The eccentric rod is fastened to a rocker
arm having motion swinging about a pin or bearing in the governor
slide, which may be raised or lowered by a cam operated by the
governor. The cut off slide is of cylindrical shape and incloses a
spring and dash pot with disks attached by means of which the valve is
closed. The motion for operating the valves is relatively in the same
direction, the cut off eccentric having the greatest throw and greater
angular advance to cause it to open earlier and quickly before the
main valve is ready to admit steam. The cut off eccentric rod swinging
the rocker arm, the tappets thereon engage with those upon the cut off
valve rod and open the passages to the main valve, and in their
movement compress the spring in the main valve. According as the speed
of the engine, the rock arm will be raised or lowered so that the
tappets upon the eccentric rod may keep in engagement a shorter or
longer time before they disengage, thus allowing the spring that has
been compressed by the movement of the cut off valve to close that
valve quickly and the supply of steam to the engine, the cut off valve
traveling with the main valve for the balance of the stroke. This
device will give a remarkably quick opening and a quick cut off, but
in view of the fact that the governor has so much to do, its delicacy
is impaired and a quick response to the demands of the load changing
not so likely to occur. The cut off cannot be as quick as in some
other engines, because the valves are moving in opposite directions,
and while this fact would help, so far as shortening the distance to
be traveled before cut off, the resistance of the valves to travel in
opposite directions, or rather the tendency of the valve to travel
with the main valve, hinders its rapid action.

[Illustration: FIG. 3.]

This is one great objection to the rack and gear operated by the
governor, that two flat valves riding upon each other and sliding in
opposite directions at times require a considerable amount of force to
move them, and as only a slight change in load is required by the
load, the governor cannot handle the work as delicately as it should.
It is too much for the governor to do well. To overcome this
difficulty the Ryder cut-off, shown in Fig. 3, was made by the
Delamater people, of New York. The main slide valve is hollowed in the
back and the ports cut diagonally across the valve to form almost a
letter V. The expansion valve is V-