Pack Flow Control Valve — Engineering Deep Dive

The foundation articles gave the PFCV its role — the pack chain's intake gate (Main Airflow §2 node ①), pneumatic + electric, fail-open on power loss, six auto-close conditions. This deep-dive opens that up: the actual control law, the threshold numbers, the timing, the ECAM signal chain, and the cross-chapter interfaces. It is the hardware basis for understanding the PACK pb, the PACK FAULT light, and most pack failures. This is the first of the component deep-dives (Stage B).

1. The PFCV in the pack chain — FIN and interfaces

        ATA-36 bleed manifold (HP/IP/LP @ 30–50 psi / ~200 °C)
                          │
                          ▼
            ┌─────────────────────────────┐
            │ Ozone converter             │ ◄── FIN 5511HB / 5512HB
            │ converts O₃ → O₂ (altitude) │     (AMM 21-51-00)
            └────────────┬────────────────┘
                         ▼
            ┌─────────────────────────────┐
            │ Pack Flow Control Valve     │ ◄── FIN 511HB / 512HB
            │ - pneumatically operated    │
            │ - electrically controlled   │
            │ - no air → spring closes    │
            │ - no power → opens (per cfg)│
            └────────────┬────────────────┘
                         ▼
            ┌─────────────────────────────┐
            │ Flow sensor                 │ ◄── FIN 513HB / 514HB
            │ measures actual flow →      │     (closed-loop feedback)
            │ pack controller             │
            └────────────┬────────────────┘
                         ▼
            ┌─────────────────────────────┐
            │ Pack (air-cycle cooling)    │ ◄── pack 1: 521HH / pack 2: 522HH
            └─────────────────────────────┘

   Controllers: pack controllers 531HH (pack 1) + 532HH (pack 2)
   — read the flow sensor, command the PFCV, monitor compressor-outlet
     and pack-outlet temperatures, drive the PACK pb FAULT logic.

Two points: the ozone converter is upstream of the PFCV (converts altitude ozone O₃ to O₂ — a "hidden component" the foundation articles did not mention); the flow sensor is downstream of the PFCV (it measures the PFCV's actual output, not its commanded position — the feedback node of the closed loop). When maintenance reports "511HB FAULT", that is PFCV 1 — the FIN-to-pilot bridge.

2. The dual control law — pneumatic + electric

   upstream bleed pressure (from ATA 36)
        │
        ▼
   ┌──────────────────────────────────┐
   │ PFCV body                        │
   │   ┌──────────────┐               │
   │   │ pneumatic     │ ← bleed pressure drives the valve
   │   │ actuator      │               │
   │   └──────┬───────┘               │
   │          ▼                        │
   │   ┌──────────────┐               │
   │   │ control       │ ← 28 V DC signal from the pack controller
   │   │ solenoid      │               │
   │   └──────┬───────┘               │
   │          ▼                        │
   │   valve position (meters flow)   │
   └────────────┬─────────────────────┘
                ▼
            downstream flow (to the pack)

   Failure modes:
   - no bleed pressure  → spring closes the valve (fail-safe closed)
   - no electrical power → valve opens (default detent per configuration)

• Pneumatic operation = the energy that actually moves the valve — the upstream bleed pressure itself drives the valve body.
• Electric control = the signal + position logic — a 28 V DC signal to the solenoid tells the actuator which way to move.
• No bleed pressure → spring closes (fail-safe to closed) — protects the pack from running dry.
• No power → opens to a default flow detent (fail-safe to flow, so the cabin is not starved of air) — which detent depends on the effectivity (§4).

The PFCV's interfaces: upstream bleed system (30–50 psi / ~200 °C); the pack controller (28 V DC flow signal); the flow sensor (actual-flow feedback, closing the loop); the PACK pb (crew ON/OFF + FAULT light). Six external sources can command it closed: the bleed monitoring computer (low upstream pressure), the compressor-outlet temperature sensor (overheat), the engine FADEC (start N3), LGCIU + engine state (maintenance door), the ENG FIRE pb (ATA 26), and the DITCHING pb (ATA 21-20).

