Timeline for Why do compasses develop bubbles?
Current License: CC BY-SA 3.0
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| Jun 18, 2020 at 8:23 | history | edited | CommunityBot |
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| Mar 16, 2018 at 18:46 | comment | added | cbeleites | @mattnz: the diaphragm is a soft spot in the housing. I guess the difficulty is that OP didn't realize the problem is low pressure, not high pressure. And that low pressure just isn't the same as high pressure and that there's no way to cheat around the fact that a substance has a certain vapor pressure at given T and p. And: that there are different compass bubbles: a) bubble is symptom of leakage and loss of liquid. b) intended bubble for the perfectly valid construction strategy that a sealed and rigid housing can easily be used if you leave a small but sufficient gas space as buffer. | |
| Mar 16, 2018 at 17:44 | comment | added | Charlie Brumbaugh | @user1256923 See outdoors.stackexchange.com/questions/18731/… | |
| Mar 16, 2018 at 17:40 | comment | added | user1256923 | Thanks for thoughtful comments. A rigid capsule could take any increased pressure caused by an expanding liquid if strong enough (we are not talking kilobars!). A flexible capsule could also work. All shows that there might be viable solutions -- why they are not explored puzzles me. | |
| Mar 16, 2018 at 1:02 | comment | added | user5330 | Solution is actually to make the housing softer, not harder. If the volume inside expands and contracts with the liquid as temperature changes there would be no pressure differential between the inside and outside of the housing, no reason for a bubble to form. Filling the soft housing so it has a low pressure will encourage any gas molecules to migrate out (Think how balloon that deflates slowly with time). Why not do this - I suspect because bubbles and the myth that the compass is ruined by their presence means ongoing sales. | |
| Mar 16, 2018 at 0:57 | history | edited | Charlie Brumbaugh | CC BY-SA 3.0 |
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| Mar 16, 2018 at 0:12 | history | edited | Charlie Brumbaugh | CC BY-SA 3.0 |
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| Mar 15, 2018 at 21:17 | comment | added | cbeleites | @user1256923: well, if you fill in the volume cold, and the liquid expands in warmer temperatures, that added volume needs to go somewhere. Maybe a not very rigid case (with added bubbles in high altitude because of low pressure), or the diaphragm mentioned in the answer. If the case is rigid and filled by liquid, it will crack at high temperature. Or you go for a rather cheap but very robust technique that can buffer such volume changes: a gas bubble which as a gas is compressible. Aaaaha. | |
| Mar 15, 2018 at 20:33 | history | edited | Charlie Brumbaugh | CC BY-SA 3.0 |
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| Mar 15, 2018 at 18:00 | history | edited | Charlie Brumbaugh | CC BY-SA 3.0 |
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| Mar 15, 2018 at 17:37 | comment | added | user1256923 | @cbeleites what is stopping compass manufacturers from filling the capsule with cold dampening liquid, which will expand but not suffer from contraction in those occasions when temps dip? or use a capsule/liquid combo with similar expansion and contraction? | |
| Mar 15, 2018 at 16:52 | comment | added | cbeleites | @user1256923: the cold-temperature bubbles appear with rigid housing, i.e. volume in the housing changing much less than the density of the liquid, in first approximation leaving you with lower volume of liquid + a little vaccum bubble. Of course, the bubble is not really vacuum (2nd approximation): it is filled with evaporated compass liquid according to vapor pressure at the given temperature. | |
| Mar 15, 2018 at 16:50 | comment | added | user2766 | If you can invent a material that does then I think you will be a very rich man. All materials expand and contract with heat/pressure. | |
| Mar 15, 2018 at 15:02 | comment | added | user1256923 | wouldn't it be simpler to make a rigid housing that does not expand at ~ 1/3 sea level pressure and does not let air in? | |
| Mar 15, 2018 at 14:41 | history | answered | Charlie Brumbaugh | CC BY-SA 3.0 |