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Thoughts on post roll-offs and first stage hose routing

Discussion in 'Cave Diving' started by Tortuga68, Feb 18, 2011.

  1. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    Thinking out loud:

    'Conventional' doubles hose routing is long-hose primary on the right post and secondary on the left post

    In an accidental overhead roll-off (closing of the valve), the left post is more susceptible to roll offs given that the diver is most often moving forward

    This could lead to closing your secondary, which you wouldn't notice immediately (eventually you should notice via your SPG)

    Potentially you could donate your primary to an OOG diver/as part of an S-drill, switching to your secondary and *oops* no gas

    While it shouldn't be a big deal to reach back and turn the valve back on, it's not an ideal situation

    Your thoughts? Does anyone reverse their hose routing for this reason? etc
     
  2. BabyDuck

    BabyDuck Rebreather Pilot

    # of Dives: 500 - 999
    Location: Winterville, NC
    5,614
    430
    no, that's the main reason it's done that way.

    if you have a roll-off, the reg most likely effected will be your backup. someone comes at you for gas, you give them your long hose and go to backup. you go to take a breath and don't get anything, and just reach back & turn your valve back on. if you gave your buddy the dud, now s/he doesn't have gas for a longer time and has to climb over you to get to your valves? no.

    that's a big reason for the emphasis on valve drills. plus my instructor wanted to see us checking for roll-off every time we checked our spg's.

    so, take-home - the second is in the 'weak' position so that the strong person will have the issue to deal with if there is an issue to deal with.
     
  3. cool_hardware52

    cool_hardware52 Dive Equipment Manufacturer

    7,582
    1,789
    1) Flow checks

    2) Do think preferable to roll off the out of air diver or yourself during an air share exit?

    Tobin
     
  4. Ste Wart

    Ste Wart Master Instructor

    # of Dives:
    Location: England
    1,613
    573
    I have trouble with this belief that you can 'roll off' a valve. This would mean that your buoyancy is shocking that there is so much contact with a cave roof; therefore you should not even be cave diving.
    I keep my long hose left. The reason? if it does roll off I'm the first person to know about it.
     
  5. PfcAJ

    PfcAJ Contributor

    # of Dives: 5,000 - ∞
    Location: St Petersburg, Fl
    7,922
    7,293
    Roll offs do happen. It's happened to me passing restrictions.

    The answer to this problem is to check your valves whenever you contact the ceiling.

    The long hose needs to be on the right. If your long hose is on the left and your sharing gas on exit, and pass a restriction that rolls off your left post...Its easy to imagine the outcome.

    Your buddy is now completely out of gas, in a restriction, and can't tell you whats happening. Dead.
     
  6. Cave Diver

    Cave Diver Divemaster

    17,866
    2,518
    Not really. There is a fairly wide variance in valves. I've seen some that require multiple full turns to open or close and some that seem to take only about 3/4 of a turn. Also the material of the valve knob can make a difference. Soft rubber knobs are more susceptible to rolling off than hard plastic ones in my experience.

    If you're going through a tight enough passage with the right (wrong?) combination a roll off can happen fairly easily.

    If this happens during an air share on a left post long hose, you wont be the first person to know, the person ahead of you on your long hose will. If they're on your long hose, they've already had one OOA. A roll off for them in a restriction could cause panic and if they get stuffed up in a restriction that you still haven't passed, well, I'll let you do the math. :wink:
     
    aquaregia likes this.
  7. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    This is the answer I was looking for, thanks to those who posted it
     
  8. Ste Wart

    Ste Wart Master Instructor

    # of Dives:
    Location: England
    1,613
    573
    A valid reason, I agree.

    However the scenario is a huge 'what if' IMHO. We're assuming that a cave-diver who is capable of dealing with some seriously tight restrictions has actually been negligent enough to forget to check is SPG.
     
  9. ianr33

    ianr33 Solo Diver

    # of Dives: 200 - 499
    Location: Wah Wah Land
    5,166
    976
    Hopefully too obvious to mention,but anytime you contact the ceiling left post should be checked immediately afterwards. (Not that I ever have to do that of course!)
     
  10. ianr33

    ianr33 Solo Diver

    # of Dives: 200 - 499
    Location: Wah Wah Land
    5,166
    976
    Disagree.

    Check spg before restriction. Lets say its 2900. Go through restriction. Check spg, now 2850. Is the left post still open? No way of knowing unless you check the valve or breathe the backup reg.

    Of course,this is just another reason to dive sidemount!
     

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