3. LO / NORM / HI — three effectivity configurations

[!warning]- A330 variation: three PFCV configurations — check your MSN

Different A330 effectivities give three different PACK FLOW selector detents + power-loss defaults. A pilot must know which configuration their aircraft uses — check the "Applicable to: MSN …" effectivity at the top of the FCOM section. The three are not interchangeable.

PACK FLOW selector: LO (80 %) – AUTO – HI (120 %). In case one bleed fails, the flow is limited to 80 %. Any selection is irrelevant in single pack operation, or with APU bleed. Note: If there is no electrical power, the flow valves remain open and permit HI flow. — FCOM DSC-21-10-50 (Config 3)

[!important]- Config 3 precise figure: single-pack / APU forces 125 % In the Config 3 effectivity, single-pack operation or APU bleed overrides the selector and the system automatically selects 125 % flow (5 % above HI's 120 %). The other effectivities (Config 1/2) may differ — defer to each aircraft's current FCOM.

Config 1: LO (80 %) – NORM (100 %) – HI (115 %). … If there is no electrical power, the flow control valves remain open and permit 120 % flow. Config 2: LO (80 %) – NORM (100 %) – HI (120 %). … If there is no electrical power, the flow valves remain open and permit NORM flow. — FCOM DSC-21-10-50 (P 2/26, P 6/26)

[!warning]- Power-loss defaults differ — this is a configuration difference

Config 1 → 120 % (above HI 115 %); Config 2 → NORM 100 %; Config 3 → HI 120 %. The "fail-open to 120 %" described in the foundation articles is the Config 3 case — other aircraft may fail to NORM or 115 %. Check your own FCOM.

Three forced-HI conditions (all effectivities): single-pack operation (the remaining pack must supply the whole aircraft — 125 % on Config 3); APU bleed (APU flow management + ventilation guarantee — 125 % on Config 3); and one bleed failed, which limits flow to 80 % (this overrides the forced-HI — the bleed cannot support high flow).

4. The six auto-close conditions + timing

PACK pb On: The pack flow control valve is automatically controlled. It opens, except in the following cases: ① Upstream pressure below minimum ② Compressor outlet overheat ③ Engine start sequence … ④ Any door is not closed and locked, aircraft on ground, and any engine running ⑤ Fire pushbutton pressed for the engine on the related side ⑥ Ditching is selected. — FCOM DSC-21-10-50

① Low upstream pressure — the BMC detects bleed pressure too low to drive the pack; the PFCV closes to protect the ACM (which needs a stable upstream pressure to run the air cycle).

4.1 ② Compressor-outlet overheat — three thresholds

[!important]+ Three different thresholds, three independent events — the most-confused point

Temperature	Event	Source
235 °C	pneumatic sensor 521HH22 vents → the PFCV closes pneumatically (hardware action)	AMM 21-53-00 §3.G
260 °C	ECAM BLEED-page compressor-outlet field turns amber (visual alert)	FCOM DSC-21-10-50
180 °C	ECAM amber clears (alert reset — NOT the PFCV reopen condition)	FCOM DSC-21-10-50

The hardware protection (235 °C), from the AMM (the Chinese FCOM does not carry AMM content; the English AMM is the fact source):

The flow control valve has a safety feature which prevents a pack overheat. A pneumatic compressor-overheat sensor 521HH22 (522HH22) at the compressor outlet is connected to the actuator of the flow control valve 511HB (512HB). If the temperature at the compressor outlet becomes higher than 235 deg.C (455.00 deg.F) the sensor opens and vents the pressurized air in the actuator. The pressure in the actuator decreases and the flow control valve closes. The valve will open again if the compressor outlet temperature decreases. — AMM 21-53-00 §3.G

