The trunk piston, C, is made
hollow, and formed with a shield covered by refractory material to
protect the packing of the piston and the surface of the lower part of
the cylinder from heat. The pistons of the two cylinders are connected
by rods, D, to opposite cranks on the shaft, E. This shaft, by means of
bevel gear, F, works a revolving cylindrical valve, G, situated in a
casing between the two cylinders. The lowest part of this casing is
supplied with combustible gas and with air, in proportions capable of
being regulated by stopcocks or valves. The highest part of the casing
communicates with a discharge-pipe; and the middle part of it with a
reservoir which can be cut off from communication by a stopcock, so that
the charge in the reservoir may be retained when the engine is stopped.
The middle space of the hollow valve, G, communicates, by a number of
holes, with the middle space of the slide casing. It also, by means of a
port at its lower part, communicates alternately with the annular spaces
of the two cylinders; this communication in each case being made when
the piston is performing the latter part of its downstroke.
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