within each area are served by smaller pipes connected to the larger ones. If possible, the network is planned so the whole pipe system consists of loops, and no pipes come to a dead end. In this way, water can flow to any point  in  the  system  from  two  or  more  directions.  This eliminates  the  need  to  cut  off  the  water  supply  for maintenance work or to repair breaks. Older water systems frequently were expanded without planning and developed into a treelike system. This consists of a single main that decreases in size as it leaves the source and progresses through the area originally  served.  Smaller  pipelines  branch  off  the  main and divide again, much like the trunk and branches of a tree. A treelike system is not desirable because the size of  the  old  main  limits  the  expansion  of  the  system needed to meet increasing demands. Also, there are many dead ends in the system where water remains for long periods, causing undesirable tastes and odors in nearby service lines. MIL-HDBK-1005/7 provides specific guidance to follow when planning the location of mains. In general, mains  should  be  located  so  they  are  clear  of  other structures and should be adjacent and parallel to streets but not within roadways, if possible. Mains also should be separated from other utilities to ensure the safety of potable water and to lessen interference with other utilities  during  maintenance. VALVE LOCATIONS 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. HYDRANT  LOCATIONS 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. GENERAL  REQUIREMENTS  FOR WATER DISTRIBUTION DRAWINGS The following text provides general information on the contents of water distribution plans and details. Plans The MINIMUM information that you should show on a water distribution plan is listed as follows: 1. 2. 3. 4. Locations and lengths of mains Sizes  and  types  of  piping  materials Locations, sizes, and types of all valves Location of fire hydrants; meter pits; outlets on piers; elevated, ground, or underground water storage reservoirs; water wells; pump houses; and valve boxes, vaults, and manholes 5. Capacities and heads of all water pumps in pump houses, including minimum average and maximum residual pressures at points of connection to municipal water  systems 6.  Exterior  sprinklers  or  fire  mains,  including indicator  and  main  shutoff  valves 2-18