COMPARISON OF IMPULSE AND REACTION TURBINES

Applications of the principles generally called, reaction and impulse often appear in the same turbine, and either is adopted without hesitation as may best suit a particular design, size of unit, or place in a unit. Impulse turbines of low output are less costly and more efficient than reaction turbines, but with increase of size these differentials disappear, and in the large sizes there is little to choose as to efficiency or as to cost for equal efficiency. High efficiency is expensive in either type, but it cannot be said that either has any absolute superiority.

COMPARISON OF STEAM TURBINES WITH STEAM ENGINES

The advantages of large steam turbines over large reciprocating engines are very great. They occupy less space, permit smaller buildings and foundations, their original and maintenance costs are less, their economy is greater (in part owing to their ability to use high vacua and high superheats), and they may be built in units of far greater output, reducing greatly the cost of attendance. Engineers engaged in designing small plants often find, however, that it is there preferable to use reciprocating engines, on account of the better economy of small engines than small turbines and the disadvantages of the reduction gearing usually necessary in applying small high-speed turbines to industrial uses. The reverse is usually true, however, and reciprocating engines of all sizes have been scrapped and replaced by turbines long before their useful lives were over. When it is admitted therefore that certain difficulties still meet the designer, the builder, and the operator of steam turbines, it is not to be understood that the overwhelming superiority of the turbine to the reciprocating engine for most power-plant purposes is in any way questioned.

(Church E. F.)