Doubles

[SeanQ]

I find it hard to believe that anyone would be stupid enough to put different gasses in each tank of a set of doubles. Not only would such a technique defeat the purpose of ahving doubles (redundency) but it introduces the very real possibility of accidentally changing the mix one is breaathing by accidentally opening the isolation valve. Someone who would do this would race a train across the tracks. Darwin will have his day.

Not necessarily. What if you left the O2 closed until you needed it and left the isolator open? To switch you would need to close the isolator, open the O2, purge the regulator attached to that post and start breathing that gas. Then you could shut down the 30/30 (or whatever) open the isolator and purge the regulators again to regain use of both regs with a known mix. You still have the redudancy of two first stages.

I wouldn't attempt it because the risk of screwing up and not noticing is too high for my liking. What happens if you need to hand off a reg while making the switch? Sounds like a Charlie Foxtrot waiting to happen.

 

[MXGratefulDiver]

Its very handy. Allows you get rid of a tank. Use tri-mix on the left side and 100% O2 on the other, and you wouldn't need to take a deco bottle.

... and what if your dive buddy needed your backup reg ???

... Bob (Grateful Diver)

 

[pants!]

Not necessarily. What if you left the O2 closed until you needed it and left the isolator open? To switch you would need to close the isolator, open the O2, purge the regulator attached to that post and start breathing that gas. Then you could shut down the 30/30 (or whatever) open the isolator and purge the regulators again to regain use of both regs with a known mix. You still have the redudancy of two first stages.

I wouldn't attempt it because the risk of screwing up and not noticing is too high for my liking. What happens if you need to hand off a reg while making the switch? Sounds like a Charlie Foxtrot waiting to happen.

Would you ever get in the water with manifolded doubles on, one side of which has 100%, and the other side of which has 30/30?

If not, why would you continue into a dive that way?

If so, well..... well.

 

[cornfed]

... and what if your dive buddy needed your backup reg ???

Jeff prefers to dive solo so I doubt that situation will come up.

 

[JeffG]

... and what if your dive buddy needed your backup reg ???

... Bob (Grateful Diver)

Well...To quote Will Smith....."Get jiggy with it"

 

[wedivebc]

Do you always remember what your tanks analyzed to last dive? Even after you get back from vacation and haven't dove your doubles in awhile? And if the gas mixes are dissimilar can you figure out how the 30/30 on one side and the 10/60 on the other will analyze out after you open the isolator?

Its easy for me now, I don't go below 120 fsw and tend to dive 30/30 or EAN32 all the time now, but in the future it'd be a bad habit for me to think i can just open my isolator and continue the dive...

I may be getting older and senile but I can remember from one day to the next what mix I was using. I see your point though and I do understand why one would want to abort a dive after finding the iso closed. I just think if you find yourself in that position so many things have gone wrong prior to that thumbing the dive is your best option.

 

[JeffG]

Jeff prefers to dive solo so I doubt that situation will come up.

Plus my backup is bungied around my neck...so he will never get it anyways.

 

[captndale]

Not necessarily. What if you left the O2 closed until you needed it and left the isolator open? To switch you would need to close the isolator, open the O2, purge the regulator attached to that post and start breathing that gas. Then you could shut down the 30/30 (or whatever) open the isolator and purge the regulators again to regain use of both regs with a known mix. You still have the redudancy of two first stages.

OK, what happens if you breath down your "30/30 (or whatever)" by, say 1/2, and then accidentally bump your iso valve and have it open slightly? The O2 would flow into the top of the tank you are breathing from; you would start breathing nearly pure O2 and ox-tox would be only a few breaths away.

 

[captndale]

Not necessarily. What if you left the O2 closed until you needed it and left the isolator open? To switch you would need to close the isolator, open the O2, purge the regulator attached to that post and start breathing that gas. Then you could shut down the 30/30 (or whatever) open the isolator and purge the regulators again to regain use of both regs with a known mix. You still have the redudancy of two first stages.

I just re-read this post and realized that the writer does not understand how a doubles manifold works. The valves at each end of the manifold are referred to as post valves; the valve in between is called the isolator valve. Each post valve controles gas flow to the regulator mounted on it only. The isolator valve controls flow of gas from one valve and regulator and the other. If you close a post valve you close off the gas to the regulator mounted on that post, but gas from the tank on that side will still flow through an open isolator valve to the other side. If you put different gasses in each tank (which I have already stated would be ill advised) the only way to keep them seperated is to keep the isolator valve closed.

 

[lamont]

I may be getting older and senile but I can remember from one day to the next what mix I was using.

i was pleasantly surprised the other day to analyze one of my tanks and find it full of EAN32, when i thought it only had air in it... felt almost like getting a christmas present in the middle of summer...

p.s. why are you all debating anything as stupid as intentionally diving with different mix and a closed isolator? now i feel sorry for bringing up the whole closed isolator issue to begin with...