The rod or stem of the cut
off valve passes through the main valve rod and slide. Upon the outer
end of the cut off valve rod are tappets fastened to engage with
tappets on the eccentric valve rod. Connection between the cut off
eccentric, therefore, and the cut off valve is only by means of the
engagement of these tappets. 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.
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