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Old 24th November 2008, 21:12   #1 (permalink)
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Head Condensation points- a real concern?

Hi,
whilst inspecting old sensors, I saw a fair bit of green where it should not have been. Obviously from some former condensation, or moisture.

From my years as a student I knew condensation would take place mostly on the inside of my single pane windows, especially when cold outside.

When looking for thermodynamic windows in the Inspos head, the big metal chunks fixing the cables to the head (handsets, beeper) spring to attention.

Has anyone ever observe the flat metal surface which is inside the head, as a specific point of condensation?

If so, has anything been done to fight this? Like attaching a felt glider on it, to enlargen the surface area for evaporation; or thermally isolating the big metal parts outside ?

Greets,
Matthias
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Old 25th November 2008, 06:27   #2 (permalink)
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Re: Head Condensation points- a real concern?

At risk of setting off the prophets of doom again with a 'known fault' when I started it was pointed out that the battery case screw was a condensation drip point and if you lay it on its back that dripped nicely into cell two.
Hence we never left them yellow side down.

The condensation is virtually all post dive and the majority of the water comes from the scrubber reaction so you probably aren't going to reduce it. I like to get the head open, après dive, and let the breeze dry it off. Since the cells are fully within the loop they tend not to be a focus for condensation so having it go for the metal bits is probably a benefit.
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Old 25th November 2008, 07:32   #3 (permalink)
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Re: Head Condensation points- a real concern?

Quote: (Originally Posted by nigelh) View Original Post
The condensation is virtually all post dive and the majority of the water comes from the scrubber reaction so you probably aren't going to reduce it.

I don't agree. The head condensation appears to form during the dive on the non insulated plastic of the head and likely when cold O2 is injected into warm moist gas. I have a non standard head which allows multi hour dives, keeping the cells COMPLETELY dry from condensation. The guts of the head reach a good working temperature, the O2 is injected into the exhale side and there is zero condensation on the cells during or post dive.

The head has a very small cell chamber and scrubber mass above the cells as well as below. This very effectivly insulates the cells, with only a small band of head wall not insulated and exposed to the cold water. (and provides additional scrubber duration)

John
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Old 25th November 2008, 07:54   #4 (permalink)
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Re: Head Condensation points- a real concern?

The GREEN colour is the ELECTROLYTE fluid used inside the Galvanic Cell and it has leeked. Nothing to do with water damage, not likely, unless you had a major flood or cell failure - BOTH of which would be known by you anycase. Take an old cell and see for yourself by revealing the insides! Not trying to defame, just clarifying your question.

From other posts I understand this...
Water VAPOUR is a direct result of the chemical exothermic reation that takes place during the dive, inside the scrubber material. Breathing adds a small amount also, but tops-out quickly. This is because the divers lungs only give a small amount of water vapour off before the humidity given off by the scrubber reaction EXCEEDS that of our lungs.
That vapour CONDENSES (appears as liquid drops) on cool surfaces is a natural law that cannot be broken. The inevitable appearance of water drops is incontavertible. Question is or SHOULD BE, does it harm anything?
No. not if the manufacturers post dive procedures are done properly.
I remove the head from the unit and hang it si the handset is highest, in the breeze, but out of direct sunlight. In cold weather I plug the cell holder off and direct a fan at the head for up to 24 hours.
Of all the bits to attract water in the head, I prefer the metal bits to be drenched first, this is benign.
Hope this helps a bit. If not try searching posts for more infor and comments.
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Old 25th November 2008, 09:14   #5 (permalink)
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Re: Head Condensation points- a real concern?

Quote: (Originally Posted by divemasterrob) View Original Post
Question is or SHOULD BE, does it harm anything?
on long dives (several hours plus) there does seem to be a change in the way the system behaves, possibly due to moisture in or near cells. I can't quantify exactly how it changes, but no condensation on the cells anytime in the dive can only be good thing.

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Old 25th November 2008, 10:30   #6 (permalink)
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Re: Head Condensation points- a real concern?

Quote: (Originally Posted by divemasterrob) View Original Post
The GREEN colour is the ELECTROLYTE fluid used inside the Galvanic Cell and it has leeked. Nothing to do with water damage, not likely, unless you had a major flood or cell failure - BOTH of which would be known by you anycase. Take an old cell and see for yourself by revealing the insides! Not trying to defame, just clarifying your question.

