IMPROVEMENTS IN SLIDE VALVES FOR STEAM ENGINES
Year: 1864

page_text: LETTERS PATENT to John Coates, of No. 4, Victoria Road, Limehouse,
in the County of Middlesex, for the Invention of "IMPROVEMENTS IN
SLIDE VALVES FOR STEAM ENGINES."
Sealed the 5th July 1864, and dated the 11th January 1864.
PROVISIONAL SPECIFICATION left by the said John Coates at the Office
of the Commissioners of Patents, with his Petition, on the 11th January
1864.
I, JOHN COATES, of No. 4, Victoria Road, Limehouse, in the County of
Middlesex, do hereby declare the nature of the Invention for "IMPROVEMENTS
IN SLIDE VALVES FOR STEAM ENGINES," to be as follows:-
This Invention has for its object improvements in slide valves for steam
engines.
In constructing slide valves according to this Invention they are arranged
in such manner that for the latter portion of the stroke of the piston the ports
leading to the two ends of the cylinder shall be both closed by the valve, by
which means the interior of the cylinder is shut off both from the steam from
the boiler and also from the exhaust or condenser. When the piston arrives
at the end of the effective portion of its stroke both of the ports commence to
be uncovered nearly simultaneously, so that one end of the cylinder communi-
cates with the steam from the boiler, and the other with the condenser or
exbanst; both ports then continue open for a portion of the return stroke of
the piston, they are then again nearly simultaneously closed and remain so until

page_text: the piston bas again almost arrived at the end of its stroke, when they both
commence to open as before. For this purpose I place the exhaust passage
of the valve face in the centre between two steam passages as is usual. The
sliding valve I make with a hollow, having on each side of it a flat surface as
before; this hollow, however, I make of smaller dimensions than heretofore, as
I make it of such a width that when the valve is in its central position both of
the steam ports of the valve face shall be covered by the flat surfaces that are
on each side of the hollow, and so that these flat surfaces shall overlap the side
or edge of the steam ports that is towards the exhaust to an extent nearly
equal to the amount that it overlaps them on the opposite side or edge of the
ports, these overlapping portions being in the proportion of about 59 to 60, so
that one port may open the exhaust to that extent before steam can pass to
the other port. The extent to which the flat surfaces overlap the steam ports
of the valve face is governed by the extent to which it is desired to expand
the steam. By making the valve in this manner when one edge of the hollow
in the valve coincides or nearly so with the outer edge of one of the steam
ports in the valve face the outer end of the flat surface that is furthest from
this edge nearly coincides with the inner edge of the other steam port. The
valve is in this position at the end of its stroke, at which time both steam ports
are fully open, one to the steam and the other to the exhaust. As the valve
moves towards the opposite end of its stroke the end of the flat surface that
before coincided with the inner edge of the steam port that was open to the
steam gradually passes over and closes this port, the other port is at the same
time closed by the flat surface of the valve that is on the opposite side of the
hollow passing over it; both the ports then remain covered until the piston has
completed the effective portion of its stroke; the valve has then been so far
moved that the steam ports in the valve face commence to be uncovered by
the flat surfaces of the valve moving beyond them, the valve continues to travel
until both ports are full open, one to the steam and the other to the exhaust,
and then commences to move back, when the same operation is repeated.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said John Coates in the Great Seal Patent Office on the 11th
July 1864.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
COATES, of No. 4, Victoria Road, Limehouse, in the County of Middlesex, 3
send greeting.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria,. by Her Letters
Patent, bearing date the Eleventh day of January, in the year of our
Lord One thousand eight hundred and sixty-four, in the twenty-seventh
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said John Coates, Her special licence that I, the said
John Coates, my executors, administrators, and assigns, or such others as J,
the said John Coates, my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times thereafter
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
SLIDE VALVES FOR STEAM ENGINES," upon the condition (amongst others)
that I, the said John Coates, my executors or administrators, by an
instrument in writing under my, or their, or one of their hands and
seals, 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 John Coates, do hereby declare the
nature of the said Invention, and in what manner the same is to be per-
formed, 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 slide valves for steam
engines.
In constructing slide valves according to this Invention they are arranged in
such manner that for the latter portion of the stroke of the piston the ports
leading to the two ends of the cylinder shall be both closed by the valve, by
which means the interior of the cylinder is shut off both from the steam from
the boiler and also froni the exhaust or condenser. When the piston arrives
at the end of the effective portion of its stroke both of the ports commence to
be uncovered, so that one end of the cylinder communicates with the steam
from the boiler and the other with the condenser or exhaust; both ports then
continue open for a portion of the return stroke of the piston, they are thën
again nearly simultaneously closed and remain so until the piston has again
almost arrived at the end of its stroke, when they both commence to open ȧs
before. For this purpose I place the exhaust passage of the valve face in the
centre between two steam passages as is usual. The sliding valve I make
with a hollow having on each side of it a flat surface as before; this hollow,

