Very little
movement will effect a considerable change in the lappage of the
valve, the valve turning about one-quarter a revolution for the
extremes of cut off. The cut off valve rod works through a bracket and
its end terminates in a ball in a socket on the end of the eccentric
rod. In this case the governor has not as much to do as in other
instances.
[Illustration: FIG. 4.]
Still another method of effecting this change in cut off, but hardly
by increasing the lap of the valve, is shown in the next drawing, Fig.
4. The cut off valve is held upon the main valve by the pressure of
steam upon its back and rides with it until it comes in contact with
the cut off wedge-shaped blocks, when its motion is arrested, and the
main valve continuing its movement the steam port is closed by the
main valve passing beneath the cut off valve. Thus the main valve
travels and carries the cut off valve upon its back again until the
cut off valve strikes the wedge on the other end and the cut off is
effected. The relative positions of the blocks are determined by the
governor, that will raise or lower them so that the cut off valve will
engage with them earlier or later as desired.
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