FLASHBOARDS 



97 



El. 1120 



engages a rack to prevent slipping. The principle of operation is 

 simply a balancing of the moments of force. The pressure on the 

 flashboards is transmitted to the drums through the cables which 

 act to roll the counterweight up the track, while its dead weight 

 tends to roll it down; the two forces balancing each other when 

 the water level is at the fixed elevation. Hand-operated winches 

 are also provided, and their general construction is clearly shown in 

 the illustration. 



The above dam consists of 10 spillway openings, 6 of which are 

 provided with these automatic spillway gates. The other 4 

 openings, which are located towards the intake side, are pro- 

 vided with flashboards of the ordinary stationary construction, 

 and are so designed that if the water in the pond rises 1 foot 

 above the normal level, the boards will give away. 



Trainter Gates. This type of gate is generally built of steel 

 throughout, its general construction being clearly shown in Fig. 48. 

 In order to make it water- 

 tight the bottom of the 

 gate may be fitted with a 

 sill block of oak, which 

 takes a bearing on a steel 

 plate set in the top of the 

 concrete sill. Along the 

 ends may also be fitted 

 rubber strips for making a 

 tight joint with the side 

 walls. 



The gates are usually 

 raised and lowered by 

 chains attached to the 

 bottom edge of the gate 

 and wound upon drums on a shaft above. They may be either 

 hand- or motor-operated. 



Rolling Gates. The principle of these gates is implied in the 

 name, that is, the weir body is moved away from its closed posi- 

 tion by rolling on an inclined track. In the simplest form it con- 

 sists of a large hollow cylinder of a diameter corresponding to the 

 height to which it is desired to raise the water, and of a length 

 equal to the width of the opening to be closed. This cylinder is 

 built up of boiler plate, substantially braced to withstand the 



Gate Support 

 3 thick ^ 



FIG. 48. Tainter Gate. 



