HOT-AIR
ENGINES."
Sealed the 7th January 1870, and dated the 1st November 1869.
PROVISIONAL SPECIFICATION left by the said Beauchamp Tower at
the Office of the Commissioners of Patents, with his Petition, on
the 1st November 1869.
BEAUCHAMP TOWER, of Moreton near Ongar, in the County of
Essex, do hereby declare the nature of the said Invention for "Ix-
PROVEMENTS IN HOT-AIR ENGINES," to be as follows:-
This Invention has for its object improvements in hot-air engines or
engines for obtaining motive power by the expansion of air by heat.
The air to be heated passes directly through the furnace and in contact
with the fuel, and mixing with the gases of combustion passes into the
working cylinder, as has heretofore been proposed. Now a great difficulty
and drawback to the use of such engines hitherto has been that the

page_text: furnace has of necessity to be made air-tight and closed by air-tight
doors (there being a high pressure of air within) and has to be fired
through hoppers and double valves, thereby preventing the man from
attending to and working it properly, and necessitating the stoppage of
the engine whenever the fire has to be cleaned or ashes to be removed;
and a main feature of my Invention consists in a contrivance for
removing all these difficulties, and enabling the attendant at all times
to have as complete a control over and access to the fire as he now has
over the furnace of a steam boiler. The way in which I propose to
effect this is by surrounding the furnace and, by preference, the engine
with an air-tight casing of a form and of materials suitable for with-
standing an internal pressure, and of such a size as to enable the
attendant to work within it, attend to the engine, and fire the furnace.
In other words I make an air-tight engine room or stoking chamber
charged with air at the working pressure of the engine, in which the
man would work under pressure in the same way that he would in a
pneumatic pile or a diving bell, in which men work without inconvenience
under a pressure of air two or three times the normal pressure of the
atmosphere. Entrance and egress would be effected by double air-tight
doors in the same manner as it is in pneumatic piles, the doors acting like
lock gates, sufficient room being provided between them for the men or
materials entering or leaving the engine room to stand during the
operation of opening one door and closing the other and equalizing
the pressure; this contrivance is well known and is called an "air lock."
The furnace may be constructed in fire-brick or other refractory material,
and the air for supplying it and also for the man to breathe is forced into
the air chamber by suitable pumps; this air will be considerably heated
by compression, and consequently the part for the man to breathe has
to be cooled by passing through tubes surrounded by water or by other
well-known means, but the air for supplying the furnace and working
the engine passes by a pipe or pipes through the regenerator, which is an
apparatus, which I will afterwards describe, for further heating the
supply air by means of the hot exhaust air from the engine, or it might
pass to the furnace direct without passing through such an apparatus,
the regenerator being an additional means of obtaining economy without
being absolutely necessary for the working of the engine. Now the
only things which are necessarily contained within the air chamber
(which is the name by which I prefer to call the air-tight engine room
which I have described) are the mouth or entrance to the furnace, the