The visual alert (260 / 180 °C), from the FCOM:

Pack compressor outlet temperature indication: It normally appears in green. But, it appears in amber, if the temperature is higher than 260 °C. It remains amber, as long as the temperature is not lower than 180 °C. — FCOM DSC-21-10-50

Typical sequence: temperature rises → approaches 235 °C → the PFCV closes pneumatically → bleed cut → temperature falls back → it usually never reaches 260 °C → the ECAM field may not go amber. So when the 235 °C protection works, the crew sees only the PACK FAULT light + pack flow = 0; an amber compressor-outlet field means the 235 °C protection failed or lagged → a real emergency → act on the ECAM procedure immediately. The 260/180 °C hysteresis (80 °C band) prevents the field chattering near the threshold (the same philosophy as the 88/70 °C cargo duct hysteresis in ata-21-05).

4.2 ③ Engine start sequence — timing

Engine start sequence: 1. One valve (or both, if the crossbleed valve is open) closes when: ‐ The MODE selector is set to IGN, when on ground (valves reopen if MASTER switch or MAN START pushbutton are not set to ON within 30 s); ‐ The MODE selector is set to IGN (or CRANK) and when (on either engine): The MASTER switch is set to ON (or MAN START pushbutton is set to ON) and, the start valve is open and N3 < 50 %. 2. On ground, reopening of the valves is delayed 1 min to avoid an extra pack closure cycle during subsequent engine start. — FCOM DSC-21-10-50

ENG MODE selector → IGN
   │
   ▼
PFCV closes (one or both, per crossbleed valve state)
   │
   ▼
MASTER switch → ON (or MAN START → ON) within 30 s
   ├─ no  → PFCV reopens ("looked like a start but abandoned — restore air")
   ▼ yes
MASTER → ON + start valve open
   │
   ▼ N3 < 50 % (PFCV stays closed through the start)
   ▼
N3 reaches 50 % (start complete)
   │
   ▼
PFCV reopens (+ 1 min delay on the ground)

Why close the PFCV during start: the start consumes a lot of bleed for the starter; letting the pack also draw bleed would "steal" it → slow/failed start. Closing the PFCV gives all the bleed to the starter. Why the 1-minute ground delay (integrative reasoning): in a sequential two-engine start, reopening immediately after engine 1 would let engine 2's start close it again — an open-close-open-close cycle that thermally stresses the pack; the delay lets both engines finish before reopening, cutting thermal stress and PFCV mechanical fatigue.

④ Maintenance door not closed (three AND: any door unlocked + on ground + any engine running) — bleed reaching an open door is a hazard (ground crew could contact hot bleed), so the PFCV closes. ⑤ ENG FIRE pb pressed — the associated-side bleed shut-off valve closes, so the PFCV loses upstream pressure (and the spring closes it) — double protection even if no electrical close signal arrives. ⑥ Ditching selected — the DITCHING pb closes the PFCV + outflow valves + emergency ram-air inlet + avionics overboard valve together (the below-waterline openings — see Ditching).

5. Main-deck smoke → pack 1 closes by default

In case of Main Deck smoke, one pack (pack 1 by default) shuts down due to the closure of the Main Deck Shut Off Valves. — FCOM DSC-21-10-50

Why pack 1 (integrative reasoning): the MSOV closure isolates the main deck, so the main-deck recirc fans can no longer recirculate to the mixing unit; pack 1 is connected by default to the main-deck return path (per AMM 21-26), so its flow becomes abnormal and it auto-closes. Pack 2 keeps running to supply the cabin with fresh air (the freighter cabin uses pack 2 — ata-21-04 §7).

