Low pressure manifold?

[scubaalblake]

Ok
This has been on my mind for a couple of weeks. It *seems* like a good idea.....but I'd really like someone to point out the flaw in my reasoning and why it wont work. Its a bit convoluted so please bear with me while I try to explain.
OK - in many circumstances I use doubles - sometimes manifolded, sometimes not. We have all repeated ad nauseum the manifold vs. not arguments which essentially boil down to:
Manifold reduces task loading on dive due to reg switching, at the increased risk of having a potential manifold failure that could lose all your gas supply if you don't shut it down fast enough and you have to be fast because its HP....and.....independent doubles are, well, independent, the most you'll lose from a single failure is half your gas...but on a dive without failures you have to continually swap regs.

So far so good. Now I started thinking of side-mounting and that in most configurations they are completely independent - therefore requiring reg swaps to keep gas balanced. So I thought - why cant they be manifolded? Now obviously you cant have a rigid manifold but why not a flexible hose one...argh everyone screams what a failure point you've now got a flexible HIGH PRESSURE link between your gas supplies...are you mad? But...then I thought why not LOW PRESSURE.
Why couldn't you simply have an extra quick disconnect LP BC feed from each first stage plugged into a simple 'double-adapter'. You've now manifolded the tanks together on the LP so you don't have to reg swap as they will balance each other on the LP side (I think). If you have a manifold failure any leak is slower (its LP) and all you have to do is use the quick disconnect to break the manifold and breathe off the tank that's ok.
You could even route the manifold across your chest from L-R...not round your back where a) you can get to it and b) you can disconnect easily if you have to.
Oh and the whole thing is built from standard scuba hoses....apart from the 'double-male' connector in the middle of manifold - which would be trivial to fabricate.
So - whats wrong here? What have I missed. Why wont it work? I cant find evidence that anyone has done this before...which makes me think it wont work ...but I don't know why and its really bugging me!
Al.

 

[triplecove]

"If you have a manifold failure any leak is slower (its LP) and all you have to do is use the quick disconnect to break the manifold and breathe off the tank that's ok."

If I am not mistaken, a failure on the low pressure side will drain your tanks faster than a failure on the high pressure side of your 1st stage. due to the very small orfice that your HP side has. The low pressure will allow much larger volume if you have a line failure. This by no means says your idea wouldn't work, just wanted to point it out.

 

[elan]

I think your assumption about them balancing each other on lP side is incorrect IMHO. That would be the case if the IP on both regs are exactly the same. If my understanding of physics is correct in reality the reg with higher IP will be overrunning the reg with lower IP and the corresponding tank will be used up faster.

 

[nimoh]

the only problem I can see that this would solve is when you have a broken second stage, and so then you can breathe both tanks through the other second stage.

if you have a first stage issue, you can't shut it down and still use the gas in the tank as with a manifold.

 

[triplecove]

the only problem I can see that this would solve is when you have a broken second stage, and so then you can breathe both tanks through the other second stage.

if you have a first stage issue, you can't shut it down and still use the gas in the tank as with a manifold.

I think the OP means 2 1st stages with a lp line between them and I suppose that you could have a 2nd stage off of either or both 1st stages. Correct me if I am wrong?

 

[elan]

regardless if one first broke the tank is gone.

 

[nimoh]

I think the OP means 2 1st stages with a lp line between them and I suppose that you could have a 2nd stage off of either or both 1st stages. Correct me if I am wrong?

that's the way I interpreted it, although I assume both first stages have a second stage (as in a normal sidemount setup)

 

[rhwestfall]

LP balancing won't work between the two first stages as Elan said in post #3. HP "could" work as it is not through the regulator, but you likely can't move enough gas between them due to the very small orifice in a HP outlet to achieve the performance of the manifold ..... (refer to DIY transfill whip velocity/flow issues)....

 

[triplecove]

LP balancing won't work between the two first stages as Elan said in post #3. HP "could" work as it is not through the regulator, but you likely can't move enough gas between them due to the very small orifice in a HP outlet to achieve the performance of the manifold ..... (refer to DIY transfill whip velocity/flow issues)....

Would it drain 1 tank and then the other with this set up? depending on the lp setting on each 1st stage?

 

[jcaplins]

the UTD Z system has an isolation manifold for their sidemount setup. From what I can tell it doesn't attach to the tank valve like a typical doubles manifold, but looks to use the LP ports from your 1st stages.

http://www.utdequipment.com/new/pdf/isoconfig.pdf
UTD Equipment Z Side-Mount System


Sounds like what the OP is asking for? I have no experience with the setup, So I'm not 100% as to how it is configured. (pretty sure it doesn't address the balancing issue, so probably best to just ignore me.)