Overview
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Replace with overview of bleed sources, manifolds, isolation logic, and consumers.
The pneumatic system distributes high-pressure, high-temperature air from engine compressors, the APU, or external sources to consumers including air conditioning packs, wing/engine anti-ice, hydraulic reservoir pressurization, water tank pressurization, and engine start. Each engine has two bleed taps (low/intermediate and high stage), automatically selected by a Pressure Regulating Valve (PRV) and High Stage Valve (HSV).
Architecture
Sources:
HSV = High Stage Valve
PRSOV = Pressure Regulating Shutoff Valve
ISO = Isolation Valve
ACM = Air Cycle Machine
Aircraft Zones — Side View
Overhead Panel — Controls
Components
| Bleed Sources | 4 engines (low + high stage) + APU + external |
| PRSOV | Pressure Regulating Shutoff Valve per engine |
| HSV | High Stage Valve per engine (selects 8th-stage when low) |
| Isolation Valves | Split manifold into L (1+2), C, R (3+4) |
| Pack Inlet Valves | 2 (one per pack) |
| Consumers | A/C packs, wing AI, eng AI, hyd reservoirs, water pressurization, eng start |
Bleed Logic
- Low N2: HSV opens, drawing from high-stage tap for adequate pressure
- High N2: HSV closes, drawing from low-stage tap (more efficient)
- APU bleed available on ground and up to flight altitudes (per APU FCOM limit)
Failures & Abnormals
CAUTION — Bleed Air Leak / Duct Overheat
- Affected bleed isolation valve / engine bleed switch — OFF
- Isolate the leaking section using isolation valves
- Monitor pack outputs and cabin altitude
Limits
- APU bleed altitude limit — per AOM (typically 17,000–20,000 ft for bleed only)
- Engine bleed temperature monitored on EICAS
Notes / Personal
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User notes.