1st Stage Freeze Up Prevention

[urbanrob]

My local shop told me the same thing...that icing and overpressure usually affects the 2nd stage or octo, but rarely, if ever, the BC inflator. He said nothing is impossible, just never heard of it.

The diff in water temp at Dutch Springs varies greatly due to the thermo clines. The surface is wetsuit territory but I marked 48 degrees on my second dive at 66 feet and then 48 again at 63 feet. My dive buddy marked 45 degrees at 93 feet (the dive I aborted). Of course, the temp gauges delay a bit in their reading, especially if you don't stay in the area long.

BTW, my tanks are PST high pressure 120s. I asked about dewpoint in the air fill. However, I'm told that the fill station is considered "clean" because they dispense Nitrox as well.

 

[WarmWaterDiver]

Go back further in this thread on relationship between first stage inlet pressure (tank pressure) and dew point - the higher the differential pressure, the more J-T effect is achieved. Even ANDI SafeAir specs are insufficient to eliminate the possibility of internal first stage icing at a -50 degrees F dew point. And then recheck what it's like for emergency rescue workers in a crummy air heat sink in colder climates - like Canada. Pufferfish provided some excellent info on this.

The loss of tank pressure through a 'stuck' LP outlet, like an inflator hose, could reduce the tank pressure sufficiently that the J-T effect in the ports / hoses etc. to the second stages was not as great as when the freeflow in the other outlet was initiated & sustained.

The first stage environmental kit question would have more to do with potential external icing. There have been posts by all sorts of folks regarding the Scubapro Mk25 and water temperatures at / below 50 degrees F being a risk, so it's a point of data, and the full data set you've provided it's not a strong indicator external first stage icing was a culprit.

But, I don't see enough evidence to completely dismiss internal first stage icing as a potential culprit - others may, but I don't. Your use of high pressure tanks in cooler waters directionally indicates a higher probability. And, the fact your fill station evidently thinks the water content of Nitrox isn't important - I'm a bit lost on their reasoning. Many such fill stations take their 'air' fill lines off upstream of the additional filtration etc. needed to produce O2 compatible air or clean up the air enough for Nitrox partial pressure blending - so only the compressed air used for Nitrox blending receives the additional pretreatment, extending life of those components.

If ambient air at 72 degrees and any reasonable portion relative humidity is compressed to 3500 PSIG range and cooled to 100 degrees F or less, it will be moisture saturated - 100% relative humidity, as free water will be knocked out in the trap. The ambient air would have to have a pretty low absolute humidity at 1 ATA to not acieve saturation after compression and cooling.

We can do the math if needed to produce the numerals, but within orders of magnitude, this is accurate science.

You might check out the full configuration of the equipment at your air fill station, to see where 'air' fills are drawn vs. air for Nitrox blending. It might be different. And in either case, whether the system uses any chemical dessicant on the compressed air, whether for 'air' fills, Nitrox blending, or both.

 

[Warren_L]

My local shop told me the same thing...that icing and overpressure usually affects the 2nd stage or octo, but rarely, if ever, the BC inflator. He said nothing is impossible, just never heard of it.

During a few ice dives this past winter, my BC inflator has frozen open on me, as has my drysuit inflator. This has generally been in waters in the 32-33F range. No big deal, just unplug and continue.

BTW, my tanks are PST high pressure 120s. I asked about dewpoint in the air fill. However, I'm told that the fill station is considered "clean" because they dispense Nitrox as well.

Dew point requirement for oxygen compatible air would have to be -50F or lower.

 

[WarmWaterDiver]

During a few ice dives this past winter, my BC inflator has frozen open on me, as has my drysuit inflator. This has generally been in waters in the 32-33F range. No big deal, just unplug and continue.



Dew point requirement for oxygen compatible air would have to be -50F or lower.[/QUOTE]

For what first stage differential pressure?

Check post #34 in this thread.

 

[Warren_L]

For what first stage differential pressure?

Check post #34 in this thread.

My tank pressures have never started more than 3000 or so, but has happened probably due to ambient surface temperatures in the 20F range or low.

 

[Sideband]

• 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.

It took 20 something posts but someone finally got to the one I was going to say. I was given that tip by a DM friend that does a lot of deep/tech diving in cold water. He pulled back the rubber from my first stage connections when I was gearing up for a dive on the "Willie", out of Milwaukee. I think we were looking at temps in the upper 40's at 90 feet.

Joe

 

[Warren_L]

It took 20 something posts but someone finally got to the one I was going to say. I was given that tip by a DM friend that does a lot of deep/tech diving in cold water. He pulled back the rubber from my first stage connections when I was gearing up for a dive on the "Willie", out of Milwaukee. I think we were looking at temps in the upper 40's at 90 feet.

Joe

If you're talking about the hose protectors, I don't use them at all.

 

[WarmWaterDiver]

It took 20 something posts but someone finally got to the one I was going to say. I was given that tip by a DM friend that does a lot of deep/tech diving in cold water. He pulled back the rubber from my first stage connections when I was gearing up for a dive on the "Willie", out of Milwaukee. I think we were looking at temps in the upper 40's at 90 feet.

Joe

Good tip. This would help to allow the metal fittings to assist in heat exchange with the surrounding water. Directionally should help.

I had wondered last year whether there would be an aftermarket niche for heat exchangers, that you could connect much like a swivel, between the second stage and the LP hose, or now thinking, even between the BC inflator or drysuit inflator LP hose and first stage. Maybe even a heat exchanger with a swivel all together as another option. If you look at the 'built-in' heat exchager on say the AL Glacia second stage, it certainly doesn't look like something difficult to machine.

Well, since my diving's staying in the warmer waters, I'll leave that as a thought for some cold water entrepreneur to explore. I'll soon be moving to a more southerly latitude which should assist in more frequent opportunities for warmer water dive trips - I'm ready for the change after experiencing 5 Great lakes area winters, personally!