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tripplec
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Re: Isolation manifolds & modern DH extended range diving

Sun Jan 28, 2018 1:55 pm

Thank you. Doesn't sound like I would be happy with a manifold. Wish I could find a cheater bar rated for hp tanks. That is a bit of a concern when using my Fabers and the only reason I'm looking at other ideas. At least the regulator can offers a flack shield between the bar and myself.

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Re: Isolation manifolds & modern DH extended range diving

Sun Jun 03, 2018 7:11 pm

This was an exceptional thread. I was not aware of the level of complexity and debate surrounding the use of a manifold for double tank usage.

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Re: Isolation manifolds & modern DH extended range diving

Thu Jun 14, 2018 2:33 pm

This is a complex discussion because lots of people have different approaches, and also because technical diving is diving that is higher risk and more catastrophic when failures occur. I consider myself a relatively crazy guy. I was Army Airborne. I've been in combat. I've been shot. I'm not going to drown because of an o-ring though.

Really, what we actually need is a manifold that takes a double hose and can be isolated. This is a case where our limitation is the technology. Cave divers operated that way for years, and lots of them died because of it.
The impossible missions are the only ones which succeed. -JYC

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tripplec
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Re: Isolation manifolds & modern DH extended range diving

Sun Dec 23, 2018 5:24 pm

Thought I was reading something new until I got to the end and saw my own comments. Had a new question though. Anyone ever hear of a failed oring or burst disk at half a tank? No one starts a dive already in deco.

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antique diver
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Re: Isolation manifolds & modern DH extended range diving

Sun Dec 23, 2018 9:10 pm

tripplec wrote:
Sun Dec 23, 2018 5:24 pm
Thought I was reading something new until I got to the end and saw my own comments. Had a new question though. Anyone ever hear of a failed oring or burst disk at half a tank? No one starts a dive already in deco.
Something similar, but not all the way down to one-half air pressure. A good friend on my survey team had a sudden and significant oring leak develop at a DIN connection about 1200' penetration into Phantom Cave in west Texas. Max depth had been 68', with the average about 30. I was still outside the cave and I don't know their depth at the time leak developed. It was the oring at the DIN reg to valve connection on one side of her isolation manifold. She started with 3000-3100 psi, but I don't know the remaining pressure at the time of incidence. (probably around 2500) They had been moving slowly taking compass shots and line measurements, so had been in a while longer than would have been necessary to normally get to that point. She was able to shut down the valve in textbook fashion. Her husband was close by all the time to assist if necessary, and they made a safe and easy return to the cave exit.

Our on-site examination of the equipment and the condition of the oring led us to conclude that the DIN connector had not been tightened snugly enough into the valve, letting the oring extrude from the sealing position. User error. She was a little p/o'd at herself, but it was a good lesson. Filled her tanks with our portable compressor and they resumed diving with no further problems.
"I get plenty of excercise just pushing my luck!"

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tripplec
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Re: Isolation manifolds & modern DH extended range diving

Sun Dec 23, 2018 9:38 pm

Done that myself on other fittings. I hate feeling like the novice again.

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mdw
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Re: Isolation manifolds & modern DH extended range diving

Fri Dec 28, 2018 3:45 pm

OK, so I took the time to read through all posts in this thread and nobody has mentioned the simplest solution (IMO). That is just go ahead and use a regular modern isolation manifold. Put your DH on the left post and a regular long hose SH reg on the right. Route the LP inflation hoses as normal, route the long hose as normal (tuck into waistband and bring around neck, over top of the DH loop which replaces the bungee necklace second stage) but clip it off instead of breathing it as the primary. Instead you breathe the loop under normal situations and only bail out to the long hose if there is a problem that forces you to shut down the left post. If you need to share gas with a buddy, you still hand off the long hose, except it's coming off the clip on your right shoulder instead of from your mouth. In this way, almost everything is the same as with a Hog / DIR / Cave setup except which reg is normally in your face. All the valve shutdown procedures would be the same for any anticipated failure scenario. The main "new" skills involved are just remembering your long hose is clipped off if you have to donate it, and remembering to close the DSV if you are removing the loop from your mouth to switch over to the SH second stage.

