Re: Equalizing the pressure in a sealed box

On Sun, 14 Dec 2008 18:08:20 +0000, John Devereux <john@xxxxxxxxxxxxxx>
wrote:

Archimedes' Lever <OneBigLever@xxxxxxxxxxxxxxxxxx> writes:

On Sun, 14 Dec 2008 13:46:24 +0000, John Devereux <john@xxxxxxxxxxxxxx>
wrote:

Archimedes' Lever <OneBigLever@xxxxxxxxxxxxxxxxxx> writes:

On Sat, 13 Dec 2008 16:43:04 +0000, John Devereux <john@xxxxxxxxxxxxxx>
wrote:

Hi,

We have an IP67 box with a membrane front panel with window. At
temperature extremes the air inside will change pressure, up to ~0.3
bar - enough to cause significant bowing of the window and probably
enough to break the adhesive seal.

I would have thought this is a common problem - is there some kind of
low cost pressure equalization/relief valve that can be fitted in the
wall of the box?

Thanks,


Depends on the box size. There are those 1.5 inch diameter military
chassis relief valves in use on gear everywhere...

They are not small footprint items, there has to be clearance inside
the box. They have a small, manual operation button on them about 2.5mm
diameter in the center of the vent on the outside as well.

So, 1.5" x 2" with about .25" to .375" of that on the outside.

Thanks, those would be too big for us though. But it looks like there
are smaller versions, as well as the "gore-tex" based solutions. The
membrane under the lid idea in fact looks do-able too, and could also
keep out water vapour.

Place the internal assembly in a clear ESD bag and remove practically
all the air from it, then there will not be much 'air' to regulate, and
the bezel/touchpad should remain as intentionally fixtured.

Sorry, I don't quite follow what you mean here.


An ESD bag because that keep static generating devices away from your
circuitry. A clear ESD bag, because they make them now.

Remove the air from it after you place your assembly in it, add a
desiccant bag, then seal it. What little air that remains will not
expand much. A test would be to simulate the pressure at 70,000 ft and
see how far the bag bloats, if at all. Place that assembly inside your
box, along with your desiccant bag. Your pressure sensitivities should
be dispersed.
.

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