Installed AFFF Equipment

The installed AFFF equipment includes the water motor proportioners, the positive displacement pump, the centrifugal pump, and the balanced-pressure proportioner.

The installed water motor proportioners and the centrifugal pumps are being phased out and replaced with positive displacement pumps or balanced-pressure proportioning systems.

WATER MOTOR PROPORTIONERS.- The two most common installed water motor proportioners are the FP-180 and the FP-1000. The installed FP-180 is a modified portable FP-180. The modifications to the proportioner should conform to NAVSEA drawing number 803-2145520 current revision before the unit is installed. The portable FP-180 was discussed earlier in this chapter.

The FP-1000 water motor proportioner (fig. 5-10) consists of a positive displacement water motor connected to a positive displacement rotary gear pump. The proportioner will give

Figure 5-10.-High-capacity FP-1000 water motor proportioner (viewed from above). 5-9

the most accurate proportioning with flows of 200 to 1,000 gpm when the water motor inlet pressure is between 100 and 175 psig.

CENTRIFUGAL PUMPS.- Centrifugal pumps have limited use in AFFF generating systems. Currently only one system, the FP-1000 water motor proportioner, uses the centrifugal pump as a booster pump. The unit consists of a 440-volt, 60-hertz, three-phase motor connected to the pump by a flexible coupling. The maximum pump capacity is 100 gpm with a minimum static head. The higher the static head, the less efficient the centrifugal

pump. These pumps do not require a relief valve because of their 100-percent slippage capability.

POSITIVE DISPLACEMENT PUMPS.-

Positive displacement pumps installed in AFFF generating systems are a sliding vane and rotary gear type. The pump capacity ranges from 12 to 80 gpm of AFFF concentrate. The unit consists of a 444-volt, 60-hertz, three-phase motor that is connected to the pump by flexible couplings or a belt and pulley assembly. The horsepower rating of the motor will vary with the capacity of the pump used. The unit may be installed as an injection pump or a transfer pump or as a subassembly to supply AFFF concentrate to a

Figure 5-11.-Type II proportioner. 5-10

balanced-pressure proportioning system. All positive displacement pumps require a relief valve to prevent excessive pressure buildup and pump damage.

BALANCED-PRESSURE PROPOR-TIONERS.- Balanced-pressure proportioners are demand type. The proportioner will only proportion the amount of AFFF concentrate necessary to produce a satisfactory AFFF/ water solution over a wide range of flows and pressures. Two types of proportioners are currently used in the Navy. The type II and the type III. Both proportioners use the venturi principle to mix AFFF concentrate and water together. The capacities of the type II and the type III proportioners range from 60 to 1,000 gpm of the AFFF/water solution.

The type II proportioner (fig. 5-11) consists of a proportioner body that is flanged for piping connections. The body houses a concentrate sleeve, a concentrate float with a guide rod, a water sleeve, a water float with guide rod, and a water float return spring. The concentrate float is connected to the water float. Any movement of the water float will cause the AFFF float to move proportionately.

The type III proportioner (fig. 5-12) also consists of a proportioner body that is flanged for piping connections. The body is essentially a hollow tube with flow restriction and no moving parts. The amount of AFFF concentrate entering the proportioner is controlled by an orifice plate. The size of the orifice is determined by the total demand placed on the proportioner.

Figure 5-12.-Type III proportioner. 5-11