IMPROVEMENTS IN STEAM ENGINES
Year: 1868

page_text: PROVISIONAL SPECIFICATION left by Charles Hyndman Mitchell
at the Office of the Commissioners of Patents, with his Petition,
on the 13th June 1868.
I, CHARLES HYNDMAN MITCHELL, Manager of the Fereneze Mills,
near Barrhead, in the County of Renfrew, North Britain, do hereby
declare the nature of the said Invention for "IMPROVEMENTS IN STEAM
ENGINES," to be as follows, that is to say :-
This Invention has for its object to construct and work steam engines
in an improved manner with the view of economising fuel. The
principal feature of novelty is a pecular mode of combining a high-
pressure cylinder and a low-pressure cylinder with one port face so
that one valve may serve both cylinders, and so that the expansion
of the steam which is admitted directly from the boiler to only one
end of the high-pressure cylinder may be carried to an unusually
great extent without the great variation in the strain on the crank
shaft associated with ordinary modes of working very expansively. The
action of the valve is such that the steam from the boiler having first
acted in one end of the small or high-pressure cylinder next expands
in the other end of that cylinder and simultaneously in one end of
the larger or low-pressure cylinder, after which the steam thus expanded

page_text: in the large cylinder passes to the exhaust, whilst the partly expanded
steam in the second end of the small cylinder expands in the second
end of the large cylinder, at the same time that a fresh supply from
the boiler is acting in the first end of the small cylinder. The two
cylinders may be placed side by side or end to end; in the former
case the exhaust port is in the middle, and next it on each side are
the ports to the large cylinder, those to the small cylinder being beyond
these. The valve is made with the usual exhaust cavity for covering
the exhaust port and one or other of the large cylinder ports, and
in addition it is made with two cavities near the ends which com-
municate with each other by a passage along the valve. When the
valve is in one position it uncovers one end port to the boiler steam
and puts the other end port in communication (through the passage)
with one inner port, the other inner port being then in communication
with the exhaust. When the valve is in its other position the end
ports are put in communication with each other and with one inner
port, and the other inner port is then in communication with the
exhaust. When the cylinders are placed end to end the two small cylinder
ports are together at one end of the port face and the exhaust port
is between the two large cylinder ports, the valve being proportioned
to correspond. A clack valve is placed in the passage in the valve to
prevent the return of steam from the second end of the small cylinder,
as it will tend to do after a part of the stroke is performed from
the more rapid expansion in the large cylinder. The valve chest is
made cylindrical and the valve is made with pistons at the ends to
prevent the full boiler pressure from acting on the back of the valve.
In cases where it may be desirable to at any time largely increase
the power of the engine the valve may be fitted with a stop valve
which can be adjusted by a rod passing out through a stuffing box
or otherwise so as to admit the boiler pressure into one end of the
passage in the valve, which will have the effect of allowing the full
pressure to act in the second end of the small cylinder as well as in
the other end of that cylinder.