IMPROVEMENTS IN AND CONNECTED WITH COMPOUND STEAM ENGINES
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Robert Duncan at the Office of the
Commissioners of Patents on the 7th May 1880.
ROBERT DUNCAN, of Glasgow, in the County of Lanark, North Britain.
"IMPROVEMENTS IN AND CONNECTED WITH COMPOUND STEAM ENGINES."
This Invention relates to certain improvements in steam engines of the class
in which a reversing action is obtained without the use of a link motion and its
attachments, by admitting the steam to the cylinder or cylinders and their valve
casings through a supplementary duplex piston valve, which is actuated by a piston
rod and hand lever outside to traverso one of its pistons to one side or the other
of the main steam admission port, for the purpose of changing the course of the
pressure and exhaust steam and thus reversing the engine.
In this class of engines the engine valves cannot advantageously be made to cut
off the steam during the stroke (as when the engine is reversed there would not
be a free escape of the exhaust steam) and it has not hitherto been found
practicable to work such engines expansively; but by the present improvements
the advantages of the expansive working of the steam are obtained by applying an
arrangement of this supplementary duplex reversing valve or pair of valves to
compound condensing or non-condensing engines, in which the steam is first used
at high pressure in one cylinder and thereafter expanded and used in the larger or
low pressure cylinder, whence it may either pass into a condenser or be freely
exhausted to the atmosphere, and which form the essential improvements of this
Invention.
In one simple arrangement or modification of the improvements a pair of these
supplementary duplex reversing piston valves are fitted in separate casings or
chambers, formed preferably in a space between the ordinary valve casings of the
high and low pressure cylinders, the valve rods of both being carried out through
stuffing boxes at one end and connected by a cross-head or other equivalent so as
To one of these
to be actuated simultaneously by one reversing hand lever.
supplementary valve casings the steam for the high pressure cylinder first enters
by an inlet branch orifice formed in the casing, and a corresponding outlet orifice
is formed in the other casing for the egress of the exhaust from the low pressure
cylinder to the atmosphere or to the condenser. The duplex piston valves are
arranged and traversed in their casings by means of their hand lever for the
reversing of the engines, so that these admission and exhaust openings or orifices

page_text: shall be situated between the two pistons of each valve or beyond the pistons, that
is, to one side or the other of one of the pistons of each valve, according as the
engine is to be driven in one direction or the other.
The high and low pressure cylinders are each fitted with an ordinary duplex
piston valve for controlling the admission of steam by the usual ports to either end
of the cylinders, the outer ends of the casings of these valves beyond the valve
pistons being in direct communication with each other by means of long side
ports, and when the steam is first admitted by the inlet orifice into the
supplementary valve casing between the pistons of that duplex valve, it passes
through a port in this casing directly into the ordinary valve casing of the high
pressure cylinder, between the pistons of that valve also, and is admitted through
the ports to either end of that cylinder alternately by the reciprocation of the
piston valve, the exhaust passing through the opposite ports to the ends of the
casing beyond the pistons of the engine valve, and being thence led by a
communicating passage through the ends of the supplementary valve casings (open
only in this position of their pistons) to the outer ends of the valve casing of
the low pressure cylinder. But when the supplementary valve pistons are traversed
by means of the reversing hand levor, so that the steam first enters this supple-
mentary valve casing by the inlet branch orifice above or at either end beyond
these pistons, then the steam at initial pressure passes directly through the
communicating port, which was previously the exhaust port, at the ends of the
valve casing of the high pressure cylinder, and is admitted by its piston valve to
either end of this cylinder, the exhaust now being led through between the pistons
of the valve and through the communicating port to the supplementary valve
casing, between the pistons here also. Thence this high pressure exhaust steam
passes through a port communicating between the two supplementary valve casings,
which is open in this new position to which the pistons have been traversed, and
entering between the second pair of supplementary valve pistons the steam
continues through a central port into the valve casing of the low pressure cylinder
between the pistons of that valve. This steam is then admitted by the reciprocation
of the valve through the usual ports to either end as required of the low pressure
cylinder (depending on the relative position of the pistons in the high and low
pressure cylinders), there works expansively, and the exhaust from this cylinder
returns through the ports to the ends of the valve casing outside its pistons, and
thence passes by a communicating port to the exhaust outlet orifice in the end of
the second supplementary piston valve casing to be led to a condenser or to the
atmosphere. But when the exhaust from the high pressure cylinder is led as first
described, for the reverse direction of the engine's motion, to the outer ends of the
low pressure cylinder valve casing, and is admitted and expanded in this cylinder,
the low pressure exhaust returns through between the pistons in the valve casing,
thence through the central port into the second supplementary valve casing, between
its pistons also, and through the outlet orifice to the condenser or the atmosphere,
the outlet orifice_being in this position of the piston's traverse between these
pistons.
By a slight modification of the arrangement of reversing valves described only
one supplementary duplex piston valve and casing are used, but of proportionately
increased diameter, and this valve casing is divided into two compartments by the
piston rods of the duplex pistons, which is flattened out or made in the form of a
dividing, web or partition across the valve casing, fitting quite steam tight. The
piston rod is carried out in this web form through stuffing boxes at both ends,
and is actuated for traversing the valve to reverse the engine by a hand lever at
one end. The inlet orifice for the steam to the valve casing is on one side of the
dividing web and the outlet orifice on the other, and the communicating port
through this supplementary or reversing valve casing from the high pressure
exhaust to the valve casing of the low pressure cylinder is formed by an annular
recess in the supplementary valve casing, which allows the steam to pass round the
dividing web at the recessed part either between the valve pistons or outside, as

page_text: may be required by the position of these pistons and consequent direction of motion
of the engines, the action in this arrangement being otherwise substantially the
same as described in reference to the first modification.
Although duplex piston valves only have been described as used for the supple-
mentary reversing valves and for the engine valves, it will be understood that
other forms of hollow slide or hollow cylindrical valves might be used for either
or both, and thus also afford a means of communication between both ends of their
casings.