Page 234 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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6.1 Distribution Systems 195

Static Static
Night Average
Average Maximum
Maximum

Gravity flow Double gravity flow

Static
A
Static
Average
Maximum Night Average
Static
B
Average Maximum
Maximum

Direct pumping Dual flow
Figure 6.1 One- and Two-Directional Flow in Distribution Systems

doubles the delivery of the grid (Fig. 6.2c). In large systems, feeders are constructed as
pressure tunnels, pressure aqueducts, steel pipes, or reinforced-concrete pipes. In
smaller communities the entire distribution system may consist of ductile-iron pipes.
Ductile iron is, indeed, the most common material for water mains, but plastics, in gen-
eral, in the case of small supplies, are also important.

6.1.3 Pipe Grids

The gridiron system of pipes stretching over all but the outlying sections of a commu-
nity (Fig. 6.2) may consist of single or dual mains. In the Northern Hemisphere, single

Branch
Feeder Gridiron Feeder Gridiron

Feeder

(a) Branching pattern (b) Gridiron pattern with (c) Gridiron pattern with
with dead ends centrial feeder looped feeder
High-value district is cross-hatched

Figure 6.2 Patterns of Water-Distribution Systems