regulator freeze up

[Lost Yooper]

By tuning the reg down you certainly won't have a high performance reg, but it is certainly capable of giving you all you'll need. It's just coming at you at a lower pressure.

This is all quite simple. There's only so many factors that cause freeze ups. Eliminate the factors the best you can and hope for the best. Regardless, all down stream valve regs are prone to freeze up due to their second stage design. If cold air meets moist air and interferes with the mechinisms that make it work, you got a freeze up.

There are steps you can take pre dive to help ensure freeze ups don't occur, but if you have moist air in the tank, nothing else matters. The volume of gas inhaled is only really relevant to the second stage freeze up -- assuming dry air is in the tank and the FS is sealed.

Mike

 

[The Chairman]

Stop comparing your regs to refrigerators... it is NOT the same set of principles involved... To get the cooling involved in a freezer/refrigerator/AC unit, you HAVE to have a phase change. Freon is compressed (Hot, hot gas), Freon is then cooled in the condenser (cool liquid) Freon is then metered (orifice or valve) out as a low-pressure liquid... this liquid evaporates in the evaporator absorbing any heat present to do the job. This phase change is far more drastic than just expansion... take the heat it takes to increase one gram of water one degree centigrade... only one calorie! So, it takes 80 calories to get room temp water (20C) to 100C... now getting that one gram of water from 100C liquid to 100C GAS will take 600 calories. THATS a lot. So don't confuse the two... the mere expansion of gasses (though considerable) is far less cooling than a phase change.

 

[buff]

The reason you can compare a reg. to a frigerator is not because the gas goes through a phase change-I even I know you don't dive with liquid air- but because it expands, and cools-hence the term adiabatic expansion.
The processes are similar but not the same....duhhhhh
If you don't believe that gases can greatly cool as they expand try this:
Take a small CO2 cartridge that is used to inflate flat tires on bikes. They have about 150lbs PSI of CO2 in them. Put the thing in a vice and place your hand on it as you puncture it. Then call the burn unit-it will freeze your finger off. That is how much cooling can take place in a gas expansion from just 150psi to ambient pressure-it's very surprising. It won't freeze a turkey but it will burn your finger. And the cooling of a gas will freeze a reg. and that's what we are discussing here.

 

[The Chairman]

Originally posted by buff
The processes are similar but not the same....duhhhhh
If you don't believe that gases can greatly cool as they expand try this:

Nope, not the same! Not similar! Refrigeration DOES NOT rely on adibiatic forces! As great as adibiatic forces are, phase change forces are greater by several factors of ten. In fact, refrigeration has to overcome adibiatic forces to work efficiently. Check any engineering handbook on refrigeration and you will see a multitude of calculations for phase changes, but none for adibiatic forces. Well, it might be a foot note at the bottom some where. You can belittle what I have written with a "duhhhhh" all you want. I hope I never have to resort to that kind of argument to bolster my contentions. I'll stick to the facts and logic instead.

 

[Bob3]

Are you trying to tell us that an expanding gas does NOT absorb heat upon expanding?

If that's the case, what causes half an inch of ice to grow on our first stages? :cold:

 

[The Chairman]

I am NOT saying that expanding gas does not cool... check out my first (and subsequent posts). I am saying that is not where the BULK of heat transfer occurs in a refrigeration system. This is due to phase changes. Gas to liquid and then back again. There is only a pound or two of Freon in a typical car... If you were to open a can of Freon (back when we had 12 oz cans) you would notice that the pressure is not that high (35 to 45 psi at ambient temps) but that a HUGE amount of frost would accumulate on the can as the liquid to gas phase change occurred! Any further expansion of the gas would occur OUTSIDE the bottle, and yet the container would be far colder than if it had been filled with ONLY gas.

Rule of thumb...

adiabatic cooling... cold!
phase change cooling... way way way cold!

I'm sort of sorry I brought it up, but I hate fallacious reasoning! I -personally- want to understand fully what is actually happening in a given system. After I saw the second comparison to refrigeration, I thought I would point out that there ARE differences in how the two systems work. Sorry for the controversy, and if you feel better saying they are the same, then by all means, I will withdraw the contention! Ignorance CAN be bliss...

 

[CheeseWhiz]

...but the simple expansion of a gas is enough to cause icing, even without a phase change.

For those of you old enough to remember carburetors, you will recall there was a cheap bit of corrugated hose which led from the exhaust manifold to the air cleaner snorkel. This warm air was fed into the carburetor and was enough to prevent carburetor icing. Without it, a carb will quickly ice up in cool/cold weather. The ice is caused (and I know, because I've been stuck by the side of the road, poking a screwdriver blade down into the carb to knock the ice off) by the pressure drop of air through the venturi. No phase change involved or needed.

