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Need a question answered

Discussion in 'DIR Diving' started by stevehusauk, Jun 24, 2017.

  1. stevehusauk

    stevehusauk New Member

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    Diving a twin set with no manifold , what's the comment re an additional back up reg for air share


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  2. nickb

    nickb Active Member

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    I think you're probably in the wrong forum for this question but, to which cylinder would you attach it?
     
  3. Wibble

    Wibble Fish don't talk
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    The sidemounters use two regs, one with a longhose for donation. Seen people dive with three regs on twindies. Also seen people with two recreational-style reg sets with two octopus.

    Under the one failure "rule", two regs is all you need. That's what the manifolded people have.
     
  4. stevehusauk

    stevehusauk New Member

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    Understood however I have been looking at scenarios re 30 m plus with a failure of lp hose and it seems Diving with the manifold is more risky than breathing down equally . Response time alone dictates a huge issue with air loss etc etc

    The question re a back up reg I was considering either diving with an additional tank 3/7 l with a designated backup or indeed just adding an additional to one side of the twin


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  5. Wibble

    Wibble Fish don't talk
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    If you dive with a manifolded twinset you do need to learn how to manipulate the valves to shut the down in an emergency. It takes some practice, and becomes much easier the more you practice, just like anything.

    A "standard" twinset configuration is manifolded with an isolation valve, your primary regulator on a long hose and wing inflate on the left hand post, and your backup short hose regulator on a neck bungee plus drysuit inflate hose on the left post.

    Shutdown procedures, for a unknown leak such as a burst hose, is isolate first to save half your gas, then shutdown the right post. If the bubbles stop then switch to your backup reg. if the bubbles don't stop, re-open the right then shutdown the left. The bubbles should stop unless there's a (rare) manifold or cylinder neck seal problem in which case your buddy is carrying your spare gas.

    It's vital to practice this procedure to build up "muscle memory". Some agencies favour other processes.

    A front-mounted backup stage cylinder with bottom gas will be easier to diagnose in case of leaks, but they dangle down a bit.
     
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  6. stevehusauk

    stevehusauk New Member

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    I think you have about 35 seconds to realise the issue and deal with it less at greater depth why would the non manifolded option not be a better solution


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  7. jb2cool

    jb2cool Moderator
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    with an isolation manifolded system, if there is anything wrong with either regulator then you still have access to your entire gas supply. with independants, if angthing goes wrong with the reg then you potentially lose that half of the supply.

    Sure, there are some issues that the manifold brings and its own unique failure modes but to my eyes, the benefits outweigh the downsides. i guess you have to plot the different failures that could happen, the consequence of them happening and the liklihood on them happening.

    i myself am sticking with an isolation manifold.
     
  8. Wibble

    Wibble Fish don't talk
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    Why 35 seconds?

    Do you know the timings for emptying cylinders at depth with burst hoses? A lot longer than you think.

    It's two to three minutes for a burst LP hose and about 30 mins for an HP hose (there's a tiny hole for the gas to go through).

    Twindies guarantee you have at least half your gas as *one* failure cannot affect the other cylinder. Or do they? You need to balance your gas consumption between the cylinders. If you don't, you'll breathe down one and leave gas in the other. If "the other" was the failed one, you've a partially empty cylinder you're relying in.

    For a manifold, your gas consumption is balanced across the cylinders, therefore if you isolate quickly -- that's what I said in my previous post -- you've got, say 45% of your remaining gas left and can now work on resolving the problem. Once the problem side is identified, you can shut that down and save that gas. Re-opening the isolator and you've got a lot more than 45% available on the other side.

    With twindies, short of feathering the broken cylinder, you've got whatever's left in the working cylinder.

    The key here is there's procedures for both systems which need to be followed and regularly practised - i.e. on every dive you should do a "flow check" where you check that the valves are on (turn them back half a turn, open them until they reach the stop, back off a gnats cock).


    ...
    I can see there are benefits for twindies, particularly as you've two separate cylinders which are easier to carry & fill. TBH ideal for diving with recreational shops/livaboards where you could dive with a twinset made up of two singles. I can also appreciate that the cylinders are completely separate systems where a failure on one will not affect the other.

    However, like @jb2cool, I'm diving with my manifolded twinsets and wouldn't consider twindies.
     
  9. stevehusauk

    stevehusauk New Member

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    http://www.divernet.com/training-general/p302007-you-have-35-seconds-starting-now.html

    This is what started me thinking re the separates over manifolded


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  10. stevehusauk

    stevehusauk New Member

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    http://www.divernet.com/training-general/p302007-you-have-35-seconds-starting-now.html

    That's the article that got me thinking, personally I think I might go with the manifold on a slob knob as it substantially speeds up the isolation in my opinion


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  11. Wibble

    Wibble Fish don't talk
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    Which is why you practice. My isolator will be closed in a couple or five seconds. Why do I know this? Because I will do a flow check regularly, so I know I can reach my valves. Once the isolator's closed, then I'll work through the other valves, probably right first. Won't take long to close it down; the re-open; then try the left.

    I'm going to question the 35 seconds too. You've a twinset which contains twice as much gas than a single which that will be tested with, so that'll be 70 seconds. There's other tests which I've seen which puts it longer than that - couple or three minutes.

    Slob-knobs aren't the solution, they're just adding additional failure points; practice is the solution. So is your buddy/team.
     
  12. Wibble

    Wibble Fish don't talk
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    I've a bulging LP hose which I've recently swapped out.

    Who fancies playing around next month in Swanage with a stage cylinder and filming how long it'll take to empty when the hose is cut?
     
  13. stevehusauk

    stevehusauk New Member

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    The comment that is relative is how much gas your holding when failure occurs relative to depth and hitting surface etc .


