[2135]. Compound engine, with T connecting rod and one crank, no dead centre.
Crank motions. See [Section 21].
[2136]. Three-cylinder high-speed box engine, single acting.
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[2137]. American type of walking beam paddle engines.
[2138]. Diagonal engine, with vertical air pump, worked by a bell-crank lever.
Vacuum engines. Two forms of this type of engine have been manufactured in which steam is employed at atmospheric pressure and condensed in a jet or surface condenser, the working pressure being therefore atmospheric and never exceeding 14 lbs. per square inch absolute. These engines and their boilers are free from risk of explosion, but require a good supply of condensing water.