Manual Control Valve (Neutral/Open, Two Port). -This manual control valve (fig. 5-21) is used to actuate (open only) powertrol-type valves. It is positioned at remote AFFF/water solution outlets. When the valve is in the neutral position, water is isolated within the valve. In the open position, the valve routes the water through the outlet port, thus pressurizing the operating chamber of powertrol-type valves. This valve is used in conjunction with the closed/neutral/open, three-port manual control valve to reset the powertrol-valves.

Manual Control Valve (Closed/Neutral/ Open, Four Port). -This manual control valve (fig. 5-22) is used to actuate hytrol-type valves that are used in conjunction with bilge sprinkler systems. When the valve is in the neutral position, water is isolated within the valve. When the valve is in the open position, the water is routed through the closed port and the open port is aligned with the drain. With the valve in the closed position, the water is routed

Figure 5-22.-3-way 4-port manual control valve. 5-19

through the open port and the closed port is aligned with the drain.

Solenoid Operated Pilot Valve (SOPV).- SOPVs are electrically or manually operated pilot valves (fig. 5-23) that actuate hytrol- or powertrol-type valves. Coil assemblies (open or closed), when energized via actuation switches, create a magnetic field. This causes a linkage arrangement, which is connected to the stem, to rotate the valve to open or close it. The stem may be manually rotated by a T handle or knob assembly, counterclockwise to open and clockwise to close the valve. A switch assembly is activated when the linkage arrangement moves either by electrical or manual operation. This sends an electrical signal to a motor controller or alarms/indicator lights. When the SOPV is in the closed position, the water is routed through the odd-numbered port(s) and thereby pressurizes the operating chamber of hytrol-type valves. As the water is routed through the odd-numbered port(s),

Figure 5-23.-Solenoid operated pilot valve.

Figure 5-24.-Balancing valve.

the even-numbered port will be aligned with the drain port, thus venting the operating chamber of the powertrol-type valves. When the SOPV is in the open position, the water is routed through the even-numbered port. This pressurizes the operating chamber of powertrol-type valves to open the valve. The odd-numbered port will be aligned with the drain port to vent the operating chamber of the hytrol-type valves, thus opening the valves.

Balancing Valve. -The balancing valve (fig. 5-24) is a diaphragm-type, hydraulically operated, globe regulating valve. It is installed in the recirculation line of balanced-pressure systems between the concentrate pump discharge and the AFFF service tank. The balancing valve has two operating chambers with sensing lines. The line on top of the diaphragm senses water pressure, and the line on the bottom of the diaphragm senses AFFF concentrate pump pressure. Any fluctuation in water pressure will cause the balancing valve to regulate the AFFF concentrate discharge pressure to equal the water pressure.