All About Engines

158 All About Engines —that is to say, they do not run straight across from side to side. The force exerted by one wheel or the other is, therefore, continuous and more uniform than when the teeth run parallel to the shaft. In order to avoid the enormous velocity obtained in the de Laval turbine, Rateau and others invented turbines in which the full force of the steam was r of blades but upon several rings in succession. Thus the rings of blades in the Westinghouse modification of Rateau’s turbine are mounted a short distance apart on the curved face of the disc, and the spaces between are occupied by rings of blades on the rims of discs or diaphragms ie casing and which, there- exerted not upon one Fig. 90.—Diagram of blades of impulse turbine which are attached to fore, do not rotate. Fig. 90 shows, diagrammatic- ally, this arrangement. In each ring of fixed blades the steam expands and acquires velocity, which enables it to give a succession of impulses to the moving blades. The amount of expansion at each stage, and, therefore, the velocity acquired, depend upon the shape of the fixed blades. With a parallel flow the pressure never drops to less than '58 of the original pressure ; with an expanding orifice the drop may be greater ; with a contracted orifice the drop may be less. From an exact knowledge of