6. PACK pb FAULT light — three triggers

FAULT lt: The amber light and associated ECAM caution come on, when ① the pack flow control valve position disagrees with the selected position, or in the case of ② compressor outlet overheat or ③ pack outlet overheat. — FCOM DSC-21-10-50

1. Position disagreement — commanded ON but actually closed (or vice versa): mechanical fault / lost signal.
2. Compressor-outlet overheat — the three thresholds (§4.1): 235 °C PFCV pneumatic close (AMM), 260 °C ECAM amber, 180 °C clear.
3. Pack-outlet overheat — > 95 °C trips / < 60 °C clears (§7).

Operationally: a FAULT light does not immediately mean a mechanical fault — it can be an overheat. Scan ECAM: the BLEED page compressor-outlet temperature and the COND-page pack-outlet temperature tell which. Note the compressor-outlet field may not be amber — when the 235 °C pneumatic chain has acted, the FAULT light is on but the temperature may already be falling, never reaching 260 °C; in that case pack flow = 0 is the tell.

7. Pack-outlet overheat — 95 °C

Pack outlet temperature indication: It normally appears in green. But, it appears in amber, if the temperature is higher than 95 °C. It remains amber as long as the temperature is not lower than 60 °C. — FCOM DSC-21-10-50

The 95 / 60 °C hysteresis (35 °C band) is smaller than the compressor-outlet's (260/180 = 80 °C). Why 95 °C: pack outlet is normally 5–30 °C (ata-21-01 §2), so 95 °C far exceeds normal — an ACM failure + excess bypass heat + temperature-control-valve fault; and 95 °C is near the cabin-tolerable limit (scald prevention).

8. Forced 125 % / 80 % logic

Any selection is irrelevant in single pack operation, or with APU bleed. In case one bleed fails, the flow is limited to 80 %. — FCOM DSC-21-10-50

Single-pack forced 125 % (Config 3): the other pack failed, so the remaining pack must run 125 % to supply the whole aircraft (cabin + cargo + avionics) — the pack controller forces the PFCV high and refuses LO/NORM commands. APU forced 125 %: APU bleed flow is limited (vs engine bleed) and needs a stable demand, so high flow uses the full APU capacity and avoids APU regulation hunting. One bleed failed → limited to 80 %: a single bleed supporting two packs cannot reach high flow → forced low to prevent overload and pressure collapse. When both forced cases coincide (rare), the 80 % limit wins (it is a physical ceiling; 125 % is unachievable).

9. Operations

9.1 PACK pb states

Important: per the FCOM, OFF closes the PFCV "if the pack flow control valve is electrically powered" — on power loss the OFF command is ineffective (the PFCV's state is set mechanically by the spring + pneumatics; the electrical OFF signal cannot reach the solenoid).

9.2 ECAM BLEED-page PFCV fields

PFCV: in-line green = open / cross-line amber = closed. Flow indication: green needle, 12 o'clock = 100 %, LO = 80 % / HI = 120 %. Compressor-outlet temperature: amber > 260 °C / clears < 180 °C. Temperature control valve: C green = closed / H green = open. Pack-outlet temperature: amber > 95 °C / clears < 60 °C. Emergency ram-air inlet: off-line green = normally closed / in-line green = full open / amber = abnormal. (Per FCOM DSC-21-10-50.) Scan order: PFCV field → flow needle (vs the selector) → compressor-outlet temperature → pack-outlet temperature.

9.3 Five pack-fault roots (detail in ata-21-21)

9.4 Maintenance view (brief)

AMM 21-51 carries the PFCV 511HB/512HB removal/install tasks, the flow-sensor 513HB/514HB calibration, and the ozone-converter 5511HB/5512HB replacement (a periodic consumable). The pilot does not deal with these directly but should map "511HB FAULT" → PFCV 1. PFCV dispatch (single/dual) is in MEL Dispatch.

Self-test

[!note]- Q1. What is the PFCV's FIN, and what does it interface with upstream and downstream?

