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Bob,
I'm a little surprised here. The deformation of the door is limited by the latches, which carry a rather large load. That deformation has a relatively fixed limit. The proper question then is not whether 12 PSI will seal the gap. The proper question is whether the rubber in the seal will allow sufficient expansion to cover the space.
LaPlace's law states that Tension equals Pressure times Radius. Thus, as the gap increases, the seal will tend to grow to fill it, and its wall tension will increase, making the seal more effective. Obviously, this would imply the nonsensical conclusion that we should make the gaps very large.
If the gaps became very large, the rubber in the seal would reach its failure point and the seal would rupture. But within the limits created by the latches and pressure-induced door deformation, this should not be an issue. Neither should we concern ourselves with the seal failing to hold against cabin pressure. Regardless of the area of seal exposed, its internal pressure is 12 PSI acting against 5.5PSI in the cabin. It's no contest. The seal wins.
Seal failure comes when the surfaces are irregular and do not allow a seal, or if the seal ruptures due to overexpansion or material aging.
Ted Noel
----- Original Message ----- From: "Robert Pastusek" <rpastusek@htii.com>
To: <lml@lancaironline.net>
Sent: Monday, February 02, 2009 3:16 PM
Subject: [LML] Re: Door Seal Test
Ed,
I'd be surprised if 12 psi will hold the door seal under a pressurized
cockpit. My experience was that it tended to "lift away" from the door frame
at lower pressures, allowing an air gap that limited the differential I
could maintain. I still haven't verified that I'm getting the full 5.5 PSI
differential the system is supposed to produce. ...really need to get that
big jack hammer compressor hooked up to my snout to test it all out...
BOB
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