Engine Feed

Every other part of the fuel system — storage, venting, transfers, CG control — exists so that this part never stops working: pressurised fuel delivered to two engines, in all flight conditions. This article follows the feed path from the collector cell to the engine LP valve, establishes the "each side feeds its own engine" normal configuration, and explains why the shut-off function is wired around the fuel computers rather than through them.

1. The feed path

        LEFT WING                                   RIGHT WING
 ┌────────────────────┐                       ┌────────────────────┐
 │ INNER TANK          │                       │ INNER TANK          │
 │ ┌────────────────┐ │                       │ ┌────────────────┐ │
 │ │ COLLECTOR CELL │ │                       │ │ COLLECTOR CELL │ │
 │ │ ● MAIN PUMP 1  │ │                       │ │ ● MAIN PUMP 1  │ │
 │ │ ● MAIN PUMP 2  │ │                       │ │ ● MAIN PUMP 2  │ │
 │ └───────┬────────┘ │                       │ └───────┬────────┘ │
 │  ○ STBY PUMP (aft   │                       │  ○ STBY PUMP        │
 │    division)        │                       │                    │
 └─────────┼──────────┘                       └─────────┼──────────┘
           ▼ engine feed line                            ▼
   ════════╪═══════════ X FEED valve ════════════════════╪═════════
           │            (normally closed —               │
           ▼             splits the system in two)       ▼
     [LP VALVE 1]                                  [LP VALVE 2]
           │                                             │
           ▼                                             ▼
       ENGINE 1                                      ENGINE 2

Normal configuration: left inner tank feeds engine 1, right inner tank feeds engine 2, each through its own pumps and LP valve, with the crossfeed valve closed between them. The two halves are mirror images — a failure on one side stays on that side until the crew deliberately opens the crossfeed (crossfeed).

Inside each half the redundancy is layered: two main pumps in the collector cell (either one alone carries the engine), a standby pump outside the cell that starts automatically when main-pump pressure is lost (main fuel pumps), and below all of that, gravity feed as the unpowered floor (pump failures and gravity feed).

The feed lines themselves run inside the tanks wherever possible — a pipe surrounded by fuel cannot leak into a dry bay or onto a hot surface; where the line must cross dry structure it is shrouded. The same philosophy as the trim-pipe shroud in tank venting.

2. The LP valve — the engine's fuel tap

One low-pressure valve per engine sits at the wing root, the last gate before the pylon:

Two commanders, both hard-wired. Setting the ENG MASTER lever to ON opens the LP fuel valve as the first step of the start sequence (per the FCOM engine-start description), and MASTER OFF closes it at shutdown. The second commander overrides everything:

"Using the engine fire pushbutton will force the LP fuel valve to close. The engine will shut down after a time delay."

The valve uses two motors fed from two different buses (one of them battery-backed), so a single electrical failure cannot leave an engine impossible to isolate. And critically, the command path does not pass through the FCMS: with both fuel computers dead, the MASTER lever and the FIRE pushbutton still close the valve. Cut-off is a hard-wired right, not a software service.

[!warning]- The LP valve answers to the MASTER and FIRE circuits — not to the fuel computers The FCMS schedules pumps and transfers; it has no authority over engine fuel isolation. This segregation recurs across the system (the SPLIT valve in tanks and storage is wired the same way): anything that must work in the worst case is kept out of the computers' hands.

On the SD FUEL page each LP valve shows as the standard Airbus valve symbol: in-line green (open, flow), crossline green (closed, normal after shutdown), crossline amber (closed when it should be open — or in transit), amber XX (position unknown). The disagreement case has its own ECAM alert, FUEL ENG 1(2) LP VALVE FAULT — a Crew awareness procedure whose real content is the status of your isolation capability (see fuel alerts index).

3. IDG cooling return — the loop inside the loop

The engine does not consume everything the pumps deliver. Part of the flow cools the Integrated Drive Generator and returns to the inner tank:

"...gets heated fuel from the Integrated Drive Generators and returns it to the inner fuel tanks."

Fuel is the aircraft's working coolant — the IDG return is one reason inner-tank fuel temperature can climb on the ground (see fuel temperature faults for the HI TEMP logic this feeds).

4. Dispatch — the indication is part of the valve

Some operators' MEL treats the engine LP valve with zero tolerance in an instructive way: not only must the valve itself be operative — its SD position indication must be operative too. An LP valve you cannot see is treated like an LP valve you do not have, because the fire drill depends on confirming the fuel is actually cut. The same "the light is part of the function" logic appears in the crossfeed and SPLIT-valve items.

Self-test

[!note]- Q1. What is the normal engine-feed configuration? Each inner tank's collector-cell pumps feed their own side's engine through their own LP valve, crossfeed closed — two mirror-image, independent halves.

[!note]- Q2. Name the redundancy layers between a collector cell and its engine. Main pump 1, main pump 2 (either alone suffices), automatic standby pump, and finally unpowered gravity feed — plus the crossfeed to borrow the other side entirely.

[!note]- Q3. Both FCMCs have failed. How do you shut off fuel to engine 2? Exactly as always — ENG MASTER 2 OFF or the ENG 2 FIRE pushbutton. The LP-valve command path is hard-wired and never passes through the FCMS.

[!note]- Q4. Why are feed lines routed inside the tanks? A pipe immersed in fuel cannot leak into dry structure or onto hot surfaces; where it must cross a dry bay it is shrouded — leak containment by geometry.

[!note]- Q5. Why would an MEL ground an aircraft for a dead LP-valve indication when the valve works? Because isolation must be confirmable: the fire drill requires knowing the valve actually closed. The indication is treated as part of the shut-off function.

Key takeaways

Point	Value
Normal feed	each side feeds its own engine; crossfeed closed
Redundancy ladder	main 1 / main 2 → auto standby → gravity; crossfeed across sides
LP valve	one per engine; ENG MASTER or FIRE pb; dual motor, dual bus
Segregation	cut-off hard-wired around the FCMS — survives double computer failure
IDG return	heated cooling fuel returns to the inner tank
Dispatch	LP valve and its SD indication both zero-tolerance

References

FCOM DSC-28-10-40 (engine feed, LP valve control); DSC-28-10-20 (collector cell).
AMM 28-23-00 Description and Operation (feed architecture, LP valve motors and supplies, line routing).
Some operators' MEL, engine LP valve item (valve + indication).
The segregation framing and routing rationale are integrative synthesis from the cited sources.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.