14 



BULLETIN 57, U. S. DEPARTMENT OF AGEICULTUEE. 



THE GRAVITY SYSTEM. 



In the gravity system water is forced into an elevated tank placed 

 higher than the highest discharge cock. A storage tank may be placed 

 in the attic, on the roof, or on a tower outside. The agricultural ex- 

 periment station at Ames, Iowa, has designed a silo with the storage 

 tank placed on top. Figure 12 shows a gravity system with the stor- 

 age tank in the attic and 

 figure 13 (p. 16) shows the 

 storage tank placed on the 

 windmiU tower. 



Since there is consider- 

 able frictional resistance to 

 the flow of water through 

 the distribution pipes, the 

 tank should be placed at 

 least 10 feet higher than 

 the highest discharge cock 

 to insure a flow under 

 pressure. 



Water weighs 62o5 

 pounds per cubic foot, or 

 aboilt 8.4 pounds per gal- 

 lon, so that in placing a 

 tank in the attic or on the 

 roof the supports should be 

 made sufficiently strong to 

 uphold this weight. 



Either wooden or gal- 

 vanized metal tanks may 

 be used. Wooden tanks 

 may be obtained of almost 

 rjiy size, either circular or 

 rectangular in shape. 

 They are generally built of 

 cedar or cjrpress, and are 

 slightly conical. They are 



Fig. 12.— Gravity supply system with storage tank in attic. USUally k n O C k C d d O Wn 



when shipped, and should be set up and filled with water as soon as 

 received. The foundation should be good and solid and the weight of 

 the tank should rest on the tank bottom and not on that part of the 

 stave which projects below. The capacities of chcular tanks may be 

 found by the following: Capacity in gallons equals diameter in feet, 

 squared, multiplied by 0.7854, multiplied by the depth in feet, 

 multiplied by 7.48. One cubic foot equals 7.48 gallons. Wlien 

 located in buildings wooden tanks are commonly made rectangular. 



