Tanks shall be cylindrical steel ASME pressure vessels with a full Buna-N
impregnated nylon inner tank or bladder designed to contain AFFF
concentrate and to be used in conjunction with the concentrate ratio
controller. Tanks shall be designed for working pressure of [793 kPa
(gage)] [115 psig] [_____] and hydrostatically tested at 1.5 times the
working pressure in accordance with ASME standards at the factory. Tanks
shall have UL or FM label and ASME stamp affixed to the vessel. 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 tanks(s) of equal capacity. Permanently label
each tank with its capacity, type and percentage of concentrate, which
system(s) it serves, and whether it is a main or reserve tank.
Conspicuously post filling instructions near each group of tanks. Provide
a gage or unbreakable sight glass to permit visual determination of level
of tank contents. Prior to shop painting, abrasive blast clean tank
exterior surface in accordance with SSPC SP 6 to a surface profile not to
exceed 0.05 mm 2.0 mils and provide a MIL-P-24441 or SSPC coating system to
the tank exterior. Prime tank exterior with one coat of MIL-P-24441/1,
Formula 150 or SSPC Paint 22 primer applied to a dry film thickness of
0.076 mm 3 mils and topcoat with one coat of MIL-P-24441/7 Formula 156
(red) or SSPC Paint 22 topcoat (red) applied to a dry film thickness of
0.076 mm 3 mils.
2.15.2
Concentrate Ratio Controller
Ratio controller shall be a modified venturi device with AFFF concentrate
feed line from diaphragm tank(s), and integral concentrate metering
orifice. Size for specified flow rate(s).
2.16
BALANCED PRESSURE PROPORTIONING SYSTEM
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NOTE: Select the method of proportioning best
suited for the project.
Diaphragm pressure proportioning systems operate by
water pressure, require no electrical power, and
minimal control circuitry for automatic operation.
Maintenance requirements are minimal, however
refilling the tank is a difficult operation
requiring the services of a qualified technician to
avoid rupturing the diaphragm.
Balanced pressure proportioning systems require
reliable electrical power and more complex control
circuitry for automatic operation. In some cases an
emergency generator will be required. The primary
advantage of the non-diaphragm systems is the ease
in refilling the tanks. Tanks may be refilled even
while the system is in operation, if necessary.
Skid-mounted balanced pressure proportioning systems
perform proportioning at a central location,
avoiding long runs of concentrate lines. They are
well suited for systems such as deluge sprinklers
and monitor nozzles which have a relative narrow
range of flow rates.
In-line balanced pressure proportioning is useful
SECTION 13958N
Page 31
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