IMPROVEMENTS IN ROTARY STEAM ENGINES
Year: 1866

page_text: LETTERS PATENT to Aaron Charles Baldwin, of Boston, State of
Massachusetts, in the United States of America, for the Invention of
"IMPROVEMENTS IN ROTARY STEAM ENGINES."
Sealed the 31st August 1866, and dated the 7th March 1866.
COMPLETE SPECIFICATION filed by the said Aaron Charles Baldwin
at the Office of the Commissioners of Patents, with his Petition and
Declaration, on the 7th March 1866, pursuant to the 9th Section of
the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, AARON
CHARLES BALDWIN, of Boston, State of Massachusetts, in the United States of
America, send greeting.
WHEREAS I am in possession of an Invention for "IMPROVEMENTS IN
ROTARY STEAM ENGINES," and have petitioned Her Majesty to grant unto me,
my executors, administrators, and assigns, Her Royal Letters Patent for
the same, and have made solemn Declaration that I am the first and true
Inventor' thereof.
NOW KNOW YE, that I, the said Aaron Charles Baldwin, do hereby
declare that the following Complete Specification under my hand and seal
fully describes and' ascertains the nature of the said Invention, and in what
manner the same is to be performed, in and by the following statement:-

page_text: My improvements consist in novel constructions, combinations, and dis-
positions of the parts by which an effective engine is produced with the steam
acting directly to turn the shaft with a continuous rotary motion, and with
the working parts mostly or entirely on the exterior of the cylinder, where
they are easily accessible for adjustment, oiling, or repairs.
The first part of my Invention relates to the arrangement on the main
shaft of a central disk or wheel of reduced thickness toward the periphery with
two pistons attached, one on each face, and rotating in annular spaces in the
cylinder, and so arranged that one shall pass its abutment at the time when
the other is receiving the full action of the steam.
The second part relates to firmly supporting the abutment which closes the
aunular working space of the cylinder, and against which the steam acts to
force the piston forward.
The third part relates to a form of piston to diminish the useless steam
space.
The fourth part relates to the construction and arrangement of the valves.
and ports so that one valve reciprocating at each revolution of the engine'
shall serve for the steam and the exhaust ports, and that the exhaust port
shall be open during the whole revolution, while the steam port shall be open
only at intervals, thereby securing efficient and economical action and perfect
facility of reversal with very simple and durable mechanism.
The fifth part relates to a simple system of packing for preventing the
leakage of steam inward from the annular steam space in the cylinder.
. The sixth part relates to means for adjusting such packing.
The seventh part relates to relieving the pistons from friction during that
part of their revolution in which they exert no power.
I will first proceed to describe in detail what I consider the best manner
of carrying my Invention into practical effect, and will afterwards point out
what features I consider new. For the more perfect understanding thereof
I have prepared a Sheet of illustrative Drawings, forming part of this
Specification, and have marked the same with letters of reference corre-
sponding with those in the following explanation:-
Figure 1 is a side elevation of the entire engine; Figure 2 is a plan view,
partly in section, the section is on line X, X, in Figure 1; Figure 3 is an
end elevation, partly in section, with the eccentrics and eccentric rods omitted, 3
the section is on line Y, Y, in Figure 2; Figure 4 is a longitudinal section
on the line Z, Z, in Figure 2, with the valve removed; Figure 5 is a diagram
or sketch showing a side view on a smaller scale of a simpler arrangement of

page_text: certain of the parts; Figure 6 is a plan view of the same.
reference indicate like parts in all the Figures.
Similar letters of
r
A is the main shaft of the engine; B is a fixed external cylinder, of which
B1, B2, are the heads, which are also fixed and are the supports or bearings
in which the shaft A rotates. In the center between these bearings is a solid
wheel or disk a firmly secured upon and rotating with the shaft A, and
tapering slightly toward its circumference, where it fits steam-tight within'
the cylinder B by means of ordinary steam packing upon the edge, not:
indicated in the Drawing. At a suitable distance within the external cylinder B,
and concentric to it, are two cylinders B³, cast upon the inside of the heads B',
B³, respectively, and extending to the faces of the disk. The annular spaces
between the external and these inner cylinders constitute the actual working
chambers of my engine. Two pistons a¹, a², fitted accurately to the annular
spaces above described are firmly bolted on the opposite faces of the disk
a at points so far out of line with each other that each piston passes its dead
point while the other is receiving the full force of the steam. The division of
the annular space into two chambers by the disk a makes this effectively a
double engine, each side working independently of the other. When in
the description I speak only of one side, the other is understood to be formed
and to operate in the same manner. C are movable parts, which, operated
by the rods c, c, slide in and out through corresponding rectangular apertures
in the external cylinder B to close the annular chambers when required, and:
serve as abutments for the action of the steam. As each piston arrives
nearly in contact with its abutment C the latter begins to be withdrawn; and
after the passage of the piston it immediately begins to be carried back to its
place, throughout the movement just avoiding contact with the outline trace
of the piston. A recess a prepared in the interior cylinder B³ receives the
end of the abutment C when fully home, and supports it as represented. So:
soon as this is done the steam is admitted and the piston begins to con-
tribute to the power of the engine by impelling the disk. The pressure of
steam on the abutment forcing it firmly against one side of the groove x,
diminishes the necessity of packing on the end. The sides of the abutment,
which are packed in the usual manner, are tapered or bevelled slightly to
correspond with the before-described bevel of the disk a, and with a similar
bevel of the heads B', B; by this form of the parts the abutment is insured.
from striking the disk when entering, and friction is diminished by avoiding
contact until the abutment is nearly on its seat. The easy removal and
replacement of the abutment as above described allows a very rapid rotation

