Environmental Engineering FOURTH EDITION

128 ENVIRONMENTAL ENGINEEFUNG

D=6"

L= 1400'

Pipe 110.3 Pipe no.4

ce( Dig'; ( ,D=6'' E

L=4W L=600'

Actual pipes

Figure 6-12. (a) Equivalent pipes, parallel. (b) Equivalent pipes, series.

3. Using Fig. 6-11, find head loss for pipes 3 and 4.
   Pipe 3: D = 8 in., L = 400 ft, Q = 500 gpm, h' = s1 x L1= 0.008 x 400 =
   3.2 ft
   Pipe 4: D = 6 in., L = 600 ft, Q = 500 gpm, h1 = s1 x L1= 0.028 x 600 =
   16.8 ft
   Total head loss in both pipes = 20 ft.


4. Using Fig. 6-11 with head loss = 20 ft, s = 20/1000, and Q = 500 gpm,
   equivalent pipe size is found to be 6.5 in. in diameter.

More complex systems may be reduced to a single equivalent pipe by piecework
conversion of real and equivalent pipes. Although the calculations become tedious,
solutions of network flow problems are dependent on the same basic physical principles
as those for single pipes; that is, the principles of energy conservation and continuity
must be satisfied throughout the network.

Pumps and Pumping1

Pumps are mechanical devices for converting other forms of energy to hydraulic energy.
When interposed in a pipe, they add energy to the liquid passing through the pipes.
The added energy is almost always pressure energy. Pumps, like motor vehicles, are
not individually designed for public works projects, except for very large and unusual

'This discussion on pumps and pumping is adapted from E E. McJunkin and P. A. Vesilid, Practical

Hydraulics for Public Works Engineers, published as a separate issue by Public Works Magazine (1968).