TURBINES 



227 



units may also have one or more runners, as previously explained, 

 and when a pair of runners are used the question arises whether 

 an outward discharge, requiring two draft tubes, or a center dis- 

 charge, requiring only one draft tube, is to be used. 



Horizontal Turbines: The multi-runner horizontal turbine of 

 the open flume type is open to the objection that the gate mechan- 



FIG. 118. Horizontal Double-runner Open Flume Turbine with Cast-iron 

 Draft Chest and Steel Draft Tube. (S. Morgan-Smith Company.) 



ism is submerged and cannot be efficiently lubricated, while the 

 entire machine is less accessible for inspection and repairs. The 

 only advantage which can be claimed for this unit is its higher 

 speed. 



The most approved type of horizontal unit at present is either 