PFCV FIN: 511HB (pack 1) / 512HB (pack 2). Upstream: the ozone converter (5511HB / 5512HB, O₃ → O₂). Downstream: the flow sensor (513HB / 514HB, actual-flow feedback to the pack controller). Controllers: pack controllers 531HH / 532HH command the PFCV. Crew controls: PACK 1/2 pb (2HB1 / 2HB2). "511HB FAULT" = PFCV 1.

[!note]- Q2. What are the three PACK FLOW effectivity configurations, and how do their power-loss defaults differ?

Config 1: LO 80 / NORM 100 / HI 115 %, power-loss default 120 % (above HI). Config 2: LO 80 / NORM 100 / HI 120 %, power-loss default NORM. Config 3: LO 80 / AUTO / HI 120 %, power-loss default HI 120 %, with single-pack / APU forcing 125 %. The configurations are not interchangeable — a pilot checks the FCOM "Applicable to: MSN …" effectivity for their own aircraft.

[!note]- Q3. The compressor outlet has three thresholds — PFCV close, ECAM amber, amber clear. What are they and which is the hardware protection?

235 °C — the pneumatic sensor 521HH22 vents the actuator and the PFCV closes (AMM 21-53-00 §3.G) — the hardware protection, independent of the pack controller. 260 °C — the ECAM BLEED compressor-outlet field turns amber (the visual danger line the crew sees). 180 °C — the amber clears (80 °C hysteresis). Typical sequence: temperature rises → ~235 °C → PFCV closes → bleed cut → temperature falls → usually never reaches 260 °C → field may not go amber. An amber field means the 235 °C protection failed or lagged → emergency.

[!note]- Q4. During an engine start the PFCV auto-closes — when does it close, when reopen, and why the 1-minute ground delay?

Closes when MODE → IGN on the ground (reopens if MASTER/MAN START not ON within 30 s), or MODE IGN/CRANK + MASTER ON (or MAN START) + start valve open + N3 < 50 %. Reopens at N3 ≥ 50 % + a 1-minute ground delay. The delay (integrative reasoning) prevents an open-close-open-close cycle during a sequential two-engine start, cutting pack thermal stress and PFCV fatigue. The close itself gives all the bleed to the starter for a fast start.

[!note]- Q5. The PACK pb FAULT light is amber — what are the three possible causes and how does the crew tell them apart?

Three triggers (FCOM): ① position disagreement (commanded ON but closed) — mechanical/electrical fault; ② compressor-outlet overheat (235 °C PFCV close / 260 °C ECAM amber / 180 °C clear); ③ pack-outlet overheat (> 95 °C / < 60 °C clear). Tell apart by scanning ECAM: BLEED compressor-outlet amber = ②, temperature truly reached 260 °C (235 °C protection failed/lagged) → emergency; FAULT + flow = 0 but compressor field not amber = ② the 235 °C pneumatic chain acted (protected early); pack-outlet amber = ③; all normal = ① position disagreement.

Key takeaways

Common misconceptions

Scope — what this deep-dive covers and defers

References

A330 specifics per FCOM DSC-21-10-50 (PACK pb states and the six auto-close conditions with their timing; the main-deck-smoke pack-1 close; the power-loss fail-open defaults across the three effectivities; the PACK FLOW selector across the three configurations including the forced 125 % single-pack/APU case and the 80 % one-bleed-failed limit; the FAULT-light triggers; and the ECAM BLEED-page fields with the 260/180 °C compressor-outlet and 95/60 °C pack-outlet thresholds) and AMM 21-53-00 §3.G (the 235 °C pneumatic compressor-overheat sensor that closes the PFCV — the English AMM being the fact source where the Chinese FCOM carries no AMM content) and AMM 21-51-00 (PFCV / ozone-converter / flow-sensor / pack-controller FINs). The dual-control-law physics, the fail-safe philosophy, the 1-minute-delay rationale, the main-deck-smoke pack-1 mechanism, and the forced-flow priority analysis are integrative syntheses.

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.