Eccentrics are entirely dispensed with and the time-honored link
gear abandoned, the motion is taken direct from the connecting rod, and by
utilizing independently the backward and forward action of the rod, due to
the reciprocation of the piston, and combining this with the vibrating
action of the rod, a movement results which is suitable to work the valves
of engines, allowing the use of any proportions of lap and lead desired,
and giving an almost mathematically correct "cut-off" for both sides of
the piston and for all points of expansion intermediately, as well as a
much quicker action at the points of "cut-off" and "release" than is given
by a link gear.
The machinery for accomplishing this is both less costly and less
complicated than the ordinary link motion, and is shown in elevation on
cut, which is a view of the complete motion as on the first London and
North-Western locomotive. Here E is the main valve lever, pinned at D to a
link, B, one end of which is fastened to the connecting rod at A, and the
other end maintained in about the vertical by the radius rod, C, which is
fixed at the point, C. The center or fulcrum, F, of the lever, E,
partaking of the vibrating movement of the connecting rod at the point, A,
is carried in a curved slide, J, the radius of which is equal to the
length of the link, G, and the center of which is fixed to be concentric
with the fulcrum, F, of the lever when the piston is at either extreme end
of its stroke.
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