First Regulator Set Purchase

[Eric Sedletzky]

I've been doing some reading and wondering about this point. Particularly after I had 3 separate free flow incidents on the same day, from 2 different 2nd stages, while using a sealed diaphragm 1st stage in 38F water (and was breathing really hard, admittedly). I originally thought it was because my 2nd stages iced up. But, the more I've replayed the incidents, the more I think that it was (or, at least, could just as easily have been) an iced up 1st stage.

I've been emailing with a diver who is VERY experienced with very deep and very cold. He avoids sealed first stages for really cold. His explanation is that it's always going to be negative (below 0C) inside the reg (at least, in the context of cold water diving). Water that circulates into the 1st stage will, by definition, be warmer, thus delivering heat into the reg. Sealing the water away prevents it from warming the internals of the reg.

I responded with, "but if you keep the water out, how would it ever ice up inside?" His answer was that even the best fills will generally have SOME moisture in them. He's had people with free flows whose tanks were measured and found to be just barely under the limit (not sure whose) for scuba tank air moisture content. The free flows were from ice that came from moisture inside the tank, not from external water.

The bottom line (my interpretation of him): if your tank gas has 0 (ZERO) moisture in it, you won't get a free flow from icing in the 1st stage, no matter which type you have. But, if you do have ANY moisture in the tank air, then having a sealed 1st stage will just keep the (above 0) water from circulating inside and warming the internals, so you'll be more likely to get ice inside and a free flow.

That all seems to make sense to me, but I'm curious about other opinions.

The way I understand it, and I certainly may be wrong, but when you're diving extremely cold water (almost ready to freeze), all the metal parts of the system including the tank and the air inside eventually matches the temp of the water. When air is released from high pressure (the tank) down to ambient (inside the first stage) it gets even colder (similar to how A/C works). The metal components closest to the super cold air get even colder than the surrounding water. So any water that's close to or up against metal that has been super cooled (by super cold air) can freeze affecting the movement of a diaphragm or a piston resulting in a stuck open first stage = free flow.
So by sealing off water from getting into contact with the moving parts of a first stage (either piston or diaphragm) the operation of the moving part can continue no matter how cold it gets.
I've let a piston first stage run wide open on dry land when I use a scuba tank to run pneumatic power tools, and the first stage forms ice on it. This is in 80 degree air temps.

I don't think there is enough water content in a tank to do anything. I never see any rust or haze in my tanks so that tells me it's pretty darn dry air. I would think it would have to be several drops worth of water to do anything inside a reg. If there was even two drops of water in one of my tanks I would see it's affects.