Page 257 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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6.8 Management, Operation, and Maintenance of Distribution Systems 217

Roof tank (tank may be at
any other level as well)
Float-controlled valve
Overflow

Frost boxes

Check valve closes when To sprinkler system or
pumps are in operation process-water system
Check valve

From private supply

Surface water

From municipal supply
To building Fire pumps or
distribution system process-water pumps

Figure 6.16 Use of Industrial Water Supply without Cross-Connection (After Minnesota State Board of Health)

6.8 MANAGEMENT, OPERATION, AND MAINTENANCE OF DISTRIBUTION SYSTEMS

For intelligent management of distribution storage, reservoir levels must be known at all
times of the day and night. Where levels cannot be observed directly by gauges or floats,
electrically operated sensors and recorders can transmit the required information to operat-
ing headquarters.
Well-kept records and maps of pipes and appurtenances are essential to the
efficient operation and maintenance of distribution systems. To avoid the occasional
discharge of roiled water, piping should be flushed systematically, usually through
hydrants. Dead-ends need particular attention; a bleeder on a dead-end will counteract
the effects of sluggish water movements. Disinfecting newly laid or newly repaired
pipe is important.
There is little flow through service pipes at night, and they may freeze in very cold
weather. If water mains themselves are placed at a reasonable depth and enough flow is
maintained in the system, they should not freeze. Pipes deprived of adequate cover by the
regrading of streets or subjected to protracted and exceptionally cold weather can be pro-
tected by drawing water from them through services. Pipes exposed on bridges or similar
crossings should be insulated. Large and important lines may be heated where exposure is
severe. In very cold climates, water and sewer pipes are often laid in a heated boxlike con-
duit, known as a utilidor.
Frozen pipes are usually thawed by electricity. A transformer connected to an electric
power circuit, or a gasoline-driven generator of the electric-welding type, supplies the