bi-linear cross connect, side mounting

[D1V3R]

So, a lot of you guys are doing the "bi-linear" side mount setup now, you have two separate linear systems, something fails on one tank, you have the whole other tank there for you.

the only thing is, you have to switch regulators to be able to breathe both tanks down together (a third on this, a third on that).

I was thinking, why doesn't somebody use Y-valves on both tanks, and put a cross conect between the two tanks (like with a high pressure flexible hose), that way you can breathe the tanks down equally, and if somthing fails, you can just isolate it as if you had a manifold.

has anybody ever done this? and if not, why not?

[Kelly Jessop]

why not?

That could make it very difficult with tank removal when negotiating a restriction

[Tegg]

You add fail points by doing that, and the whole point of sidemounting is to go into small passages, thus removing one and both tanks sometimes very often. A hose connecting them would not be a good idea...

I don't find the gas management to be an issue.

I also don't breathe 1/3 and then switch... you'll find that doesn't work very well with the way the tanks sit... I keep the tanks pretty close, no more then 500psi difference, most times around 300psi. The smaller the passage, the closer I keep the tanks.

[lonestarfl]

Been there done that...here are the issues. I elected to use two H-valves. The problem is when... to connect and pressurize. If you wait till your in the water, it is hard to keep water out of the "open" hose and valve. If you do it at the vehicle or on the bench. It is very difficult to get into your tanks to walk them to the water with the crossover hose present...worse of course with the hose under pressure. And, your rig must be strong enough and stable enough to tolerate the load of the tanks on the walk to the water...most harnesses are not. If you overcome these obstacles and get to actually make a dive with the cross over hose ( I ran mine across my back under the BC...I rigged and walked) the system worked well. I always kept the CO hose pressurized, but turned off at each end. And the tanks had to remain attached for the duration of the dive.
I no longer dive that system because of the logistcal issue as reviewed. I went to a simpler back up system. I still realized the need of access to BOTH tanks at all times and the near impossible task of switching regs between tanks underwater on a single breath. So, I now use a single H valve on my right tank for my primary reg and a back up reg which is pressurized and then stowed turned off at the valve. I keep the left side free for stage bottles. So, I now have a primary reg on each tank and a spare reg that can be switched while still able to breath normally on a working regulator. And both tanks remain independent of each other for maximum flexability.
Well that's my system and I have seen a few other experienced sidemount divers that adopted this same configuration after I explained the rational behind it. But I have also seen good sidemount divers that dive only a single reg on each tank but use k-valve with yokes. Even though this system does not have the advatages of an entrapped o-ring, it is much quicker process to swap a yoke valve....possibly even on a single breath:>).
Good luck with your adaptation to the sidemount world of cave diving.
Lee Gibson

[D1V3R]

hmmm, i didnt know it was possible to go no-mount with a side-mount system

i was just curious, because a cross-connect is supposed to bump upredundancy by quite a bit.

and tegg, if you dont breathe 1/3 then switch, what happens in you breathe down 2/3 of one tank, begin exiting only to find there is a problem with the other tank?

what happens in you breathe down 2/3 of one tank

You don't.

[D1V3R]

what happens in you breathe down 2/3 of one tank

You don't.

tegg does lol

[lonestarfl]

hmmm, i didnt know it was possible to go no-mount with a side-mount system

i was just curious, because a cross-connect is supposed to bump upredundancy by quite a bit.

and tegg, if you dont breathe 1/3 then switch, what happens in you breathe down 2/3 of one tank, begin exiting only to find there is a problem with the other tank?

On my sidemount rig , I can unclip at the waist and flip both tanks foward still attached at the shoulder via the bungie loops to the tank valves. I can then have a set of "no mount doubles" for short tight excursions.
Lee

[Ken Roop]

Lee,

Do you mind showing me that setup sometime?

Best wishes and safe caving.

[Tegg]

what happens in you breathe down 2/3 of one tank

You don't.

tegg does lol

You obviously don't see the logic in the gas management I stated.

Let me clear it up for you...

Here is an example of a dive in big clear cave, PSI numbers at each switch: (x) is the tank I used at the switch.


Tank 1 Tank 2
---------------------
3600 3300 (x)
3000 (x) 3300
3000 2700 (x)
2400 (x) 2700
2400 2400


Then turn the dive.

If failure happens on the tank I am breathing, then I have more gas in the other tank then the one that fails. If failure happens in the one I am not breathing, I have more then enough to exit the cave.

I can switch just fine in one breath with the way my regs are setup.