page_text: of the engine without jarring or sudden wrenching of the parts, but the piston.
has time to pass the abutment some little distance before the latter comes:
fully to its place, and is ready to receive steam, thereby leaving a space to be
filled with steam at each revolution before any effective work can be done,"
consequently I form my pistons in section much thicker at their inner than at
their outer edges, and fill up the useless space in this manner as much as is
posssible without producing an actual contact between the inner edge of the
abutment and the inclined sides of the piston as the abutment is moved.
outward and inward. I impel the abutments by a cam motion derived from
the main shaft. D¹, D³, are eccentrics fixed on the main shaft A, so that one
is one-quarter of a revolution in advance of the other; E is a countershaft]
or supplementary shaft, having two crank pins e', 'e; placed quartering like
the eccentrics, and of exactly equal throw with them; d', d, are eccentric.
rods, which communicate motion from the eccentrics to the crank pins, so that
the shaft E is caused to revolve in the same time with the main shaft A.
The shaft E carries two large face canis E; E, each having a working groove
around its interior face, as indicated in dotted lines in Figure 1, and in strong
lines in Figure 4. There is a separate rock shaft H or an equivalent rocking
sleeve upon it for each side of the engine, each moving independently of the
other; and a wheel h on the lower arm of each rock shaft is received in the
.cam groove above described; thus by the rotation of the cams a rocking motion
is communicated to the shafts, and by means of the upper arms' H', H2, con-
nected by the links I, I, to the abutment rods c¹, c³, the required movements
.are trasmitted to the abutments C.
A will now describe the means through which the steam is admitted to and
discharged from the engine so as to forbid the access of steam to each chamber
while the abutments are being withdrawn and returned, and to allow of the
reversing or working of the engine in either direction. The exterior cylinder
B is thickened or built out on the side in which the abutments are mounted,
. so as to provide for the several ports and passages required, or it may be
formed in one or more separate parts bolted steam-tight thereto. Referring
to Figures 2, 3, and 4, which exhibit in section one side of the engine, the
steam is admitted from the boiler through the passage J horizontally into the
steam chests K', K. From each of these steam chests open the two ports
or narrow passages m and n communicating with the interior steam chamber
and adapted to allow the steam to be either admitted or discharged at a
proper distance above and below the abutments C; also in each chest ar
the two ports P and Q communicating freely with the exhaust passage L

page_text: A single slide valve R is reciprocated up and down in each steam chest. by.
means of the valve stem r, and controls the action of the steam. The form
of the valve and its relation to the several parts is indicated in. tolerably,
correct proportions in Figure 3. The exact proportions of the lead and, lap,
etc. in the adaptation of the slide valve and ports to each other is a matter of
very great importance, and no attempt is made in these Drawings to indicate>
the precise conditions in these respects, but only to show the relations of the
parts, so as to enable skilful engineers to properly construct the engine. The
valve R may be reciprocated at two stages according to the direction in
which the engine is turning, the highest point of the movement in its low
stage being a little below the lowest point of the movement in its high stage..
There are two hollow throats in the valve, one of which may cover the ports.
m and P, and the other the ports n and Q, and they are at such distance>
apart that when the valve is worked at its low stage, as represented, the.
upper throat will cover the exhaust port P alone, while the lower throat.
will constantly cover and connect together the port n and exhaust port Q, so.
as to cause them to constantly and freely communicate, and thus exhaust all
the steam which presents itself to the port n. At each downward movement:
of the valve R under these conditions the port m is uncovered entirely during
a portion of the revolution, and during that portion receives steam at full.
boiler pressure from the steam chest, and leads it into the working chamber:
of the engine to impel the piston. At each upward movement of the valve.
R the port m is covered and closed entirely by the solid part of the valve.
When the valve R is worked at its high stage for moving the engine in the.
opposite direction the upper throat constantly covers and connects m and P,
which then exhaust freely, while the lower throat constantly covers the port Q.
The valve R at its upward movement opens the port n for the admission of
steam, and closes it at its downward movement. The valves R with their
valve stems r receive motion from the loose rocking sleeves T¹, T, carried
upon the fixed shaft T, and impelled by eccentrics F1, F2, on the main shaft.
and rods f, f, as will be readily understood from the Drawings. There are
two arms on each sleeve for receiving this motion and communicating it
through the working arm t¹ or t, and the links U to the upper ends of the
valve stems r. The motion is received through the upper or the lower arms
by connecting the eccentric. rods f, f, to the upper or lower arms, according
as the engine is required to rotate. in one direction or the other, by working
the valve at its high or low stage. I have represented a very simple locking
spring and thumb-piece to enable the hook or recess on the eccentric rod to

