Auto Re-circulation on a Refueller to control the pumping pressure of Air Crafts. Solenoid Override or Pneumatic Override to safeguard the system. This can be operated remotely to re-circulate full flow. When installed in Main line, it prevents upstream pressure dropping below preset value. When installed on a By-Pass line, it controls main line pressure by relieving excess pressure in By-Pass/sump. Ideal for pump by pass to protect the downstream equipments. Relief pilot (F16) is normally closed due to spring tension. With increase in upstream pressure above set value, Pilot (F-16) opens which makes Main Valve to open fully. Spring Range: Standard: 20-200 psig. Optional: 5-30 psig.