Toby

[DivingGal]

seahunter once bubbled...
WetVet and DivingGal have mentioned a phenomena that I don't believe exists - a double header freeflow. ...

It isn't the second stage that freezes and causes a freeflow. It's the first stage. ....
Even freezing is a misnomer since steel and plastic can't freeze. What's happened is that water in the air or reg has frozen in the first stage and the resulting ice on the HP seat won't let it close completely ....

What causes a double header? As the IP (intermediate pressure) rises from the frozen open first stage, the second stage will let it escape - it freeflows.

I agree it's the first stage not the second that "freezes", and I also agree that freezing is a misnomer. I believe what WetVet was meaning a freeflow from his first stage, and thought what Dopper meant was to share the octo from that kit (but Doppler meant, I believe, to use the buddy's octo).

I have, in my short diving career, both the reg and octo freeflow at the same time. It was in cold water (I believe low 40s) with equipment that was actually due for annual servicing in a couple months. So rare, yes, but it does occur.

--- a short and I hope sweet response, no need for a soapbox.

 

[weight_for_me]

I agree...I had the same thing happen a couple of weeks ago...first dive, cold water...breathing a little hard. Told my LDS about it..he also said the fist stage froze. BUT, as the freeflow increased, (and the thing about gases expanding and getting cold) it also caused the second stage to freeze. As a matter of fact, when I got back to shore, there was a chunck of ice in the mothpiece. Anyway, it happened at about 30'...signaled my buddy..I kept breathing through the freeflow (as I was taught) and had a very successful ending to the experience.
Randy...

 

[cat]

Water's still pretty cold on the surface right now and the temperature profile the last 2 weekends (of my diving) has been inverted - ie the 4 C water is the warm stuff, so it's the *upper* layer that's cooler. This would make a reg "freeze" (umm, why is this a misnomer if it's ice forming in there?) seem that much more likely on the way up - ie been working hard at depth, then ascended into a colder layer. Only takes half the heat loss (from Joule-Thompson expansion) to freeze at 2C as it does at 4C.

We (MWC and self) think this is what happened to his reg on Sunday (no FF, no OOA, no real distance to surface by the time breathing go difficult so no unpleasant results other than a surface swim). Does this make sense? Do ice divers and others diving in water <4C experience occasional ice-related problems during ascent?

 

[wetvet]

What I meant by the double header free flow is that if your reg free-flows.....you turn off your tank and breathe off your buddy's octo....then, because 2 people are breathing off of the same 1st stage, it is more likely to free flow. Now you have one tank off...which may or may not fix the problem...and 2 folks breathing off a 1st stage which is free flowing. Even if the octo doesnt freeflow (due to the reduced pressure from the primary freeflowing), you are in worse shape than if you just surfaced breathing on the origional free-flow.

Im not trying to be arguementative....I am really curious as to whether 2 folks breathing off a 1st stage increases your risk of a free-flow. This impacts whether or not I would consider turning off a tank to correct the problem. Thanks.

Wetvet

 

[Doppler]

wetvet once bubbled...
What I meant by the double header free flow is that if your reg free-flows.....you turn off your tank and breathe off your buddy's octo....then, because 2 people are breathing off of the same 1st stage, it is more likely to free flow. Now you have one tank off...which may or may not fix the problem...and 2 folks breathing off a 1st stage which is free flowing. Even if the octo doesnt freeflow (due to the reduced pressure from the primary freeflowing), you are in worse shape than if you just surfaced breathing on the origional free-flow.

Im not trying to be arguementative....I am really curious as to whether 2 folks breathing off a 1st stage increases your risk of a free-flow. This impacts whether or not I would consider turning off a tank to correct the problem. Thanks.

Wetvet

If breathing off an octo causes a freeflow, then why do we use them? I started a new thread for this but a freeflow is not normal behavior for a reg... tell you what, go read the other thread!

Doppler

 

[DivingGal]

wetvet once bubbled...
What I meant by the double header free flow is that if your reg free-flows.....you turn off your tank and breathe off your buddy's octo....then, because 2 people are breathing off of the same 1st stage, it is more likely to free flow.
<snip>

That I have never had happened to me, or to anyone I know.

In our waters here, I think it's just one more reason to have the right equipment for diving. Sure I don't really think 60F (or 50F) is "cold water".... but to scuba equipment (and some of those "southern divers", I think it is. (Though if I'm wrong please remind me what is considered cold for the manufacturers). My point is this, use the equipment necessary for the diving you do. If it is cold water, have the reg set-up for it, otherwise you just may be asking for trouble.

 

[seahunter]

Yes! WetVet is quite right!
The greater the volume of air passing through the first stage the greater the likelihood of a freeflow. It's a simple application of the physical law that governs the adiabatic drop in temperature as a pressure drop in a gas occurs. That's how a refridgerator works and lots of other cooling devices.
A refridgerator compressor raises the pressure of the coolant gas just as an air compressor fills your tanks and heat is given off as it does so. Feel the back of the fridge. It's warm like your freshly filled tank. The greater the pressure of the gas or the greater the volume being compressed, the greater the amount of heat given off.
Then the opposite occurs. The coolant is allowed to drop in pressure as it flows through a reducer (read: regulator). As the pressure drops, heat is absorbed so the surrounding structure (the ice box) gets cold. The greater the pressure drop or the greater the volume of gas passing through the reducer, the greater the amount of the temperature drop.
In the case of your scuba regulator, any moisture in the reg will freeze or the moisture in the air may reach its dew point and condense and freeze. This can occur in water temperatures as high as 40 to 45 degrees F.

Two people breathing off a reg creates a condition more likely to result in a freeze-up and free flow.

Unfortunately there is no regulator system that will not freeze given the right circumstances. Some have special features that may reduce the likelihood but they all can be made to freeze up in normal cold water diving. Two hose regulators from years ago were very good in cold water. Regulators with environmental protection are usually a little better but not for the reason you may think. Store staff will tell you that they keep the water out so they don't freeze but it's not the surrounding water that freezes any way. It's the water or moisture inside the reg that freezes. Environmentally sealed regulators (Sherwood, Genesis and to a lesser extent those with an add-on rubber kit) will still freeze but are slower to reach the temperature that causes it. So slow that they may not freeze during a dive. Every regulator made will freeze. I've been on training Ice Dives on very cold days and even seen several Blizzards freeze up.
With a good sealed regulator, kept warm until the last minute, well-maintained, using very dry air, not breathing from the regulator until well underwater and not engaging in activities that require large volumes of air, you may dive in very cold water and have no problems.
All this is covered in any good equipment course or ice diving course.

One thing that's not been discussed is the increased likelihood of a freeze-up and free flow on deeper dives. The deeper you go the more volume of air passes through the regulator and the greater the adiabatic temperature drop.

Check out Doppler's thread under "Procedure for Dealing with a Free Flow" for more good ideas.