All About Engines

Steam Turbines 149 mechanical construction had been overcome and the theory had been worked out, it was rapid, and the in- crease of steam turbines, both in numbers and size during the last twenty-five years, forms one of the romances of applied science. The simplest, but not, in point of time, the first successful, invention was that of de Laval. It depends upon the principle that when any gas escapes under pressure from a suitably shaped nozzle the pressure is converted into velocity—the same principle, in fact, that is involved in the injector. When steam escapes from a small hole from which it enters the atmosphere abruptly, its velocity is relatively small. The effect is as though it were “ throttled.” In fact, the velocity acquired, no matter how great the pressure may be, is approxi- mately no greater than would occur under a pressure of 107 lb. per square inch, as shown by the FIg- 87-—Section through r * 7 nozzle of de Laval turbine gauge ! In order to utilise larger pressures a nozzle, expanding towards the mouth, as in Fig. 87, is needed. In such a nozzle the steam expands during its passage, and if the inlet pressure is high, as in modern boilers, and the nozzle dis- charges into a condenser, a velocity of 3,000 feet to )))))))))))))))