Type II proportioner . The Type III proportioner houses
no internal moving parts and uses the venturi principle
to allow for complete mixing of AFFF/sea water
solution. An orif ice p late controls t he volume of
gallons of AFFF concentrate entering the proportioner .
The size of the orif ice is determined by the maximum
demand for fire-f ighting agent placed on the system.
The water -sensing line connection for the Type III
proportioner is piped directly from the proportioner
body to the balancing valve. Type III proportioner
systems use a positi ve displacement, sliding vane
VENTURI AND ORIFICE
UPPER FLANGE 1 1/2"
Figure 6-14. Balanced-pressure proportioner (Type II).
Water and AFFF concentrate enter the proportioner
at the same pressure; hence, the name balanced
pressure-proportioning system. The balanced pressure
theory is a direct result of the balancing valve. One
sensing line is located downstream of the hycheck
valve, and another is located upstream of the AFFF
concentrate dischar ge check valve. The y route the water
pressure and AFFF concentrate pressure to the
operating chambers of the balancing valv e. The
water -sensing line is piped to the top operating chamber
Figure 6-15. Balanced-pressure proportioner (Type III).
and the AFFF concentrate-sensing line is piped to the
lower operating chamber . As the gallonage is increased
AFFF SPRINKLER SYSTEM
or decreased through the proportioner due to demand,
the water pressure will decrease or increase,
Sprinkler systems are a convenient and quick
respecti vely, in the water -operating chamber . When this
method for the fire party to apply AFFF/w ater solution
happens, the balancing valve will automatically re gulate
or water to lar ge areas of burning fuel. The system
the AFFF concentrate pump dischar ge pressure to equal
consists of a lar ge header pipe with smaller branch
the water pressure. The balancing valve will constantly
connections and attached sprinkler heads. A sprinkler
recirculate the AFFF concentrate to the service tank.
group control valve (powertrol or h ytrol with test
The amount of AFFF concentrate returned to the service
connection) will control the dischar ge flow t o the
tank through the recirculating piping varies. It depends
sprinkler heads. An SOPV or a manual control valve
on the position of the balancing valve, which is directly
may actuate the group control valve. Some sprinkler
controlled by pressure in the water -operating chamber .
systems are acti vated by a manually operated cutout
Water and AFFF concentrate will be correctly
valve. Actuation controls for the group control valves
proportioned in the proportioner due to the venturi
may be located in primary flight control, the
principle and then dischar ged into the distrib ution
na vigational bridge, the helo control, a conflagration
station, locally at the AFFF generating station, and at
various locations throughout the ship, depending on
Balanced-Pressure Proportioner (Type III)
the sprinkler system installation and type of ship. An
AFFF sprinkler system is a subsystem of AFFF
The purpose, actuation of system, and balancing
generating systems. Some of the different types of
valv e theory for the Type III balanced-pressure
sprinkler systems aboard na va l ships are listed below.
proportioner (fig. 6-15), are identical to those of the