IMPROVEMENTS IN ROTARY STEAM ENGINES
Year: 1874

page_text: LETTERS PATENT to Robert Duncan Milne, of Los Angeles, in the
County of Los Angeles, and State of California, one of the United
States of America, Engineer, for the Invention of “IMPROVEMENTS
IN ROTARY STEAM ENGINES."
Sealed the 1st December 1874, and dated the 1st September 1874.
COMPLETE SPECIFICATION filed by the said Robert Duncan Milne at
the Office of the Commissioners of Patents, with his Petition and
Declaration, on the 1st September 1874, pursuant to the 9th
Section of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ROBERT
DUNCAN MILNE, of Los Angeles, in the County of Los Angeles and
State of California, one of the United States of America, Engineer,
send greeting.
tion for 66 TOURYPT

page_text: for the same, and have made solemn Declaration that I am the true
and first Inventor thereof.
NOW KNOW YE, that I, the said Robert Duncan Milne, 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, reference being had to the accompanying Drawing forming a
part of this Specification :-
The object of my Invention is to provide an improved device for
the economical use of steam, and it consists in the employment of
an elliptical vessel or shell, within which is placed a cylinder of smaller
diameter whose axis falls upon the conjugate axis of the ellipse in
such a manner that all diameters of the ellipse passing through the
centre of the inner cylinder are equal. This smaller cylinder has one
point of contact with the interior of the elliptical case or vessel, the
latter being provided with steam and exhaust ports upon each side of
this point. A slide passes through the centre of the cylinder, and its
ends just touch the interior of the ellipse at all points during the
rotation, and against this slide the steam acts.
DESCRIPTION OF THE DRAWING.
Figure 1 is a transverse section of an engine embodying my Invention;
Figure 2 is a longitudinal section of the same; Figures 3 and 4 shew
detached portions thereof drawn to an enlarged scale.
A is the shell or case, within which the steam is admitted to do its
work, and which may be properly called the cylinder. This vessel is
elliptical in its transverse section, and of any suitable length. Within
this elliptical case is placed a cylinder B, whose axis C falls upon the
conjugate axis of the ellipse, and whose diameter is twice the shortest
radius of the ellipse, so that when in position the cylinder B will be in
contact with the interior of the vessel or shell A at the point of its
shortest radius. The steam ports D and the exhaust ports E are upon
each side of the point of contact. The exhaust ports F are constructed
to open into the shell or vessel A in a line with the axis C, and all these
ports are operated by the valve G, so that when steam is admitted upon
one side of the point of contact the exhaust ports upon that side will be
closed and those upon the opposite side will be opened.
The cylinder B has a slot made through its centre, and a solid slide H

page_text: fits into the slot. The length of this slide is equal to all the diameters
of the ellipse which pass through the axis of the inner cylinder, conse-
quently both ends of the slide will at all times touch the interior of the
case or vessel A, and against this slide the steam acts.
The slide is packed all around so as to be steam tight, and the point
of contact between the cylinder B and the interior of the case or shell A
is also packed.
Where the revolving slide H lies on the cylinder heads it is packed
by two separate pieces of metal lying in a groove which runs along
the whole length of the slide. These metal pieces nearly meet each
other at the centre of said slide, and are acted upon by separate springs
lying beneath them in the groove. The object of these separate packing
pieces is to equalize the wear, which is greater at the ends of the slide
than at its centre.
The valve is operated by suitable connections to drive the piston or
slide H, and with it the cylinder B, in either direction, as may be
desired. The steam entering at either side of the point of contact of
the two cylinders (take for example the direction of B, H, in Figure 1)
necessarily acts upon that part of the slide H which opposes it, and
accordingly presses it towards the point M. But the other end of the
slide meanwhile travels in the opposite direction, because the form of
the elliptic cylinder and the slot through which it slides compel it to
act inversely to its opposite extremity, therefore when the lower end
of the slide reaches the point M the upper end passes the point of
contact of the cylinders and shuts the steam port D to the right of that
point. The steam being thus shut off from the larger portion of the
slide begins to exert its expansive power upon both extremities of the
slide, but as the surface of the lower extremity is so much greater than
that of the upper extremity the expansive power upon it is consequently
greater, and the lower end of the slide continues to be driven in
the direction of the left-hand exhaust F, the upper end of the slide
meanwhile moving towards the right-hand exhaust F. When these
points F have been reached, it is evident that the full power of the
expansion has been reached, since the surfaces of both extremities of
the slide are now equal, and therefore the exhausts are placed at these
points. The steam expands upon the upper extremity of the slide, but
this expansion is more than counterbalanced by the constant action of
the steam from the port D at the other side of the slide, and thus

page_text: practically the power of expansion on the lower extremity of the slide is
assisted instead of being retarded. Any surplus steam left in the cylinder
is driven through the other exhaust E at the point of contact.
The steam ports and exhausts at the point of contact of the cylinders
may be better worked by the common sliding valve and steam chest, thus
making them steam ports and exhausts alternately when it is necessary
to reverse the engine. The side exhausts may either be combined in
this arrangement or opened and shut by hand when necessary to reverse
steam.
Having thus fully described the nature of my said Invention, and the
manner of performing the same, I wish it understood that I claim the
elliptical vessel or shell A, having the interior rotating cylinder B with
its slide H so placed that it fits against the sides of the vessel A. and
acts as a piston, together with the steam and exhaust ports D, E, and F,
as herein set forth and for the purpose specified.
In witness whereof, I, the said Robert Duncan Milne, have here-
unto set my hand and seal, this Sixth day of August, in the
year of our Lord One thousand eight hundred and seventy-
four.