The vital air service maintains what pressure?

• A. 125 PSIG
• B. 150 PSIG
• C. 100 PSIG
• D. 60 PSIG

Answer: (A)

Vital air is a dedicated, independent pneumatic supply kept at a fixed pressure to ensure reliable operation of critical, emergency, or safety-related pneumatic devices even if the main air system is down. The pressure is set at 125 PSIG because that level provides enough driving force to actuate valves, starters, and other control components across the aircraft’s operating conditions, without over-stressing the hardware. If the pressure were significantly higher, components could be exposed to unnecessary stress or leakage paths; if it were lower, actuators might not respond promptly or reliably during start, shutdown, or emergency actions. In short, 125 PSIG is chosen to balance dependable actuation with system tolerances, which is why it’s the specified value.