Metal vs. Plastic 2nd stage

[rescuediver009]

Kidspot.. Seeing as how you are in Maui I would recommend a plastic reg because a metal second stage (as mentioned) is harder to keep clean of corrosion.

 

[kidspot]

I actually had not considered that (even though rmediver pointed it out - duh) so thanks - doesn't actually sound like there's much of a difference from what everyone's said other than that and the weight issue (actually the plastic is sounding more practical . . . and cost effective . . .not a bad combination)

I appreciate everyones comments

Tim

 

[Diver0001]

The first stage is generally the site that freezes in cold water not the second.

...snip...

Really? I dive in nearly freezing water for several months of every year and I've seen dozens and dozens of regs freeze. To date the vast majority (like in nearly all of them) were 2nd stage problems. From where I'm sitting this thing about the 1st stage being the weak link seems like some kind of urban legend to me.

R..

 

[Diver0001]

Kidspot.. Seeing as how you are in Maui I would recommend a plastic reg because a metal second stage (as mentioned) is harder to keep clean of corrosion.

Really? Aren't most metal regs made from aluminium? In my experience aluminium isn't particularly prone to rusting.... For example I have a 30 year old metal Aqualung with maybe 6 or 7 hundred dives on it and aside from some dings and scratches there is no sign of corrosion on it anywhere.

R..

 

[Greg Barlow]

Really? I dive in nearly freezing water for several months of every year and I've seen dozens and dozens of regs freeze. To date the vast majority (like in nearly all of them) were 2nd stage problems. From where I'm sitting this thing about the 1st stage being the weak link seems like some kind of urban legend to me.

R..

It is the case, as several US Navy tests have borne out. The first stage freezes in an "open" position, which leaves the second stage free flowing. It appears that the second stage is the culprit, but it is merely releasing the excess gas flow.

Greg
Former Science Editor for Rodale's Scuba Diving Magazine

 

[Greg Barlow]

Really? Aren't most metal regs made from aluminium? In my experience aluminium isn't particularly prone to rusting.... For example I have a 30 year old metal Aqualung with maybe 6 or 7 hundred dives on it and aside from some dings and scratches there is no sign of corrosion on it anywhere.

R..

Metal second stages are typically composed of marine grade brass that has been plated with nickel and chrome. Aluminum alloys are lightweight, but have a tendency to dent rather easily. Aluminum will also quickly oxidize under salt water conditions unless it is anodized. I've been diving for nearly 30 years, and don't recall aluminum second stage bodies as ever being commonplace.

Greg

 

[Diver0001]

Well.....to know for sure what you're seeing you'd need to be able to block the 2nd stage and see if it starts to flow out of the octopus..... What I've seen more often than not is that one of the 2nds starts to flow during entry and won't stop. Even the octopus. In the case of a frozen 1st you wouldn't expect the octopus to start flowing would you. Even aftre turning off the octopus for a couple of minutes and trying again you often still hear it hissing. If the 1st stage were the problem you'd expect to hear the primary hissing wouldn't you?

R..

 

[rescuediver009]

Really? Aren't most metal regs made from aluminium? In my experience aluminium isn't particularly prone to rusting.... For example I have a 30 year old metal Aqualung with maybe 6 or 7 hundred dives on it and aside from some dings and scratches there is no sign of corrosion on it anywhere.

R..

I mentioned corrosion referring to salt crystalizing and corroding the sameway it would on a brass first stage (that green stuff) Not rust like you have mentioned just from water. I am talking about corrion due to incomplete rinsing of the salt water

 

[Greg Barlow]

Well.....to know for sure what you're seeing you'd need to be able to block the 2nd stage and see if it starts to flow out of the octopus..... What I've seen more often than not is that one of the 2nds starts to flow during entry and won't stop. Even the octopus. In the case of a frozen 1st you wouldn't expect the octopus to start flowing would you. Even aftre turning off the octopus for a couple of minutes and trying again you often still hear it hissing. If the 1st stage were the problem you'd expect to hear the primary hissing wouldn't you?

R..

If you blocked the mouthpiece exit, then the air would merely flow from the exhaust valve. The primary will usually flow before the alternate, as the cracking pressure is typically lower. The path of least resistance would apply. Plus the alternate is usually openly exposed to the warmer water, and thus little ice should be present.

The Navy tests that I mentioned were done in a lab setting and the first stage intermediate pressure was monitored. The adiabatic cooling effect is much more pronounced in the first stage due to the substantial pressure differential. The second stage would most likely freeze if the moisture content of the gas were too high, or if it were breathed from in frigid air temps.

Whenever a second stage goes into a free flow situation, the first stage really goes into an overload. The huge gas flow really drops the temperature in the regulator body, and then the surrounding ambient water can literally freeze into a block of ice. The ambient water chamber's spring and other parts can quickly become encased in a block of unrelenting ice.

Greg

 

[aquaoren]

If you blocked the mouthpiece exit, then the air would merely flow from the exhaust valve. The primary will usually flow before the alternate, as the cracking pressure is typically lower. The path of least resistance would apply. Plus the alternate is usually openly exposed to the warmer water, and thus little ice should be present.

The Navy tests that I mentioned were done in a lab setting and the first stage intermediate pressure was monitored. The adiabatic cooling effect is much more pronounced in the first stage due to the substantial pressure differential. The second stage would most likely freeze if the moisture content of the gas were too high, or if it were breathed from in frigid air temps.

Whenever a second stage goes into a free flow situation, the first stage really goes into an overload. The huge gas flow really drops the temperature in the regulator body, and then the surrounding ambient water can literally freeze into a block of ice. The ambient water chamber's spring and other parts can quickly become encased in a block of unrelenting ice.

Greg

Didn't the Navy tests include flooding of the first stage prior to pressurizing?
Are there no benefits for cold water diving in a metal second stage?