An Improvement in Valve Gear for Steam Engines Working Expansively.
Year: 1894

page_text: Date of Application. 21st Sept., 1894-Accepted, 27th Oct., 1894
COMPLETE SPECIFICATION.
An Improvement in Valve Gear for Steam Engines Working
Expansively.
JOHN ERNEST WALLIS, Erdesley, Basingstoke, Engineer, and WALLIS &
STEEVENS LIMITED Basingstoke, Engineers do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This invention relates to a means of altering the movement of the main slide
valve of a steam engine so as to reverse the engine and at the same time to reverse
the movement of the expansion valve, but in such a way that the opening and
closing of the ports remain relatively the same when working in either direction.
The expansion valve may be held at complete, or varying cut off, as for instance if
it be set to cut off at half stroke when the main valve is reversed the expansion
valve is also reversed, but remains still at, or about half cut off on the reverse
stroke.
This invention provides for the expansion valve gear to be controllable either by
hand or automatically by a governor as we shall describe referring to the accom-
panying drawings.
For the purpose of more clearly describing this invention we show on the
accompanying drawing the eccentrics and link motion driving the main valve at
Figure 1 and the eccentrics link motion and other parts driving the expansion
valve at Figure 2 and it must be understood that these two link motions are placed
side by side and only shown separately here for the clearness of the drawing.
A is the crank-shaft common to both drawings and i. the bell crank arm to
which the lifting levers of both links are attached, the point on which the bell
crank works, the bell crank arm connected to the rod 3 are also common to both
drawings. Figure 3 is a part longitudinal section showing how the main and cut off
valves may be arranged. In this M is the main slide valve governing steam and
eduction ports in the usual way and E is the expansion valve (which may
be a plain valve as shown, or balanced) governing the ports in the main slide
valve.
On the engine shaft A we fix eccentrics a. b. c. d. which are fitted with eccentric
straps a bed and impart the reciprocating motion to the links B. and C. through
the connecting rods a²² c² d² which are attached by pins to their respective links.
The eccentrics c. and d. are set at an advanced angle (relative to the crank) to the
eccentrics a. b.
e. is a rod connecting the main valve M with the link B. passing through a guide f.
and attached to the link B. by a block on which the link slides when reversing.
The links B and C are supported by lifting links g. and g¹ both being connected at
The arm of
their lower end to the arm of the bell crank lever i. pivoted at i¹.
the bell crank is connected to a rod 3 which can be moved to and fro by a hand
lever or otherwise and retained in any desired position. By the movement of the
bell crank both links are simultaneously raised or lowered and the motion of the
engine thereby reversed. j. is a rod connecting the link C. to the expansion link D.
This rod works in a guide k. and is attached to the links C and D by sliding
blocks and r.
The link D. is pivoted at 1. This link is made with two radiating slots the one
connected by the block r. to the rod j. and the other by the sliding block n. to the
connecting rod n¹ which is connected to the expansion valve spindle n². The
block n. working in the link D. and attached to the rod n¹ is free to work up and

page_text: down in the link and by thus shortening or lengthening the stroke it gives a
complete cut off to the valve, or regulates the period of cut off according to the
position the die maintains in the link. The rod n¹ is connected by a link O. to
the lever O' worked by a centrifugal governor when automatic regulation of the
expansion is desired; or when it is desired to regulate the expansion by hand the
link O. is disconnected and the rod n' is then connected by a link p. to an arm pl
of a bell crank lever pivoted at p². The arm p³ of the bell crank is connected to a
rod p' which can be moved to and fro by a hand lever, or otherwise and retained
in any desired position.
As the expansion link D. swings from a point l. and has its motion communicated
through block r. and the rod j. which at its other end is connected to the block r²
working in the link C., it follows that when the link C. is raised, or lowered, the
actions of the eccentrics c. and d. are reversed and that the reversed motion is
thereby imparted to the link D. Thus, while the stroke of the cut off valve is
increased or diminished by the movement of the block n. (either by hand, or
automatically by the governor) farther from or nearer to the point l., the
cut off being thus made to take place at a later or earlier period of the
stroke, the period of the cut off so determined is in no way altered by the act
of reversal.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. An arrangement of valve gear for an engine working expansively, whereby
the period of cut off, determined by the position of the sliding block connected to
the cut off valve in its oscillating slotted link is not altered when the movement
of the engine is reversed, substantially as herein described.
2. An arrangement of valve gear for an engine working expansively whereby
the movement of the engine may be reversed by the action of a single lever
without affecting the period of cut off of the expansion valve, substantially as
herein described.
3. The arrangement of cut off valve gear such that the period of cut off can be
varied by hand, or automatically by a governor when the engine is running in
either direction, substantially as herein described.
Dated this 20th day of September 1894.
JOHN ERNEST WALLIS.
For WALLIS & STEEVENS, LIMITED,
JOHN ERNEST WALLIS, Secretary.