1st Stage Freeze Up Prevention

[roakey]

Probably the absolute best 1st stage for ice diving a the Sherwood with the "dry bleed" system. This way no water comes in contact with the piston at all, and it doesn't require any goop or sealed containers of alcohol or anything.

They're not great performing regulators, but they're great workhorses.

The one problem is that you have to get used to everyone coming up to you after the dive and telling you your reg is leaking (the dry bleed system produces a small, slow stream of bubbles from a grommet on the first stage).

Roak

 

[Chaos]

All Aqualung and Apeks 1st stages have dry chambers as well. But I must say that my Scubapro MK25AF's have never frozen up either. The worst I did with it was a 30 minute dive in 2-4 C/36-38 F water at 165 ft depth. Of course the dewpoint of the air we fill is pretty low at 2mg/M3 moisture content. I think this helps a lot.

 

[jonnythan]

All Aqualung and Apeks 1st stages have dry chambers as well.

Not sure about Aqualung, but not all Apeks 1st stages are dry sealed. They make the US1 and US4 which are unsealed first stages.

 

[pufferfish]

All Aqualung and Apeks 1st stages have dry chambers as well. But I must say that my Scubapro MK25AF's have never frozen up either. The worst I did with it was a 30 minute dive in 2-4 C/36-38 F water at 165 ft depth. Of course the dewpoint of the air we fill is pretty low at 2mg/M3 moisture content. I think this helps a lot.

That is some nice dry air you have there at -70 C (-95 F). I have taken the same reg with air and similar low dewpoint and tried to encourage a few freeflow in water about 2 C with little luck. The few times I have had the MK25AF's just starting to want to FF have been when using air with unknown dewpoint in close to freezing water. Still think there are better regs than the MK25AF for very cold water diving. Some first stage designs just seem more likely to FF when the dewpoint starts to rise when the ambient water is around freezing. My buddy has used the Aqualung LX Supreme which is a sealed first and had no problems whatsoever.

Just curious, do you remember what manufacturer did that study with the temperatures achieved in the first stage? Someone else mentioned that a while back and said -50 F below ambient achieved in the first stage air flow. Do you know if that was on the bench or actually on a real dive? If you actually assumed an internal first stage pressure dewpoint at 3000 psi of anywhere near those temps mentioned, you would need an atmospheric dewpoint well below -75C (-100 F) to keep things from freezing up. That is pushing the sensitivity of most hygrometers and the air would have about 1 mg/m3 of moisture. Now that is real dry but totally agree that dry air is paramount in minimizing freeze failures.

 

[roakey]

But the point about the Apeks sealed 1st stages is just that -- they're sealed. The Sherwood system is much, much simpler -- it just uses a constant bleed of gas from behind the piston to keep the water out of the pressure-sensing chamber. All you have is a "leaky grommet" to keep the water out rather than the sealed diaphragm that the Apeks has.

Now, all that said, my Sherwood is relegated to my recreational one-reg setup, whereas my Apeks are my dual reg setup I use in Cave and Ice. Reason being, the Sherwood design has been around for so long you're guaranteed to be able to find in-stock parts just about anywhere in the world. As I said, it's not a great performing reg, but it's a real workhorse.

Roak

 

[Chaos]

I meant Scubapro. Their technical director in France told me about the tests. Because they have a dry ANSTI test bench, I assume it was under load, and without heat exchange with water. I could be wrong though. I would have to call him and check.

The temps measured were on the inside surface of the piston stem, which is the point of most gas expansion (together with the swiveling head with the LP ports). I recall that it was at 300 bar/4500 psi supply pressure, which is terrible for cold water diving. The regs never froze - and neither do mine on winter dives. I use 320 bar/4650 psi tanks (yes, they're designed for that, I don't overfill ) which really isn't such a great idea in near freezing water.

More good cold water tips:

• Keep the reg warm before the dive. It could hurt if the reg was pre-chilled to -10 C before the dive.

• Pull the sleeves back from the metal crimp on the LP hoses, especially on piston first stages. The more surface you expose to water, the more heat exchange you get.

• Don't fill tanks to rated pressure if you're not going to need that much air. The pressure drop in the first stage changes with tank pressure, and so does 1st stage cooling. Going from 150 bars to 10 bars IP is a 15:1 drop, compare that to 300 bars to 10. So it's better to dive doubles at half rated pressure than a single at rated pressure.

• For the 2nd stage, the tank pressure is irrelevant, it's always about 10:1 (IP to ambient). Perhaps a little too much info (I love details), but for Aqualung regs, the first stage is overbalanced so 2nd stage pressure drop increases with depth. That means thermal load of the 2nd stage increases with depth, and you add that to the increased amount of air demand at depth (=cooling).

 

[divereh]

Doubles -- if a reg freezes you shut down that post, let it thaw (30 seconds?) and turn it back on.

Roak

I think he is just recreatioal

 

[roakey]

I think he is just recreatioal

Yes, probably, which begs the question:

Why is an overhead, equipment intensive, high taskloading and high failure environment treated as "recreational"?

You wouldn't catch me under the ice on a single, that's for sure!

Roak

 

[Norm]

I've seen a clear coating over first stages and hoses u/w and seen them completely frozen over topside. I've never had that to affect the reg's performance though. (I used Sherwood or Zeagle first stages)
I have seen many second stages freeze up/freeze open though. Once it starts it's usually to late to stop it, (whether it's u/w or topside)
It's a snowball effect that is self-perpetuating and gets worse fast. It's amazing how fast they will thaw out once the gas flow is turned off, as Roak pointed out. This is where redundancy is a lifesaver.
Norm

 

[Norm]

Someone else mentioned that a while back and said -50 F below ambient achieved in the first stage air flow. Do you know if that was on the bench or actually on a real dive?
Yeah, that was me. I believe it was an article in U/W Magazine that stated that research in Panama City showed that at 3000 PSI, you have a 50 degree drop, (below ambient) in gas temperature. That is a given. This reinforces what someone above said about diving with a full cylinder in coldwater causing more temperature drop.
Norm