Is it normal for a compass to develop an air bubble at high altitude?

Question

I live in Denver, Colorado. Going above 10,000 ft. (3,000 metre) always results in an air bubble large enough for me to want to tilt the compass to prevent the bubble from interfering with the needle. Is that normal behavior for a compass?

I contacted the manufacturer (Brunton) which responded: "Extremely high elevations can cause temporary air bubbles to occur (also very cold temps can do that), so I wouldn’t be surprised if you see that with any liquid filled compass." Brunton kindly offered to replace my unit. I will measure the size of the bubble. If it does not exceed 1/4" there is no point in seeking a replacement.

Answer 1

I wouldn't call it normal, but it does happen and if the bubble is large enough it will effect your accuracy. In that case you may want to purchase a new one or if possible send it back to the manufacturer.

From Silva's FAQ page

We intend that our compasses are free of bubbles; however, if a small bubble forms in the liquid-filled capsule, it has no influence on the accuracy of the compass. Its appearance and disappearance are due to changes in temperature and atmospheric pressure.

If a bubble larger than 1/4" in diameter appears, it is probably the result of a leaking capsule, usually caused by some form of shock damage, and the capsule will have to be replaced. In that case, just call our customer satisfaction department for a return authorization number and shipping address.

I have had this happen to one of my compasses, and it seems to happen more frequently to the cheaper versions.

Answer 2

I have observed the same thing with compasses as well as level gauges.

I'd say that it's normal unless it is hampering the accuracy beyond an acceptable degree of error. That regular small bubble is left in order to prevent the outer casing from breaking when the liquid expands when it gets heated. Liquids are not compressible, so that air bubble which is compressible, provides an additional volume in the casing for accommodating the liquid when it is expanded.

Go to higher and/or colder regions you'll find that that air bubble has gotten bigger. Heat/Warm it up a bit and the bubble should get smaller as compared to that when colder.