(2000 ft long)(8 ft/1000 ft) = 16 ft (4.9 m) of water. This is also the friction-head loss in
pipe b.
Since pipe b is 3000 ft (914.4 m) long, the friction-head loss per 1000 ft (304.8 m) is
total head loss, ft/length of pipe, thousands of ft = 16/3 = 5.33 ft/1000 ft (1.6 m/304.8 m).
Enter Fig. 10 at this friction-head loss and C= 100. Project in the same manner as de-
scribed for pipe a, and find the required size of pipe b as 33 in (838.2 mm).
If the district being supplied by either pipe required a specific flow rate, this flow
would be used instead of assuming a flow rate. Then the pipe would be sized in the same
manner as described above.
- Compute the single-pipe equivalent length
When we deal with several different sizes of pipe having the same flow rate, it is often
convenient to convert each pipe to an equivalent length of a common-size pipe. Many de-
sign engineers use 8-in (203-mm) pipe as the common size. Table 4 shows the equivalent
length of 8-in (203-mm) pipe for various other sizes of pipe with C = 90, 100, and 110 in
the Hazen-Williams equation.
From Table 4, for 12-in (305-mm) pipe, the equivalent length of 8-in (203-mm) pipe is
0.14 ft/ft when C= 100. Thus, total equivalent length of 8-in (203-mm) pipe = (1000 ft of
12-in pipe)(0.14 ft/ft) = 140 ft (42.7 m) of 8-in (203-mm) pipe. For the 14-in (356-mm)
pipe, total equivalent length = (600)(0.066) = 39.6 ft (12.1 m), using similar data from
Table 4. For the 16-in (406-mm) pipe, total equivalent length = (1400)(0.034) = 47.6 ft
(14.5 m). Hence, total equivalent length of 8-in (203-mm) pipe = 140 + 39.6 + 47.6 =
227.2 ft (69.3 m).
- Determine the friction-head loss in the pipe
Enter Fig. 10 at the flow rate of 2000 gal/min (126.2 L/s), and project through 8-in
(203-mm) diameter to the pivot axis. From this intersection, project through C = 100
to read the friction-head loss as 100 ft/ 1000 ft (30.5 m/304.8 m), due to the friction
of the water in the pipe. Since the equivalent length of the pipe is 227.2 ft (69.3 m),
the friction-head loss in the compound pipe is (227.2/ 100O)(IlO) = 25 ft (7.6 m) of wa-
ter.
TABLE 4. Equivalent Length of 8-in (203-mm) Pipe for C= 100
Pipe
diameter
in mm C=90 C=IOO C=IlO
2 5 1 101 2 85 1 71 2
4 10 2 3 4 2 9 24. 3
6 15 2 4. 8 4.0 6 3. 4
8 20 3 1.1 9 1.0 0 0.8 4
10 25 4 0.4 0 0.3 4 0.28 5
12 30 5 0.1 7 0.1 4 0.11 7
14 35 6 0.07 8 0.06 6 0.05 5
16 40 6 0.04 0 0.03 4 0.02 9
18 45 7 0.02 3 0.01 9 0.01 6
20 50 8 0.013 7 0.011 5 0.009 6
24 61 0 0.005 6 0.004 7 0.003 9
30 76 2 0.001 9 0.001 6 0.001 3
36 91 4 0.0007 8 0.0006 6 0.0005 5
