AN IMPROVED VALVE GEAR FOR STEAM ENGINES
Year: 1884

page_text: COMPLETE SPECIFICATION.
I, ABRAHAM HILL, of 3, Bridge Buildings, Marlborough, Wiltshire, Locomotive
Engine Driver, do hereby declare the nature of the said invention for "AN
IMPROVED VALVE GEAR FOR STEAM ENGINES," 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 an improved valve motion for locomotives, double
cylinder stationary, portable, traction, marine or other engines, in which one engine
or cylinder can be made to work the valve of the other.
In ordinary engines in which the valves are worked by eccentrics the motion of
the valve is slower at the commencement and end than at the middle of its stroke;
the-steam is consequently admitted to the cylinder but slowly at first and the
piston does not therefore receive the full pressure of steam until it has travelled
some distance. Similarly the steam is cut off slowly, the comparatively slow
motion of the valve at the commencement and end of its stroke thus giving rise in
both instances to the evil known as wire drawing. Moreover the eccentrics cause
considerable friction, occupy space on the crank shaft, and when there is any play
in the bearings of the crank shaft, the eccentrics partake in this play of the shaft
and communicate it to the valves thereby causing the engine to work very
irregularly.
The object of my invention is to avoid theso imperfections by substituting for
the eccentrics in double cylinder engines a gear whereby the valves will be caused
to open and shut quickly, the said gear being operated from the piston rod
crossheads, the crosshead of each engine working the valve of the other. The
valvo gear being wholly independent of the crank shaft is unaffected by any play
of the latter.
For convenience I will describe the gear as applied to a locomotive, but it will
be understood that it can be applied to all double cylinder engines in which one
engine can be made to work the valve of the other.
Referenco is to be had to the accompanying drawings formning part of this
specification wherein figure 1 is a side elevation of part of a locomotive with the
side frame removed Figure 2 is a plan and Figure 3 is a sectional elevation on
line 1-1, in figures 1 and 2.
The locomotive is supposed to be running in forward gear as shown by the
arrow.
14

page_text: The nearer engine or cylinder is designated A and the farther one A¹. The
cylinders, the valves (with the exception of the lead and lap) the pistons,
crossheads, slide bars, connecting rods and reversing gear are similar to the like
parts in the ordinary locomotive and need no special description.
Alongside the guides of each crosshead is pivoted (at a point d or d opposite the 5
middle of the crosshead stroke, and at a suitable distance from the plane of motion
of the crosshead) a slide link or its equivalent preferably in the form of a
Tshaped lever of which the cross member c or o³ is slotted and curved to suit the
direction and extent of travel of the valve. In this slotted member works a slido
block b or b' pivoted on the pin a or a¹ of the adjacent crosshead, the two and fro 1
motion of this slide block in tho slotted member producing an oscillating motion
of the T lever.
In the example shown the T levers are situated outside the cross head guides
and on the side nearest the centre of the engine and are pivoted to one of the
crosshead guides at a point below the plane of the crossheads, but the levers might 1
be variously arranged according to circumstances the operation being similar in all
When both T levers are pivoted on the same side of the plane of motion of
casos.
the crosshend their slotted members must be oppositely curved.
The other members of these levers are respectively coupled by connecting
rods e, e' to levers ff' fixed respectively on solid and tubular rocking shafts g 2
and g¹ working the one inside the other, and which are carried in bearings which
may be bolted to the cross plate carrying the slide bars. On the inner rocking
shaft is fixed a two armed lever connected by the two rods and j¹ to the
reversing link k¹ which is placed as shewn with its concavity towards the valve
(that is, the contrary of the position of the same link in the ordinary locomotive) 2
this position being necessary because the rods are not radial to the shaft which
works them.
This reversing link acts on the ordinary valve rod in the usual way.
On the external rocking shuſt f' is fixed a two armed lever h connected by
rods i and j to a reversing link k which is similar to k¹. The means of shifting the 3
position of the links and k' is similar to that in ordinary use.
The valves should have a very slight amount of lap on the steam side (say
1/8th of an inch) and a slight clearance on the exhaust side (say 1/10th of an inch)
but the proportions here mentioned may be varied according to circuinstances.
Suppose the engine to be in the position shewn in the drawings when steam is
turned on. The engine A receives full steam and turns the crank shaft as shown
by the arrow. Immediately the cross head of this engine begins to move from its
central position it begins to move the valve of the other engine A¹ which is
thereby quickly opened to its full extent both because the crosshead of an engine
travels quickest at the middle of its stroke and also on account of the short
leverage at which the crosshead acts on the slotted member of the T lever when
the crosshead is near the middle of its stroke.
This leverage is greatest when the crosshead reaches the ends of its stroke and
the motion of the valve thereby operated is consequently slowest at the ends of its
travel when it is full open and quickest at the moment of cutting off and admitting
the steam.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declaro that what
I claim is:-
1 A slide valve gear in which the motion of the valve is produced by the
oscillation of a pivoted slide link or its equivalent actuated by the reciprocation
of the piston crosshead substantially in the manner herein shown and described.
2nd In a double cylinder engine the method of operating the slide valves of the
two cylinders, respectively, each by the piston crosshead of the other cylinder
substantially as specified.
"

page_text: 3rd The combination and arrangement of parts constituting the valve gear for.
a double cylinder engine, wherein the valves of the two cylinders are operated
respectively each by the oscillation of a pivoted slide link or its equivalent actuate l
by the piston crosshead of the other cylinder, substantially as herein shewn and
described.