370 



ENGINEERING ON THE FARM 



half full, the pressure is about 15 pounds, and when three- 

 quarters full, about 45 pounds. Ten pounds' pressure is 

 as little as is of any value, for when water is used the pres- 

 sure drops very rapidly. It is then necessary to use the 

 air pump and force in more air, in order to utilize all the 

 water in the tank. When the air stands under pressure, it 

 is absorbed by the water and is drawn off when a faucet 

 is opened. This air must be supplied by the air pump. 

 The most convenient scheme is to use a combination of 

 water and air cylinders and make the windmill or engine 

 do both pumping and compressing. Some trouble is encoun- 

 tered in cold weather with the operation of the valves in 

 the hydropneumatic cylinder. It is therefore advisable to 

 protect this cylinder by placing it a little lower in the well, 

 or by a reasonably tight house over the well. A storage 



Sery/ce fofe^ 

 Pressure r7e</ucer 



Cfec/r 1/ff/ye^ 



Re/eoJe 



We// 'Cas/vf 



W<7#r 



After University of Minnesota 



Fig. 288. The pneumatic system. This is aranged with a switch operated 

 by air pressure to stop the engine when maximum pressure is reached. 



tank should be of from 750 to 1,000 gallons' capacity. This 

 will prove very little protection against fire unless the pump 

 is kept running. 



