10–7. SYSTEM DESCRIPTION (cont)

TM 1-1520-238-T-7 10–47 10–7. SYSTEM DESCRIPTION (cont) 10–7 (b) The pressure fuel manifold (fig. 10–23) contains a SPA and a CCA. Each adapter has a spring-loaded check valve that is forced open when the fuel nozzle is connected. (c) The fuel vent shutoff valve and the fuel transfer shutoff valve are opened when the REFUEL VALVE switch on the refueling panel is placed to the OPEN position. The fuel vent shutoff valve allows air trapped in the top of the fuel cells to be vented overboard during refueling operations. When closed, the valve prevents the loss of nitrogen pressurization. The fuel transfer shutoff valve allows refueling/defueling of the aft fuel cell. (d) The air vent/pressure relief valves equalize the pressure inside the fuel cells and vents excess pressure overboard during refueling and vent fuel overboard in case of automatic fuel shutoff failure. The forward air vent/pressure relief valve pressure is 1.5 ±0.13 psi. The aft air vent/pressure relief valve pressure relief is 2.0 ±0.13 psi. (e) The pilot and fuel shutoff valves combine to form an automatic fuel shutoff system during pressure refueling and fuel transfer operations. (f) The vent tubes and overboard vents relieve excess pressure overboard during refueling and drain fuel overboard in case of automatic fuel shutoff failure. (g) The sump drain valves permit fuel sampling checks for contamination, water content and the draining of the fuel cells. (h) During pressure refueling (fig. 10–24), the REFUEL VALVE switch on the refueling panel is placed to the OPEN position. The aircraft battery supplies 24 VDC through the FUEL FILL circuit breaker (CB32) to the refuel/transfer valve. The refuel/transfer valve motor drives to the open position, allowing a fuel path to the aft fuel cell and lighting the OPEN indicator on the refueling panel and the REFUEL VALVE OPEN indicator on the pilot’s caution/warning panel. Pressurized fuel is connected to the pressure fuel manifold and flows through the flow check valves and pilot valves into the fuel cells. (i) The AFT and FWD TNK LVL CONT VALVES switches and indicator lights are used to check the operation of the fuel shutoff valves and pilot valves. When the switches are set to the CLOSE position after refueling begins, the fuel shutoff valves closes, ending refueling and causes the CLOSED AFT and FWD indicators to light. When the switches are set to the OPEN position the indicator lights go out and fuel flow continues. This procedure checks the automatic shutoff function of the refuel system. (j) The refueling panel refuel indicator (fig. 10–25) receives 24 VDC battery power through the fuel quantity IND ON/OFF switch via the FSC. The FSC converts forward and aft fuel cell analog sensor data to linear zero to 5 VDC. The FUEL QTY indicator changes the electrical inputs into mechanical outputs. The mechanical outputs move the FWD and AFT FUEL QTY pointers along the scale.