Figure 33  General 15 – Fire Hydrant Supply

Systems that provide water for fire fighting are usually designed to include redundancy into the system. Laying out water mains in a grid, with feeder and distributor pipes connecting at roadway intersections and other regular intervals, provides several advantages:

1) Water can still be distributed throughout the system, even if a damaged section has to be isolated. 

2) Water will feed fire hydrants from multiple directions. 

3) During periods of peak flow demand, less impact from "friction loss" will occur, as several mains 

    pipes supply the flow, thus reducing velocity within each individual main.

4) Hydrants will not be supplied by 'dead end' mains therefore discharges will remain more stable, 

    even when multiple hydrants are used simultaneously.

Systems should be designed to provide pressures between 65 and 85 psi, however there may be some variation to these target pressures due to the location and elevation of particular fire hydrants. Pressures from as low as 50 psi and up to as high as 100 psi may be acceptable where elevation factors dictate.

Recommended pipe sizes: 16" mains; 12" feeders; 8" in streets.

This system shows the pressures available when a total of 3800 US gpm is being delivered at various hydrant locations.