80 
BULLETIN 414, U. S. DEPARTMENT OF AGRICULTURE. 
In practice, the pressures given in the table will not force the water 
to the heights indicated because of the pipe friction. The amount 
of this friction depends upon the size and length of pipe, and the 
velocity at which the water is forced through it. The values given 
in the following table represent the friction al loss in feet of lift per 
100 feet of pipe in pipes from three-fourths of an inch to 2 inches in 
diameter, discharging from 5 to 40 gallons per minute: 
Table 10. — -Frictional loss in feet for 100 feet of clean iron pipes. 1 
Gallons 
per 
minute. 
f-inch. 
1 inch. 
11 inches. 
1 \ inches. 
2 inches. 
5 
10 
15 
20 
25 
30 
35 
40 
7.6 
29.9 
66.0 
115.9 
181.4 
1.9 
7.3 
16.1 
28.3 
43.7 
63.3 
85.1 
110.4 
0.7 
2.4 
5.5 
9.4 
14.7 
21.0 
28.5 
37.0 
0.3 
1.1 
2.2 
3.8 
6.0 
8.6 
11.6 
15.0 
0.1 
.3 
.6 
1.0 
1.5 
2.1 
2.8 
3.7 
1 From Ellis and Holland's experiments. 
The use of the foregoing tables is best explained by means of an 
example, as follows: 
Example: It is desired to find the air pressure which will be neces- 
sary in a hydropneumatic tank to force water to two faucets, each 
20 feet higher than the tank, at the rate of 5 gallons per minute to 
each faucet, the water for both being conducted for 150 feet through 
a 1^-inch main and then through two branch pipes each 30 feet long. 
Solution: (1) The theoretical height to which the water is to be 
forced is 20 feet. (2) From Table 10 the frictional loss in forcing 
the water through 100 feet of l§-inch pipe at the rate of 10 gallons 
per minute is equivalent to an additional height of 1.1 feet, and for 
150 feet it will be 1.5 X 1.1 = 1.65 feet. (3) Also from the same table 
the frictional losses in forcing the water further through the two f-inch 
pipes for distances of 30 feet at the rate of 5 gallons per minute in 
each are equivalent to 2x0.3 X 7.6 = 4.56 feet. Adding (1), (2), and 
(3), the total equivalent height will be 20.00 + 1.65 + 4.56 = 26.21 
feet. The pressure necessary to force water to this height is found 
from Table 9 to be 11.5 pounds per square inch. 
