Engine fuel feed - center tank fuel scavenge jet pump
(Courtesy B777 SDS 28-22-00-005)
1. Purpose
The fuel scavenge jet pumps take fuel from the low points in the center tank and send it to the main tanks. This increases the amount of usable fuel in the center tank. Float-operated shutoff valves prevent fuel scavenge when the main tanks are full.
2. Location
There is one fuel scavenge jet pump in each side of the center tank. They are in the left and right wheel wells on the rear spar.
There is an outlet float-operated shutoff valve in each main tank. You get access to these valves through the fourteenth fuel tank access door.
There is an inlet float-operated shutoff valve in each side of the center tank. You get access to these valves through the first fuel tank access door.
3. Functional Description
The jet pumps operate automatically when the boost pumps are on. They use fuel from the boost pumps as motive fuel. The flow of the motive fuel through the jet pump causes suction that takes fuel from the center tanks. The fuel goes through the jet pump discharge lines to the main tanks. When the main tanks are full, the outlet float-operated shutoff valve closes to stop fuel flow through the discharge line.
The inlet float-operated shutoff valve prevents motive flow to the jet pump until the center tank is almost empty. This prevents the fuel from flowing into the main tank too early if the outlet float-operated shutoff valve fails. A check valve in the jet pump prevents fuel movement from the main tank to the center tank.
Keep in mind that 4 H2O scavenge jet pumps exist in the system too.
Hope this helps
cod