Re: Compass with air inside

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Posted by Ian on February 10, 2007 at 08:53:32:

In Reply to: Compass with air inside posted by Jeff Shaw on February 09, 2007 at 21:42:54:

Compasses are usually filled with air, water, alcohol or mineral oil. The "filling" does NOT indicate the quality of the compass (I have a very expensive Brunton Pocket Transit - professional survey gear - that is air filled that is a superb instrument costing well over $200). I do not know of any compasses that are "refillable" by the user.

The point in filling the compass with a liquid is to dampen the swing of the magnetic needle. A happy side effect for diving is that the liquids are not compressible and liquid filled compasses are, therefore, suitable for diving. I have seen "cheapo" compasses where all the filling has leaked out and the remaining bit has hardened enough to prevent the needle from moving. If this is the case, all you have left is trash.

On the other hand, if the needle still moves, you still have a working compass, even if some of the damping liquid has leaked out. I have a Suunto Pocket Ranger I bought in England the summer I was 16 (now almost 49) that began to leak a few years ago, but it still tells me where north is! The only problems when diving would be; 1) the liquid leaking into the UW environment, 2) is the air bubble is sufficiently large enough, compression of the compass housing sufficient to stop movement of the needle, and 3) sufficient compression at depth to implode the compass housing.

Having said that, as Chuck says, get yourself a GOOD compass. Quit wasting your money buying cheap ones and invest in a good one. If you added up how much you paid for your four leakers, could you have bought a really good compass instead? (Thatís the lesson here!)

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