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Crossbar and isolator valve: do they help?

Discussion in 'Technical Diving Specialties' started by 2airishuman, Jul 17, 2017.

  1. helodriver87

    helodriver87 DIR Practitioner

    # of Dives: 500 - 999
    Location: Alabama
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    I looked, but couldn't find it. Got it handy?
     
  2. stuartv

    stuartv Seeking the Light ScubaBoard Supporter

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  3. helodriver87

    helodriver87 DIR Practitioner

    # of Dives: 500 - 999
    Location: Alabama
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    The left post roll off? At least that's what I gathered from reading the description. That doesn't have anything to do with an isolator. Check your valves when you bump em.

    I actually had an interesting one last year. On the surface, thankfully. We were setting up a downstream Emerald dive. My doubles were assembled and checked, valves open, and upright in my truck bed. We're going over the details in the parking lot and I hear a "POP-WHOOSH" as gas starts dumping out of my doubles. I tried to shut down the right post but couldn't do it. So we isolated and tried to figure out what it was, as gas was coming out of the handwheel. Ended up being an extruded bonnet nut o ring. That was the root cause, at least. For whatever reason, the valve stem got jammed up when that happened and we had to basically let that side drain and break down the valve to close the HP seat with a flathead. Would've been bad news underwater on a straight bar manifold.
     
    kensuf, ls23, Dark Wolf and 1 other person like this.
  4. Mark IV

    Mark IV Barracuda

    # of Dives: 2,500 - 4,999
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    Really interesting thread. Among other things, it's given me a new appreciation for the set-up I most frequently used back when still cave diving: Three hp120's, one backmounted, and two side mounted. I loved the redundancy, and the easy access to the valves, and I always felt more nimble than with a big honkin' set of doubles on my back, which never felt natural or comfortable, to me. Though I used them when I had to, I could never bond with the complexity of an isolation manifold, or it's awkward location.
     
    markmud likes this.
  5. stuartv

    stuartv Seeking the Light ScubaBoard Supporter

    # of Dives: 200 - 499
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    I was thinking of the doubles that ended up with all O2 on one side and EAN32 on the other. Just remembering to open the isolation valve before jumping in the water was not going to help that guy.
     
    markmud likes this.
  6. cerich

    cerich ScubaBoard Supporter ScubaBoard Supporter

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    OK.. let's talk this thru.

    The most catastrophic gas loss will come from a burst disc. Isolating will save the most gas, by far.

    A tank neck oring is very, very, very unlikely to be a catastrophic gas loss or complete failure.

    Most first stage failures manifest at the second stage, when it starts freeflowing like mad, knowing which post to shut down shouldn't be hard to determine. Following a preset right, left center or whatever pattern an agency or instructor pushes is just wasting gas.. if a second starts freeflowing like mad, shut down the post the first stage that is attached to the second stage is on.

    A first stage failure that leaks gas, very few are catastrophic unless parts fall off (seen a turret do that) but most are moderate at best and for most divers, even in hoods they can tell which side from the noise. Some can't but most can.

    I teach if it suddenly sounds like a freight train behind you (which a burst disc will sound like) of escaping gas, isolate. Otherwise isolate what is obvious or they think it is. If that doesn't fix it, move to isolator and isolate, then sort out if the post you didn't shut down before will sort it out if you shut it down.

    I also teach that if you have determined that is isn't a reg issue and it's isolated, that breathing from the side with a bad neck oring or burst disc until the gas is gone is also a good idea.. because the gas is leaving and you may as well use some of it.

    It should be a thinking divers game, not route at these levels IMHO
     
    ls23, Dark Wolf, -JD- and 1 other person like this.
  7. helodriver87

    helodriver87 DIR Practitioner

    # of Dives: 500 - 999
    Location: Alabama
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    The way I was taught was this: before you splash, check all three valves are full open. If the isolator was closed, open it and stay out of the water until you can validate both pressure and contents. You do that before every dive, no isolator issue should ever bite you.
     
    kensuf, ls23 and Dark Wolf like this.
  8. cerich

    cerich ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 5,000 - ∞
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    why would a shut valve that once opened make you distrust your spg?

    I agree with reanalyze gas (from both posts with isolator shut actually in this case) but I really don't follow the validate pressure part. Sure, if you have the isolator shut each tank can be a different pressure, but following what you said, that has already been sorted by opening the isolator
     
  9. cerich

    cerich ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 5,000 - ∞
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    oh.. I also do not agree that following what you outlined that a diver can be confident that no isolator issue will ever "bite them" .
     
  10. helodriver87

    helodriver87 DIR Practitioner

    # of Dives: 500 - 999
    Location: Alabama
    332
    536
    93
    Might change your gas plan if the equalized pressure is lower than what you were reading previously. Just verifying that you have enough and the right kind of gas before proceeding.
     

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