494 



WATER SUPPLY AND SEWAGE DISPOSAL 



short rods or levers which control the valve. When the valve is 

 to be opened, a wrench applied to the projecting portion of the 

 rod at the top of the hydrant is turned counter-clockwise. This 

 revolving of the rod forces the upper burr upward and the lower 

 burr downward. The levers spread as the burrs separate and 

 the valve is drawn back away from its seat, thus permitting 

 the water from the main to rush into the hydrant. 



A B 



FIG. 302. City fire hydrant. 



579. The Fire Hydrant Drip. To prevent the water in the 

 city main from freezing and bursting the pipe, the main must 

 be laid below the frost line. It is evident that the water in 

 the fire hydrant will also freeze and burst the hydrant if per- 

 mitted to remain in it. The draining of the hydrant is accom- 



