WATER CONDUCTORS 117 



where 



r = hydraulic radius = - for circular pipes, d being the diameter 



v = velocity in feet per second ; 



rdraulic 



in feet; 

 s = hydraulic slope = y, where h f represents the loss in head 



due to friction and I the length of pipe, both in feet; 

 c = friction coefficient. 



In using the latter (Williams and Hazen) formula, the following 

 values of the friction coefficient are recommended: 



For cast-iron pipe .................... c= 120-1 10 



For riveted steel pipe ................. c = 105-100 



For wood-stave pipe ................. c = 130-120 



To facilitate the calculations when using their formula, 

 Williams and Hazen have published a book entitled " Hydraulic- 

 Tables," which contains a series of tables giving the values of 

 friction losses for pipes of different materials and sizes, and also 

 different degrees of roughness and for various velocities. This 

 book is very useful, and may be obtained from John Wiley & 

 Sons, Inc. 



Merriam in his " Treatise on Hydraulics " states the following 

 in regard to the friction loss: 



1. The loss of head in friction is directly proportional to the 

 length of the pipe. 



2. It is inversely proportional to the diameter of the pipe. 



3. It increases nearly as the square of the velocity. 



4. It is independent of the pressure of the water. 



5. It increases with the roughness of the interior surface. 

 Thus 



The friction factor, /, depends upon the degree of roughness 

 of the surface, the values given in Table XXXI being applicable 

 to clean cast-iron or wrought-iron pipes. 



