Solo sidemount configuration

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Sorry so why not use this? product code: 33049 Dual Tank Valve (Used with Neptune Space and Neptune II NIRA masks) Permits the connection of the NIRA to two different gas sources (air/ nitrox), allowing alternate use of gasses without removing the full face mask Why do you want to go around this connector? This connector seems like it would do what you want... Taken from the site you gave me.

 
Basically because if I have only one 2nd stage and it freeflows and I cannot stop it, I am in trouble.
If I have two 2nd stages and one of it freeflows, I can close the tank valve and continue with the other 2nd stage.
Plus it's expensive, almost 250 euro.
 
Ok last question - and it may be personal - by why do you need a Full Face Mask? Seems like you are doing a lot of work for something that it may not have been built for...
Of course if you have dual tanks and it free flows - it seems you could get to the surface before they both get to zero pressure. That said how deep are you thinking you need to dive with the limitations you are putting on yourself?
 
Several reasons. The waters nearby me are quite cold and breathing through nose improve the thermal comfort. Sometimes breathing dry air through mouth causes me discomfort ( I had some nasty coughing episodes under water, not often but I had) and I feel mentally more comfortable knowing that the thing supplying me air cannot be removed as easily as a normal 2nd stage. Especially that I am diving solo most of the time.
Yes, freeflow should not be a deadly issue, even with one 2nd stage, I should reach surface before the tank empties. Depth limitation, will be no more than 30 meters or so, I am not eager to feel narced. But most of the time is much less, around 10-15m.
 
If you are set on a FFM - call the manufacturer or write to them and explain your needs - see what they suggest.

My thought is you may not be suited for cold water diving and it may turn out to be a waste of money if you dont continue to dive (FFM can be expensive and you are modifying it). But that is me - I try to find the easiest/safest way to dive that is cost effective for my wallet. Good luck.
 
Good point. Maybe I will just remove the mask, rip the other 2nd stage from the mask (not the one built into the mask) and put it in my mouth. It takes less than 10 seconds. I will have to keep it with my hand/teeth since it has the mouth piece removed but it will supply air. And perhaps a spare mask will be nice to have.
But I never heard of this scenario. Are you aware of such incidents? When and most importantly, under what circumstances will a ffm break? Except very hard impacts which will most likely render me uncoscious. And in this case, a normal mask+regulator won't make any difference.
 
Well, I'm fairly sure commercial divers are trained for such incident.
If you think you'll be able to remove a ffm, remove a 2nd stage of it, breathe it off, when your mask might flood after you've exhaled, go ahead. I wouldn't, but if you're fine with that, no problem here.

Remember, everything gets more complicated underwater. I honestly doubt it takes 10 seconds to do the whole procedure underwater. And even if it would, those 10 seconds might seem awfully long.


My vision is that every piece of gear I use will break at some point during a dive. It's just a matter of time. So everything that is vital is completely separated as long as possible. (hence the 2 tanks, independent, with each their 2nd stage, again independent)
 
This drill I did not do, mainly because ripping the regulator will probably break the adapter which keeps the regulator attached to the mask. But when it's life and death situation, I am willing to do it. It will come out, the adapter is attached to the regulator like the mouthpiece and secured with a zip tie. On the other side, I performed the standard drills for a ffm (ffm removal, put standard regulator, put spare mask) in approx 10 seconds, give or take few more. Reversed operation takes a little more time because of time required to adjust the straps of ffm after donning it.
My vision is also that everything will break eventually, I'm an engineer. As you say, this is why I keep 2 tanks, 2 1st stages, and 2 2nd stages even on ffm. This is the reason I am not willing to use a gas switch block and rely only on one 2nd stage. But I really want to understand what possible scenario will result in mask failure (except regulators). At this moment, all I can think of is a hard impact with a rock or boat. But if that happens, my problem will be bigger and presence of another standard configuration (regular mask and two normal 2nd stages) won't solve it.

On the other hand, I just came from the pool, today is the first time when I tested this configuration. As expected, there were some differences between theory and practice. It was a successfull test, it performed more or less like I expected and for me this is a green light to go on further with this configuration.
Some observations about the test:
-it was performed in a 4 meter pool, no bcd, 2x4 liters steel pony sidemounted with 2 apeks ds4 1st stages and apeks atx40 2nd stage besides the built in 2nd stage. Also, shortie wet suit and 3kg weigth. A bit negative with empty lungs, a bit positive with full lungs.
-balancing the air flow was easier than expected. It was fairly easy to adjust cracking pressure on both regulators to a point where air is consumed simultaneously and in fairly equal quantities from both tanks.
-from the cracking pressure of the 2nd stages, I was able to completely close the mask built in regulator and breathe from apeks 2nd stage, but I was not able to completely close the apeks and breathe only from mask built in regulator. Mainly because apeks is tuned from factory to have quite low cracking pressure, to be easier to breathe. But I will adjust it a bit to be harder to open. On the other hand, mask regulator have a very wide range of adjustment, at one end it freeflows no matter what, at the other you almost cannot breathe without pressing purge button.
 
https://www.shearwater.com/products/peregrine/

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