All About Engines

i78 All About Engines of this fact to effect the reduction of pressure to that required for heating by passing it through a turbine on its way to the vats. By this means the steam pressure can be reduced, say, from 200 lb. to 20 lb. on the square inch, furnishing a considerable amount of power and leaving the steam still hot enough for most industrial operations. The same result can be obtained in another way, as shown in Fig. 107. Here the steam can either pass through the turbine or go direct to the heaters through a reducing valve. The turbine is the most perfect form of steam engine for large powers. It has a low steam con- sumption, it occupies a relatively small space, and owing to the absence of reciprocating parts there is practically no vibration, and heavy foundations are unnecessary. Since the steam exerts a turning effect all round the wheel or drum, the motion is uniform, and it is an ideal machine for driving electric gene- rators. For this purpose, and also for centrifugal pumps, its high speed is an additional advantage, because high speed enables weight and size to be reduced. On the other hand, the turbine demands the highest excellence in material and manufacture. In the early days there were many breakdowns. Gradually, one by one, and with infinite labour, the causes were discovered and alterations made in design which largely prevented their recurrence. But there are still some which cannot be forecasted. And the story of patient labour, of scientific and mechanical skill, of hope and disappointment and