# Altimeter vent holes

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#### bigdog

##### Member
When using 2 altimeters,both mounted in same payload bay(1 for primary ejection, 1 for backup charges). How many vent holes are needed? Example each requires a 1/4"hole. Would a 1/4" vent hole be needed for each altimeter or would 1 hole be sufficient in the bay for both to function?

I can't imagine that having two altimeters in the same bay would change the number of vent holes that either one needs, unless the "free" volume of the altimeter bay determines how many vent holes are needed.

So... I'd say you use the same number of vent holes that a single altimeter needs.

The calculation is based on the volume of your altimeter bay, so if you packed two altimeters in the same bay it would be the same. Another thing to think about is splitting that one hole up into three holes with equal area. I have found this to help out on getting deployment right at apogee and letting the bay 's pressure change faster to ambient pressure.

Edward

Originally posted by edwardw
The calculation is based on the volume of your altimeter bay,

Somewhere there is a calculator / program that figures the size of the vents holes needed for the size of the electronics bay.

Originally posted by edwardw
Another thing to think about is splitting that one hole up into three holes with equal area. I have found this to help out on getting deployment right at apogee and letting the bay 's pressure change faster to ambient pressure.

I use 4 vent holes on my electronics bays.

Thanks guys appreciate the info.

URGENT!!! if you use 3 or 4 vent holes make sure you do this to find out there size. Say you need a 1/4 vent hole. First convert that to area then divide by 3 or 4 and then convert back to diameter. If you take just the diameter and divide it by the needed vent holes they will be about 50% to small!!!

Originally posted by jraice
URGENT!!! if you use 3 or 4 vent holes make sure you do this to find out there size. Say you need a 1/4 vent hole. First convert that to area then divide by 3 or 4 and then convert back to diameter. If you take just the diameter and divide it by the needed vent holes they will be about 50% to small!!!

That's a really good point. It's just the kind of mistake I make when I get in a hurry. In fact I have. Luckily they're too small, not too big, and the drill is still sitting next to it. Thanks.

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