All About Engines

166 All About Engines square inch, or *58 of the original pressure, if the nozzle is 1 square inch in area there be a pressure of 84 lb. per square inch, tend- to force the vessel backwards in the direc- of the arrow. With a properly designed nozzle, 185 lb., the difference between 200 lb. on the inch and the the and will ing tion however, it would be possible to increase this differ- ence to square Fig. 101.—Diagram to explain principle of reaction turbine pressure of the atmosphere. And if the discharge took place into a condenser the force tending to thrust the vessel backwards would be still greater. It will be interesting and instructive to examine the application of this reaction principle to steam turbines in the same way that we studied the application of the im- pulse principle. to represent a nozzle con- Suppose c in Fig. 101 veying the working fluid (in a scientific sense, as you know, the term fluid includes both liquids and gases) to the vanes or blades a b and e f, which themselves form practically a curved nozzle, which is seen in section. If the blades are regarded as fixed, it is clear that the fluid will tend to force the blades in the direction of the arrow. But whereas in the impulse machine the pressure at inlet and outlet is the same and, except for a small friction effect, the speed of the fluid over the surfaces does not change,