158 DOMESTIC WATER SUPPLIES FOR THE FARM 



its original volume. These pressures are equivalent to approxi- 

 mately 15, 30 and 45 pounds, respectively, and will lift the water, 

 when the outlet valves are open, to 34, 69 and 103 feet. In other 

 words, each pound of pressure, as shown on the gage, will raise 

 the water about 2.3 feet. From these figures and the known ele- 

 vation of the highest tap in use, it is easy to compute the pressure 

 that will be required to distribute the water. 



It is always necessary to carry a certain amount of excess 

 pressure so that the system will continue to deliver supplies until 

 the tank is fully emptied. Ten pounds of such excess pressure is 

 usually sufficient in the case of an ordinary farmhouse. Con- 

 siderable volumes of air are absorbed by water, especially under 

 pressure, and the supply in the pneumatic tank is soon depleted. 

 New air then has to be pumped into the tank, preferably when it 

 is nearly empty. 



In a recent form of the pneumatic system the air is forced into 

 the tank by a hand or power compressor and thence by a pipe to 

 a submerged pump at the well. As soon as any water is drawn 

 from the system at the house or elsewhere the pump is automati- 

 cally started by the compressed air and the water forced to the 

 house and tap, thus giving a constant supply of water fresh from 

 the well. 



The size of the pressure tanks may be computed from the data 

 in the preceding section, it being borne in mind, however, that the 

 tank is rarely filled to more than two-thirds its full capacity. In 

 locating the tank, the chief essential is to select a spot where it 

 will be protected from the frost. It may be placed in the cellar 

 of the house, in the stable, or beneath the ground. The cellar, 

 if the house is provided with one, will probably be the most con- 

 venient location, since the tank will always be open to quick and 

 convenient inspection. 



The pneumatic system has many advantages over other 

 systems, and, although it has been in practical use less than 

 twenty years, it is already found in hundreds if not thousands of 

 localities. It provides a system simple in operation and one in 



