regulator freeze up

[buff]

How does regulator freeze up occur? I have read posts saying that to prevent freezing- lower the interstage pressure. Won't this increase the chance of freezing in the first stage? Perhaps this helps prevent freezing in the second stage but at the expense of freezing in the second stage?



Mike

 

[buff]

I meant to write:

"decreasing interstage pressure will decrease the chance of second stage freezing but at the risk of INCREASED chance of first stage freezing?"

 

[TexasMike]

Being from the southern edge of the swamp, I don't have an answer, but will add to the question list since this is an interesting topic:

• Which stage is most likely to freeze? 1st or 2nd?
  
• If your primary 2nd stage freezes up, how likely is your backup 2nd to be frozen since you have not been breathing through it.

--TM

(with weather I'm having today (very cold, wet, rainy, sleet) I'm reminded why they call this area NORTH Texas!)

 

[The Chairman]

I think I understand the physics behind the "freeze-up", but we don't have it happen too many times down here in Sunny Florida. Any time gas is vented the temperature of the remaining gas drops, as does the temperature of the escaping gas. This is opposite of what happens when you charge the tank and it becomes hot. As the temperature in the first stage decreases, there is a possibility that ice may form in the equalization chamber. Ice would cause a binding of the piston in the chamber and thus a free flow! Pistons are far more susceptible to this, unless they are "sealed" or use the Sherwood technique of a constant airflow to keep the water out. Diaphragm regs are less susceptible to this although it is a good idea to seal them as well.

"Detuning" or reducing the intermediate pressure of your regs will create a bigger "buffer zone" that will ameliorate the possibility of a free flow due to binding.

The same phenomenon occurs in the second stage as well, and small heat exchangers are used on the internal valve to use the heat from exhalation to warm things up a tad as well as heat exchangers going out into the warmer water to do the same thing. It is even more important to regulate your breathing under these conditions.

 

[buff]

"De tuning" a reg by decreasing the interstage pressure will increase the chance of a first stage freeze up-I would think?.
You are right in what you are describing, NetDoc, it's called adiabatic expansion-the expansion of a gas without the infusion of heat-it's how air conditioners and freezers function.

I underatand the physics but not the mechanics of a reg. Decreasing the interstage pressure will INCREASE the pressure difference between the first stage and second stage. This increase in pressure difference will result in a greater adiabatic expansion and a greater chance of first stage freeze. On the other hand there will be less of a chance of second stage freeze since the gas pressure drop from interstage to mouth has decreased.

I guess I don't know the mechanics of regs. well enough to work this out on my own.

 

[Lost Yooper]

Nope. The higher the pressure, the colder the first stage, the greater the chance of free flow. The same thing can be said about second stage freeze ups -- the greater the flow, the cooler the reg, and the greater chance of ice build up. A lower IP actually puts less stress on the guts of a reg and makes it more reliable.

The worst thing for first stage freeze ups is moisture rich air from the compressor -- not normal. Nitrox helps this a bunch with all the filtering going on. I think most freeze ups are second stage freezes in hi-pro regs tuned up for extemely easy breathing (ie. high flow) from the factory. I've had my sealed T50D freeze up, but the IP was set at the factory way too high for cold water diving, and I ain't talking the panzy 45-50F cold that reg manufacturers call cold. I'm talking about really cold waters less than 35F.

If you get a freeze up, catch it early (they start slow and build up), isolate it, switch to redundant reg, swish the reg around for a while and try it. The ice should melt, and you'll be good to go.

Mike

 

[Ontario Diver]

This is something that those of us from north of the 49th are concerned about as should be any who dive deep/cold.

Allow me to start with the easy questions.. Texa Mike's

1) it is the first stage that freezes not the second.
2) If the first stage freezes it affects everything, and 2nd stages don't freeze up...

buff; freeze up occurs when (as the good NetDoc) has stated when air moves through the 1st stage quickly. As the air goes though it expands (from ~3000 to ~150 PSI) and this sucks heat from the environment, mainly the 1st stage itself or the moisture that is in the air (tank air is never completely dry). This moisture turns to ice and then due to Murphy's law, cakes up on the piston or (for a diaphram ) the seat pin. Actually it tends to form where the air moves fastest, that being the little holes in in the piston or in the littel hole where the seat pin lives in the diaphragm regs. Voila - freeze up.

The usual cause of this is pulling too much air out of the first stage - more than it is designed to feed (either a free flow, or you and buddy using both the primary and alternate regs while inflating the dry suit etc.) This causes the feed system (piston or diaphram seat pin) to stay open and the rush of air causes the problem. Cold water regs have both heat sinks in them and are designed to feed more air without difficulties (4800 lpm vs 2400 lpm). Environmental sealing doesn't have any impact to this at all (Sorry Pete).

Decreasing the IP doesn't do much in these situations. I have heard people talk about it but never gotten a good reason why/if it works. Perhaps it worked with older 1st stages?

Once there is a freeze up, you cannot do anything about it except return to the surface and thaw it out.

Usual caveat is in force. I'm a new diver who has researched this alot recently because I'm buying a regulator which will be used, cold and deep. Anything that I said wrong - somebody please do me the favor of correcting me.

 

[buff]

I don't know that much about the mechanics of regulators. That being said:
The IP(inter stage pressure) is the pressure as it comes out of the tank and before it enters the second stage-correct? Then a LOWER pressure here will increase the chances of 1st stage freeze up due to an increase in pressure differences. This increases adiabatic expansion. By this same reasoning a lower IP will decrease the chances of a second stage freeze since the difference in pressures is lower and therefore decrease the amount of adiabatic expansion. There might be mechanical subtleties in regulator design that I'm not accounting for but I know my physics is right on.

Mike

 

[buff]

From what I'm hearing I agree with Ontario Diver.
The first stage freezes due to the adiabatic expansion of the gas as it moves from area of high pressure(tank) to an area of lower pressure(IP). Lowering the interstage pressure by 25-50mmHg probably won't have a big impact in a system that has about 2800lbs of pressure difference(AL 80' tank at the beginning of the dive). As a matter of fact LOWERing the IP will actually increase the chance of freeze up since it's the difference in pressure that creates the expansion of the gas.
Second stage freeze is most likely the result of a regulator that has been breathed before diving or placed in water then in cold air and then dove with. The ice was present before the dive and formation continued during the dive. I am specualting on the last paragraph.
I have a Poseidon Jetstream and Rainreg(from the scubaboard) told me it's an excellent cold water/ice regulator with a history of zero freeze ups(at least in the US Navy). But I wonder why it's such a good cold water reg. Does anybody know what makes it special for ice diving?

 

[Lost Yooper]

I beg to differ with OD. Second stage freeze ups do occur and is precisely the reason why Apeks places a metal heat exchanger in their second stages. I believe these are the most common freeze ups and are easily dealt with underwater.

Mike

I can assure you, Buff, that lowering the IP will not make the reg more prone to freeze up -- the opposite is true.