][2.14.2
In-Line Balanced Pressure Proportioning System
Size system for required flow rates. AFFF concentrate pump shall be
positive displacement, electric motor driven, drip proof, 240/480 volts, 60
Hz AC. System operation shall be fully automatic, with manual over-ride
and manual shut-down. Provide a pressure regulating device in the AFFF
concentrate pump return line to maintain constant pressure on the
concentrate piping system at all AFFF solution flow rates. Provide an
in-line balanced pressure proportioning device at each system riser to
automatically balance the AFFF concentrate pressure with the water pressure
at the riser to provide correct proportioning over the range of flow rates
calculated for that riser. The pump and all piping, valves, and fittings
in contact with the foam concentrate shall be of materials resistant to the
corrosive effects of the AFFF concentrate. Provide permanent engraved
rigid plastic or corrosion-resistant metal instruction plate for emergency
manual operation, along with a similarly constructed label for each control
device.
]2.14.3
AFFF Concentrate Storage Tanks
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NOTE: Designer must calculate foam tank capacity
based on maximum flow for maximum duration to
determine size of tank and space required. Do not
label foam tank capacity on drawing. Exact tank
size (which may be larger) will be determined by
Contractor's hydraulic calculations.
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NOTE: Consult the Division or District Fire
Protection Engineer to determine need for reserve
tanks.
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Tank shall be designed for storage of AFFF concentrate at atmospheric
pressure, and shall be [horizontal] [or] [vertical] cylindrical, fiberglass
or polyethylene construction. Tank shall have the following: Drain valve
located at the lowest point in the tank, connections for concentrate supply
and return lines to the proportioners, top-mounted fill connections and
inspection hatch, and a pressure/vacuum relief vent. All openings and tank
connections shall be installed at the factory, no holes shall be made in
the tank shell in the field. Tank shall include all necessary supports for
free-standing installation. Provide a gage or unbreakable sight glass to
permit visual determination of level of tank contents, unless liquid level
is clearly visible through shell of tank. Size tank to provide sufficient
AFFF concentrate for the time specified when the system is discharging foam
solution at total maximum system flow. [Also provide connected reserve
tank(s) of equal capacity.] Permanently label each tank with its capacity,
type and percentage of concentrate, which system it serves [, and whether
it is a main or reserve tank].
2.15
LINE PROPORTIONING (VENTURI TYPE) SYSTEM
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NOTE: Select the method of proportioning best
suited for the project.
Diaphragm pressure proportioning systems operate by
SECTION 13957N
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