Discussion: Bubble in Moscow compass

Today, I went out for field check. I noticed my moscow compass has a bubble in it. It apparently leak somewhere but couldn't find. Strange, the bubble disappeared when it brought inside home. Does it effect
with chilly weather? It was around in the 40's.

Sounds like pretty typical behavior for a Moscow. The biggest problem with that brand (maybe the only problem) is the propensity to develop bubbles. I've had for or five of them, I think, and only two are still usable. The bubbles do disappear sometimes if they're small, which is good, but once they get bigger, they stay. Try taking one up to Wyoming and you'll almost certainly get a bubble. It does seem to be a temperature/pressure phenomenon, but I can't say that I understand the physics of what's happening.

Liquids absorbs more gases when cold, so I don't think that's a good explanation. Was there a change in the barometric pressure? Were you at a higher altitude when outside?

It happens in either high altitude or low temperature. My biggest problem is with my Silva wrist compass that's now over 20 years old. When I take it out in cold weather it develops a nice big bubble. Back inside in the warmth and the bubble goes away entirely. It's done this ever since it was new. There is no leak. Unfortunately, I bought it for ski-O. :-(

I've heard a scientific explanation for this phenomenon but I never bothered to remember it.

Both of my Moscows get small bubbles if I leave them in the sun (say, on a car dashboard), take them to altitude like jj said, or if the barometric pressure changes dramatically. Never noticed any problem with cold, but that may be a selection effect. The bubbles have always gone away after a while - even at altitude. I try not to let the compass sit in direct sunlight for this reason.

I have a bunch of Moscow compasses with bubbles. (I also have an Arrow and a Nexus with bubbles, but they're older; Moscows are the most bubble prone.) Once a Moscow compass develops a bubble, the bubble always gets bigger when taken outside in cold weather, then smaller again (or even disappears) when brought inside and put where it's warm. When I have to use a compass with a bubble in cold weather, I put the compass over the defrost heating vent of the car on the way to the meet and the bubble is gone when I arrive and begin orienteering. Then it continually grows as the race progresses. Which can make trouble by the end. A large enough bubble, of course, can seriously affect the settling speed and accuracy of the compass.

I don't know what to say, from a physics perspective, gases should become more soluble when cold...

The only idea that comes to mind is some sort of chemical reaction in dynamic equilibrium, which is exothermic in the direction of the gas formation.

Certain people have suggested that compass fluid is related to kerosene or some other organic compound.

Ok, mystery solved.

If the liquid contracts more than the housing due to a drop in temperature, then the pressure inside the housing drops, and the gas comes out of the liquid.

It seems the liquid can turn to age to cause the bubbles. Didn't have that kind of problems when it was new. I believe the compass is only about 1 and half years old. Interesting.......

Wow! Thanks mindsweeper, for getting up so early Sunday morning to locate this informative link. Obviously some people are giving this problem a lot of thought.

So your second citation nullifies the suggestion in your first citation...which I can remember trying unsuccessfully myself, back in 1996:

The IR spectrum of compass fluid closely resembles kerosene.
When the compass becomes unusable, I sometimes have had success by creating a small hole with a syringe, filling the compass with kerosene and sealing the hole with epoxy glue.

Knowing mindsweeper, my guess is that he hadn't yet got to bed on Saturday night in California.

I can understand the issue for bubble formation in low temperature, assuming the capsule is rigid, and it doesn't even have to be dissolved gases, it could be the liquid itself turning into vapor if the decrease in volume results in the pressure of the liquid getting below the vapor pressure of the liquid. But if the capsule is rigid, then I don't understand how taking the compass to altitude causes a bubble. Unless the capsule is resistant to getting smaller, but is compliant in terms of getting bigger, which I suppose is at least remotely possible.

A side note - I was under the impression putting compasses on the dashboards of cars was risky since car radios have magnets in them that could affect the needle. Anyone car to say whether this is true, nonsense, true once upon a time but radios have changed...?

Yeah, the speakers have small magnets in them. But with the demise of vacuum-tube radios with their big, hot cathodes drawing lots of current, I don't think solid-state digital radios generate measurable magnetic fields.

Most modern cars don't have either the speakers or the radio itself anywhere near the top of the dashboard.

I will note that I know of few compasses that have developed magnet problems. The only one of mine that ever did (magnet reversed) might have happened when the compass was in the glove compartment of my car, but I doubt it had anything to do with the radio.

Bubble in my compass after running the chilly Traverse today — let's see if it goes away after being indoors for a while.

Ditto. One of my two good Moscow compasses that had never developed a bubble got one today, pretty good sized, while doing the Traverse with temp in the 20's. It's much smaller now, six hours later, but not entirely gone. Unfortunately, I've found that once you get a bubble in a compass - either from cold or from altitude - it tends to keep recurring. This may be it for me with Moscow compasses (which I otherwise quite like).

