Module 11A.16–11A.17 — Pneumatic/vacuum (ATA 36) and water/waste (ATA 38)

Levels

• 11.16 Pneumatic/vacuum — A1 level 1, B1.1 level 3 (layout, sources, pressure control, distribution, indications, interfaces; pressure and vacuum pumps).
• 11.17 Water/waste — A1 level 2, B1.1 level 3 (water and toilet systems, servicing, draining; corrosion aspects).

11.16 Pneumatic system (ATA 36)

Sources

Source	Notes
Engine bleed air	Taken from an intermediate-pressure (IP) stage at high power and a high-pressure (HP) stage at low power (HP valve opens automatically when IP pressure is insufficient); check valve prevents back-flow into the IP stage
APU	Load compressor or bleed from the APU compressor — ground air conditioning and main engine starting; can supply in flight below an altitude limit
Ground supply (HP air cart)	Connects to the pneumatic manifold — engine start and air conditioning on the ground
Compressors	Engine-driven or electric compressors (bleedless aircraft use electric compressors for air conditioning)
Reservoirs	High-pressure air/nitrogen bottles on some aircraft for emergency gear extension, brakes, door actuation

Pressure and temperature control

• Pressure-regulating and shut-off valve (PRSOV) — controls bleed pressure into the manifold (typically about 40–45 psi) and shuts off bleed (engine fire, leak, overpressure).
• Pre-cooler (heat exchanger cooled by engine fan air through a fan-air modulating valve) limits manifold temperature (around 200 °C).
• Over-pressure valve protects against PRSOV failure; over-temperature sensors close valves.
• Bleed monitoring computers (BMC) control and monitor valves on modern aircraft.

Distribution

• Pneumatic manifold/ducts (titanium/stainless steel with insulation) left and right, connected by an isolation (cross-bleed) valve — normally closed on many types, opened for single-source operation or engine cross-start.
• Couplings (V-band clamps), expansion joints/bellows, duct supports.

Indications and warnings

• Duct pressure gauges, valve position, bleed fault lights.
• Duct leak / overheat detection: sensing loops (similar to fire loops) along ducts in the wings, pylons, fuselage and wheel wells — on detection, the relevant bleed and isolation valves close; crew warning "BLEED LEAK".

Interface with other systems

Air conditioning packs, cabin pressurisation, wing and engine anti-ice, engine starting (air turbine starters), hydraulic reservoir pressurisation, potable water tank pressurisation, air-driven hydraulic pumps, cargo heating, thrust reverser actuation on some engines, inerting (ASM supply), and pneumatically driven instrument/de-icing boots on smaller aircraft.

Key fact: The HP bleed valve opens at low engine power when IP pressure is too low; the pre-cooler uses fan air to cool the bleed air.

11.16(b) Pumps — pressure and vacuum

On turbine transport aircraft, vacuum is rarely engine-pump generated; it may be produced by venturis/ejectors using bleed air (e.g. to hold de-icing boots down). Light aircraft use engine-driven vacuum (or pressure) pumps for gyro instruments (see Modules 11B/11C):

Pump	Features
Wet vane pump	Steel vanes lubricated by engine oil; exhaust contains oil → oil separator returns oil to the engine
Dry vane pump	Carbon vanes self-lubricating; no oil allowed in or near (oil causes failure); shear coupling drive; vane wear → sudden failure
Venturi	No moving parts; works only in flight (airflow)
Electric pump	Standby source

System parts: suction relief (regulator) valve, central air filter and garter filters, suction gauge (typically 4.5–5.5 inHg for gyros), check valves (twin-engine).