When line proportioners are used in a fixed piping systems,
the foam concentrate is usually stored in a permanently
installed storage tank with permanent piping
between
the tank and foam concentrate connection of
the
line proportioner.
The line proportioner may be
mounted
up to a maximum height of 6-ft (1.8m) above
the
tank bottom. A minimum of 24 inches (610 mm) of
straight
unobstructed pipe should be installed upstream
and
downstream of the line proportioner.
In fixed installations
using Alcohol Resistant AFFF foam concentrates,
the
line proportioner should be installed at the bottom of
the
foam concentrate storage tank in order to provide a
flooded
suction at all times. A normally closed shutoff
valve
in the foam concentrate supply line will prevent
possible
siphoning of the foam concentrate.