Coldwater diving octo

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Raphus

Contributor
Scuba Instructor
Divemaster
Messages
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Location
Germany
# of dives
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Hey, i prepare myself for coldwater diving in the wintertime.

Currently i got:
12 liter tank with 2 valves.
Mk17evo g260 and r195 octo.

I am buying one more mk17evo.

Now my questions:
1. Is the octo r195 fine as a second regulator in coldwater or should i buy a second g260?

I read a lot in sb. And most people say you have to dive 2 identical second stages. But i hear quit often the opposite..
The cost of one more second stage, that needs to be serviced adds up with all the stuff i have/want to buy.
But i am not sure if the r195 octo is good enough fas a secondary in cold water diving.

2. Is 1 regulator per firststage enough? I think so? Also where do you atach your gauge? On both first stages, or only on the backup one?

I would like to hear your opinion :)
Thanks!
 
1. R195 is fine, most cold water issues are operator error. G260 is better, but your choice. I prefer matching second stages, but it's not something I'm adamant about.

2. do not have more than one second stage per first. Second stages are the biggest risk in cold water diving, and you don't want the added complexity for a myriad of reasons

3. SPG goes on the left post per standard DIR hose configurations
 
1. R195 is fine, most cold water issues are operator error. G260 is better, but your choice. I prefer matching second stages, but it's not something I'm adamant about.

I too prefer the same brand of safe-second; and generally prefer something which can be desensitized by a knob or switch, such as the Jetstream. On my regs, with octopuses, they have been tuned identically; and I have never had any issues with them in cold water, to freezing.

The problem that can arise, is a safe second, coupled with a given regulator, which is designed to run at a different or higher IP . . .

The cost of one more second stage, that needs to be serviced adds up with all the stuff i have/want to buy.

The difference, in price, of servicing one second stage over another, is fairly nominal, between the two options that you've chosen . . .
 
I too prefer the same brand of safe-second; and generally prefer something which can be desensitized by a knob or switch, such as the Jetstream. On my regs, with octopuses, they have been tuned identically; and I have never had any issues with them in cold water, to freezing.

The problem that can arise, is a safe second, coupled with a given regulator, which is designed to run at a different or higher IP . . .
The r195 is from the same brand as g260. And they are designed to use the same firststage. So i guess they use the same ip?
 
The r195 is from the same brand as g260. And they are designed to use the same firststage. So i guess they use the same ip?

Yes, I would think so. I was thinking more of the Poseidon Cyklon, an oddball which runs at 11.5 bar, which pretty much eliminates every other regulator brand, as a contender for a safe second . . .
 
I require an in water adjustable, and a metal air barrel (actually, the more metal the better) second. I dive Mk17/g250 seconds for my modern rig (or Poseidon XStream), and a double hose/156 seconds on my vintage stuff. Wife & daughter dive HOG D1/Classics.

This is Great Lakes cold, and Ice Diving. Under ice, it is an independent rig.

Like @tbone1004 said, issues are mostly user error, but I also want even higher odds.
 
The r195 is from the same brand as g260. And they are designed to use the same firststage. So i guess they use the same ip?
Poseidon is the only modern brand that runs at strange IP's and the Cyklons are the only ones that become an issue to use with other regulators.
The reason to stay with the same brand is to make less hassle when you need to get them serviced.
 
A few words about free-flows

One of the problems caused by cold water is the greatly enhanced risk of a regulator free-flow, which drains your gas faster than you would want.

Sometimes free-flows happen at the surface already but in these cases we are talking about ice diving in freezing surface temperatures (and the water is relatively warm then). A good ice diving course would cover surface operations (including but not limited to: do not exhale into the reg while in freezing cold air and once the reg submerges, it stays submerged).