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  14. Wibble

    Wibble Fish don't talk
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    Yes, so it could be less than 35 seconds. Which just underlines the need for constant practice and the need to shutdown quickly. With or without a slobknob, you need to be able to do it now.

    I don't like slob knobs as they're just adding more clutter and another possible failure point. Agreed, there's some people who can't reach their valves for which a slob knob is one of several options. Interestingly twindies is one option for them as they can simply leave the broken cylinder to empty knowing that they've got spare gas. Caveats are using them properly. Sidemount and inverted are other options along with stages.

    BTW the things I've seen fail more than once are those swivel things on LP hoses next to regulators. Was in a mine once where the other guys had left their kit beside the water and were outside scoffing lunch. As we stepped out of the water and put our kit down, suddenly there was a large hiss coming from their kit. Went over to discover that a hose swivel had decided to fail at that point. Turned off his gas and told him, so no problems. Amazing how the thing had decided to go phut at that point. I've seen these swivels fail I think at least two other times.
     
  15. Tel

    Tel Super Moderator
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    I've done about 1400+ dives using twindies (+ about 500 with manifolds) and have tried every config going inverted
    side/slung you name it. I can say without a shadow of a doubt that a standard long-hose primary donate is a
    CF in the making.

    Why? Because the whole point of indies is that you need to gas manage and that means swapping regs at least twice
    on a dive (yes that's all you need to do*). No matter what way you cut it sods law says the one in your mouth at the time
    is the necklaced (not long-hose) one. So what you say? i'll just donate the one that i'm not using which will be the long-hose.

    Congratulations that's a standard Octopus rig :) Yep by donating the spare and not the one in your mouth it's no longer
    primary donate and now secondary donate.

    If prepared to do that at least 50% of the time then all bets are off and IMO why bother just do it 100% of the time.
    Which is why I dive three reg indies :) This has two short hose regs that come over my right shoulder (left/right post).
    The third is the dedicated alternate on a long-hose that i'll donate in a fubar. Now the hose routings are clean and no
    question which reg to go for or will be donated in any pre-dive briefs etc. Based n the KISS principle and it works
    extremely well.


    *Lot of BS is talked about gas swaps, well it's easy.
    Assuming 2x 12lts 240.
    Right post 80bar > swap to Left post 80 bar > swap back to original 80 bar
    Total used on dive = 240
    Reserve in right 80
    Reserve in left 160 (this is the one the alterbnate is attached to)
    No of swaps on the whole dive = 2

    The above is also why having two long-hoses so that the one in your mouth can always be donated is also a fail.
    Ignoring the hose routing CF etc. the idea of gas management is that the user should always have enough reserve
    in each to go home. The additional reserve in one is for the buddy, which means the long-hose needs to be attached
    to this cylinder. Can do that with three regs, can't do that with two.
     
  16. stevehusauk

    stevehusauk New Member

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    Can you post a picture im also in favour of this


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  17. Mako-JD

    Mako-JD Active Member

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    Ok I have zero experince of twins indies or SM don't don't slam me for this question.

    If manifoled I can imagine primary and secondary on separate 1st stages to have redundancy. Where would the third reg go. If you had a reason to isolate one side for whatever reason, would that not give you a 50% change of having no reg to donate if that was the side your 3rd reg was on
     
  18. Tel

    Tel Super Moderator
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    Not at home, so will have to describe :)

    A: Primary 1 - Is an ATX40/DST with a black standard mouthpiece, is on a short hose and goes on the right post along with a blue Uwatec single gauge and drysuit feed.

    B: Primary 2 - Is a TX40/DST with a clear comfy-bite MP, is on a standard length reg hose and goes on the left post along with a red Uwatec single gauge and LP inflate hose.
    The alternate ATX40 is fixed to this left post. I have part of a stupidly cheap hose clip on my shoulder strap the ones where you press the hose in. Works better than a necklace
    and still gives me full range (albeit a short range) if someone grabs any primary in error.

    C: Gauges go under the armpit and trapped by the shoulder strap. My ability to sign contents has never been an issue in 20 years of diving while monitoring gas and especially
    as on indies it's critical, so a glance to my chest sees both.

    D: With two regs on the right over my right shoulder and now no SPG hose to get in the way my alternate goes on the left and is the only hose on that side.
    It will donate the right way up and if we need to swim side-by-side, it will be at it's full extension from the first stage.

    E: If I take a stage that's on the right and no I don't take more than one (two would be beyond the scope of indies IMO) and I don't have a scooter anyway :)

    F: While we are on it I swap cylinders around all the time, so none are handed, which makes roll-off a non-issue hence no need to put LP right and as i'm right-handed makes
    more sens to put drysuit right + it's neater and better for RIBs or when the lift breaks down.


    So in practice ...................
    1. Each cylinder has a reg and independent buoyancy (wing/drysuit) = full redundancy.
    2. The whole point of indies is that you DON'T have to mess around with shutdowns as you always have enough to go home in either cylinder.
    3. If you have to donate you'll be doing that from the left post, which will always have the most gas as you started the dive on the right.
    4. In the event that your buddy is chuffing like a train on the left post you have the option of staying on the reserve on your right and giving him
    your redundancy on the left. This DOUBLES the available gas for your OOG buddy.
    5. If on the other hand the rescue has depleted your reserve a bit much, then you still have access to that larger supply.

    And finally :)
    Indies work on the principle of if you mess up, swap regs to whatever is working you go home, do not pass go, do not wait around, just get the F*** out of there :)
    There is no comparison with isolating h the manifold as you'd already be half-way up before the shutdown was completed :)
     
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  19. Mako-JD

    Mako-JD Active Member

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    That's a whole lot to digest tel :)
     
  20. Tel

    Tel Super Moderator
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    Hey it took me a decade of testing to get here :)
     
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