Regulator Freezing

[gbirch]

OK, I know that regulators do not freeze (they are made of metal, plastic & other soft bits and are therefore, by definition, already frozen) but I got you attention, because I have a question regarding regulator icing:

I understand (I think) the discussion on piston vs. diaphragm, sealed vs. not etc, but my question is, if the real cooling engine in a SCUBA regulator is the adiabatic expansion of gas in the first stage between cylinder pressure and intermediate pressure, why is it a common practice (and, I understand, advocated by some regulator manufacturers) for cold water/ice divers to lower the IP for ice diving? Would this not make the situation worse (bigger difference between cylinder pressure & IP = greater adiabatic cooling effect, which is described in this paper by Dive Lab where it is clearly demonstrated that having a lower cylinder pressure to start with leads to less cooling because the cooling effect is less as the difference in pressure drop becomes less).

What am I missing?

 

[tbone1004]

most icing problems are in the second stage not the first stage *though first stage is worse if you have an unsealed regulator*. Lowering the pressure differential in the second stage lessens the cooling effect to some extent. Either way, I don't subscribe to it as an issue since most of it is diver error.

 

[gbirch]

most icing problems are in the second stage not the first stage *though first stage is worse if you have an unsealed regulator*. Lowering the pressure differential in the second stage lessens the cooling effect to some extent. Either way, I don't subscribe to it as an issue since most of it is diver error.

"most icing problems are in the second stage" - Not sure I agree with this. For sure the manifestation of the problem affects the second stage more as cold air from the first mixes with moist air from the diver but I'm convinced that most problems start in the first stage.

"Lowering the pressure differential in the second stage lessens the cooling effect to some extent". This seems to be the opposite of what the physics would imply. What is your rationale for this?

Not trying to be contentious - just trying to understand.

 

[tbone1004]

"most icing problems are in the second stage" - Not sure I agree with this. For sure the manifestation of the problem affects the second stage more as cold air from the first mixes with moist air from the diver but I'm convinced that most problems start in the first stage.

"Lowering the pressure differential in the second stage lessens the cooling effect to some extent". This seems to be the opposite of what the physics would imply. What is your rationale for this?

Not trying to be contentious - just trying to understand.

what normally happens is water from your breath/spit/whatever in the second stage body freezes from the cooling coming out of the second stage valve. Nothing to do with the first stage.

 

[gbirch]

what normally happens is water from your breath/spit/whatever in the second stage body freezes from the cooling coming out of the second stage valve. Nothing to do with the first stage.

So your position is that first stage cooling (drop from 3000-130 PSI above ambient) is irrelevant, or at least eclipsed by, second stage cooling from 130 to ambient, so knocking 10 to 20 PSI off the IP helps reduce this cooling effect? I can somewhat buy that (although I'm not fully convinced by your overall description of the icing process).

Full disclosure, I am Ice certified, dive regularly in cold water (New England through the Winter) and religiously de-tune my IP each season. This year I will be teaching the ice diving class so I really wanted to understand the physics before I pass on a piece of advice to students that might be more folklore than science.

 

[tbone1004]

So your position is that first stage cooling (drop from 3000-130 PSI above ambient) is irrelevant, or at least eclipsed by, second stage cooling from 130 to ambient, so knocking 10 to 20 PSI off the IP helps reduce this cooling effect? I can somewhat buy that (although I'm not fully convinced by your overall description of the icing process).

Full disclosure, I am Ice certified, dive regularly in cold water (New England through the Winter) and religiously de-tune my IP each season. This year I will be teaching the ice diving class so I really wanted to understand the physics before I pass on a piece of advice to students that might be more folklore than science.

