80 



BULLETIN" 414, U. S. DEPAETMENT 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 frictional 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.^ 



Gallons 



per 

 minute. 



f-inch. 



1 inch. 



IJ inches. 



1 J 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 Howland'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 wiU 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 IJ-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 IJ-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 wiH 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 2x0.3x7.6 = 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. 



