OPERATION
The normally closed, spring loaded pilot, sensing pump discharge pressure, opens when pressure exceeds the spring setting, allowing the main valve to open. As the pump pressure increases the pilot controls the main valve to open further. Pressure is maintained at the controlled set point over a wide range of flows regardless of back pressure in the downstream piping. The valve closes gradually as pressures decrease below the set point.

SCHEMATIC

COMPONENTS
The Model 108FC consists of the following components, arranged as shown on the schematic diagram:

1. Model 65 Basic Control Valve (angle pattern shown), a hydraulically-operated, diaphragm-actuated, globe or angle valve which closes with an elastomer-on-metal seal.
2. Model 1330FC Pressure Relief Pilot, a two-way, normally-closed pilot valve which senses upstream pressure under its diaphragm and balances it against an adjustable spring load. An increase in upstream pressure tends to make the pilot open.
3. Model 126 Ejector, a simple “tee” fitting with a fixed orifice in its inlet port. It provides the proper pressure to the diaphragm chamber of the main valve depending on the position of the pressure relief pilot.
4. Model 141-1 Check Valve, that prevents the valve from opening under a vacuum condition that may be encountered with a vertical turbine pump.
5. Model 159 Y-Strainer The strainer protects the pilot system from solid contaminants in the line fluid.
6. Pressure Gauge
7. Model 155 Visual Indicator (optional), enables user to determine valves’ operating position.

SIZING

Fire pump relief valves are sized per the guidelines in NFPA 20, and are based on the rated flow of the pump.

TYPICAL INSTALLATION