This situation is that my proposed subdivision will be served by an 8" city water main that will not meet fire protection (20psi). The county has a 16" main across the street. We are going to tap onto the 16" main with a valve that will "open" only when the pressure on the city side goes below a certain set amount (20psi). This will work in a fire situation. The flow will be metered by the county and charged to the city, who will then spread it out to the homeowners in the subdivision. Use a 'pressure reducing-pressure sustaining' valve Assume normal pressure is 60 on both sides set the pressure reducing control to 40 sensing the city side, when the city side drops below 40 the valve will open and maintain 40, if demand increase beyond what the 40 will provide, the pressure on both sides will drop, to prevent the city from over tapping the county, set the pressure sustaining side sensing the county to 30, this will ensure that no matter how bad the demand on the city side gets, the county will still provide service to its customers. This type of valve will operate completely on the pressure in the system, no power, no solenoids, no batteries. Use a brand of ball valve that is common in your area, where you can get parts and reliable service. These valve require maintenance at least every 5 years. They should be operated at least once a year. Install it in a place where the valve can be gotten to. Have operations learn how to adjust it so when the firefighter says he wants more water it can be tweaked in the field.

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