Sign in to follow this  
Followers 1
leatherman

Do all liquid filled compasses develop air bubbles?

27 posts in this topic

I bought a Brunton Eclipse compass at REI, a year ago. I opened it today at a cache and found a bubble in it.

I thought only cheap compasses developed bubbles. Good compasses are supposed to have low gas liquid in them, aren't they?! It was $85, so I thought it was an upper end compass. Oh well.

 

REI is great. After a year, without a receipt, they exchanged it. No questions.

 

39197_2100.gif

Do not extend your expectations unto others, you will not be disappointed by the stupid things they do.

Mokita!

0

Share this post


Link to post

My impression of this situation is that it's normal. There is supposed to be a small bubble to prevent the case from breaking when the liquid expands when it is heated. Liquids are considered incompressible; the air bubble is a buffer of sorts as air is very compressible. It was cold here in WA today, thus the air bubble will have gotten bigger. In the summer the bubble will be very small and not as noticeable.

 

http://fp1.centurytel.net/Criminal_Page/

0

Share this post


Link to post

I second the motion that REI is great. I buy from them whenever I can. Also, I feel your pain regarding your compass. I also had a Brunton (not an $80 one though) that developed an air bubble whenever I was over 4000 feet. That really sucked because the bubble interfered with the needle movement. I got rid of it and bought a Silva Trekker. It hasn't developed a bubble and I've used it for about two years now. Any compass that develops a bubble is defective in my opinion.

 

"Wise men talk because they have something to say. Fools talk because they have to say something."

-- Plato

0

Share this post


Link to post

Exactly

quote:
Originally posted by Geo Quest:

Any compass that develops a bubble is defective in my opinion.


Once a bubble starts, it only gets bigger. A compass should work at any altitude and any temperature, without developing a bubble. Why would a company make compasses that self-destruct in a years time?

Criminal

As for buying it with a bubble, preventing breakage, I've never bought a compass with a bubble.

I've never seen a Military compass with a bubble, unless it was broken. Am I expecting too much? Am I a sheltered military Brat?

 

39197_2100.gif

Do not extend your expectations unto others, you will not be disappointed by the stupid things they do.

Mokita!

0

Share this post


Link to post

I think I've read about this before somewhere on a compass site. As long as the bubble goes away on descent it is normal. Anyway I use to carry cheap silva compasses up to 10,000' on Rainier. They'd develop a bubble which didnot go away when you descended. Thus the seal leaked under pressure and liquid was lost. I then took my Brunton eclipse to 10,000' and it also developed a bubble, and I thought "darn"! But when I desended the bubble disappeared. This is good because the seal has held. At least this is how I recall it, but I could not tell you the physics involved. It doesn't seem like you should see a bubble at altitude.

What is interesting is to take a small package of Dorittos up there. The higher you climb, the fatter the package gets, until it finally explodes, POP!

 

4497_300.jpg

0

Share this post


Link to post

From Silva:Bubbles

''At altitude (above 500 to 1000 meters) bubbles may form in the fluid. The cause is a drop in atmospheric pressure and/or low temperature. This can occur in any compass. The bubble will disappear, when normal conditions return.

Obviously, air can get into the fluid through crack damage in the capsule. A hairline crack damage in the surface of the capsule may not cause a leak to occur for weeks or even months. Such damage is not covered by warranty.

It is not economically viable, to repair a cracked capsule, but it can be replaced by your SILVA dealer at much less then the the cost of a new compass.''

 

and from a physics prof:

 

Date: Sun Oct 7 12:37:10 2001

Posted By: Gareth Evans, Senior Research Associate

Area of science: Physics

ID: 1001607723.Ph

--------------------------------------------------------------------------------

Message:

 

 

Thanks for an interesting question. The “ideal gas laws” are of course

only approximations but are accurate enough for this purpose. The bubble

is there because the amount of liquid is not sufficient to fill the volume

of the compass chamber and a small amount of gas, probably air, remains to

fill this shortfall.

