Freeflow

[sky50960]

I heard and read so many things about freeflow an wath caused it, for example heavy breathing in cold water(<4 degrees C)causing freezing.
I also know that the laws of thermodynamics tells us that when pressure is dropping in the first stage, so do the temperature,add this to low outside temp. and heavy breathing and you might freeflowing via freezing.

But where does the freezing start in the first and/or second stage of the regulator?

Does humidity within the tank ( introduced while filling the tank ) can lead to freeflow?

When freeflowing is there a way to breathe thrue a freeflowing regulator?

Fa

 

[TexasMike]

I will have to defer your first two questions to those more knowledgable about such things than I. But I remember us practicing breathing with a freeflowing 2nd stage during open water training by holding the purge button down. Essentially, we let 1/2 of the mouthpiece dangle out of our mouth and breathed from the bubble stream. And I remember not getting any water in my mouth.

 

[rcohn]

I hear breathing from a freeflowing regulator is an entirely different experience when the water is in the mid 30s or colder (I haven't had a freeflow yet). The air comes out very cold and can freeze water on your face. Also, I know my mouth is usually very stiff in temps below 40 degrees it would be very difficult to grip the regulator just right to allow air to escape and still keep the water out.

Ralph

 

[Warhammer]

It's pretty easy to breath from a free-flowing regulator. The trouble is that the air doesn't last very long, espeacially if you are deep. A couple buddies of mine, both instructors, had a hairy moment a few months ago with a free-flowing reg. They were at 145 ft, and all of the sudden one of them's Apeks TX100 started freeflowing. They said the tank, an HP120 at that, was empty in a matter of seconds. So quick that about the same time the one with the freeflow switched to the others octo, the tank was empty. If not for the swift action of the both them, it could have been tragic very quickly. The freeflow was caused by a metal flake that had dislogded in the 1st stage. So be carefull out there and get your gear serviced regularly.

 

[kcbdiver]

The freezing portion happens in the second stage and eventually travels to the first stage. This is why metal and titanium regs are popular for cold water diving. The metal and titanium are primarily in the second stage so that they retain heat from your breath to prevent freezing.

If you bleed a tank dry (0 psi) and leave the valve open before filling it again, moisture will develop. If you bleed a tank dry and change it in water, the tank will take on water. Besides these circumstances, there is no moisture exchange in the action of filling a tank - only heat transfer. The next time a shop fills you tank, wait for it and feel it afterwards, it's hot. That is sometimes why they overfill the tank (i.e. 3300 psi v. 3000 psi). Because once it cools, it will be at the desired 3000 psi. They also should not be filling the tank more than 600 psi per minute for safety purposes.

Freeflowing can be caused by more than a malfunctioning reg. Swimming against a swift current can cause the purge button to push in slightly causing free flow.

Warhammer, you learned the easy way to breathe off of a freeflowing reg. The way I learned was to put your thumb in the middle of the opening to the mouthpiece and basically swipe (pulling the mouthpiece open and across your mouth), pull it away and so on. Of course, you don't get much air because it is coming out so fast; but maybe that will help with stiff lips in cold water!

 

[Kane(adian)]

Breathing from a freeflow...did it in the pool. Thought it was easy. We did it for a minute, just bit on the right tab, tilted head to the right, and breathe easy. Thought it was neat, especially because the air was cold, the only bad thing was that under 2 feet of water, I went through about 500# in that minute.

I would imagine that the freeflow is often caused by the moisture in the air that we exhale.

 

[turnerjd]

Originally posted by kcbdiver
The freezing portion happens in the second stage and eventually travels to the first stage. This is why metal and titanium regs are popular for cold water diving. The metal and titanium are primarily in the second stage so that they retain heat from your breath to prevent freezing.
<snip>
Besides these circumstances, there is no moisture exchange in the action of filling a tank - only heat transfer.

On both these points I beg to differ.

Freezing is a problem with the first stage almost uniquely. Regs freeze simply because expanding air (by fundamental thermodynamics) cools significantly. Where there is the greatest pressure change, there is the greatest cooling.

If we consider the pressure change between tank and IP, and then IP and ambient, The difference (on a full 232 Bar tank) is 222 Bar, whereas IP - Ambient is about 9 Bar. If you look at divers in and out of very cold water (eg UK in the middle of winter) there is often visible ice on the outside of the FIRST stage. (IP = intermediate pressure, sometimes called interstage pressure)

Also, if you think about manufacturers claims that metal parts retain heat from your breath you will also quickly realise that these claims are entirely suspect. Think back to the OW course. Water conducts heat some 25x more efficiently than air. Put a large piece of metal in the water and breath on it. What is happening? What will win? heat transfered from exhaled air, or the 25x more efficient transfer from the water? I would bet that the body and internals of a second stage are far closer to the water temperature than 37°C.

Due to the cooling of the air as it expands in the second stage (a pressure change of 9 bar) there is some cooling, most regs have small heat exchangers on the inlet hose to stop the actual valve getting too cold (If you have an Apeks TX 40, 50 or 100 look at where the hose joins the second stage - that is the heat exchanger there just inside the plastic housing).

For cold water diving, favoured cold water regs (apeks, scubapro etc...) DON'T have much metal in their second stages. Scubapro and Apeks have large plastic bodies, with very small heat exchangers. However, they do have large metal first stages to conduct heat away. Scubapro take this further and have water flowing through their FIRST stage to activly bring it up to ambient water temperature to avoid freezing (Apeks go the other way and eliminate all water - if there isn't any water in there it can't freeze). If you can get to a large diving exposition where most manufacturers are present, talk to people like apeks, scubapro and poseidon (the big 3 for cold diving) and they will quite happily explain the physics of what happens.

The whole point of this post can be proven quite simply. Take a cheep second stage (for example the apeks T20 - it doesn't have a heat exchanger or any controls etc..) and put it on a top of the line first stage. Then go diving with it in extreem cold temperatures. When I did this with my T20 there was absolutely no problem, even though there was ice on my FIRST stage.

The second point (about moisture) is also wrong (although this point is just being pedantic). When you get a fill, you always get a certain ammount of moisture in the air. Compressors take in normal air, normally air is around 40-50% RH unless of course you are in the middle of the sahara desert where it is 0(100%RH is when the air can take no more moisture, 0 is totally dry) so these is a significant ammount of water in the air. Compressors have a chain of filters to get rid of a number of things, the most important being oil, and moisture, however, the two are never really 100% effective. Scuba air is never completely dry, although it is usually pretty dry. There is always SOME moisture there.

Jon T

 

[sky50960]

I forgot thank you for " illuminating me "