GATES AND VALVES 



149 



wedge, bringing pressure to bear on the backs of both discs, from 

 central bearings, thus forcing them apart and squarely against 

 their seats. 



In opening the valve, the first turn of the stem releases the 

 upper wedge from contact with the lower wedge, thereby instantly 

 releasing both discs from their seats before they commence to rise. 



All gate valves and sluice gates should be fully bronze-mounted 

 to prevent corrosion. That is, the disc and seat rings should be 

 made of bronze, as well as the threaded portion of the stem, the 

 operating nut and the wedging appliances. 



Where the water pressure is very great, by-pass valves may 

 be provided for equalizing the pressure on both sides of the valve 

 before it is opened. 



Operation and Control. Sluice gates and gate valves may be 

 operated either by hand, water or electrically, the two latter 



FIG. 75. Gatehouse, Showing Gate-Lowering Mechanism. 

 River Power Company. 



Mississippi 



methods being used extensively, resulting in a saving of labor, 

 while on the other hand acting as a protection in the case of 



