Page 58 - HVAC Pump Handbook

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Piping System Friction
Piping System Friction 55

TABLE 3.6 Values of C for the Williams-Hazen Formula

Values of C
Type of pipe Range Average value Design value
Cement asbestos 160–140 150 150
Fiber — 150 150
Bitumastic- or enamel- 160–130 148 140
lined iron or steel,
centrifugally applied
Cement-lined iron or — 150 140
steel, centrifugally
applied
Copper, brass, or glass 150–120 140 150
piping or tubing
Welded or seamless steel 150–120 140 140
Wrought iron 150–80 130 100
Cast iron 150–80 130 100
SOURCE: Cameron Hydraulic Data, 15th ed., Ingersoll Rand Company, Woodcliff, N.J.,
1977; used with permission.

For values of C,

1. Range: High is for smooth and well-installed pipe; low is for poor
or corroded pipe.
2. The average value is for good clean and new pipe.
3. The design value is the common value used for design purposes.
Note. The American Iron and Steel Institute recommends a C fac-
tor of 140 for steel pipe for hot and chilled water systems.
There is some confusion in the industry about the use of the Williams-
Hazen formula. It is very adequate for cold water such as chilled water. A
number of organizations publish Williams-Hazen data for various pipe
sizes; organizations such as the American Iron and Steel Institute provide
manuals on piping that include Williams-Hazen friction data on the water
flow in the commercial sizes of steel pipe. It is very adequate for cold
water such as chilled water. Since it cannot easily accommodate viscosity
or specific gravity corrections, it should not be used for hot water systems.

3.3.5 Review of pipe friction and velocities
The preceding recommendations are the result of my experience;
every designer should develop parameters based on his or her experi-
ence. It should be pointed out that pipe friction is not an exact science.
A study of the available literature will demonstrate the variations
that can exist with pipe friction when manufacturing tolerances and
specific aging processes are included. This has caused some designers
to use much larger safety factors in their design of piping.

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