One thing that may be sub-optimal about this is that your DH will not be right between the shoulder blades; it should still be able to be low enough on your back but it will be just a few inches to the left. It seems like this will not cause an exceptional increase in WoB, but I have not tried it yet. It seems like many here think this will be a big problem and are willing to jump through any hoops to build a custom manifold out of Chinese parts just to get that DH perfectly centered. I think I will try the easy way first and see how that goes. I will do this with a Kraken, so I expect the slight change in position will not hamper the performance. The case may be different for something unbalanced or more vintage. This test will probably happen either in February when I go to Florida, or in the spring when I start diving more regularly here at home. I''l post my findings when I have some to report.

If that goes well, I may then also try to add to this config a crossover LP hose to allow breathing from the loop even if the left post is shut down or the isolation valve needs to be closed (for the reasons these things may need to be done in a failure scenario). This would necessarily require the crossover LP to have a shutoff as well, in case either regulator is free flowing (to prevent gas from going from the good first stage out the free flowing bad second stage). This would solve another scenario a number of people think is problematic (i.e. having to come off the loop onto another reg in an emergency). I don't think that's really a problem, but if you think it is, this would be a solution.

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tripplec
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Re: Isolation manifolds & modern DH extended range diving

Fri Dec 28, 2018 4:35 pm

They used to make longer hoses for a DA if I remember right. I have been thinking your same thought. I think I may have even seen a picture somewhere of someone who pieced two hoses together for the outer most hose and used a long hose for the inside. A picture from the black and white days. I imagine the hoses would have to float the same height to keep breathing normal.

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mdw
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Re: Isolation manifolds & modern DH extended range diving

Fri Dec 28, 2018 11:53 pm

tripplec wrote:
Fri Dec 28, 2018 4:35 pm
They used to make longer hoses for a DA if I remember right. I have been thinking your same thought. I think I may have even seen a picture somewhere of someone who pieced two hoses together for the outer most hose and used a long hose for the inside. A picture from the black and white days. I imagine the hoses would have to float the same height to keep breathing normal.

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I was suggesting a long (5' or 7') LP hose for the SH reg on the right post of the manifold (as per "normal" tech setup). You seem to be talking about lengthening the corrugated hose on the right horn of your DH reg by a couple inches to account for the 7 inch offset of the cans to the left. I would think this would be unnecessary, as standard length loop hoses should still reach your mouth easily. Maybe not; I guess I'll find out when I try it. If anything, you could maybe shorten the left side of the loop a little or add a weight to keep it from floating up higher than desired (though this may also not be necessary). I'm going to start by trying it with the standard loop hoses it came with, both for simplicity and ease of switching back and forth between singe and doubles diving without having to change out the loop hoses. We'll see how that goes.

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Re: Isolation manifolds & modern DH extended range diving

Sat Dec 29, 2018 12:03 am

BTW, I may also try side mounting a tank with the Kraken on there. If it works for side mount rebreathers (and it does, even better than on backmount rebreathers because the counter-lung is now perfectly even with your lungs in the water column), it may also work for the loop on a DH reg. Maybe have to actually de-tune the cracking pressure so it doesn't want to free-flow into your mouth all the time (cans lower than normal with respect to your lungs and mouth). I'll give that a try after I figure out if the left post on my double works decently. Maybe around summer 2019.

I almost hope this doesn't work because if it does I will want to buy a second DH for the tank on the other side (8-). Unlike the back mount doubles setup, this will most likely require longer loop hoses to reach from under my arm to the mouthpiece (or 90 degree elbows like they use on side mounted rebreathers). More money I don't have, but lots of fun if it works.

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