Water Motor Proportioner (FP-1000)

The FP-1000 water motor proportioner system (fig. 5-30) is activated by an SOPV electrically or manually. The SOPV will vent the operating chamber of the hytrol valve and pressurize the operating chamber of the powertrol valve. As the water is discharged through the hytrol valve, the water flow will pressurize the water motor inlet. This will cause the rotary gear pump to inject a metered amount of AFFF concentrate into the water stream of the water motor proportioner discharge, thus producing the AFFF/water solution. A centrifugal pump assembly is sometimes installed in conjunction with the water motor proportioner. This is done when the inlet flow

Figure 5-30.-FP-1000 water motor proportioner system. 5-26

rates to the water motor may drop below 200 gpm, where the proportioner will not produce an effective AFFF/water solution. A pressure switch is used to activate the pump assembly via the motor controller to boost the pressure of AFFF concentrate entering the rotary gear pump. This arrangement will produce an effective AFFF/ water solution when the flow rates drop below 200 gpm.

Balanced-Pressure Proportioner (Type II)

The balanced-pressure proportioner (fig. 5-31) proportions the correct amount of AFFF concentrate necessary to produce effective AFFF/ water solution over a wide range of flows and pressures. The system is actuated (fig. 5-32) by activating an SOPV, electrically or manually. The SOPV will vent the operating chamber of the hycheck valve and pressurize the operating chamber of the powertrol valve. The switch assembly of a SOPV will cause electrical activation of the pump assembly (positive displacement, sliding vane or rotary gear) via the motor controller. The pump assembly will pressurize the AFFF concentrate piping to the demand proportioned and balancing valve. Water flow through the proportioner will move the water float towards the large opening of the water sleeve, depending on the gallonage required for fire fighting. The AFFF concentrate float is directly controlled by the movement of the water float, thus influencing the amount of AFFF concentrate that enters the water stream. 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

Figure 5-31.-Balanced-pressure proportioner. 5-27

Figure 5-32 - Type II balanced-pressure proportioner system

valve, and another is located upstream of the AFFF concentrate discharge check valve. They route the water pressure and AFFF concentrate pressure to the operating chambers of the balancing valve. The water-sensing line is piped to the top operating chamber and the AFFF concentrate-sensing line is piped to the lower operating chamber. As the gallonage is increased or decreased through the proportioner due to demand, the water pressure will decrease or increase respectively in the water operating chamber. When this happens, the balancing valve will automatically regulate the AFFF concentrate pump discharge pressure to equal the water pressure. The balancing valve will constantly recirculate the AFFF concentrate to the service tank. The gallonage of AFFF concentrate returned to the service tank through the recirculating piping varies. It depends on the position of the balancing valve, which is directly controlled by pressure in the water operating chamber. Water and AFFF concentrate will be thoroughly proportioned in the proportioner due to the venturi principle and then discharged into the distribution piping.

Balanced-Pressure Proportioner (Type III)

The purpose, actuation of system, and balancing valve theory for the type III proportioned are identical to those of the type II proportioner. The type III proportioners house no internal moving parts and use the venturi principle to allow for complete mixing of AFFF/water solution. The gallonage of AFFF concentrate entering the proportioner is controlled by an orifice plate. The size of the orifice is determined by the maximum demand for fire-fighting 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 (fig. 5-33) use a positive displacement, sliding vane pump.