MECHANICS 



75 



in which the letters have the same meaning as in the preceding 

 formula. This formula may be used when the length of the 

 pipe exceeds 10,000 times its diameter. 



The actual head necessary to produce a certain velocity 

 V m may be calculated by the formula 



(3) 



If the head, the length of the pipe, and the diameter of the 

 pipe are given, to find the discharge, use the formula 



Q = . 09445 <# 



hd 



(*) 



'/H-.125<* 



in which Q = discharge in U. S. gallons per second. 



To find the value of /, calculate V m by formula 2, assuming 

 that /= .025, and get the final value of /from the following table: 



EXAMPLE. The length of a pipe is 6,270 ft., its diameter is 

 8 in. and the total head at the point of discharge is 215 ft. 

 How many gallons are discharged per minute? 



7.67 ft. per sec., 

 = 8 (see table), 



1.025X6.270 



nearly. Using the value of /= .0205 for V-, 



. 09455X82 



215X8 



- 22.03 gal. per sec. 



.0205X6,270 + (.125X8) 

 = 22.03X60 = 1,321.8 gal. per min. 



If it is desired to find the head necessary to give a discharge 

 of a certain number of gallons per second through a pipe 



