The steam inlet is at F, which is one-eighth of the distance around the cylinder, and the exhaust is at G, the same distance from the point D, on the other side. The inlet and the outlet pipes are, therefore, at the contracted parts of the channel.
The drum has a pair of radially-movable blades H H´, which may move independently of each other, but usually they are connected together, thus dispensing with the use of any springs to keep their ends in contact with the shell.
When steam enters the inlet F the pressure against the blade H drives the drum to the right, and the drum and shell, by contacting at D, form an abutment. Each charge of steam drives the drum a little over a half revolution.
A great deal of ingenuity has been exercised to arrange this abutment so that the blades may pass and provide a steam space for a new supply of steam. In certain types a revolving abutment is formed, as shown, for instance, in [Fig. 116].
The shell A, in this case, has two oppositely-disposed inlet and outlet ports, B, C, respectively, and between each set of ports is a revolving gate, formed of four wings D, mounted on a shaft E, in a housing outside of the circular path F, between the drum G and shell A.
The drum G is mounted on a shaft H which is centrally within the shell, and it has two oppositely-projecting rigid blades I. When steam enters either of the supply ports B, the drum is rotated, and when the blades reach the revolving gates, the latter are turned by the blades, or, they may be actuated by mechanism connected up with the driving shaft.
Caloric Engine.—This is an engine which is dependent on its action upon the elastic force of air which is expanded by heat. The cylinder of such a motor has means for heating it, and thus expanding the air, and a compressor is usually employed which is operated by the engine itself, to force compressed air into the cylinder.
It is not an economical engine to work, but it is frequently used in mines, in which case the compressor is located at the surface, and the engine operated within the mine, thus serving a double purpose, that of supplying power, and also furnishing the interior with fresh air.