release is very quick and as we would have it. This is only possible
at the most uneconomic position of the valve as regards cut off.

The aim of many engineers has been to take advantage of these matters
by using the valve with 90° angular advance of eccentric ahead of
crank, for the admission, release, and compression of the steam, and
provide another means of cutting off, besides the one already referred
to, viz., cutting off the supply of steam to the chest, and overcome
the objection in this one of large clearance spaces. This is done by
means of riding cut off 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