HP steel tanks in cold water

[MattPSI]

I am preparing to do some cold fresh water diving (approximately 38 F). I was reading that filling tanks above 3000 psi should be avoided due to increased risk of malfunctioning regulators from freezing. I will be using HP steel tanks when available. What is the best practice in terms of water temp and fill pressure?

 

[Redshift]

Never heard anything like that. My cylinders are only rated to a little bit over 3000 psi (~3365), but it is very common to see people using cylinders rated to 4350 psi. The 1st stage should keep a constant IP independently of the cylinder pressure, so it doesn't really matter. The freezing comes from the gas expansion when gas is being delivered. Don't purge, don't breathe out of the water, if the air is also cold.

 

[Patoux01]

Just dive.. Don't overpurge a reg, don't get ****** fills full of water and you're good to go.

 

[MattPSI]

Here is a link to the article about conditions that promote regulator freezing which I am referring to: https://divelab.com/download/proced...ubaRegulatorFreezing-ChillingFacts-4-9-14.pdf.

 

[Slym]

I have also wondered this... buying AL 80's don't make sense to me when I can get way more air for a bit more money using HP tanks, even when renting a tank 10 dollars for an 80 vs 15 for HP it only makes sense using HP. Also since I am pretty fresh I still use quite a bit of air.

 

[g2]

I love the Kirby Morgan Thermo Exchanger shown in that article. How fun!

If you have a reg freeze-up, just be prepared to switch regs and end the dive. No worries.

Realistically, I wouldn't care about the tank pressure. When I enter 45F water with a HP100 filled to 3500 psi, it almost immediately drops to around 3300psi. In 38F water you should see an even more rapid decline. Using the ideal gas law (PV=nRT), if you take your tank from a 70F car and dive in 38F water, you should see an almost immediate decline in pressure of approximately 6%: 0.06 x 3500 = 210psi drop due to temperature alone. After a few minutes of breathing you'll be well below 3000 psi.

If it still worries you, just bleed off some air before the dive. Chances are you'll get cold and end the dive long before you need that gas.

 

[Doby45]

I would worry more about opening your tank valve slowly so you don't slam the seat in your first stage. Other than that, carry on.

 

[Spack9]

38F= A little too cold for me! I may be mistaken but the air your exhaling should also provide a little warming affect to the second stage? I'd just go for it but be prepared for ice. Stay alert, and enjoy the cold clear water!

 

[lerpy]

I dive steel, have for awhile now, never heard of this, and have never had any issue. I did cold water, have dove as cold as 3 degrees Celsius and had no issue with freezing. The only thing I have every been told about diving in serious cold is avoid breathing the reg on the surface to much as your warm moist breath in the very cold could cause it to freeze while above, but not sure how valid this is. I have never had an issue with a freeze up, but it certainly can happen so best is be prepared and know how to deal with it.

 

[exposure]

Never had to worry about the tank for freezing and we dive steel tanks all the time. In my view, this is more an issue with regs below 45F. Some regs are definitely not made for that. What you can do to, is to reduce the sensibility of your octopus, so that it won't go easily into free flow, that can create a freeze because of the flow of air. In all cases, be ready to face freezing in cold water Better to be ready when it not happens than not ready when it happens.