144 WATER CONDUCTORS AND ACCESSORIES 



ground, and the top of the tank is high enough above the crest 

 of the dam so that if the flow of the water in the pipe line were 



SALMON RIVER POWER COMPANY 



CROSS SfTTION THh'OlK.H PLAN! 



FIG. 69. Cross-section of Salmon River Power Company's Development. 



suddenly interrupted its energy would be absorbed by the rise 

 in level in the tank without overflow. 



A complete treatise of the surge tank problem is to be found 

 in two excellent papers by Messrs. R. D. Johnson and M. M. 

 Warren in the Transactions of the American Society of Civil 

 Engineers, Vols. 78 and 79, 1915. 



3. GATES AND VALVES 1 



Requirements. For the control of water flow in hydro- 

 electric developments gates and valves are generally used. They 

 may be either of the sluice gate or gate valve type and the selection 

 of the type, as well as the number required, is governed by the 

 nature of the development. So, for example, in low-head plants, 

 only one set of sluice gates are, as a rule, needed, these being 

 installed in front of the turbine intakes, either in a gatehouse, as 

 in Fig. 89, or outside the power-house building at the dam struc- 

 ture, as in Fig. 70. 



For high-head developments, however, two and sometimes 

 three sets of controlling devices are required, depending on the 

 pipe-line arrangement, and in order that the water may be prop- 



1 See also section on " Flashboards." 



