IMPROVE- MENTS IN STEAM ENGINES
Year: 1867

page_text: PROVISIONAL SPECIFICATION left by John Millward at the Office of the
Commissioners of Patents, with his Petition, on the 25th April 1867.
A communication from abroad by Frederick W. Gordon, of Cincinnati,
Ohio, United States of America.
I, JOHN MILLWARD, of Birmingham, in the County of Warwick, Civil
Engineer, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN STEAM ENGINES," to be as follows:-
This Invention relates to that class of devices commonly known as "balanced
steam valves" with automatic "cut-off" attachments, and the first part of the
present improvements consists in constructing the valve chest of a steam
engine with a partition or diaphragm parallel with the cylinder, forming separate
steam and exhaust chambers. The slide valves, one to each port, are hollow
or formed with central passages through which the steam passes to the upper
or exhaust chamber. The upper ends or necks of the valves pass through
openings in the diaphragm.large enough to permit the full travel of the valves,
and fitted to each is a plate sliding on the upper side of the diaphragm and
travelling with the valve, but never uncovering the openings in the diaphragm,
and these plates have central openings corresponding to the passages through
the valves. By equally proportioning the area of the surfaces from which the
valves exclude the steam from their seats and the area of the openings
through the diaphragm by which the steam acts on the upper sliding plates
the valves may be perfectly balanced throughout the stroke, except when
covering the ports and exhausting, and the excess of pressure on the valves at

page_text: this time is obviated as follows:-Recesses corresponding in position with the
ports are formed in the upper side of the diaphragm with which the plates
attached to the valves are in sliding contact, and similar recesses are formed
in the under side of the sliding plates, and which, at the proper moment
admit live steam to the recesses in the diaphragm, thus adding in an equal
degree to the counteracting influence of the sliding plates; recesses are also
for the same purpose formed in the valve seat.
The above-described improved mode of balancing slide valves is also
applicable to ordinary shut D or locomotive valves, as also to reciprocating
rotary valves.
The second part of this Invention consists in peculiar devices for actuating
the valves partly in an automatic manner, that is, by the steam within the
valve chest, and partly by the motions of the valve gearing or attachments,
both acting together in such a manner that the point of "cut off" in the degree
of expansion is regulated by the governor and thereby instantly varied in
accordance with the requirements of the engine; and the nature of these devices
is as follows:-The two slide valves, one to each port, are actuated by separate
stems secured thereto, the shorter one or that next the driving gear being
tubular, enclosing the other within it, and both working in steam-tight packing
boxes. Each end of the steam chest is fitted with a short plunger, that
nearest the driving gear being hollow and enclosing the tubular valve stem,
and both working in packing boxes; these plungers are connected to the
valves, so that when either of the valves is released from the valve gear it is
suddenly drawn outwards by the pressure of the steam on the plunger and the
port is closed. The stroke of each plunger is only sufficient to cut off steam,
but the connection with the valve allows of the further travel of the valve for
exhausting.
To operate the valves both the central and tubular stems are at their outer
ends secured to long hollow socket-shaped heads, and these heads are at some
distance apart, the hollow faces fronting each other and formed into female
clutches; betwixt these and sliding on the central stem connected to the far
valve is a sleeve or long socket which has a reciprocating motion from an arm
on a rock shaft. Each end of the sleeve has a collar fitting into the far end
of its respective socket head, and having a connection therewith by stops,
allowing a limited free motion of the head. The middle part of the sleeve,
which is larger in diameter, is formed at the outer portions into male clutches
for entering the female clutches of the valve stem heads; the sleeve is also
fitted with two thin discs, one to each clutch, capable of a partial rotary motion
on the sleeve, and having openings corresponding with the female clutches

page_text: when opposite thereto, but otherwise acting as a stop; these discs are formed
into horns at the upper part, and their position with respect to the clutches is
regulated as follows:-At a little distance above the valve stems and heads,
and parallel therewith, is fixed a guide bar baving at a proper distance apart
and sliding thereon two sockets which have inclined faces both on the same
side of the bar, but in opposite directions, and a small wheel is mounted on
the bar betwixt the two inclines, and to which the latter are connected with
rods to pins at top and bottom of the small wheel so as to be drawn together
or forced apart by the partial rotation of the wheel, which is controlled by
another rod connecting it with the lever of the governor.
At the middle of the guide bar a double wedge-shaped swell is formed on
the opposite side to the sliding inclines. The horns of the discs referred to rise
on each side of the guide bar so as to engage with the inclines when carried
against them by the reciprocating motions of the sleeve. By these means the
valves are operated as follows, confining the illustration to one of the valves:-
The sleeve sliding on the central valve stem as a guide has a reciprocating
motion by an arm from a rock shaft worked by a proper eccentric. When
the sleeve is leaving the middle of its path either way that clutch which is in
the direction of its motion is prevented from entering the female clutch of the
valve head by the interposition of the disc, and the head stem and valve are
carried with it, thus opening the port until by the motion of the sleeve the
horns of the disc are brought into contact with the sliding incline on the guide
bar, the position of which is regulated by the governor, and by which the disc
is caused partially to rotate on the sleeve, and its openings thus brought to
correspond with the clutches, and then the valve head is drawn back on to
the male clutch by the action of the plunger to the valve, as before described,
and the valve thereby is "retracted" and the port closed, say, at half stroke,
or any other proportion. In the reverse motion of the sleeve it would return
without moving the valve again until the collar on the end of the sleeve came
in contact with the stops on the inside of the valve head, and then the valve
would be carried until the port opened to exhaust. During the reverse move-
ment the horns of the disc are carried against the opposite inclines at the
middle of the guide bar, and the disc is restored to its former position. The
action of both valves is of course precisely similar.