page_text: man with his firing tools, the fuel which he is about to supply to the
furnace, and the compressed air. I say the mouth or entrance to
the furnace, because it is obvious that an air chamber could be con-
structed communicating with a furnace, and from which access to a
furnace could be had without the main body of the furnace being
contained within the air chamber. But by preference I place the
furnace engine and pumps inside the air chamber, partly because in
most cases it would be most convenient, one man being then able to
attend to both engine and furnace, but principally because then there
would be an equality of pressure inside and out of the furnace, rendering
a strong casing thereto unnecessary, and also because any leakage
that there might be in the engine past the packing would be cold air
into instead of hot air out of the engine, which arrangement would
prevent packing and working surfaces from being destroyed.
I will now describe the form of engine which I prefer to use; it is so
arranged as to work with the pressure outside the engine instead of
inside, so as to cause all leakage to the cold air into instead of hot air
out of the engine. The lower part of the cylinder is lined with fire-
brick or other refractory and non-conducting material, as are also the
passages wherever practicable, and the valves are covered with the same
wherever exposed to the hot air, except just where they come in contact
with the seats. The valves are of the ordinary puppet kind, but made
hollow and are provided with an internal circulating tube, and a con-
tinual stream of cold water is caused to circulate through them to keep
them cool. The cylinder and piston are so arranged as to secure the
working surfaces of the cylinder and piston from contact with anything
but cold clean air, while the hot gas and air from the furnace, which gas
and air are charged with smoke, dust, and soot, which would of course
be injurious to working surfaces, are kept below, and in contact only
with the hot non-conducting substance with which the lower part of the
cylinder is lined. The upper part of the piston works in a bored
cylinder, and is made air-tight by ordinary packing rings, and hanging
from and forming a continuation of this piston is a plunger protected
partly or entirely by a covering of fire-brick; this plunger works loosely
through a projecting internal flange which forms the bottom of the
bored part of the cylinder; on the upper side of this flange several rings
of wire gauze are secured, which press against the plunger and form a
partially tight joint to prevent dust and dirt from getting up into the

page_text: bored cylinder. As the plunger is a little less in diameter than the
piston an annular space is left between it and the bore of the cylinder,
which space is provided with an exhaust and supply valve which work
simultaneously with the exhaust and supply valves of the lower part of
the fire-brick cylinder, the only difference being that while the lower
part of the cylinder is taking its supply of hot air and gas from the
furnace the annular space is taking its supply from the cold high-
pressure air with which the air chamber in which the engine stands is
charged, and as the velves of each open and close at the same moment
there will always be an equal pressure in the space and the lower part
of the cylinder, and consequently no tendency for cold air to leak out of
or hot to leak into the annular space past the wire gauze flange.
The hot exhaust air from the cylinder may be caused to pass among a
system of tubes through which the fresh supply air delivered from the
forcing pumps should pass and become heated on its way to the furnace;
this is the apparatus which I mentioned before as the regenerator. A
cold water casing may surround the cylinder and passages and over all
parts from which heat would otherwise radiate, so as to carry off the
heat and prevent the air chamber from becoming inconveniently hot.
The valve seats are made hollow, and water passes through them to keep
them cool.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Beauchamp Tower in the Great Seal Patent Office
on the 30th April 1870.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, BEAUCHAMP
TOWER, of Moreton near Ongar, in the County of Essex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the First day of November, in the year of
our Lord One thousand eight hundred and sixty-nine, in the thirty-
third year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Beauchamp Tower, Her special
licence, that I, the said Beauchamp Tower, my executors, adminis-
trators, and assigns, or such others as I, the said Beauchamp Tower,
my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thercafter

page_text: 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
"IMPROVEMENTS IN HOT-AIR ENGINES," upon the condition (amongst others)
that I, the said Beauchamp Tower, my executors or administrators,
by an instrument in writing under my, or their, or one of their hands
and scals, 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 Beauchamp Tower, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement thereof, that is to say :-
This Invention has for its object improvements in hot-air engines, or
engines for obtaining motive power by the expansion of air by heat.
The air to be heated passes directly through the furnace and in contact
with the fuel, and mixing with the gases of combustion passes into
the working cylinder, as has heretofore been proposed. Now a great
difficulty and drawback to the use of such engines hitherto has been
that the furnace has of necessity to be made air-tight and closed by
air-tight doors (there being a high pressure of air within), and has to
be fired through hoppers and double valves, thereby preventing the
man from attending to and working it properly, and necessitating the
stoppage of the engine whenever the fire has to be cleaned or ashes to
be removed; and a main feature of my Invention consists in a con-
trivance for removing all these difficulties, and enabling the attendant
at all times to have as complete a control over and access to the fire as
he now has over the furnace of a steam boiler. The way in which I
propose to effect this is by surrounding the furnace, and by preference
the engine, with an air-tight casing of a form and of materials suitable
for withstanding an internal pressure, and of such a size as to enable the
attendant to work within it, attend to the engine, and fire the furnace.
In other words, I make an air-tight engine room or stoking chamber
charged with air at the working pressure of the engine, in which the
man would work under pressure in the same way that he would in a
pnematic pile or a diving bell, in which men work without inconvenience

