MIL-HDBK-1164
d)
Make advance arrangements with a municipal utility, a public works
department, or an outside contractor for the use of large construction equipment (for
example, power shovels, cranes, etc.) that may be needed but are not normally stocked
by the installation.
Leak repair techniques depend on the type of leak. Understanding
the methods of installation and the most advantageous use of each technique will help
you make the proper selection for any particular repair. Table 22 covers various leak
repair procedures.
7.3.2.2
Flushing. Matter deposited in the distribution system over time can often
be removed by periodically flushing the system. The frequency varies for different
waters and pipe materials, but annual flushing is usually enough. Dead-end pipes
should be flushed and disinfected at least once a year. Flushing and disinfection are
required whenever mains are opened for repair.
Flushing water mains near a nuisance, particularly at dead ends, may
remove or reduce problems with taste, odor, color, or turbidity. Flushing may
permanently resolve problems caused by foreign material left in new or repaired mains.
If complaints about quality are received, investigate the possibility that stagnant water
in dead-end lines may be the cause and take remedial action. Find and eliminate
conditions that make repeated flushing necessary: a dead end or a low point in the
main may allow sediment to accumulate, or growth of slime organisms may be caused
by insufficient chlorination. Flushing is also helpful in clearing the non-potable part of
the water system.
a)
Flushing Procedure. Start flushing at the supply source and
continue to the ends of the distribution system. Do not start flushing at the ends of the
system because accumulated debris must then be drawn through the entire length of
the system. For maximum scouring velocity, flush each section of pipe independently
by closing off intersecting pipelines. This process directs the full flow through the
section to be flushed. A velocity of 2.5 feet per second (0.76 meters per second [mps])
is recommended for flushing. With a main pressure of 40 psi (280 kiloPascals [kPa]), a
2.5-inch (65-mm) hydrant outlet will discharge approximately 1,000 gpm (60 Lps); a
4.5-inch (115-mm) hydrant outlet will discharge approximately 2,500 gpm (160 Lps).
Table 23 gives the number of hydrant outlets required to flush various size water
mains.
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