If the load should increase at such a time the governor could not
control it under these conditions, and it would lead to a decrease in
speed unless the lap was again changed to give a later cut off. On
this account the general practice soon becomes to leave the cut off at
the later point and give range to the throttle, and we come back once
more to the plain slide valve cutting off at half stroke, and the only
gain there is, is in a quick port opening and quick cut off. But these
matters are more than offset by the wire drawing between the steam
pipe and chest, through the throttle, and the fact that there is added
to the friction of the engine the friction of this additional slide
valve and a considerable liability to have a leaky valve.
In the case where the governor changes the position of the cut off
valve a greater decree of economy would result. In this engine, of
which the Lambertville engine is a type, the main valve is a long D
slide, with multiple ports at the ends through which the steam enters
the cylinders. It is operated from an eccentric on the crank shaft in
the usual manner. The cut off valve is also operated from the motion
on an eccentric fixed upon the crank shaft.
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