page_text: under a pressure of air two or three times the normal pressure of the
atmosphere. Entrance and egress would be effected by double air-tight
doors in the same manner as it is in pneumatic piles, the doors acting
like lock gates, sufficient room being provided between them for the
men or materials entering or leaving the engine room to stand during
the operation of opening one door and closing the other, and equalizing
the pressure. This contrivance is well known, and is called an "air
lock." The furnace may be constructed of fire-brick or other refractory
material, and the air for supplying it and also for the man to breathe
is forced into the air chamber by suitable pumps. This air will be
considerably heated by compression, and consequently the part for the
man to breathe has to be cooled by passing through tubes surrounded
by water or by other well-known means, but the air for supplying the
furnace and working the engines passes by a pipe or pipes through the
regenerator, which is an apparatus, which I will afterwards describe, for
further heating the supply air by means of the hot exhaust air from the
engine, or it might pass to the furnace direct without passing through
such an apparatus, the regenerator being an additional means of
obtaining economy without being absolutely necessary for the working
of the engine. Now the only things which are necessarily contained
within the air chamber (which is the name by which I prefer to call the
air-tight engine room which I have described) are the mouth or entrance
to the furnace, the man with his firing tools, the fuel which he is about
to supply to the furnace, and the compressed air. I say the mouth or
entrance to the furnace, because it is obvious that an air chamber could
be constructed communicating with a furnace, and from which access to
a furnace could be had without the main body of the furnace being
contained within the air chamber; but by preference I place the furnace,
engine, and pumps inside the air chamber partly because in most cases
it would be most convenient, one man being then able to attend to both
engine and furnace, but principally because then there would be an
equality of pressure inside and out of the furnace, rendering a strong
casing thereto unnecessary, and also because any leakage that there
might be in the engine past the packings would be cold air into instead
of hot air out of the engine, which arrangement would prevent packing
and working surfaces from being destroyed.
T11

page_text: inside, so as to cause all leakage of the cold air into instead of hot air
out of the engine. The lower part of the cylinder is lined with fire-brick
or other refractory and non-conducting material, as are also the passages
wherever practicable, and the valves are covered with the same wherever
exposed to the hot air, except just where they come in contact with the
seats. The valves are of the ordinary puppet kind, but made hollow,
and are provided with an internal circulating tube, and a continual
stream of cold water is caused to circulate through them to keep them
cool. The cylinder and piston are so arranged as to secure the working
surfaces of the cylinder and piston from contact with anything but cold
clean air, while the hot gas and air from the furnace, which gas and
air are charged with smoke, dust, and soot, which would of course be
injurious to working surfaces, are kept below and in contact only with
the hot non-conducting substance with which the lower part of the
cylinder is lined. The upper part of the piston works in a bored cylinder,
and is made air-tight by ordinary packing rings, and hanging from and
forming a continuation of this piston is a plunger protected partly or
entirely by a covering of fire-brick; this plunger works loosely through
a projecting internal flange, which forms the bottom of the bored part
of the cylinder. On the upper side of this flange several rings of wire
gauze are secured, which press against the plunger and form a partially
tight joint to prevent dust and dirt from getting up into the bored
cylinder. As the plunger is a little less in diameter than the piston an
annular space is left between it and the borc of the cylinder, which
space is provided with an exhaust and supply valve, which work
simultaneously with the exhaust and supply valves of the lower part of
the fire-brick cylinder, the only difference being that while the lower
part of the cylinder is taking its supply of hot air and gas from the
furnace the annular space is taking its supply from the cold high
pressure air with which the air chamber in which the engine stands is
charged, and as the valves of each open and close at the same moment
there will always be an equal pressure in the space and the lower part
of the cylinder, and consequently no tendency for cold air to leak out
of or hot air to leak into the annular space past the wire gauze flange..
The hot air exhaust from the cylinder may be caused to pass among a
system of tubes through which the fresh supply air delivered from the
forcing pumps should pass and become heated on its way to the furnace ;.
this is the apparatus which I mentioned before as the regenerator. A
cold water casing may surround the cylinder and passages and over all

