GATES AND VALVES 



145 



erly shut off in case of emergency should, for example, one of the 

 valves become damaged or stick. In such plants sluice gates 

 are installed as headgates at the forebay or reservoir intake, while 

 gate valves are provided in the pipe line at the point where this 

 branches off to the different turbine units, and sometimes also 

 at a point close to the wheel casing in addition. 



The gates should be of sufficient size to pass the required max- 



FIG. 70. Sectional Elevation of Power House, Turners Falls Power and 

 Electric Company, Showing Headgate Arrangement. 



imum flow of water, and also of sufficient strength to withstand 

 the shocks and excessive pressures resulting from a quick closing 

 in case of emergency. This is a point which must be considered 

 in determining the minimum time in which the gates may be 

 closed. As mentioned under the chapter on Waterhammer and 

 Surge Tanks, the longer time allowed for closing the gates the 

 less will the excessive pressure caused by waterhammer be. 



