STEAM TURBINES 



223 



STEAM TURBINES 



ECONOMICAL CONSIDERATIONS 



Steam Consumption. The relation between the brake 

 horsepower of the steam turbine at full load and the steam 

 consumption is shown in the accompanying table. The values 

 in this table are taken from published tests of steam turbines 



STEAM CONSUMPTION PER HOUR OF TURBINES 



that have attained the greatest commercial success. The 

 turbines used saturated steam of from 115 to 140 Ib. per 

 sq. in., gauge pressure, and exhausted into a vacuum of from 

 26 to 28.5 in. of mercury. Better results than those noted 

 in the table can be obtained by the use of highly superheated 

 steam. 



Effect of Vacuum. The better the vacuum, the greater is 

 the economy in the use of steam, both in the steam engine 

 and in the steam turbine. A high vacuum is of greater value 

 to the turbine, however, because the turbine can take advantage 

 of a greater range of expansion. The degree of vacuum to be 

 carried is a matter of dollars and cents; that is, it may cost 

 more to create and maintain a high vacuum than may be saved 

 in steam consximption. In a comparative test of a turbine 

 and a triple-expansion engine under like conditions, it was 

 found that, in the case of the reciprocating engine, little or 

 nothing was to be gained by carrying a greater vacuum than 



