THE FLOW OF WATER, IN CONCRETE PIPE. 7 



which may be arranged in the same form as formula 10, becoming 



T71.852 



#=fc^r 7 (8) 



The authors of the formula suggest the following values of G w : 



For masonry conduits of concrete or plaster, with very smooth surfaces, when 

 clean, values of C w =140 may be observed. Generally, such surfaces become slime 

 covered, reducing the values of C w to 130 or less in a moderate length of time; and 

 if the surfaces are only a little less smooth, say in such shape as is represented by 

 ordinarily good work, the value of C w is reduced to 120. 



It is to be remembered that at the time the above recommendation 

 was made there were very few experimental data upon the carrying 

 capacity of cement-plastered and concrete pipes or conduits. How- 

 ever, with all the data now available, the writer does not make any 

 material difference in his recommendation given on page 64. 



(e) The Moritz formula 1 for " concrete pipe built continuously 



with steel forms," 



# = 1.31 D2J H °- 555 (9) 



or 



9.11 P- 8 _ 0.40 7 1 - 8 



^1.26 D 126 



Moritz suggests reducing the above coefficient of 1.31 from 5 to 10 

 per cent for " jointed pipes, depending upon the amount of care used 

 in producing a smooth interior surface." 



(/) For the reasons set forth on pages 45 to 49 the writer offers 

 the following formula, which differentiates between various classes 

 of concrete pipes by means of a coefficient G s . This formula is new 

 to the extent of suggested coefficients only. 



V = C s H°- 5 d°- 625 (11) 



V 2 



H =Ql!jUh ( lla ) 



Q = 0.00546 C s d 2 ™ H . 5 (lib) 



in which the following values are suggested for the coefficient C s : 



Class 1. C s = 0.267. For old California cement pipe lines. It 

 appears to have been the general practice throughout southern 

 California during the early eighties to lay the pipes with a gen- 

 erous supply of mortar and make little or no effort to remove the 

 "mortar squeeze" at the joints; hence these pipes, even though 

 perfectly clean, offer great retardation to the flow of water. This 

 coefficient is also recommended for pipes of class 2 used to convey 

 sewage. The present practice is to wipe all joints carefully and the 

 resulting surface approaches that of class 2. 



1 Working Data for Irrigation Engineers. By E. A. Moritz, New York, 1915, p. 66. Also see Flow of 

 Water in Pipes, E. A. Moritz, Eng. Rec, vol. 68, No. 24, p. 667. 



