IRRIGATION 237 



weight of water and to see that the supports 

 are amply strong. For example, a lo-barrel 

 tank of water will weigh, in addition to the 

 tank itself, more than one and a quarter 

 tons. 



The pressure to be obtained from elevated 

 tanks depends upon their elevation, each ad- 

 ditional foot giving a pressure of about 0.433 

 pounds per square inch. The following table 

 shows the pressure (disregarding friction) 

 to be obtained at various heights. 



Height in feet Pressure per sq. inch 



10 4.33 pounds 



20 8.66 



30 12.99 



40 17.32 



50 21.65 



60 25.98 



70 30.31 



80 34.64 



90 38.97 



The advantage of the pneumatic tank lies 

 in the fact that it may be placed in any out- 

 of-the-way place in the basement, or it may 

 be buried in the ground below the frost line. 

 There is little danger in its use if it is pro- 

 vided with a pressure gauge and safety valve. 



Capacity of Storage Tanks. The capac- 

 ity of storage tanks is not difficult to arrive 

 at by simple mathematics, unless they are 



