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. This
feature is valuable when prolonged fire fighting
operations may be encountered.
Skid-mounted balanced pressure proportioning systems
perform proportioning at a central location,
avoiding long runs of concentrate lines. They are
well suited for systems which have a relative narrow
range of flow rates.
In-line balanced pressure proportioning is useful
when there are multiple hazards with widely varying
discharge rates which are to be supplied from the
same proportioning system, and any time it is
desired to proportion foam remotely at risers or
discharge devices instead of at the pump room. Their
disadvantage is the need for much more concentrate
piping in the field.
Line proportioners (venturi type) are fixed-flow
rate devices which are useful on relatively small
systems which have only one set flow rate per
proportioner. They require no electric power but
have limited application, since they require high
water pressure and low discharge back pressure.
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Foam solution shall be produced by introducing AFFF concentrate into the
water stream by the balanced pressure proportioning method using a pump and
proportioner. [Provide proportioning system and storage tanks for hose
lines independent of main proportioning system and tanks.]
[2.14.1
Skid-Mounted Balanced Pressure Proportioning System
**************************************************************************
NOTE: Choose this paragraph or the paragraph below
entitled "In-Line Balanced Pressure Proportioning
System."
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Self-contained, skid-mounted system, fully assembled at the factory and
delivered complete and ready for use. Field connections shall be limited
to water, electrical, and AFFF concentrate inputs, foam solution output,
and foam concentrate return line to storage tank. Size system for required
flow rate(s). The concentrate pump and all piping, valves, and fittings in
contact with foam concentrate shall be of materials resistant to the
corrosive effects of the AFFF concentrate. Concentrate pump shall be
electric motor driven, drip proof, 240/480 volts, 60 Hz AC. Activation and
operation of system shall be fully automatic, with manual over-ride and
manual shut-down. 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.
SECTION 13957N
Page 29
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