I've had several bubbles go away temporarily (long-term temporarily) when exposed to the heat of my trunk in the summertime.

It is definitely possible to apply too much heat. I've seen a compass left in the hot sun inside a car, and it was toast.

I've heard guesses that the fluid is Stoddard Solvent (which smells like kerosene).

I've seen several peoples' attempts to drill, fill, and reseal compass capsules, and I've never seen any that seemed to be permanent. Does anyone know how the manufacturing process does it? The difficulty of a repair seems to be that the glue/epoxy/sealer doesn't stick to the fluid-wetted surface very well. Perhaps it's possible to find a sealer that works with the fluid, or to degrease the hole before sealing and then filling it very carefully so it doesn't contaminate the surfaces. It might be worthwhile to consider trying to do the operation in specific temperatures, or even differential temperatures (plastic v. fluid), or while pulling a little vacuum on the system to deaerate the fluid. One of my ideas was hot glue, although I see that I'd have to use the low setting on my glue gun because the high temperature would exceed the initial boiling point of the fluid (assuming it's Stoddard Solvent). Another idea would be to try to find a glue/epoxy/sealer that will float on the fluid. It might be possible to apply it gently enough to not mix into the fluid. What do Dentists use that hardens under UV?

I won't be worrying for the time being. I only have two with bubbles right now. The bubbles will have to get bigger before I start thinking too hard about a repair process. (Although---I do have two old compasses with no fluid, including a Silva with an aluminum bezel. Hmmmm.)

Wierd, I've had Moscow Compasses for many many years and not one has developed a bubble. Not even when weather, altitude and whatnot change... Maybe mine are aclimatized to altitude?

My Moscow developed a bubble this fall when the temp was -2 celsius. The bubble disappeared when the temp warmed up, but it was very annoying. The needle seemed to bounce off the bubble and not did not track nearly as fast or accurately. You would think that hailing a cold climate, this company would have the low temperature problem solved. And the bad part is that where I live, -2 celsius is not *NOT* really that cold.

I have seen that happen in my compass when I take it on an airplane - so I agree w/ those who think pressure change is the answer. The bubble goes away after landing.

My brunton doesn't have a bubble. It's gone milky. Now, there may actually be milk in it as I found it in my kitchen sink (courtesy of one of my kids I guess) and milk, among other things, may have been dumped on it. Or maybe it's done it on its own. But I thought they were supposed to be sealed????

What's the scientific explanation for that assumng it is actually a seald unit?

I got bubble in Bruunton thumb compas at CNYO Turkey Trot. It's semi-new - about 1 1/2 years old. I checked for bubble yesterday and it was gone.

cedarcreek has it that, "I won't be worrying for the time being. I only have two with bubbles right now. The bubbles will have to get bigger before I start thinking too hard about a repair process. (Although---I do have two old compasses with no fluid, including a Silva with an aluminum bezel. Hmmmm.)"

You know you're an orienteer when owning two completely non-functional compasses and two more which have developed troubling symptoms of trouble to come doesn't mean you ought to start thinking about how to repair any of them to ensure you'll have a functioning compass when needed. Though perhaps the simple fact of owning four compasses is enough evidence.

I think he has four defective compasses. He hasn't mentioned how many good compasses he has.

Normally I would just say I have no comment about how many compasses I own. But I want to caution against starting to talk about how many compasses we own.

Nothing good can come of it.

If, for example, I have more than you, then you're going to think it's okay to buy more.

If, for example, you have more than me, then I'm going to think it's okay to buy more.

We'll start buying compasses, and the prices will go up. The older, more codgerly types will have bumper stickers printed that say, "1 God, 1 Country, 1 Compass". Worse, they'll make fun of us compass-hoarders.

Compass futures will skyrocket, and then the manufacturers will spool up production; but the market will be glutted, and we'll all be poor because we've spent too much on compasses; and then the manufacturers will go bankrupt and the secrets of fine compass manufacture will be lost.

And then it'll be chaos.

I certainly don't want that to happen.

I would think that when someone has a bumper sticker that says "1 God, 1 Country, 1 Compass". they are referring to their moral compass...

"My brunton doesn't have a bubble. It's gone milky"

I've had a Silva that did that too. Dunno why though... It may have been left in the sun for too long and the glue around the middle of the needle may have started to dissolve (but I'm guessing. I haven't even looked at a compass for nearly six months...)

I am now on my third Moscow thumb compass with a bubble. All of them have first shown up at the Possum Trot. I think a reasonable scientific explanation is a Possum allergy.

I think I will be looking at a new brand at this point

Yesterday, I was orienteering with same compass that show bubble couple weeks ago. It show no bubble this time at Patapsco state park in Elkridge, MD with damp and chilly weather. I will go back to Wheaton Regional park to see if the bubble will come up or not. Will let you know the result.

>> I haven't even looked at a compass for nearly six months...)

AHA!!! I hardly use mine, too. They're dying of neglect. Or that glue thing.