Tanks and Storage Architecture

A330 fuel tanks are not containers fitted inside the wing — they are the wing. Front and rear spars, upper and lower skins and sealed ribs enclose the volumes; sealing turns structure into tankage (the integral, "wet wing" concept). This article walks the physical architecture: where each tank begins and ends, how the collector cell guarantees feed under negative g, what the INNER TANK SPLIT pushbutton really operates, how the trim tank holds its fuel in unusual attitudes, and why a water drain valve can be changed with fuel in the tank.

1. Wet wing — and what it means for leaks

"Each fuel tank is a part of the aircraft structure. The inside of each tank is coated with a paint that contains leachable chromate. This chromate helps to prevent microbiological contamination..."

Because the tank wall is the wing, a fuel leak is usually a structural sealing problem — sealant runs, fastener wet-installation — not a "replace the container" job. It is also why the fire-prevention configuration rules (CDCCL) treat tank work so strictly.

The AMM fixes each tank's boundaries by wing station and rib:

"...the LH(RH) inner tank is between STA0/RIB1 and STA1530/RIB23 ‐ the LH(RH) outer tank is between STA1530/RIB23 and STA2190/RIB33 ‐ the LH(RH) surge tank is between STA2190/RIB33 and STA2557/RIB39."

  wing root STA0/RIB1                                  wing tip STA2557/RIB39
   ├──────────────── INNER TANK ───────────┼─ OUTER ──┼── SURGE ──┤
   │  (collector cell between RIB2–RIB3)   │  TANK    │  TANK     │
   │                                      RIB23      RIB33      RIB39
   └── sealed ribs divide; walls = spars + skins ("wet wing") ────┘

Capacities (AMM table; the quantities are minima — actual may be higher):

Plus three vent surge tanks: one per wing outboard of the outers, one on the RH side of the THS.

2. The collector cell — negative-g feed by pure mechanics

Inside each inner tank sits a small compartment, the collector cell — the "well" from which the two main pumps and the forward APU pump drink:

"Each inner tank contains a fuel collector cell which is made between: STA73/RIB2 and STA147/RIB3 (for the sides), the center spar (for the front), a sealed diaphragm forward of the rear spar (for the rear). At the bottom of STA73/RIB2 are three flap-type check valves. These let fuel flow into the collector cell, but prevent a fuel flow out of the collector cell. At the top of STA73/RIB2 are openings which let fuel fall back into the inner tank. At the bottom of STA220/RIB4 are three other flap-type check valves..."

"Each inner tank contains one collector cell that: ‐ Maintains a fuel reservoir for the fuel booster pumps and provides negative 'g' protection to feed the engines. ‐ Is maintained full and contains about 1 000 kg (2 200 lb) of fuel."

            INNER TANK
   ┌───────────────────────────────────────────┐
   │  high level ┌── top openings ──┐ overflow  │
   │      ────►  │                  │ ◄────     │
   │  inner fuel │  COLLECTOR CELL  │           │
   │   ──►╫╫╫──► │ (kept full ≈1 t) │ ● main 1  │──► engine
   │  3 flap     │                  │ ● main 2  │
   │  check vlvs └──────────────────┘ ● fwd APU │──► APU
   │  (in only)     3 more flap check valves     │
   │                at STA220/RIB4 (one-way)     │
   └───────────────────────────────────────────┘
   Negative g: check valves hold the cell's fuel in —
   the pump inlets stay wetted with no electronics involved.

[!warning]- Negative-g protection is not an electronic logic It is three flap-type check valves and a compartment that is always full. When fuel floats in negative g, the flaps shut and the cell cannot drain back into the tank — the pumps keep a wetted inlet. Simple, unpowered, and therefore reliable.

The cell outlet carries a strainer; the standby pump sits outside the cell, in the tank's aft division — a placement that matters in the next section.

3. INNER TANK SPLIT — one valve, two names

The overhead pushbutton says INNER TANK SPLIT; the component's formal name is the emergency isolation valve. It divides each inner tank into two areas:

"Each inner tank is divided internally into two areas: ‐ The inner tank forward with a fuel capacity of 17092 liters (4515 USgal) ‐ The inner tank aft with a fuel capacity of 24908 liters (6580 USgal)... The two areas are connected together with a pipe. An emergency isolation valve 5109QS1(5109QS2) controls the flow of fuel through this pipe... During usual operations, the valve is open."

