MIL-HDBK-1005/7A
c)
Provide positive separations (air gaps) between
potable water lines and any units containing contaminated water,
such as hospital sterilizers, washing machines, and tanks of
dangerous liquids.
d)
Provide backflow-preventing devices at all
interconnections with nonpotable water lines that cannot be
eliminated or protected by an air gap.
e)
Provide backflow-preventing devices on irrigation
systems, refer to par. 7.7.
7.5.2
Backflow Preventers. Where it would be extremely
difficult to provide an air gap between two systems, and where
back pressures are possible, a reduced pressure principle
backflow preventer can be used. In lieu of air gaps, only
reduced pressure principal backflow preventers are acceptable.
Follow recommendations of the Manual of Cross-Connection Control
of the Foundation for Cross -Connection Control and Hydraulic
Research, University of Southern California, the criteria of
NAVFACINST 11330.11D, Backflow Preventers, Reduced Pressure
Principle Type AFI 32-1066 and, AWWA Manual M14, Recommended
Practice for Backflow Prevention and Cross-Connection Control.
7.5.3
Air Gaps. Use an air gap (between a supply pipe and
receiving vessel) whenever possible on any potable water line
discharging to any place where contamination could occur. An
air gap removes the physical link to a potential contamination
source, and is preferred over backflow prevention devices, which
are subject to failure. When installed, the air gap should be
at least twice the diameter of the supply pipe, but in no case
less than 6 in.
7.6
Service Connections
7.6.1
Piping. See Table 17 and AWWA Standard C800,
Underground Service Line Valves and Fittings, for piping
materials allowed and the advantages and disadvantages of these
materials.
7.6.1.1
Selection Factors .
Consider the following factors in
selecting service piping:
a)
Durability.
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