To permit flushing dead ends, install a blowoff at the end of
each end main. Paint the blowoff hydrants a different color from fire hydrants and
prominently mark them as blowoff hydrants. Dead ends may need flushing more often
than other sections of the system.
For additional information on hydrant flushing, see par. 18.104.22.168.
Cleaning. Corrosion, scale, and deposited matter cannot normally be
removed with simple flushing. When increased system head loss reduces system
capacity below fire flow requirements, mechanical cleaning is necessary. Clean water
mains in place using cable-attached devices or fluid-propelled devices (pigs). As a
rule, this work is done on a contract basis by firms specializing in main cleaning. After
cleaning, the mains may be relined to restore original smoothness of the interior. If this
is properly done, 95 percent or more of the original capacity can be restored. If the
mains are not lined with a corrosion-resistant material after cleaning, start chemical
treatment to prevent accelerated corrosion and red water. Additional information on
cleaning water mains can be found in the publications listed in pars. 2.1.4, 2.2.41, and
Valve Maintenance. See par. 8.3.2.
Operational Changes. Some of the conditions causing loss in carrying
capacity may be remedied by making changes in operating procedures:
If the water supply is corrosive, or lacks buffering capacity as it
enters the distribution system, it will aggravate tuberculation. To offset this condition,
institute a change in treatment to stabilize the water and increase its pH. See
par. 5.4.7 for more information about controlling corrosion.
If carrying-capacity loss is caused by slime growth, special
chlorination procedures may be adopted to remedy the condition.
Where accumulation of sediment is the cause of carrying-capacity
loss, periodic flushing of the entire system, through hydrants and blowoffs, is normally
Pipe Replacement. Eventually, most water mains will have to be
replaced. Consider lining existing water mains as an alternative where high-cost
digging is required, such as under pavements and in industrial areas. Lining a pipe
can eliminate the need for frequent or continuous flushing. Linings can be installed to
reduce or eliminate leaks through corroded areas of the pipe or through bad joints. A
smooth lining in a corroding pipe maximizes hydraulic carrying capacity and minimizes