82 
BULLETIN 414, U. S. DEPARTMENT OF AGRICULTURE. 
sure required to operate the pump. It is placed in the air pipe line 
between the air tank and the pneumatic pump, and can be adjusted 
to the proper pressure with an ordinary wrench. The working pres- 
sure required to operate the pump and raise water to the required 
height is recorded on the pump gauge placed on the air pipe line 
between the reducer and the pump. The pressure necessary may be 
determined by the use of Tables 9 and 10, as described under the 
hydropneumatic system. 
The size of tank that should be installed is governed both by the 
quantity of water to be delivered with one charging and by the pres- 
sure necessary to overcome the friction in pipes and fittings and to 
deliver the water at the required elevation. The following table 
shows the number of gallons of water that can be drawn from faucets 
with the pump under working pressures varying from 25 to 55 pounds, 
and with total starting pressures in a 1,000-gallon air tank varying 
from 60 to 100 pounds. 
Table 12. — Pumping capacity of a 1,000-gallon air tank, in gallons of water, under 
varying internal pressures. 
Pressure 
Initial pressure in pounds in 1,000-gallon air tank. 
main- 
tained in 
pump by 
pressure 
60 
70 
80 
90 
100 
reducer. 
Pounds. 
Gallons. 
Gallons. 
Gallons. 
Gallons. 
Gallons. 
55 
40 
155 
270 
415 
550 
50 
140 
270 
400 
550 
700 
45 
240 
385 
530 
685 
850 
40 
340 
500 
660 
820 
1,000 
35 
470 
650 
830 
1,010 
1,200 
30 
600 
800 
1,000 
1,200 
1,400 
25 
737 
918 
1,239 
1,350 
1,618 
For air tanks of other than 1,000-gallon capacity the amount of 
water which can be delivered with one charging can be obtained 
approximately by dividing the figures in the table by 1,000 and multi- 
plying the result by the capacity of the tank in gallons. 
For the purpose of the assumed camp of 40 convicts, an air-tank 48 
inches in diameter and 14 feet long (the same size as the hydropneu- 
matic tank selected) will supply all the water necessary for a day's 
consumption with one charging. Its volume, by Table 11, is found 
to be 1,300 gallons and if it is charged to an initial pressure of 100 
pounds per square inch, and the pressure reducer set at 25 pounds per 
square inch, Table 12 indicates that the volume of water which can be 
delivered at one charging will be ttw^X 1300 = 2,103 gallons. 
When the same tank was used as a hydropneumatic tank, it was 
found that it would be necessary to charge it twice a day, which indi- 
cates an advantage in point of convenience in favor of the pneumatic 
