The main valve rod is hollow, and the cut off valve rod passes
through it.
[Illustration: Fig. 6]
The cut off eccentric can be placed in any position to cause it to cut
off as desired, and by drawing the valve forward, by increasing the
angular advance of the eccentric, the cut off valve is caused to reach
and cover the steam passage in the main valve earlier in the stroke.
Instead of being ahead of the crank, the main eccentric in this
arrangement follows the crank, on account of the exhaust and steam
edges being exactly opposite from those in the ordinary slide. What is
the steam edge of the common slide is in this the exhaust edge, and
what is the exhaust edge in the common valve is the steam edge in this
one. The valve, therefore, must be moved in the opposite direction
from what is ordinarily the case, the main eccentric being not 90 deg.
behind the crank. It has a rapid and full opening just the same, for
it is at this point behind the crank, or ahead of it, that the
eccentric gives to the valve its quickest movement, or between the
eccentric dead centers. The cut off eccentric is considerably ahead of
the main eccentric, and about even with the crank.
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