Saturday, May 7, 2011

Location of valves and fire hydrant

The purpose of installing shutoff valves in water mains at various locations within the distribution system is to allow sections of the system to be taken out of service for repairs or maintenance without significantly curtailing service over large areas. Valves should be installed at intervals not greater than 5,000 feet in long supply lines and 1,500 foot in main distribution loops or feeders. All branch mains connecting to feeder mains or feeder loops should have valves installed as close to the feeders as practical. In this way, branch mains can be taken out of service without interrupting the supply to other locations. In the areas of greatest water demand or when the dependability of the distribution system is particularly important, valve spacing of 500 feet maybe appropriate. At intersections of distribution mains, the number of valves required is normally one less than the number of radiating mains. The valve omitted from the line is usually the one that principally supplies flow to the intersection As for as practical, shutoff valves should be installed in standardized locations (that is, the northeast comer of intersections or a certain distance from the center line of streets), so they can be easily found in emergencies. All buried small- and medium-sized valves should be installed in valve boxes. For large shutoff valves (about 30 inches in diameter and larger), it may be necessary to surround the valve operator or entire valve within a vault or manhole to allow repair or replacement.

Criteria for fire hydrants are found in Fire Protection for Facilities Engineering, Design, and Construction, MIL-HDBK-1008A. Street intersections are the preferred locations for fire hydrants because fire hoses can be laid along any of the radiating streets. Hydrants should be located a minimum of 6 feet and a maximum of 7 feet from the edge of paved roadway surfaces. If they are located more than 7 feet from the edge of a road, then ground stabilizing or paving next to the hydrants may be necessary to accommodate fire-fighting equipment. Hydrants should not be placed closer than 3 feet to any obstruction and never in front of entranceways. In general, hydrants should be at least 50 feet from a building and never closer than 25 feet to a building, except where building walls are blank fire walls

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