HP steel tanks in cold water

[stuartv]

My local quarry is 38F on the bottom. I dive there with my HP120 steel tanks filled to 3500 psi.

I had one weekend, about a year ago, where I had 3 free flows during 2 days of diving. I only had about 30-ish dives in my log book at that point and was breathing REALLY hard. It was training dives for a Wreck and Deep course, so I was trying to keep up with an instructor who was swimming very fast because he was cold and wanted to get the dives done quickly.

Never a problem since.

 

[MattPSI]

Thanks for all the comments! It seems like there are a lot of factors that can contribute to free flow and PSI may be one of them. But it doesn't seem to be a notorious precipitating factor based on what I am hearing back from the community.

 

[tbone1004]

were those freeflows from the second stage or the first stage stuart?

first stage lockup due to high pressure shouldn't be an issue as long as you have a good sealed first stage and aren't doing anything stupid like breathing or worse, power inflating, while at the surface of the water

 

[Remy B.]

A good 1st stage Regulator makes a difference, I had a free-flow at 6*C, but my regulator was not a dry-chamber at that moment ( Aqua-Lung Titan LX ), later I had a dry-chamber cold water kit installed, you can't go wrong with a Apeks either, DS4 very cheap and very good, it is a bull of a regulator, or Aqua-Lung glacial, it is more expensive but it is truly made for cold water diving, both 1st and 2nd stage.

 

[stuartv]

were those freeflows from the second stage or the first stage stuart?

first stage lockup due to high pressure shouldn't be an issue as long as you have a good sealed first stage and aren't doing anything stupid like breathing or worse, power inflating, while at the surface of the water

I can only say what I suspect, which is that it was a 2nd stage freeflow. And that is based on the fact that the reg I was breathing started to free flow, but the other did not*. I would *think* that if the 1st stage was free flowing, it would have cracked both 2nd stages before long. My theory is that I was breathing so hard that the adiabatic cooling in the 2nd stage caused some ice to form inside that kept the 2nd stage valve from closing.

I have since done several longer dives in the same quarry, when it was a whopping 1 degree F colder, and had no problems. But, I have not let myself get sucked into working so hard again, either.

*That time that it did happen, it happened to my primary 2nd stage on one dive. On the next dive, it happened to my primary again. That second time, instead of switching regs and surfacing, I switched regs and continued swimming while turning the breathing effort adjustment knob on the first one to try and get it to stop. After, I don't know, 10 or 20 seconds of continuing to swim while fiddling with my primary, the secondary 2nd stage started free flowing, too. At the point that both were free flowing, I stopped and signaled the assistant instructor, who was behind me, to show him what was happening, then made an ascent. So, maybe it was the 1st stage. I really don't know.

 

[2airishuman]

I use HP120s and have dived them in water as cold as 45 F. I have not had a problem with freeflows but I do take several precautions.

1) I use H valves or a twinset, with dual first stages, so that I have another first stage to use if my primary free-flows.
2) I use diaphragm 1st stage regulators, and my primary is environmentally sealed. (I am unsure whether the environmental seal makes much difference however)
3) I use metal second stages, which I believe have better heat transfer properties and are less likely to ice up than plastic ones.

 

[g2]

My theory is that I was breathing so hard that the adiabatic cooling in the 2nd stage caused some ice to form inside that kept the 2nd stage valve from closing.

Yup, probably the most common failure mode. Fortunately they usually freeze open.

I did some dive tending in Antarctica and never saw a 1st stage failure. The primary 1st stage will get covered in ice but that didn't seem to affect the performance. I'm not saying it can't happen, but that the 2nd stage is usually at fault.

 

[Spack9]

Holy Batman that's a chunk of ice. What's the water temps up there?

 

[g2]

Holy Batman that's a chunk of ice. What's the water temps up there?

Ha! That's after it's already partially melted off. Water temps at McMurdo were usually -2C. The ice thickness was a couple meters or so.

What's funny is the DSO told me they tried to modify the second stages to prevent freeze-up, adding copper or brass heat sinks inside to exchange heat. It didn't really improve anything. At the time, they were using stock Sherwood regs, the kind of thing you'd rent for a tropical holiday. Those apparently worked as good as anything else.

 

[Spack9]

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.