Where 90° turns are necessary, easy bends should be used instead of sharp elbows. The force of this argument must be apparent by noting the practice of steam turbine builders of placing the turbine right up against the condenser, and remembering that a high vacuum is necessary to the economical working of a turbine. See fig. 1,445, page 1,182.
Ques. What are the considerations respecting the number and type of engine to be used?
Ans. In the illustration [fig. 2,720], two engines M and M' are employed, one belted to each end of the countershaft O. These engines should be of similar or identical pattern; for a small output they may be either simple or compound, as the conditions of fuel expenditure may dictate, but if the output be large, triple expansion engines or turbines are advisable.
Fig. 2,725.—"Dry pipe" for horizontal boiler: it is connected to the main outlet and its upper surface is perforated with small holes, the far end being closed. With this arrangement steam is taken from the boiler over a large area, so that it will contain very little moisture. All horizontal boilers without a dome should be fitted with a dry pipe; most engineers do not realize the importance of obtaining dry steam for engine operation.
Corliss or similar slow speed engines may advantageously be used in either case. In all cases the engine should be run condensing unless the cost for circulating water is prohibitive; even in such cases cooling towers may be installed and effect a saving.
In operation, during the greater part of the day, one engine running two or perhaps three of the generators, will carry the load, but when the load is particularly heavy, as in the morning and evening, both engines and all the generators may be required to meet the demands.