MIL-HDBK-1191
back-siphonage shall be included in the design. Cross connection of a
municipal and installation-dedicated (well-based, base pumping station,
etc.) system shall require approval from the local Administrative
Authorities.
Generally, backflow isolation will be required on the main
supply mains serving an MTF; Designers shall coordinate backflow
prevention requirements, including requirements for maintenance
accessibility and periodic testing, with the local municipality or Base
Engineer, as appropriate.
Devices and Methods. All potable water discharge points,
9.2.3.1
such as a faucet discharging into a reservoir sink or tub, shall be
provided with an adequate air gap, in accordance with referenced
criteria. Fixtures or equipment where the discharge point is positioned
below the reservoir rim shall be fitted with a vacuum breaker. Examples
of concern include the following:
- Bedpan washers, or similar fixtures including a flushometer
valve.
- Flexible-hoses or shower heads, of length sufficient to
reach below fixture rim, typically found in procedure rooms,
hydrotherapy bath equipment, laboratories, and food service
areas (e.g. washers, steam tables).
- Laboratory or other serrated-nozzle fixtures designed to
accept flexible tubing.
- Water delivery outlets serving therapeutic, surgical, or
autopsy/mortuary procedures.
- Hose bibs.
For the protection of makeup supplies to low hazard equipment (such as
autoclaves and fire protection sprinkler systems), double-check backflow
preventers may suffice.
For the protection of sources supplying high
hazard equipment and processes, reduced-pressure backflow preventers
are required. Designers shall include provisions for drainage of the
discharge from these devices; refer to Tables 9-1 and 9-2.
TABLE
9-1
POTENTIAL BACKFLOW PREVENTER DISCHARGE RATES
Assembly Pipe
Discharge L/s (GPM)
Discharge L/s (GPM)
at 420 kPa (60 PSI)
at 1050 kPa (150 PSI)
Size mm (inch)
19- 32
(3/4-1 1/4)
4.7
( 75)
8.8
(140)
38- 50
(1 -2)
10.7
(170)
17.6
(280)
63- 75
(2 -3)
15.8
(250)
25.2
(400)
100-150
(4-6)
31.6
(500)
53.6
(850)
200-250
(8-10)
33.1
(525)
56.2
(890)
TABLE 9-2
FLOOR DRAIN FLOW RATES
9-4
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