Originally Posted by
NSEU
So you understand that the negative pressure relief valves will not assist depressurisation in a pack off descent?
Pack leakage? I guess you could say it leaks 100% into the cabin/cargo/cockpit areas. There are water drains for the water separators, but since the packs are off in your scenario, check valves should retain pressure.
Other sources: Toilet flushes (not likely during an emergency descent), drain mast outflows, faulty door seals, door sill drains.
In the scenario, X=0 (packs off) and let’s simplify with a perfectly closed outflow valve Y=0, as you mentioned the drains and other leaks, so as long as Pcabin >Pstatic, we should have some leakage, plus the opening of the Negative relief valve when
Pcabin-Pstatic > 1PSI
Do the drain check valves work both ways : positive (usual pressurization) or negative dP ?
I am not sure what you mean in your first sentence, as it is not a normal depressurization scenario where dP=0 from the trigger event.
Let me illustrate: you seal a bottle at altitude and come back down. When you open the bottle at sea level air will flow inside the bottle.
Now the bottle is a complex aluminium structure which happens to be a 737-800 fuselage with all openings (and outflow valve) closed, but Safety and negative pressure relief valve working properly.
Coming back at lower altitude Pstatic rises while Pcabin stays constant at a lower pressure.
Would we reach a point in a normal dynamic situation (timescale minutes) where differential pressure exceeds the rating of the negative pressure relief valve and attains -1.45 PSI difference, for several minutes?