 

Let’s look at the problem with some boundary conditions which may or may

not apply. Let’s say that the compass structure is absolutely solid and

does not change shape or volume if the outside pressure changes. The

structure provides an infinite resistance to these pressure changes so the

pressure inside the compass is constant. The size of the bubble is

dictated by the amount of liquid used in relation to the volume of the

enclosure in manufacturing process. Under these conditions, as the

compass is taken to a lower pressure environment, because of the rigidity

of the compass, the pressure inside does not change so the bubble gets no

bigger at higher altitudes.

 

Let’s take an extreme opposite case and make the compass out of a soft,

rubbery material with little resistance to forces on it. Now when we

reduce the outside pressure, the compass expands according to the volume

change in the bubble dictated by the well-known relationship between

pressure and volume (Charles’ Law). We are ignoring the liquid’s vapour

and dissolved gas for the moment.

 

It seems then, that the real compass in question does have some

flexibility and can change volume just a little as the outside pressure

changes. As the external pressure is lowered, the internal pressure will

drop by some fraction, probably a relatively small fraction, of the

external pressure drop but this may be sufficient to cause a noticeable

change in the volume of the bubble. We can ignore the very small volume

changes the liquid may experience with the pressure changes involved here

so the absolute bubble volume change will be the same as the volume change

of the chamber.

 

What about the dissolved gas and liquid vapour. A significant fraction of

the gas phase could be the gaseous form of the liquid used. As the

pressure drops and the bubble expands, a little more vapour is produced to

restore the partial vapour pressure. Qualitatively these is no difference

in behaviour from the condition where the liquid is non-volatile. I’d

have to work some more on this to decide whether there was a quantitative

difference but I suspect any effect will be small.

 

The air in the bubble is in equilibrium with air dissolved in the liquid.

The amount dissolved will depend on pressure and as pressure is released,

less gas is dissolved. We are all familiar with the formation of bubbles

when pressure is released from carbonated water such as a can of Coke or a

bottle of champagne. However, with only a relatively small pressure

change in the chamber due to the small volume change, not much air will be

drawn out of the liquid.

 

There are some interesting toys based on the change of a bubble’s volume

with pressure. When I was a child I used to have a bottle with a deep-sea

diver in it. The bottle was filled with water leaving a small volume in

the neck, just a cc or so. If you put your thumb on the opening, sealing

the bottle and then pushed down some more, the trapped air could not

escape and was compressed. The diver had a little balloon in its body (

so I found out years later ! ) and the pressure applied at the top of the

bottle compressed the balloon in the diver. This reduced the volume of

water displaced by the diver by a small amount. The diver was only just

buoyant, normally, so the reduction in volume just tipped the balance and

the diver sank. Removing your thumb made the diver come to the surface

again. Magic !

 

4497_300.jpg

0

Share this post


Link to post

work on a similar concept.

 

Don't even think about putting those muddy boots in my car.

0

Share this post


Link to post

After being exposed to extremely low temperatures several times, my Eclipse also developed a small bubble. It does not affect operation, the disc still moves freely and isn't obstructed in any way, and I can still get perfect readings, so it doesn't bother me. I have heard that Brunton will replace any compass with a permanent bubble if you return it to them, but I haven't done so simply because I haven't felt the need, and don't want to be without my favorite compass that long.

 

--

Scott Johnson (ScottJ)

0

Share this post


Link to post

My Eclipse developed a bubble, they offered to fix it but I needed it that month so I still have it and it still works with the bubble. The bubble goes away when I go to AZ. And returns when I return to the Mtns.

 

If you want to get rid of the bubble here is an idea I've been meaning to try. Put a valve stem on a Mason Jar and increase the air pressure. It should work.

 

Tahosa - Dweller of the Mountain Tops.