And the FCOM gives the use case:

"...if tank damage is suspected (i.e. FQI data is lost or there is a rapid FQI decrease following an engine failure), the SPLIT valve can be manually closed by using the dedicated pushbutton on the overhead panel. When split valves are closed, the fuel contained in the AFT section of INNER tanks is still usable via the standby pumps."

[!warning]- Closing the SPLIT does not write off half the tank The forward area (with the collector cell and main pumps) is the suspect side being isolated; the aft area's 24 908 litres remain usable through the standby pump — which is precisely why the standby pump was placed in the aft division.

Hardware: a 76.2 mm (3.0 in) ball valve driven 90° by two motors on two different supplies — motor 2 on DC BUS 2, motor 1 on the DC ESS shed bus — either motor alone can operate the valve, and the actuator is mounted behind the rear spar so it can be replaced without entering the tank. The electrical schematic confirms three structural points: dual motors with genuinely segregated supplies; the pushbutton drives the motor circuits hard-wired, with no FCMC in the loop (a member of the same family as the LP-valve cut-offs — emergency actions do not depend on the brain); and the button's lights are powered by an independent transformer circuit.

Dispatch logic follows the hardware: some operators' MEL allows the SHUT light to be inoperative only with a pre-flight check of the valve's closing function, and the ON light freely — but the valve itself must work, and a single failed motor already counts the valve as inoperative. The valve's "ability to close" is the only damage-isolation tool the tank has; it gets zero tolerance.

4. Centre tank and trim tank

"The center tank is located between: the STA0/RIB1 (LH) and the STA0/RIB1 (RH), the front spar FR40 and the rear spar FR47, the center wing top and bottom skin."

(Six-tank configuration only.)

"The trim tank is installed in the Trimmable Horizontal Stabilizer (THS) primary-box structure between left station 9063/rib 20 and right station 8103/rib 18... There are four flap-type check valves at station 920/rib 3 in the left and right sides of the THS. The flap-type check valves keep the fuel in the center box structure during the wing down attitudes."

[!warning]- The trim tank also relies on flap check valves — for a different reason Not as a feed reservoir, but to stop the CG ballast from migrating sideways in wing-down attitudes. Part of why trim-tank fuel can be used for precise CG control is that it stays where the geometry says it is.

5. Water drain valves — serviceable with fuel in the tank

Every tank's low point carries drain valves for water checks and maintenance defuelling. The wing-tank type is a valve-within-a-valve:

"The inner valve is installed in the outer valve and the springs keep the two valves in the closed position... When the outer valve is removed the inner valve stays closed and prevents a fuel leakage. Thus the outer valve can be replaced when fuel is in the fuel tank."

The THS uses a self-locking drain valve with two O-rings — the working seal replaceable wet, the second sealing during replacement. Centre-tank drain valves (six-tank aircraft) have no remote inlet and only drain their adjacent area.

This is the "drain" side of water management — removing water overboard on the ground. The in-flight answer (stirring water back into the fuel to be burned) is the water-scavenge system, covered in water scavenge.

Self-test

[!note]- Q1. Why is a fuel tank leak rarely a quick fix on the A330? The tanks are integral structure — the wing itself, sealed. Leaks involve structural sealing, and tank work sits under strict fire-prevention configuration control.

[!note]- Q2. How do the collector cell's check valves provide negative-g protection? Three flap-type check valves at the cell base admit fuel but cannot pass it back out. Under negative g the flaps close and the always-full cell keeps the pump inlets wetted — no electronics involved.

[!note]- Q3. After pressing INNER TANK SPLIT, which part of the tank still feeds, and with what? The aft area (24 908 L) remains usable via the standby pump, which is installed in the aft division. The forward (suspect, collector-cell) side is what gets isolated.

[!note]- Q4. What keeps trim-tank fuel from sloshing outboard in a wing-down attitude? Four flap-type check valves on each side of the THS at station 920/rib 3 hold the fuel in the centre box.

[!note]- Q5. Can a water drain valve be replaced with fuel in the tank? Yes — the dual-valve (or dual O-ring) design keeps an inner seal closed while the outer element is removed.

Key takeaways

References

• AMM 28-11-00 Description and Operation (tank boundaries, capacities, collector cell, emergency isolation valve, trim/centre structure, drain valves).
• FCOM DSC-28-10-20 (collector cell function, SPLIT valve use case).
• ASM 28-11-01 (emergency isolation valve control schematic — dual motor supplies, hard-wired pushbutton).
• Interpretive remarks (zero-tolerance rationale) are integrative synthesis.

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.