page_text: parts from which heat would otherwise radiate, so as to carry off the
heat and prevent the air chamber from becoming inconveniently hot.
The valve scats are made hollow, and water passes through them to keep
them cool.
In order that my said Invention may be most fully understood and 5
readily carried into effect I will proceed to describe the Drawings
hereunto annexed.
DESCRIPTION OF THE DRAWINGS.
Sheet No. 1 shows the general arrangement of a three cylinder hot-
air engine embodying my Invention.
Figure 1, Sheet No. 1, is a horizontal section through the axis of the
cylindrical air chamber showing the furnace and the cylinder next to it,
also a portion of the hot-air fluo fin section through the line w, wo,
Figure 4; the next cylinder is shown in plan, the air pump being removed
to show the crank shaft bearing, &c; the next cylinder is shown in plan
looking down upon the air pump.
Figure 2, Sheet No. 1, is a vertical section of the air chamber
through y, y, Figure 4, showing the furnace in section through n, n,
Figure 3, the cylinder and air pump next to it being in section
through y, y, Figure 4, and the other cylinders and air pumps are in
elevation.
Figure 3, Sheet No. 1, is a section through the air chamber and
furnace in the line x, x, Figure 1.
Figure 4, Sheet No. 1, is a section through y', y', Figure 1.
Figure 5, Sheet No. 2, shows a vertical section of a single cylinder
hot-air engine, embodying my Invention made on a larger scale, and
having the principal parts arranged so that they can be shown in one
section in order that they may be more easily referred to and the action
of the engine more clearly explained.
Figure 6, Sheet No. 2, is an enlarged section of the hollow valves
showing the arrangement of the circulating pipes and diaphragms within
them, the arrows indicating the direction of the current of water.
Figure 7, Sheet No. 2, is an enlarged section of the internal flange R
showing the wire gauze packing and the mode of fastening it.

page_text: Throughout all the Drawings similar letters and figures refer to similar
parts.
L is the air chamber, which in this case is made cylindrical, the
bed plate on which the engine stands forming part of the bottom of it;
a is the air lock provided with two air-tight doors and two valves, one
marked m communicating with the air lock and the external air, and the
other marked n communicating with the air lock and the air chamber.
When the attendant wishes to enter the air chamber he opens the
valve m, and allows any high pressure air which there may be in the air
lock to escape, and thus causes an equilibrium of pressure on each side
of the outer door, which enables him to open it and enter the air lock; ;
he then closes the outer door and the valve m, and opens the valve n,
which allows high pressure air from the air chamber to rush into the
air lock until there is an equilibrium of pressure on each side of tho
inner door; he is then able to open the inner door and enter the air
chamber. In leaving the air chamber the process is reversed. F is the
furnace lined with fire-brick and provided with grate bars and an ash-pit,
there is also a fire-door and an ash-pit door through which the attendant
supplies the furnace with fuel, cleans the fire, and removes ashes in the
same manner as in the furnace of a steam boiler and without any
interruption to the action of the engine. f is the flue along which the
hot gases pass after leaving the furnace, the main supply valve V open
into this flue, and through them the hot air and gases of combustion pass
into the cylinder D in the manner which will be hereafter explained.
U, U, are the exhaust valves for permitting the hot air to escape from
the cylinders D, D, at the proper time. These valves V, V, U, U, are
in this case concentric, the spindle of the supply valve V being annular
in cross section, and allowing the spindle of the exhaust valve U to pass
up through it with a stuffing box and gland at the top, but they are not
necessarily made so, and in some cases it may be convenient to make
them separate, in which case they would both be like the exhaust valve U.
These valves are made hollow, as shown in the enlarged section on
Sheet No. 2, Figure 6, and are provided with internal pipes and
diaphragms, in order to cause the water to pass down and up through
cach valve from end to end as shewn by the arrows for the purpose of
keeping them at an evenly cool temperature throughout. The water is
conveyed to and from these valves through telescopic pipes A, 1, which
allow the valves to be raised or lowered without interfering with tho
constant supply of water which is kept flowing from the water pump K

