valves, often called expansion valves, of
which, perhaps, the most widely known types in this vicinity are the
Kendall & Roberts engine and the Buckeye. The former is used in the
simplest form of riding cut off, while the Buckeye has many peculiar
features that engineers, I find, are too prone to overlook in a casual
examination of the engine. In these uses of the slide valve, too,
means are suggested and carried out of practically balancing the
valve.

The origin of the riding cut off is most generally attributed to
Gonzenbach. His arrangement had two steam chests, the lower one
provided with the ordinary slide valve of late cut off, and steam was
cut off from this steam chest by the expansion valve covering the
ports connecting with the upper steam chest. This had the old
disadvantage that all the steam in the lower chest expanded with that
in the cylinder, at a consequent considerable loss. This was further
improved by causing the riding cut off to be upon the top of the main
valve, instead of its chest, and resulted in a considerable reduction
of the clearance space.

This is the simplest form, and is shown in Fig. 1. The steam is
supplied by a passage through the main valve which operates exactly as
an ordinary slide valve would. That is, the inside edges of the steam
passage are the same as the ordinary valve, the additional piece on
each end, if I may so term it, being merely to provide a passage for
the steam which can be closed, instead of allowing the steam to pass
the edge. The eccentric of the main valve is fastened to the shaft to
give the proper amount of lead, and the desired release and
compression, and the expansion valve is operated by a separate
eccentric fastened in line with or 180 deg. ahead of the crank. When the
piston, therefore, commences to move from the crank end to open the
port, D, the expansion valve is forced by its eccentric in the
opposite direction, and is closing the steam port and would have
closed it before the piston reached quarter stroke, thus allowing the
steam then in the cylinder to do work by expansion. The eccentric
operating this expansion valve may be set to close this steam port at
any point in the stroke that is desired, the closing occurring when
the expansion valve has covered the steam port. Continuing the
movements of the valves, the two would move together until one or the
other reached its dead center, when the movements would be in opposite
directions.

[Ill