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Old December 28th, 2008, 02:22 PM   #1
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Peli cases and pressure valve

Hi There.

I have a vague memory of the reason for having a pressure valve on cases like the armoured Peli cases. It was something with condensation if you forgot to loosen tha valve on earlier models of Peli cases. But can anybody put my memory right?

I mean if the case is 100% air thight and strong enough to handle the difference between 6000 ft cabin pressure and sea level, then there should mot be any problems in forgetting the valve - or am I mistaken?

Kind regards
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Old December 28th, 2008, 02:31 PM   #2
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I thought it was for air travel to stop the pressure building up in the case in the hold?
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Old December 28th, 2008, 02:49 PM   #3
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simply, if you close an airtight case at a different altitude than you will open it, there is a risk that you are unable to open it.
people leaving high altitude place and going at sea level for holiday would be surprised because the difference of pressure would not allow them top open the case (and the more you try, the more it is difficult, physic 101).
the same with a trip in a low pressurized plane or in case of big difference of air temperature.
Never been trapped by a pickle jar ?
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Old December 28th, 2008, 03:48 PM   #4
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Thanks for the replys.

But if I close the valve at sealevel, then takes an air trip, lands at sea level again, then every thing ought to be OK. If I land at a higher altitude, then the higher pressure in the case will just help me open the case if the difference in pressure is not too great. But if i remember correctly then the the pressure drop will give condensation in the equipments as higher pressure air can contain more humidity?

The cabin pressure is approx 8 psi or nearly half the pressure at sea level if my memory serves.

If the the lid on the case is 20 square inches then the total pressure would be 20*8=160 pounds on the lid at cabin pressure. At sea level it would be 20*15=300 punds. But is this correct? Looks like a Pelicase in a airplane cabin could be a security risk if the auto valve malfunctions, and somebody wants a situation shot in the cabin.

Hmmm
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Old December 28th, 2008, 03:55 PM   #5
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Have to admit, I've taken Peli cases all over the world in planes and never touched the valve.
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Old December 28th, 2008, 04:18 PM   #6
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because the valve is here to be not touched, it should act automatically and let air goes in the right direction to get equilibrium.
there is a manual position usual, to force it when things go wrong.
I doubt that the valve can act on condensation effectively.
temperature act a lot more on condensation than pressure.
I doubt any regular pressure encountered by a pelican case could make any damage to it.
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Old December 28th, 2008, 04:20 PM   #7
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Thanks Grioud, are you an air pressure valve engineer, or did you just read the instruction manual!
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Old December 28th, 2008, 05:23 PM   #8
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well the new ones has an automatic valve, but the older ones does not. But maybe the automatic valve was used due to "exploding" cases in mid flight?

The best
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Old December 28th, 2008, 07:07 PM   #9
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Quote:
Originally Posted by Jos Svendsen View Post
Thanks for the replys.

But if I close the valve at sealevel, then takes an air trip, lands at sea level again, then every thing ought to be OK.
No - if you leave somewhere at sea level during a heavy depression and arrive elsewhere that is under a high pressure then there will be a negative pressure differential between the inside of the case and the outside. This difference can be quite substantial - the typical range for atmospheric pressure at sea level is 970 to 1040 millibar.

Leaving Northern Europe and heading for sunnier climes is a common example(!)
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