page_text: however, I make of smaller dimensions than heretofore, as I make it of such
a width that when the valve is in its central position both of the steam ports
of the valve face shall be covered by the flat surfaces that are on each side of
the hollow, and so that these flat surfaces shall overlap the side or edge of the
steam port that is towards the exhaust to an extent nearly equal to the
amount that it overlaps them on the opposite side or edge of the port, these
overlapping portions being in the proportion of about 59 to 60, so that one
port may open to the exhaust to that extent before steam can pass to the
other port. The extent to which the flat surfaces overlap the steam port of
the valve face is governed by the extent to which it is desired to expand the
steam. By making the valve in this manner, when one edge of the hollow in
the valve coincides or nearly so with the outer edge of one of the steam ports in
the valve face, the outer end of the flat surface that is furthest from this edge
nearly coincides with the inner edge of the other steam port. The valve is in
this position at the end of its stroke, at which time both steam ports are fully
open, one to the steam and the other to the exhaust. As the valve moves
towards the opposite end of its stroke, the end of the flat surface that before
coincided with the inner edge of the steam port that was open to the steam
gradually passes over and closes this port, the other port is at the same time
closed by the flat surface of the valve that is on the opposite side of the
hollow passing over it; both the ports then remain covered until the piston has
completed the effective portion of its stroke, the valve has then been so far
moved that the steam ports in the valve face to be uncovered by the flat
surfaces of the valve moving beyond them the valve continues to travel until
both ports are full open, one to the steam and the other to the exhaust, and
then commences to move back, when the same operation is repeated.
Having thus stated the nature of my said Invention, I will proceed more
fully to describe the manner of performing the same.
DESCRIPTION OF THE DRAWINGS.
Figure 1 shows a longitudinal section of a slide valve where there is only
one exhaust, and Figure 2 shows another longitudinal section of a slide valve
where there are two exhaust ports and the valve box is divided into two
compartments. In each of these Figures the slide valve is in the central
position, when the whole of the ports are shut off both from the steam and the
exhaust. The extent of motion of the valve in Figure 1 is indicated by the
red dotted lines, the two ends of the slide valve respectively coming to the
dotted lines as when the ports are fully open to the steam and to the exhaust.
In Figure 2 the two parts of the slide valve move as far as they can go in

page_text: each direction within their respective compartments of the valve boxes, the two
parts of the valves being as far as they can go when the ports are fully open
to the exhaust and to the steam. The two parts of the valve in Figure 2 are
both on one valve rod and go together as if the valve were only in one piece.
Motion is to be given to the slide valve in each case in such manner that at
about the middle of its stroke the ports are to be closed both to exhaust and
the steam. The ports are to be fully open at the end of the stroke.
In witness whereof, I, the said John Coates, have hereunto set my
hand and seal, this Eleventh day of July, in the year of our Lord One
thousand eight hundred and sixty-four.
JOHN COATES. (L.S.)