SHUTTER DAMS. 



2 53 



current caught them and swung them over till they were stopped by their chains in a 

 position nearly vertical. This dammed up the water, and the workmen then raised 

 the main shutters by hand. The space between the two rows was then filled with 

 water by opening curtain-valves, and the counter-shutters were pushed down and 

 latched. The lowering was done with the tripping-bar. 



Examples. Four dams were built in France of this type, the last one, that of St. 

 Antoine, having been completed in 1843. The shutters in this dam were 5.6 feet high 

 and 3.9 feet wide. In the others they were 3.3 feet high and 6.6 feet wide, the length 

 of the weirs being 156 feet and that of the passes 74 feet. 



A dam with a pass closed by Thenard shutters was also built in 1850 at Courbeton 

 on the Seine, but with needles and trestles substituted for the counter-shutters. The 

 weir was closed by needles alone. The pass was 39.7 feet long and the shutters were 

 lowered by a tripping-bar, worked by a turbine. The action of the latter was auto- 

 matic, starting or stopping as the pool level rose or fell. 



SECTION OP A GIRARD SHUTTER DAM. 



Other examples are to be found in India, in the Mahanuddee and Cossye rivers, 

 and in the Sone Canal, where they are used to close flushing-sluices. Some of them 

 are over 21 feet in length and support heads of nearly ro feet. Much trouble was 

 experienced there with the breaking of the chains of the counter-shutters, due to 

 the sudden jerk when the latter came to place. This was successfully overcome 

 by using hydraulic brakes on the up-stream side, consisting of a piston working 

 in a cylinder pierced with small holes, the piston being attached to the shutter, and 

 the cylinder to the floor. As the shutter rises it draws the piston through the 

 cylinder, and the water escapes slowly through the holes, thus checking the rapidity of 

 its movement. 



