Discussion: Compass bubble woe

I have a box full of compasses that have disruptive bubbles even in warm weather. Most of our club maps are at 7000 feet elevation or higher, so I would really appreciate recommendations for brands of compass that are not prone to bubbles at high altitude.

Past discussions on AP reflect the view that Moscow compasses are infamous for bubbles, and Silva compasses often have problems too.

Is a bubble sufficient reason to return the compass for a replacement?

my compass usually develops a bubble in CO and WY but it goes away at lower altitudes. I haven't noticed where the bubble affects the compass.

Maybe I should just place an order with the understanding I will be picking through the compasses and returning the ones that make bubbles up here. I understand they are okay at lower elevation, but this is a chronic problem for us. Hm. I should talk to local sellers of compasses about how they deal with this...

The bubble can interfere with orienting by causing the needle to stick temporarily.

I talked to a local seller. He says bubbles are a constant problem in compasses, no matter what brand he orders. He tries to "fix" them, meaning he lets them warm up indoors at the shop. If the bubble goes away he sells the compass at full price; else he sells it as a second.

Ed Hicks (Orienteering Unlimited) and Gale Teschendorf (Go Orienteering) sent me a selection of Silva blank face compasses just in time for Christmas. (Thank you guys, you are awesome!)


Micro Racer: the simplest, smallest thumb compass, wearable on either hand. Great for kids and adults with small hands.


Mapguide a clip type compass, ideal for use on map boards. Just the thing for any course setting, MTB, and Ski O.


Norcompass a large thumb compass with a really big, steady, easy to read needle. This would be my favorite except it is big for my hand and seems to be available only in a left hand model. I hold the map in my right hand.

Most of the compasses arrived here (7300 feet elevation and winter) with small bubbles. About half reabsorbed their bubble after 24 hours indoors. None had a bubble when shipped to me. I wonder if compasses would bubble less if packed inside an airtight glass or metal jar, or shipped by ground, not air service.

Here's a couple old compass bubble threads:

Bubble in Moscow compass

Repairing a Silva thumb compass

What exactly is the mechanism here? I can think of two possibilities:

1. Mismatch in thermal expansion coefficients between the plastic and the fluid.
2. Dissolved gases in the fluid near sea level when it's encapsulated that bubble out like CO2 in beer when the pressure is reduced at altitude.

So maybe it would help for manufacturers to pull a vacuum on their fluid prior to encapsulation. Maybe they need to look at making the capsules more or less stiff so any change in the volume of the fluid due to temperature is accomodated rather than allowed to pull a slight vacuum on the fluid (which I assume results in a bubble).

There might be some long-term size changes with the plastic or loss of volatiles in the fluid through the plastic.

Some sort of compliant foam or rubber mounted inside the capsule might allow some fluid volume change, but that might require the fluid to be under some slight pressure at manufacture.

Seem reasonable? Any other ideas?

All good ideas. I like prevention far more than after-the-fact repairs involving piercing the capsule to draw off bubbles.

If drawing off a bubble is the way to go, though, then the capsule should be manufactured with a built-in, self-sealing septum through which a syringe can be inserted.

Other ideas, in use among compass manufacturers, include using a fluid with properties that make it less prone to cavitation (if that is the correct term to use here?).

At sea level the few bubbles I've experienced from cold disappear & stay away as long as no prolonged cold exposure - "prolonged" might be a ski O experience. They're infrequent. I don't recall a bubble problem with the compass I used for mapping over the winter '06-7 in NH. A fluid w/ properties less prone to contract/expand seems like a promising avenue to search but probably has. Gnarly, obnoxious problem that the mfgrs. need to solve! or you might move to sea level to avoid frustration...:-).

include using a fluid with properties that make it less prone to cavitation

At a wild guess, I'd say it's a trade-off between the properties that encourage formation of bubbles (cavitation isn't the right word, but the idea's there) and the properties that impede free movement of the needle. Lighter, less viscous liquids might expand/contract more in reaction to temperature changes....it makes sense to me, anyway. :)