THE FLOW OF WATER IN CONCRETE PIPE. 3 



C w — The coefficient of retardation in the Williams-Hazen formula. (Not to be 



confused with C, C m , or C s .) 

 C m — The coefficient of retardation in Moritz's formula. (Not to be confused with 



C, C w , or C s .) 

 Qg — The coefficient of retardation in the new formula. (Not to be confused with C, 



L w , or C m .) 

 f — The coefficient of retardation in the Weisbach formula. (This formula is variously 



known as Weisbach's, Weston's, Darcy's, and Chezy's.) 

 K— The coefficient of d in the general exponential formula for flow of water in pipes 



(formula 14, p. 45). 

 Cement pipe. — Composed of Portland cement and sand or fine gravel, without coarse 



Concrete pipe. — Composed of Portland cement, sand, and coarse gravel or broken stone. 



Will also be used as the broad term applying to both kinds of pipes for the 



reason that, in reality, the so-called "cement" pipe is concrete. 

 Number. — Wherever a pipe number is given, the reference is to the corresponding 



number in Tables 3, 4, and 11, and to the description of the pipe under that 



number. 



TYPES OF PIPE. 



In so far as the bounding material and other elements that influence 

 the carrying capacity are concerned there are three distinct types of 

 pipe, as follows : 



1. Composed of an assembled length of precast units. 



2. Constructed-in-place or monolithic pipe. 



3. Cement-lined metal pipe. 



Types 1 and 2 subdivide into three kinds : 

 a. Interior surface as left by the forms. 

 h. Interior surface washed with cement mortar, neat cement 



grout, or asphalt. 

 c. Interior surface improved by troweling the joints and 

 generally "pointing up" rough places or by rubbing 

 down irregularities with an abrasive. (See p. 83.) 

 Pipes of type 1 are made with either a "dry mix" or a "wet mix." 

 A dry mix, as its name implies, is made with a minimum of water. 

 This permits the immediate removal of the inner and outer molds, 

 the pipe section being cured while resting on a cast-iron base ring. 

 This ring holds the socket end of the section true to shape, but the 

 bevel end is generally distorted to a slight extent during the removal 

 of the forms. The distortion is never sufficient to impair the sectional 

 area if the inner form is true to nominal size, but all distortion is mani- 

 fest in the assembled pipe line by offsets or shoulders which cause 

 loss of head. 



When tamped by hand an interior coating of cement mortar or 

 asphalt is necessary to make pipe of this type impervious to leakage, 

 but when the pipe is made in a machine the power tamper renders 

 the concrete sufficiently dense without a coating to withstand the 

 passage of water under ordinary pressure, 



