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

page_text: Date of Application, 17th July, 1894-Accepted, 18th Aug., 1894
COMPLETE SPECIFICATION.
An Improvement in Valve Gear for Steam Engines Working
Expansively.
We, JOHN ERNEST WALLIS, of Erdesley, Basingstoke, Engineer, and
WALLIS & STEEVENS LIMITED, of North Hants Iron Works, 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 means of altering the movement of the main slide valve
of a steam engine so as to reverse the engine without in any way affecting the
action of the cut off or expansion valve, and to an arrangement of expansion valve
gear so as to be controlled by hand or automatically by a governor, as we shall
describe referring to the accompanying drawings.
Fig. 1 shows diagrammatically the connections to the main and cut off valves,
which may be arranged as in the part longitudinal section Fig. 2, where M is the
main slide valve governing steam and eduction ports in the usual way, and E is
the expansion valve governing a single port admitting steam to the main valve
chest.
On the engine shaft, we fix an eccentric A to which is attached a piece forming
two equal and similar slotted links B, of which only one appears on the drawing,
the other being immediately behind it.
The middle point b of these links, which is pivotted on an arm b' oscillating on a
fixed pivot 62 is connected by a rod 6 to another slotted link C at its upper part c
which part reciprocates with b as determined by the eccentric A. A block D fitted
to slide in one of the links B is connected by a rod d to the main valve rod m, and
the rod d is connected by a link d¹ to an arm d' of a bell crank lever pivotted at d³.
A block F fitted to slide in the other link B is connected by a rod f to a rod
On this
guided to move parallel with m or it might be to a sleeve sliding on m.
guided rod or sleeve the slotted link C is pivotted. The rod fis connected by a
link to an arm of a bell crank lever pivotted at b. The other arms d and f^
of the two bell crank levers are both connected to a rod f" which can be moved to
and fro by a hand lever or otherwise for the purpose of reversing the engine and
can be fixed so as to retain the rods d and fin their respective positions. Thus,
when the rod f' is moved in the direction of the arrow the block D and rod d are
raised, and the block F and rod fare lowered, D taking the place of F, and F
taking the place of D. Thus the main valve rod m is moved by the eccentric A
to the same extent as before, but its movement is timed to suit the reversed rotation
of the eccentric. In the slot of the link C, is fitted to slide a block G which is
connected by the rod e to the rod of the cut off slide valve E. The rod e is
connected by a link g to a lever g' 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 g is disconnected and the rod e is then connected
by a link to an arm g' of a bell crank lever pivotted at 9. The arm go of the
bell crank is connected to a rod 9 which can be moved to and fro by a hand lever
or otherwise and retained in any desired position.
As in the case of reversal, the rods and d change places, the reciprocation of
the middle point of the link C remains the same in extent but becomes timed to
suit the reversal of revolution, and as the movement of the point c of the link
remains the same whichever be the direction of rotation, it follows that the
movement of the rode which works the cut off valve remains, on reversal, the same
in extent depending on the position of the block G in the slot, and, like the main

page_text: valve rod, becomes suitably timed to the reversed revolution. Thus, while the
stroke of the cut off valve is increased or diminished by the movement of the
block G (either by hand or automatically by the governor) farther from or nearer
to the point c, the cut off being thus made to take place at an earlier or later
period of the stroke, the period of 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. 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 17th day of July 1894.
ABEL & IMRAY,
Agents for the Applicants.