0

Share this post


Link to post

Whenever my compass gets really cold it develops a bubble, but it only takes a pocket to bring it back to proper bubble-free operation. I'd assume that the liquid in it contracts more rapidly than the plastic casing, and so the pressure inside decreases until the point where the pressure inside is less than the vapor pressure of the liquid at that temperature.

 

Can someone tell me what the liquid usually is in a $10 map compass? I'd like to look it up in some tables to see what the internal pressure must be to have a vapor bubble at that temperature. Then I could compare that to atmospheric pressure to determine the delta, which would finally tell me how much those bits of plastic can take (at least). Then I can stop being afraid I'll break my wonderful little compass. icon_wink.gif

0

Share this post


Link to post

I have a collection of a dozen or so compasses, and only one silva has ever developed a bubble for me under any circumstances. (It's over 30 years old and only gets a bubble in the cold over 9000 feet.) So far none of my other bruntons, Silvas, or el cheapo's have developed a bubble and most have been used fairly often above 12,000+ feet as I like to climb. I don't get below 4,200 very often, so I'd be kind of upset with anything that got a bubble down that low.

 

For what it's worth

 

Jeff

0

Share this post


Link to post

Quite awhile ago there was a topic on this. Though no clear answer came forth, alcohol in some form appeared to be the most common liquid used.

 

4497_300.jpg

0

Share this post


Link to post

In the liquid compass, the bowl is filled with a liquid, usually a mixture of alcohol and water.

 

_________________________________________________________

On the other hand, you have different fingers.

15777_2200.gif

0

Share this post


Link to post

If anyone doesn't mind answering....I keep my little Silva compass in a pouch with my GPSr and a pocket knife. Will the close proximity of the contents mess the compass up over time?

 

Thanks.

 

-Sushi of the fisherKings

0

Share this post


Link to post

No. I see no reason why it would. Just make sure you have the screen of the GPSr protected from the other object so it doesn't get nicked or scratched.

 

4497_300.jpg

0

Share this post


Link to post

quote:
Originally posted by ClayJar:

 

Can someone tell me what the liquid usually is in a $10 map compass?


 

I've have heard mineral oil is often used.

 

3608_2800.gif

0

Share this post


Link to post

It is usually a light mineral oil. Occasionally they're filled with water, alcohol, or a mixture of the two.

 

Aircraft magnetic compasses used to be filled exclusively with alcohol. To this day, flying a plane without the use of fancy navigational aids is called "Needle 'n' Ball 'n' Alcohol" flying, referring to the turn coordinator and compass.

 

Mineral oil is used now because it's more viscous and is better at damping out motion.

 

--

Scott Johnson (ScottJ)

0

Share this post


Link to post

I have a number of compasses. The Silva's and the K&R's have held up well and haven't developed bubbles. This includes a Silva Ranger Quadrant with a machined aluminum bezel (just to point out how long it's been around). No bubble. I also own a Brunton Eclipse and a Brunton GPS compass. The Eclipse has been back once to have the capsule replaced and it developed a bubble in less than 6 months. The GPS model has also developed a bubble. Any compass can develop a bubble, but some brands appear to be more prone to doing so.

0

Share this post


Link to post

I wonder what the record is for a zombie thread being resurrected. This is over 10 years old!

0

Share this post


Link to post

I wonder what the record is for a zombie thread being resurrected. This is over 10 years old!

 

And much more interesting than most of our new discussions. Well worth the time for a thorough read. Thanks sarboss.

0

Share this post


Link to post

Yes, it is a good subject. Personally, I avoid liquid filled compasses in favour of inert gas filled or at least dry air. Liquid fills always seem to have bubbles and they bug me greatly. I guess the bearings in air filled might degrade a bit, others seem to last well. I use a Suunto right now and don't seem to ever have problems, aside from occasional static electricity in my clothes affecting the bearings IF I get sloppy and don't choose the clothes well.

 

Doug 7rxc

0

Share this post


Link to post

The first cache I found in 2001 was a Tupperware container with "GPS " lettered on top, hidden in a very remote scenic spot, accessible only after a 1 hour hike to a part of the mountain that was not widely used.

