Compass Bubbles in Cold Weather

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big_load
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Compass Bubbles in Cold Weather

Post by big_load » Jan 26 2004 5:11 pm

Has anyone experienced bubbles in a compass capsule?

My backup, an older Silva baseplate Type 3 had a tiny bubble in it last week just after I returned from snowshoeing in in single-digit temps. Saturday I looked again when I was X-C skiing (again in single digits) and noticed that the bubble was much larger. It shrank and disappeared as it warmed between my hands later on. There is no sign of it at room temperature.

I suspect the fluid contracts in the cold, leaving a vacuum, or causing much smaller air bubbles to come out of solution and aggregate. If the bubble got much bigger, it could affect the needle's swing. However, since it is very light in comparison, the bubble tends to run away when the needle approaches.

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rk
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Could it be altitude?

Post by rk » Jan 30 2004 12:51 pm

The only time I have ever experienced this with my compass is at altitude. It is the same principle that causes the bends in scuba divers. A decrease in ambient pressure causes gases that are normally disolved in the liquid to form bubbles. When I return to lower elvation, the bubble disappears.

Could this explain what is happening in your case?

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stsimmer
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Post by stsimmer » Jan 30 2004 12:56 pm

Were you also at a higher elevation? Both cold and elevation can cause bubbles in liquid filled compasses. I have had a Silva Ranger for 30 years. Bubbles have come and gone. The bubble should not have an effect on the needle. The liquid just serves to dampen the needle's motion, but does not affect the needle's magnetic attraction.

If the bubble does not go away, you can contact Silva. They have a reputation for standing by their product (if they are even still in business!).

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big_load
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Post by big_load » Jan 30 2004 2:52 pm

I'm not at significant elevation (home is just under 900', skiing/snowshoeing about 1600'). However, the presence of dissolved air under nominal ambient conditions would certainly contribute to bubbles at altitude as well as in the cold. One factor I hadn't considered before was thermal contraction of the plastic (not just the fluid).

My only complaint is that the bubble is visually distracting, especially since its mobility increases when I hold the compass close to level. I recognize that it's a silly thing to contemplate when I should be more concerned about frostbite while standing in the freezing wind with my mitten off wondering where this bubble came from. I only use my Ranger at altitude and haven't noticed any bubbles in it, but then I was probably distracted by the waggling clinometer needle.

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