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To:  lml@lancaironline.net
Date: Tue, 03 Feb 2009 15:56:55 -0500
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From: "Ted Noel" <tednoel@cfl.rr.com>
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Subject: Re: [LML] Re: Door Seal Test
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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
>