page_text: through the valves. The valves close down upon seats which are fitted
air-tight into the metal of the cylinder, and are made hollow and supplied
with a constant current of cold water flowing through them from the
pump K through pipes, as shown. The object of this current of water
flowing through the valves and seats is to keep them cool, as they would
otherwise be destroyed by the great heat to which they are exposed; the
valves and scats are also covered with fire-brick where practicable for
the same purpose. These valves are opened and closed at the proper
times by means of levers actuated by cams on the crank shaft, as shewn,
on Figure 4.
The cylinders are made in two sections or parts; the lower part D into
which only the hot air and gases are admitted is lined with fire-brick,
as also are the passages leading to it from the valves; the upper part
stands on the top of the lower part, and is bored out to allow a packed
piston A to move freely therein after the manner of steam engine pistons
within their cylinders, hanging from and forming a continuation of this
piston. A is a hollow plunger, which is protected at the bottom by
a covering of fire-brick; this plunger works through the projecting
internal flange B, which forms the bottom of the bored part of the
cylinder. On the upper side of this flange several rings of wire gauze G
are secured, as shewn in the enlarged section, Figure 7, which press
against the plunger and form a partially tight joint to prevent dust and
dirt from getting up into the bored cylinder. As the plunger is a little
less in diameter than the piston an angular space C, C, is left between
it and the bore of the cylinder, which space is provided with an exhaust
and supply valve, say, v¹, v², which are connected by levers so as to work
simultaneously with the exhaust and supply valves U, V. When the
supply valve V is open the small supply valve v' is open; the lower part
of the cylinder D is then taking its supply of hot air from the furnace,
while the annular space is taking its supply of comparatively cool pure
air from the air space O which surrounds the furnace cylinders and flue.
When the exhaust valve U is permitting the escape of the hot air from
the lower part D through the exhaust passage E and the regenerator R to
the atmosphere, the small exhaust valve v² is open and allowing the air
in the annular space to flow into the atmosphere. The supply valves V
and are both closed shortly before the piston arrives at the top of the
stroke for the purpose of expanding the air contained in the cylinder
nearly to the atmospheric pressure, and thereby enabling the exhaust

