We all have leaky cabins.  It is just a matter of degree.  

My cabin maintains full cabin pressure at 16000' (simply for example) down to 24" MAP, but not in the flight levels.  At FL240, it is less compliant with a more rapid drop and slower recovery (degrading at 28" MAP).  

My Duke's valve is set for a slow climb (regardless of actual altitude) to avoid ear pops.  A faster Duke's response rate/setting would prevent a rapid decompression with big throttle pull (heading to lower MAP).

After a successful climb to flight levels, at FL240 level cruise, with cabin differential 5.0 psi (and stable), 34" MAP (or 31" MAP) on the throttle:  if you pull back to 28" MAP, who among us will maintain a steady 5.0 psi differential?  Or will your cabin climb (maybe above 12.5K') with the throttle pull?  And at 28" MAP, how long will it take to restore a 5 psi differential at FL 240 after some additional Duke's Valve outflow restriction (based on rate setting)?  Will your spouse's ears pop, and will she ask about the pressurization concern?

A reduction from 36.5" MAP (full power ) to 28" MAP (a 8.5" or 3 psi drop in siphoning of MAP for cabin), who does not experience a reduced cabin differential?

Likewise, if you set the cabin rate high (to avoid this rapid drop at Flight Level cruise), would you not also experience a rapid pressurization during your take off role, when the MAP rises from 10" to 38.5" inside of a few seconds, and the Duke's setting allows a rapid cabin change?  Perhaps the cabin altitude setting (airport elevation) prevents this.  Perhaps I need to change from a slow climb to a rapid climb rate.

Jeff




you probably have a leaky cabin

>If I quickly reduced MAP to 31", and particularly to 28" MAP, the cabin altitude
>would quickly climb to >14,000' and the Duke's regulator would take several minutes
>to equilibrate.  And even then, it might not be able to restore 5.0 psi
>differential (at 28" MAP).  So, all this talk of lower MAP