In a sealed regulator, the reduction in pressure to IP from supply pressure is not practically relevant to regulators freezing. They are only going to do it if you have a freeflowing second stage and the only way to solve that is to turn the tank off anyway.
Reducing the IP in the second stage reduces the cooling between IP and ambient pressure inside of the second stage body. The second stages are more prone to icing over because you are exhaling 100F, 100% relative humidity gas into a very cold chamber where it is going to condense on stuff and cool down rapidly. Now you have near freezing water droplets on the metal barrel of the second stage and when the valve opens, it cools the metal and causes the water droplets to freeze. Get enough of them on there and the valve freezes open and it freeflows.
Does the IP reduction matter significantly? With proper technique I do not believe it does as the Apeks and Poseidon regulators pass the Norsok test with no reduction in IP.
Tune the regulators to what the manufacture recommends, use sealed diaphragms, have as much metal as possible/practical in the second stages, and use proper breathing techniques with smooth/slow exhales to reheat the inside of the second stage as much as you can.
Alternatively use regulators that practically can't freeze like the Poseidon second stages due to their valve design or better yet a double hose like the Kraken where not only is the first stage sealed, but so is the second stage.

 

[lowwall]

The theory is that first stage cooling drop is less important because there is no internal moisture in the first stage to freeze. The second stage has moisture from your breath or saliva as well as any water introduced from the environment. It doesn't take much ice in the wrong place to cause a second stage freeflow.

There's also a relative drop issue. The additional cooling when going from 3000psi to 130 instead of 150 is much smaller than the additional cooling you get going from 150 to 29psi (ambient at 33fsw) versus 130 to 29.

The theoretical disadvantage of a lower IP is reduced air delivery at great depths. Since dives in really cold water tend to be shallow, this is considered a reasonable tradeoff.

 

[rx7diver]

They [i.e., sealed regulators] are only going to do it [i.e., free-flow from icing] if you have a freeflowing second stage...

[HIJACK]
Hmmm. One of the first things I was taught when I began Great Lakes diving (in the early 1990's) using a single 1st stage on a single back tank, is to NOT simultaneously inhale and power-inflate (anything), to NOT simultaneously power-inflate both your BC and your drysuit, etc., lest you risk inducing a 1st stage free-flow due to 1st stage icing. This applies even when diving a Poseidon Odin, even when the Odin 1st stage is wearing a rubber cap.

Maybe the amount of gas moving through the 1st stage, when simultaneously inhaling and power-inflating, mimics the amount when a 2nd stage is free-flowing...
[/HIJACK]

rx7diver

 

[tbone1004]

[HIJACK]
Hmmm. One of the first things I was taught when I began Great Lakes diving (in the early 1990's) using a single 1st stage on a single back tank, is to NOT simultaneously inhale and power-inflate (anything), to NOT simultaneously power-inflate both your BC and your drysuit, etc., lest you risk inducing a 1st stage free-flow due to 1st stage icing. This applies even when diving a Poseidon Odin, even when the Odin 1st stage is wearing a rubber cap.

Maybe the amount of gas moving through the 1st stage, when simultaneously inhaling and power-inflating, mimics the amount when a 2nd stage is free-flowing...
[/HIJACK]

rx7diver

the first stages can handle it, it is extra safe guards to keep you thinking. The Norsok testing is something like 3cfm sustained at 200m using heliox at near freezing temperatures. The first stages will be covered in a block of ice, but still function
This for example is what the Poseidon MK3 looks like. It still functions normally

This is what you don't want to happen...

highly recommend everyone diving in these conditions reads this guy
https://divelab.com/download/proced...ubaRegulatorFreezing-ChillingFacts-4-9-14.pdf

 

[Bigbella]

Full disclosure, I am Ice certified, dive regularly in cold water (New England through the Winter) and religiously de-tune my IP each season. This year I will be teaching the ice diving class so I really wanted to understand the physics before I pass on a piece of advice to students that might be more folklore than science.

We were ice-diving and doing other very cold-water stuff, well before those classes and certifications were ever offered; and were typically using Poseidon regulators, with alcohol-filled environmental caps. The old Cyklon 300 IP was set (per manufacturer's specs) to 12.5 bar (about 181 psi); they worked great; and we never experienced either a failure; or, so much as a single, serious freezing episode; nor were we ever tempted to "de-tune" any regulator that was used -- which was really unheard of, back then (the late 1970s).

I would be far more concerned with intelligent and responsible pre-dive behavior -- including, the quality of the air supply; keeping that gear warm; and not huffing the gas, before water entry, than in purposefully "hobbling" a regulator . . .