page_text: be retained on the uppermost arm for transmitting the motion when required.
The connection. with the lowermost arm when required. will be maintained by
gravity. More elaborate mechanism may be employed, if desired, for hooking
and unhooking, so as to allow the reversing to be effected..by the: turning
of a single lever, but I prefer. for ordinary purposes the simple mechanism
described. Care must be taken on each side of the engine to adapt the slide
valve and the parts which operate it to the different position of its piston, so
that the two sides: of: the engine shall work continuously and harmoniously.
It will now be seen: how my engine composed of two independent annular
chambers is supplied with. steam. at proper intervals and on the proper side.
of the respective pistons, how the.steam is exhausted continuously and freely.
from the opposite side of each piston, how the proper motions are communi-
cated to the two. slide valves; and how the abutments which serve for the
respective. chambers are moved inward and supported.in their recesses during
a portion of each revolution, and are. moved outward during the period while
the corresponding pistons are passing.
Several additional features. of great importance remain to be described. To
prevent the leakage of steam inward where the inner cylinder B³ abuts against.
the disk a on each side I provide the loose metallic packing rings W, V, and
between them insert a vulcanised rubber ring v. The edges of the rings W, V,
which bear against the rubber are bevelled, as shown in Figure 2, so that as the
rings. are pressed together the rubber is pressed closely between them, and also
against the inner cylinder B³, making tight steam joints at those points, while
the inner edge of the ring.V maintains a steam-tight contact with the disk a
without. following its revolution. Set screws ware inserted through the
cylinder heads and. bear. against the ring W in order to adjust the pressure of
the packing. The ring W and set screws w may be dispensed with and the
rubber inserted between, the ring V and the solid casting, and will operate
very well if the rubber ring is of just sufficient dimensions, but if it leaks or
presses too hard against the ring V. it is not easy to remedy it, while the
screws w and ring. W. allow the. adjusting of the pressure of the rings v and V.
with great perfection, and also allow of very delicate alteration to suit the
expansion and contraction of the. parts, even while the engine is in motion.
In place of the india-rubber ring. v. any, ordinary steam packing may be
used between W and V, provided only that the material be slightly elastic
and able to withstand the heat, oil,. etc. While the piston is travelling
between the ports m and n it is ineffective, and therefore it is not necessary.
that it should then fit the cylinder steam-tight; therefore between the above

page_text: points I recess the surfaces along which the piston travels, that is, the inner
surface of the external cylinder B, and the outer surface of the inner cylinders
B³, also the inner faces of the heads B', B³, so as to leave but a very slight
contact with the piston along that portion of its revolution, and thus diminish
the friction of the engine. I can dispense with the secondary shaft E, if
desired, by fixing on the shaft A two cams corresponding in form to the cams
E', E, and providing suitable connections therefrom to the lower arms of the
rock shaft or sleeves H. The outer and end faces of the pistons a¹, a³, may
be rendered steam-tight by ordinary packing. I prefer to groove the inner
and thick faces of the pistons with parallel grooves, as shown in Figure 4;
these grooves retard and prevent the flow of the steam past the piston in a
manner analogous to that where corresponding grooves are employed in
ordinary cylindrical pistons.
Having now described my improvements and their operation, what I claim
as my Invention, and desire to secure by Letters Patent is as follows:-
First, I claim the central disk a diminished in thickness toward the
periphery with its pistons a¹, a³, arranged thereon relatively to each other,
and to the correspondingly tapered abutments C, substantially in the manner
and for the purposes herein set forth.
Second, I claim supporting the end of the abutment and preventing the
escape of steam past that point by sliding it into the depression or groove x
in the part B³, substantially as and for the purposes herein set forth.
Third, I claim the within-described form of pistons arranged as specified,
the same being of a tapering or wedge form with the base of the wedge pre-
sented inward, substantially as and for the purpose herein set forth.
Fourth, I claim in a rotary engine the within-described combination and
arrangement of the reciprocating valve R, whereby the exhaust port is kept
open during the whole revolution of the engine, while the steam port is
opened and closed as required for the intermittent admission of the steam at
each revolution, and adapted to allow of reversing or working in the opposite
direction, substantially as herein set forth.
Fifth, I claim the metal ring V and yielding ring v in combination with
the disk a and the inner cylinder B³ for the purpose of preventing the escape
of steam inward toward the shaft of the engine, substantially as herein set
forth.
Sixth, I claim the adjusting screws w, or their equivalents, in combination
with the rings V, v, and adapted to adjust the compression of the elastic
packing v, substantially as herein set forth.

page_text: Seventh, I claim recessing the rubbing surfaces between the ports m and n
so as to reduce the friction of the piston through that part of its revolution,
substantially as herein set forth..
In witness whereof, I, the said Aaron Charles Baldwin, have hereunto
set my hand and seal, this Nineteenth day of January, in the year of
our Lord One thousand eight hundred and sixty-six.
Witnesses,
G. FRANK BROWN.
ATHERTON T. BROWN.
AARON CHARLES BALDWIN. (Ls.)