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Stupid question without notice... double tanks

Discussion in 'Tanks, Valves and Bands' started by ozJohnno, Mar 30, 2019.

  1. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    Or April Fool's Day.
     
  2. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    I think that you got your answer.

    The scary thing is when you mistakenly are diving with it closed but don't realize it. You are breathing from your primary (right post), looking at your SPG (left post) and thinking "wow, my SAC rate is AWESOME!", when suddenly you are sucking on a dry regulator. That's when you just switch to your backup and get the second half of your gas... IF you can figure out what the problem was.

    Not a stupid question at all, thanks for posting it!
     
    Compressor and Jiminy like this.
  3. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    Compressor likes this.
  4. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    Exactly, that's why I capitalized the "if"... It also helps if you aren't expecting the failure in training. Not sure what level the OP is, but I might have just watched my SPG for a bit while breathing out of each regulator to solve the problem. Of course, there shouldn't be any question about which direction to turn, but given that there was, there are ways to figure that out.

    I started a thread about this a while ago about how my instructor turned off my O2 in a CCR class. Many people thought that it was a terrible idea. It thought that it was one of the best lessons I ever had in ANY class.
     
    Compressor likes this.
  5. divad

    divad Solo Diver

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    ......that's just mean......
     
  6. Lorenzoid

    Lorenzoid idling in neutral buoyancy Staff Member

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    Checking the isolator before submerging is a no-brainer, but my wife and I learned the hard way that if you manipulate it underwater it can unexpectedly end up in the closed position. One might manipulate it underwater for purposes of doing valve drills. Also, a novice to doubles might manipulate it underwater because they second-guessed that they had correctly checked it before submerging. (So maybe that's where a Vindicator might have helped.) Both of those situations have happened to us. When we were first learning to dive doubles, my wife had a heck of a time with which way is open and which way is closed. For some, "righty-tighty/lefty-loosey" may be difficult to put into practice for a valve behind their head.

    So, among all of the things we have had to learn on our journey to tech diving, we had to start with the most seemingly straightforward: developing muscle memory for which way is open and which way is closed. I used a cheap plastic valve from Home Depot as a training tool and encouraged my wife to play with it now and then at home. Every once in a while I would sneak up behind her, hold the valve where it would be on a manifold in relation to her head, and say "close your isolator" (or left post or right post). Sometimes I would cleverly have it turned half way between open and closed.

    And some people wonder how my wife and I could still be holding off on signing up for a tech course as we continue to work on prerequisite skills almost two and a half years after getting the doubles. :)
     
    Compressor likes this.
  7. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    LOL. I once was watering my lawn with a hose in my right hand (I'm right-handed). I reached behind me with my left hand to turn off the faucet right behind me. I put my left hand on the knob, and could not figure out which way to turn it...wrong hand, behind me, facing the other way.... I finally had to visualize me standing there and "see" my hand on the valve, so I could turn it. Doh.
     
  8. divad

    divad Solo Diver

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    That happens to me sometimes after not diving for a while. I have to stop for a couple of seconds and visualize the end of the left valve knob in front of my face instead of behind my head..... (Please, no knob-jokes)
     
  9. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    Not everyone leaves it fully open. Once you have figured out which way is open and which way is closed, there is an argument for leaving it only partially open. I am not talking about just cracked; I mean open enough so that there is a full transfer of gas, but yet not all the way open. Their thinking is that if you are ever in a genuine emergency and need to close that valve, you will have fewer turns to get the job done.
     
  10. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    Good point. Since you don’t need anywhere near the gas flow rate to equalize pressure between tanks than you would to deliver dense gas to a hard working diver, that makes sense. Shutting down the manifold has to be done fast if you have an LP hose failure or an unrecoverable second stage free flow.

    Sort of like how rebreather O2 valves aren’t all the way open. You may need to shut them down quick but they don’t need a high volume flow during normal operation.
     

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