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56 CHAPTER 4 PHYSICAL FUNDAMENTALS
TABLE 43 Equivalent Roughness Values
for Various Materials
Material "equiv
Commercial or follower steel 0.046
Asphalted cast iron 0.120
Galvanized steel 0.150
Cast iron 0.26
Wooden surface 0.18-9
Concrete 0.3-3
4.1.5.4 Single Resistances in a Tube Flow
In addition to the friction factor, individual resistances in ducts have to be
taken into account. These resistances are created by the velocity, through
bends, branches, valves, and other obstructions in the duct.
The single resistance factor £ is defined as
The £ values for different types of resistances are available in hydraulics text-
books and also from the literature of pipe and valve manufacturers.
The pressure loss and the corresponding resistance height in Eq. (4.53) and Eq.
(4.54), respectively, are the sum of the friction losses and individual resistances:
FIGURE 4.4 Moody chart, k = 0.03 mm.