Free-flows need three predisposing factors to happen
  1. moisture in the wrong place (cylinder or 1st or 2nd stage)
  2. cooling (either in the 1st or 2nd stage)
  3. time for the ice crystals to form in the wrong place
Scenario: 1st stage free-flow

If the compressor used to fill your cylinder is not maintained and operated well, your cylinder might contain moisture. The situation is worse if you use rented gear and someone had an out-of-air event before and some water found its way into the 1st stage or maybe the cylinder. Now that you own your gear you just need to make sure the compressor is operated properly. Whatever the reason, the moist air cools down a lot in the first stage due to decompression from 200 ATA to about 10 ATA. If the water surrounding you does not warm the first stage enough, icing could take place inside the first stage - and leave something open. This would cause a wildly free-flowing regulator. No number of second stages will help you now. You will need another first stage, which hopefully is drier, or at least does not free-flow quite yet. Your options: close the cylinder valve and wait for the ice to melt and the first stage to recover its operation... although this could take time and the problem would probably repeat itself. And who knows if your other first stage is similarly affected... It's time to abort the dive nicely - and to use better maintained gear & compressor next time.

Scenario: 2nd stage free-flow

The very air you exhale is moist. This moisture will make the inside of your second stage moist (moist, but not flooded with warm, above freezing, water). You cannot stop this from happening. It's just a matter of time. At the same time a pressure drop from the "intermediate pressure" to the "ambient pressure" happens at the regulators second stage and the air thus cools down a lot. Unless the water around you is capable of heating your regulator enough, the moisture inside the second stage will cause small ice crystals to form. Those will unfortunately make your second stage leak air. This problem would probably manifest itself as some hissing and a minor air leak first, then a little bit of bubbles, then more bubbles, and if the situation grows worse, a full blown free-flow. How quickly the situation develops and grows worse varies. Solution: close the cylinder valve and wait for the ice crystal(s) to melt away. The liquid water that enters your reg will help to melt the ice crystal(s) away - it is above freezing temperature anyway [and no, we do not discuss Antarctica now]. You can use the other first stage + reg for breathing while waiting. Depending on the type of the dive (open water vs. ceiling, shallow vs. deep) and diver (used to free-flows, not used to them) aborting the dive may be a wise thing to do, but it is not always strictly necessary. Rule of thumb: abort the dive if there is no immediate access to surface or if the problem repeats. Some advanced techniques exist to manage gas flow would aborting not be possible (feathering).
 
I plan to dive the great lakes and some local lakes at depth in rec limits. So i would expect a freeflow at depth.
If my g260 freeflows i would switch to r195, Which is cold water certified, But in my opinion not as food as g260(less metal). And close the valve of course.
What i am scared about is, that it freeflows right away(or at least very fast) because its worse then g260 which freeflows already.
But on the other hand i am not sure if its realy that bad, so i have to buy another g260, or if its fine, because its very similar.
 
Well maintained cold water certified regulators rarely free-flow in 39F water during a recreational dive. I do such dives (and more advanced ones) every week and I almost never have any problems with free-flows. Just make sure the air in the cylinder is dry and there is no moisture inside the hoses and the first stage.

If both of your second stages free-flow simultaneously, then

1) there will be some noise
2) there will be copious amounts of bubbles clouding your vision
3) your lips / the reg may shake a bit
4) the air flow will cool your teeth, which can cause some pain (the same as you get when you eat ice cream too greedily)
5) you can still breathe as you have all the air your will ever want - and more - at least for a period of time. You may look like a hamster with big cheek, though.

Now, 1, 2 and 3 you can experience in a jacuzzi. Only 4 and 5 are specific to diving

The problems are easy to solve: The solution to tooth pain and too much bubbles is to hold the offending reg at an arms length and only put it in your mouth for a breath or two; continue your ascent and repeat.

ps. The usual precautions still apply: stop-think-act, breathe, stop descent, signal your buddy, ascend together, continue breathing and blow bubbles when the reg is not in your mouth [a burst lung is really really bad]
 
https://www.shearwater.com/products/perdix-ai/

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