Which pressure source is used to hold the 5th and 10th stage bleed air control valves closed during water wash or fire stop?

Which pressure source is used to hold the 5th and 10th stage bleed air control valves closed during water wash or fire stop?

• A. LP air
• B. HP air
• C. Vacuum line
• D. Atmospheric pressure

Answer: (A)

Holding the 5th and 10th stage bleed air control valves closed during water wash or fire stop is done with a small pneumatic actuator that uses low‑pressure air to keep the valve in the closed position. This LP air source provides just the right, controlled force to overcome any spring or detent and to maintain isolation of the bleed air passages during maintenance. Using high‑pressure air isn’t necessary here and could affect other systems, while a vacuum line or atmospheric pressure can’t provide the directional force needed to reliably keep the valve closed.

Holding the 5th and 10th stage bleed air control valves closed during water wash or fire stop is done with a small pneumatic actuator that uses low‑pressure air to keep the valve in the closed position. This LP air source provides just the right, controlled force to overcome any spring or detent and to maintain isolation of the bleed air passages during maintenance. Using high‑pressure air isn’t necessary here and could affect other systems, while a vacuum line or atmospheric pressure can’t provide the directional force needed to reliably keep the valve closed.