Muggles had found it and wrote "learn to use a compass!" in the logbook.

0

Share this post


Link to post

The first cache I found in 2001 was a Tupperware container with "GPS " lettered on top, hidden in a very remote scenic spot, accessible only after a 1 hour hike to a part of the mountain that was not widely used.

Muggles had found it and wrote "learn to use a compass!" in the logbook.

 

??? :blink:

0

Share this post


Link to post

Yes, it is a good subject. Personally, I avoid liquid filled compasses in favour of inert gas filled or at least dry air. Liquid fills always seem to have bubbles and they bug me greatly. I guess the bearings in air filled might degrade a bit, others seem to last well. I use a Suunto right now and don't seem to ever have problems, aside from occasional static electricity in my clothes affecting the bearings IF I get sloppy and don't choose the clothes well.

 

Doug 7rxc

 

The purpose of the liquid is to make the needle stable. Most people don't want the needle to be bouncing all over while walking or running and trying to stay on a bearing. I use a Moscow model 2 which is a very stable thumb compass, but also have a few old standard baseplate Suuntos and Silvas around. Small bubbles are annoying, but the larger ones can affect accuracy, and small bubbles will eventually become big ones.

0

Share this post


Link to post

 

The purpose of the liquid is to make the needle stable. Most people don't want the needle to be bouncing all over while walking or running and trying to stay on a bearing. I use a Moscow model 2 which is a very stable thumb compass, but also have a few old standard baseplate Suuntos and Silvas around. Small bubbles are annoying, but the larger ones can affect accuracy, and small bubbles will eventually become big ones.

 

Can't remember a needle bouncing around because it was in air/gas... besides if one walks/runs it's better to sight away and watch that target, then sight again and go. To much other stuff going on to watch a dial.

Anyway I know what you mean. The user is often the bigger problem regardless of the compass.

 

Doug 7rxc

0

Share this post


Link to post

 

The purpose of the liquid is to make the needle stable. Most people don't want the needle to be bouncing all over while walking or running and trying to stay on a bearing. I use a Moscow model 2 which is a very stable thumb compass, but also have a few old standard baseplate Suuntos and Silvas around. Small bubbles are annoying, but the larger ones can affect accuracy, and small bubbles will eventually become big ones.

 

Can't remember a needle bouncing around because it was in air/gas... besides if one walks/runs it's better to sight away and watch that target, then sight again and go. To much other stuff going on to watch a dial.

Anyway I know what you mean. The user is often the bigger problem regardless of the compass.

 

Doug 7rxc

 

Yes but as you run the needle is moving around and when you stop it continues to bounce for awhile so time is wasted. Doesn't matter much in Geocaching, but it does in an orienteering competition. That's the advantage of a liquid filled housing. Whether you need it or not is a different question.

0

Share this post


Link to post

SIMPLE WAY TO REMOVE A BUBBLE IN A COMPASS:

 

This thread comes up as the first forum hit on a Google search for "compass bubble". I hope this method that I discovered helps others:

 

Boil water in a pot, then immerse the compass and swirl it around for one minute. Do not allow the compass to touch the bottom of the pot if the stove hotplate is still very hot. Take out the compass and pinch the top and the bottom of the oil capsule very tight using both hands. Keep pinching hard until the compass cools for one minute, then pour some cold water in it, while still pinching.

 

The plastic will be formed to slightly reduce the volume in the capsule. This method worked on a Suunto MC-2G. To test that it will not get a bubble in the cold, I put it in a freezer at 0 deg F (-18 deg C) for a hour, and the bubble did not return. I hope that the repair holds up at extreme altitude.

 

My Silvas and Suuntos had all developed a permanent bubble because I bring them up to 23000 feet (7000m) and -13 deg F (-25 deg C).

 

If you try this method, please post your results.

0

Share this post


Link to post

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
Sign in to follow this  
Followers 1