Pneumatics

Question 1

What valves will open if the power is low and the bleed air is turned on?

Answer 1

Nacelle Shutoff Valves (NSOV)

Question 2

What pressure air is supplied to the air conditioning system, with the bleeds on, and a low power setting?

Answer 2

At low power settings, bleed air comes from the High Pressure port (HP).

Question 3

What pressure is supplied to the air conditioning system with the bleeds on, and a high power setting?

Answer 3

At high power settings (T/O, climb, cruise), it comes from the Low Pressure port (LP).

Question 4

What will cause a bleed hot caution light to illuminate?

Answer 4

1. Bleed Air Overtemperature
2. Bleed Overpressure
3. Bleed leak condition is detected

Question 5

What will happen if a BLEED HOT caution light illuminates?

Answer 5

The ECU shuts off bleed air by closing the related:

• HPSOV
• Nacelle shut-off valve
• P 2.2 shut-off valve

The related BLEED HOT caution light will remain illuminated even if the condition clears itself.

The HPSOV can be opened again by signal from the HP pressure switch, in order to provide sufficient pressure to the de-Icing system.

The over temperature switch in the bleed supply duct, downstream of the High Stage Precooler monitors the temperature of the bleed air just prior to the NSOV.

If it senses a bleed air temperature that is too high, it signals the ECU (electronic control unit) to close the NSOV until the temperature returns to normal. Results in the #1,2 BLEED HOT caution light.

Question 6

Can the engine bleed air and APU bleed air be used at the same time?

Answer 6

No, both engine bleed switches must be set to OFF before the APU bleed switch will provide bleed air-conditioning.