HP steel tanks in cold water

[CT-Rich]

Wow, I have a Sherwood all the way back from 1986! The reg is almost 10 years older than me. That thing hasn't ever had a problem though. I love diving with that guy who gives me that goofy look on the boat for diving a ancient reg, but his brand new expensive one free flows the whole dive while I Flintstone it up! -2C?? wow I bet testicles are not existent at that temp no matter what you wear.

Sherwood made a regulator in the 1980s called the Magnum Blizzard that had a heat sink built into the 2nd stage. I thought about buying it and then opted for the less expensive magnum.

I have no idea about how effective it was in cold water. dive magazines at the time gave everyone a good review (I think they deducted points if one of the reviewers died during testing, but, it was kept to a minimum). I am not surprised to hear the older regs holding up better than modern gear. The technology hasn't changed much in the last 30-40 years. Most of the features added to create the premium regulator are premised on improving the profit margin more so than performance. A stripped down basic regulator is less likely to have as many possible failure points as a system with lots of bells and whistles. This is all supposition, of course, but metal transfers heat much more efficiently than nylon components therefore nylon would be less likely to ice up during a dive. A reg with more metal will have a higher profit margin. I could very well see lower end regs actually out performing the top of the line regs in cold water. But again, I am not a reg expert. I wonder if anyone with more experience with regs might have a comment?

My daughter is getting certified this year and she is going to start out with my Sherwood Magnum from the 1980s.

 

[Spack9]

My Sherwood is a Magnum. Most reliable reg I've ever used. I really like the new and expensive regs but sometimes simplicity and reliability take the cake for me.

 

[dberry]

The PDF linked by the OP is long, but it includes a lot of details of how the Navy and CE test for cold water performance, as well as their own measurements. Maybe a bit TL;dr, but the background and advice seems solid. The good news is most of the tests (USN, CE, and their own) were performed assuming extreme situations: rescue divers attempting recoveries at 165 fsw and breathing at a extremely fast rate (very high workload - 62.5 lpm or 2.25 cf/min!) Both the depth and the breathing rate (gas flow) correlate with the temperature drop, and that's more severe than most recreational cold water divers will encounter. Commercial or rescue divers might be more grateful for the test conditions.

The point about fills >3000psi is technically correct: the temperature drop is related to the pressure difference across the first stage (tank / IP). And it appears they didn't just rely on theory (Joule-Thompson coefficients, etc), but used fast-reading sensors inside the 1st and 2nd stages at various places. But again, it's not clear 3000psi is a magic number, but rather their view of a safer limit.

This quote caught my eye :

In 32 - 35°F (0-2°C) degree water at 3000 psig (206 bar) if the purge valve of the second stage was depressed for just three to five seconds, the air will get down below -25°F (-31°C) at the first stage, and -5°F (-20°C) at the inlet to the second stage. This is why a second stage can freeze so fast.

It appears they used many different regs for the tests, but specifically mention the Apeks DX50 and Poseidon Xstream in this pdf. Neither free-flowed during their extreme testing, but there was some ice build-up inside the 2nd stage after the most extreme scenarios.

Question for the experienced cold water divers: Is it common to have a 2nd stage free flow after filling a lift bag or BC (or anything else with relatively high gas flow)? Or is this something you just know (or are trained) not to do?

 

[Rosborne]

I have 400 plus dives in very cold water in the Great Lakes--diving year around when the water can be just above 32 degrees. Never had a problem with my tanks being topped up and I dive steel 100s. My advice, make sure you get a good cold water regulator. I use Apex but there are many others. If you don't you do stand a chance of creating a free flow just from the compressed air moving over the working parts of the second stage. Disconcerting when it happens below 110 feet.

 

[Stoo]

The poster Stoo had just stated that the pressure in your tank wasn't relevant to the conversation, which I disagree with.

I suppose in theory, you are correct, but there are so many more significant factors involved that I don't really think the tank pressure is much of a concern... although perhaps "irrelevant" may have been too strong of a word. Much more important would be the moisture content in the air, the type of regulator, how it's tuned, how it's maintained, the way the user is breathing, depth, water temperature, air temperature at the surface and others. There are a dozen reasons why a regulator will freeze up. We routinely dive in very cold water here (I did 10 or 11 dives over the last two weekends in water that was between 38° - 41°F at depths from 100' to 180' without issues). I've been doing that for over 40 years and this is the first time I have heard of the tank pressure being raised as a concern. "Everyone" here dives steel tanks, both LP and HP (although typically the LP tanks are filled to 3000 to 3100 psi).

So again, in theory, tank pressure might be a concern, but it's WAY down the list of stuff to worry about diving in ice-cold water.