From other posts I understand this...
Water VAPOUR is a direct result of the chemical exothermic reation that takes place during the dive, inside the scrubber material. Breathing adds a small amount also, but tops-out quickly. This is because the divers lungs only give a small amount of water vapour off before the humidity given off by the scrubber reaction EXCEEDS that of our lungs.
That vapour CONDENSES (appears as liquid drops) on cool surfaces is a natural law that cannot be broken. The inevitable appearance of water drops is incontavertible. Question is or SHOULD BE, does it harm anything?
No. not if the manufacturers post dive procedures are done properly.
I remove the head from the unit and hang it si the handset is highest, in the breeze, but out of direct sunlight. In cold weather I plug the cell holder off and direct a fan at the head for up to 24 hours.
Of all the bits to attract water in the head, I prefer the metal bits to be drenched first, this is benign.
Hope this helps a bit. If not try searching posts for more infor and comments.
Nothing at all against your little extemporale on thermodynamics.
It is just that I'd like guiding the inevitable condensation as far away from the sensors as possible. That may well be farther away than the manufacturer has designed it.
Having unisolated metal appliances going through an otherwise lesser conducting material in the vicinity of sensitive ( handsets, sensors, connectors, cardboards) eqipment should be a NONO to any designer.

Condensation should take place where it may be dumped overboard. That would be exhale lung in some rigs, or canister bottom. To that goal, the loop should haold vapor as it is until passing the designed point of condensation.

You think attempting to reach this goal in an Inspo is futile?

regards,
Matthias
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Old 25th November 2008, 10:35   #7 (permalink)
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Re: Head Condensation points- a real concern?

Quote: (Originally Posted by johnv) View Original Post
on long dives (several hours plus) there does seem to be a change in the way the system behaves, possibly due to moisture in or near cells. I can't quantify exactly how it changes, but no condensation on the cells anytime in the dive can only be good thing.

John
You seem to experience a sensor long term non linearity.
I don't know if there is an answer to that, except using a concept which does not rely on sensors, or at least have system which calibrates real time, like the promised Poseidon Discovery ( said to be CEed mid January by DEKRA in conjunction with Germanischer Lloyd).

Still this would be no solution to current limited sensors, IMHO.
Unfortunately I do not know anyone at Poseidon ready to discuss these sort of things.
Greets,
Matthias
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Old 25th November 2008, 11:00   #8 (permalink)
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Re: Head Condensation points- a real concern?

Quote: (Originally Posted by johnv) View Original Post
I don't agree. The head condensation appears to form during the dive on the non insulated plastic of the head and likely when cold O2 is injected into warm moist gas. I have a non standard head which allows multi hour dives, keeping the cells COMPLETELY dry from condensation. The guts of the head reach a good working temperature, the O2 is injected into the exhale side and there is zero condensation on the cells during or post dive.

The head has a very small cell chamber and scrubber mass above the cells as well as below. This very effectivly insulates the cells, with only a small band of head wall not insulated and exposed to the cold water. (and provides additional scrubber duration)

John
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Old 25th November 2008, 11:30   #9 (permalink)
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Re: Head Condensation points- a real concern?

Thinking laterally, I wonder if there is any advantage in adding a deliberate condensation point into the loop (eg in counterlung) where excess moisture can be collected safely away from electronics ?
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Old 25th November 2008, 11:55   #10 (permalink)
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Re: Head Condensation points- a real concern?

Quote: (Originally Posted by Scubascooby) View Original Post
Thinking laterally, I wonder if there is any advantage in adding a deliberate condensation point into the loop (eg in counterlung) where excess moisture can be collected safely away from electronics ?
Since the scrubber is the main contributor on the Inspo/Vision there isn't a place to get at the gas between the scrubber and the cells. If the cells are the problems the trick must be just to keep them nice and warm and most manufacturers are well on the case with that one. Further round the loop I would expect the counterlungs to already be very good condensers so metal fins there aren't going to contribute.

As you always exhale a fixed ppH2O the humid loop makes things so much more comfortable than OC which pumps the moisture out of your lungs.
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