OPERATION
The normally closed, spring loaded pilot, sensing pump suction pressure, opens when supply pressure exceeds the spring setting, allowing the main valve to open. Should suction pressure lower to the set point, the pilot, hence the main valve will begin modulating (throttling) to prevent the suction pressure from falling any lower. The pilot system is equipped with an opening speed control that fine tunes the valve response to the system variables.

SCHEMATIC

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

1. Model 65 Basic Control Valve, a hydraulically-operated, diaphragm-actuated, globe or angle valve which closes with an elastomer-on-metal seal.
2. Model 1330HB 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 141-3 Flow Control Valve, a needle-type valve which provides adjustable, restricted flow in one direction, and free flow in the opposite direction. On the 108FPS, the flow control valve is connected as an opening speed control.
5. Model 159 Y-Strainer The strainer protects the pilot system from solid contaminants in the line fluid.
6. Model 155 Visual Indicator, enables user to determine valves’ operating position.

FLOW OF CHARACTERISTICS
where:
  Q= Flow Rate in USGPM (U.S.)
  or Q= Flow Rate in liters/sec (Metric)
  Cv= Flow Rate in USGPM @ 1 psi pressure drop (U.S.)
  or Cv= Flow Rate in liter/sec @1 bar pressure drop (Metric)
  DP= Pressure Drop in psi (U.S.) or DP= Pressure Drop in bar (Metric)
  sg= specific gravity of line fluid

RECOMMENDED INSTALLATION
Pump valve with sense line to pump suction.