WATER SUPPLY 



369 



the flow of water very materially. Freezing will not affect 

 a cistern of this type, and no protection is needed other 

 than what is necessary to protect it from dirt and the 

 approach of animals. 



Hydropneumatic system. The hydropneumatic system 

 (Fig. 287) is intended to overcome the objection to the 



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Fig. 287. The hydropneumatic system. The air cylinder is a little larger 

 than the water cylinder. If no air is wanted, it may be cut off by the 



extension rod at the curb. 



gravity tank. The installation consists of a tank equipped 

 with pressure gauge, safety valve, water column, and an air 

 pump — all placed in the cellar or in a room away from 

 frost. When water is pumped into the tank, the air is 

 compressed. When the tank is one-quarter full, the pres- 

 sure is 5 pounds. This will force the water up about 11 

 feet — not quite to the second story. When the tank is 