 

[The Chairman]

The icing in a carburetor was not caused by adiabatic cooling... it was caused by vaporizing the gasoline! As air is drawn through the venturi within the carburetor, there is a low pressure point just below the thinnest part. This is how the gas is "sucked" out of a carburetor. LIQUID gasoline can not combust as readily as VAPORIZED gasoline! Adiabatic processes allow for NO exchange of any heat... if there is an exchange of heat, it is a NON-adiabatic process. What follows is a definition taken from the net...

"THE ADIABATIC PROCESS

The adiabatic process is the process by which a gas, such as air, is heated or cooled, without heat being added to or taken away from the gas, but rather by expansion and compression. In the atmosphere, adiabatic and nonadiabatic processes are taking place continuously. The air near the ground is receiving heat from or giving heat to the ground. These are nonadiabatic processes."

While heat affects temperature, it is actually measured in calories or BTUs and NOT degrees. A rise in temperature does not necessarily need an increase in heat. Heat exchange systems (like ANY refrigeration system) and phase change processes ARE NOT adiabatic. Not, not, not!!!

In review:

The adiabatic process in a regulator WILL cause the condition know as regulator freeze (no it is not really a true adiabatic process as there is some heat transfer, but I am not trying to split hairs).

The adiabatic process in a regulator is NOT the same process (only different as one person put it) found in ANY heat exchange system. Those systems rely on a phase change from liquid to gas and back again to transfer heat, which is NOT what is happening with your regulator.

Adiabatic cooling or heating is NOT nearly as radical as that encountered in phase change processes. It only affects the temperature of the system and not the heat content of the system.

Again, I apologize to everyone for bringing up such a controversial point! It was so minor to the discussion at hand, and I meant it more as a trivial correction. As most can tell, I love to understand the whole picture… not a partial one. AND, I hate over-simplification of complex processes. There is so much more that I yet do not understand, but I will keep trying to piece it all together one concept at a time… at least until I die!

 

[Lost Yooper]

Good morning. There was a time that I was interested in respitory shock theory in which super cold air being breathed will cause the respiritory system to freeze and shut down leaving the diver unable to breath. This particular theory doesn't hold much water, but the illustration of the super cold air is interesting.

At a water temperature of 75F and tank pressure of 3000psi, the air temp coming out of the first stage is 25F; water temp of 40F the air is -10F; water temp 32F the air is -18F. These temps would be reduced with helium mixes.

Part of the problem of the respiratory shock theory is that the air is warmed considerably while it is in the hose (long hose users would see greater warming), but it cools again when it hits the valve in the second stage. The other, more important, problem is that us polar bear divers are not keeling over by the hundreds every year on ice dives and deep, cold, helium dives.

Anyway, the temperature of the air leaving the first stage is plenty cold to freeze moisture.

Take care.

Mike

Source: http://www.nitroxdiver.com/Library/coldreg.html

 

[Lost Yooper]

Since I didn't figure you guys would trust my word, I got a hold of Apeks. Here's what they said:

1. Generally 1st stage freeze ups only occur with 1st stages that are not environmentally sealed. The gas expansion in the 1st stage causes the cooling effect and with unsealed 1st stages, the spring chamber is full of the surrounding water and the cooling of the 1st stage can eventually cause the water in the spring chamber to freeze, preventing the spring from compressing, so the valve remains open and the a freeflow occurs. In an environmentally sealed 1st stage, the spring chamber doesn't have any water present, so it can't freeze. There wouldn't be enough moisture in the air being used to cause a problem of freezing.
Reducing the interstage, in theory, would make the problem of 1st stage freezing, worse, as you have increased the pressure drop from cylinder pressure to intermediate pressure, and so increased the cooling effect, but the pressure drop difference is tiny.

2. 2nd stage freeze ups are more common than 1st stage freeze ups, as there is generally more moisture present with the 2nd stage. They are caused in a similar way as the 1st stage freeze ups, as the gas expands from intermediate pressure to ambient pressure, the valve cools and moisture in the 2nd stage case can freeze the valve lever in the down position, causing the valve to freeflow.
Heat exchangers do help the situation and detuning the 2nd stage can also help. Keeping the 2nd stage in your mouth is the most important thing in cold water, as cold water entering a cold 2nd stage can freeze instantly. There is no definite cure for a freezing 2nd stage, you can only help the situation by taking precautions.

3. Yes, with a sealed 1st stage, it is only the 2nd stage that can freeze.

4. Lowering the intermediate pressure (as mentioned in 1. above) can in theory, increase the risk of a 1st stage freeze, but by very little, especially in sealed 1st stages. Lowering the intermediate pressure would more likely REDUCE the risk of a 2nd stage freeze, as you have reduced the pressure drop from intermediate pressure to ambient pressure by a greater percentage.
You would not be making the regulator any more reliable by reducing the intermediate pressure, as most of the stress is caused by the high cylinder pressure, it will easily cope with the relatively low intermediate pressure.

I hope this answers your questions.

Landon Helsby
Technical Service Manager
landon.helsby@apeks.co.uk (landon.helsby)

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From now on, I'm going to simply end my posts with BISS! -- Because I Say So!. That should be enough, right?

Take care.

Mike