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carnival30

4th May 2018 09:11

B738 cabin differential pressure exceeding limits

Hello,

FCOM says two pressure relief valves limits cabin pressure difference from exceeding 9.1 psi. So when cabin pressure difference nears/exceeds 9.1, these relief valves open? What will be the position of outflow valve at the time?

Highway1

5th May 2018 00:00

It doesnt matter. In theory for the diff px to get that high the outflow valve would be closed but it could be fully open and blocked by debris. The positive px relief valves are totally independent of the rest to the pressurization system so will respond irrespective of what is happening in the rest of the system.

vapilot2004

5th May 2018 08:59

Plenty of good information on the over-press and negative pressure valves in this recent Tech Log thread:

Diff between Outflow valves and Positive/Negative Pressure valves?

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