page_text: valves U and to be easily opened, which they are when the piston
arrives at the top of its stroke. In the down stroke the exhaust valves
U and are closed shortly before the piston arrives at the bottom of the
stroke, in order to cushion the air contained in the cylinder up to air
chamber pressure, so as to allow the supply valves to be opened easily
when the piston arrives at the bottom of its stroke. The compressing
pumps stand over the cylinder, and the upper part of the pumps pro-
trudes through the top of the air chamber; they have ordinary suction
and delivery valves. Each air pump piston is connected to the main
piston A. by means of four rods 1, 1, 1, 1. The connecting rods which
communicated motion to the crank shaft are attached at their upper
ends to the air pump pistons. The air pump pistons have packed
trunks or plungers I, I, on their upper sides, which work through the
air pump tops in bored cylinders. These plungers being smaller in
diameter than the pump cylinders leave an annular space II, II, which
forms the effective capacity of the pump, the plungers I, I, being
intended to prevent the excessive strain which would otherwise come
upon the crank shaft, &c. when the pistons are making the down stroke
by dividing the strain which would otherwise come only on the down
stroke into both the up and down stroke, and in effect making each
cylinder work as if it was double-acting. The compressed air passes from
the pumps along the pipe S. The greater part of it continues along that
pipe through the regenerator, where it is heated by the hot exhaust
air, and then enters the furnace; a smaller part passes along the pipe 8,
which is a branch from S, and into the air space O, where it circulates
all round the outside of the furnace and cylinders, in order to pick up
the waste heat which is conducted through the fire-brick lining of the
furnace cylinders, &c., and which would otherwise be radiated into the
air chamber, and make it inconveniently hot. This air space O is
formed by a casing which surrounds all the parts of the engine which
would otherwise radiate heat into the air chamber, and is itself well
clothed with felt and non-conducting material to keep the heat in.
The air after passing through the air space O passes through the supply
valve o', and forms the supply for the annular space C, C. A portion of
the air which enters the pipe & branches off from it, and passes through
a worm placed in a tank of cold water J for the purpose of cooling it; it
then passes through a cock or valve (by the opening or closing of which
its quantity may be regulated at pleasure), from whence it passes into
the air chamber to keep it sufficiently ventilated for breathing, &c.

page_text: Before starting the engine for the first time the air chamber can be
charged with compressed air by a hand pump, and when once charged it
can remain so for any length of time. A donkey engine working with
hot air would be required in some engines to keep the flues burning and
the air chamber ventilated while the main engine is standing. The speed
of the engine would be regulated by regulating the time of closing of the
supply valves; this can be effected either by hand or by a governor.
The process of starting is as follows:-The valves being all opened so
as to give a clear through communication with the chimney the fire is
lighted in the furnace, and as soon as it is properly burnt up and the
fire-brick linings heated the air-lock doors and engine valves are closed,
and steps are taken to get up the pressure in the air chamber; this being
effected we will suppose the piston to be at the top of the cylinder, a
communication is then made under the piston with the external air by
opening the exhaust valves communicating with U and v³, the piston
then descends with a force due to the pressure in the air chamber on its
whole area minus the area of the air pump, which is at the same time
drawing its cylinder full of air into the air chamber against the pressure;
the piston having reached the bottom of its stroke the exhaust valves
are closed and the supply valves are opened, an equilibrium of pressure
is thus caused on each side of the piston, and the piston is drawn up by
the descent of the other pistons; the supply valves being open hot air is
drawn from the furnace fluc into the space D, D, and cold air is drawn
into the space C, C, until the proper point of cut-off for obtaining the
required amount of expansion is reached, when both supply valves are
closed, and the piston continuing to be drawn up to the top of its stroke
expands the air under it to or nearly to the atmospheric pressure, the
piston having arrived at the top the process is repeated.
Having thus described the nature of my said Invention, and the
manner of performing the same, I would have it understood that what
I claim is, the construction of hot-air engines with an air-tight pressure
chamber, within which is the mouth of the furnace by which the air to
work the engines is heated, such chamber being so arranged that the
attendant who feeds the furnace may work within it, and that it may
contain air at a pressure sufficient to work the engine, substantially as a
lierein described.
Talso

page_text: pressure chamber so arranged that the air within it may be raised to the
pressure requisite to work the engine, such chamber containing both
the engine and the furnace by which the air to work the engine is
heated, substantially as herein described.
I also claim the construction of hot-air engines, substantially as
herein described.
I also claim the constructing hot air engines with a packed piston
contained in a portion of the working cylinder from which the highly
heated air is excluded by a plunger on the piston and a partial packing
of wire gauze or other such like material capable of withstanding a high
heat, the annular space between the plunger and the part of the cylinder
in which the piston works being supplied with comparatively cool air
by supply and exhaust valves working simultaneously with hot-air
valves, substantially as herein described.
In witness whereof, I, the said Beauchamp Tower, have hereunto
set my hand and scal, this Twenty-ninth day of April, in the
year of our Lord One thousand eight hundred and seventy.