Another SMB decision question...

[GrumpyOldGuy]

I disagree. Even environmentally sealed regs will free flow in cold water when the purge button is used to inflate a bag. The correct way to inflate an open bottom bag is by using the exhaust bubbles from the 2nd stage that's in your mouth, therefore never having to purge your backup as a lot of people do. I've never tried it, it seems like a pain in the ass. Closed bag is the way to go.

That does not change my logic:

If reg is appropriate, it should support 2 divers at elevated breathing rate in an emergency. If it is not, then you should have 2 x 1st stages. This is a much higher volume than 1 diver at rest adding a bit of air into an SMD. Even a full sized one vs an over sized condom.

I agree, you don't need to use the purge. Even of you do, no need to go full on with it. It is not a binary control, you can feather it just as with most valves.

 

[GrumpyOldGuy]

It's not the 1st stage that froze but the second. In cold water you can easily accomplish this with any second stage. In that case the person just closed the right post.

Got it. I will try this next time I am in cold water just for the experience.

 

[StreetDoctor]

That does not change my logic:

If reg is appropriate, it should support 2 divers at elevated breathing rate in an emergency. If it is not, then you should have 2 x 1st stages. This is a much higher volume than 1 diver at rest adding a bit of air into an SMD. Even a full sized one vs an over sized condom.

I agree, you don't need to use the purge. Even of you do, no need to go full on with it. It is not a binary control, you can feather it just as with most valves.

I don't think you're understanding the conversation happening here. No one is talking about breathing off a reg. If you purposely free flow a 2nd stage in cold water for an extended period of time there is a good chance it will continue to free flow. It doesn't matter what brand or style of regulator you are using.

 

[elan]

I don't think you're understanding the conversation happening here. No one is talking about breathing off a reg. If you purposely free flow a 2nd stage in cold water for an extended period of time there is a good chance it will continue to free flow. It doesn't matter what brand or style of regulator you are using.

Last weekend my friend was testing SP S600 on MK17. In the first burst for about 5-7 seconds it survived. In the second one started 5 seconds later for another 5 secs it locked up The purging was not really hard, just enough to get a constant stream of bubbles.
The water temp was 36F

 

[*dave*]

I would prefer an smb that I can fill with my secondary if I can find one that will remain inflated at the surface. If not I will just go with a fully clossed bag with an opv. I was thinking of the Halcyon DAM semi closed or closed or the DSS 1 meter oral inflate.

Any opinions on these or other suggestions?

DSS 1 meter, oral inflate has worked well for me.

It's not the 1st stage that froze but the second. In cold water you can easily accomplish this with any second stage. In that case the person just closed the right post.

I've never heard of a second stage freezing, but have seen plenty of first stages freeze. When the first stage freezes, pressure is not reduced and the downstream valve in the second stage can't hold back the pressure.

 

[GrumpyOldGuy]

I don't think you're understanding the conversation happening here. No one is talking about breathing off a reg. If you purposely free flow a 2nd stage in cold water for an extended period of time there is a good chance it will continue to free flow. It doesn't matter what brand or style of regulator you are using.

I do understand. I was referring to 1st stage freeze ups (these are the only ones I have actually seen). In this case, air volume is just that, volume. It does not matter if it is being used by 2 divers on an air share or 1 diver normally plus a short burst of air to inflate an SMB.

Once is was made clear you are referring to 2nd stage freezing, you are beyond my experience. Obviously, exhaled air will have some heat and make a difference. So I will test myself in my local 40F water, not Canada, but cold enough for me. One difference between us though is I inflate at 50-60' and so a few seconds of air is more than enough even for a big SMB.

I still think the tiny sealed SMB's look like condoms for the jolly green giant though.

 

[elan]

One way to see it: just have your second stage wet and then breath it on the surface when the surface temp is below 0. The colder the faster it happens. Sometimes you can get it if you just breath in and out off the reg with low surface temps.

 

[Troutmaster]

Two separate problems here, first stage freeze vs. second stage freeze. No one is saying purging your second will freeze your first stage. Using the purge on a second stage in cold water can and does lead to freeflow. I had a slow freeflow with a SP X650 a few weeks ago in 36 degree water just breathing off it, and that reg is supposed to be good for ice.

For those of you who have never froze a second stage, trust me it happens. I have never been bitten by a shark but I will take the word of the guy with the scars that it can happen.

Sounds like the OP could not freeze a reg unless he submerged it in a blender full of pina colata, I really like diving in water like that.

 

[jd950]

Well, as this SMB thread drifts off to the land of regulator free flows in cold water...thanks everyone for the input. I gather there is little difference between the DSS and Halcyon products and they are similarly priced, so I will pick one of those and give it a try.

I THINK I would prefer the more traditional OPV of the Halcyon.

 

[Bubbletrubble]

I do understand. I was referring to 1st stage freeze ups (these are the only ones I have actually seen). In this case, air volume is just that, volume. It does not matter if it is being used by 2 divers on an air share or 1 diver normally plus a short burst of air to inflate an SMB.

@GrumpyOldGuy: I believe what needs to be resolved is whether purging a second stage induces a higher overall flow rate in the first stage than two stressed divers during an air share. I suspect that purge rates are typically higher, but I don't know for certain. Also, by holding down a purge button, this produces a sustained demand on the first stage, which differs from the kind of demand placed on the first stage when two divers are sharing air (demand will vary over time). A high sustained demand will produce the adiabatic cooling in the first stage that leads to freeflow at cold temps.