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It's that time again, Dump Valves...

Discussion in 'Dry Suits' started by JPasquette, Jan 31, 2018.

  1. JasonP

    JasonP Member

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    I can assure you I have forgotten nothing. I have however, unlike you, thought about the maths. A empty drysuit with no-one in it holds about 75 litres. Even the old valve dumps 150l a minute. More than adequate if it's not blocked, which is likely to be the cause of a buoyant ascent.
     
  2. Wibble

    Wibble Fish don't talk
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    That 150 litre figure will probably only be when the valve is manually depressed; there's unlikely to be any difference when gas "dribbles" out when overpressured, i.e. in normal use.

    The bigger challenge when leaning to dive in a drysuit is making sure your shoulder is in the right place, at the top of the gas bag called a drysuit. In normal use gas will dribble out as pressure changes, but you can manually assist by 'hoiking' your shoulder up to 'pour' excess gas out.

    The "recreational" dump position doesn't help this as the valve's positioned on the front of the upper arm for ease of access not on the side of the arm for optimal dumping.
     
  3. Vanny

    Vanny Active Member

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    75 ltrs ? I’ll take you word for that. At the surface I assume , what happens at 30 mtrs ?? ( I appreciate the suit won’t be full ) If the Mk 1 is so good why make a Mk 2 ??

    Personally always used Apeks with no issues.
     
  4. Tel

    Tel Super Moderator
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    The Mk1 was poorly designed, the main being weakness of the stop which would break and leave the user unsure
    if open or closed. The main body was also sat in a retaining ring which yep also broke, sometimes stopping operation
    altogether. The front itself was smooth and could be hard to feel or grip with cold hands. Few more things, but think
    that's enough :) The Mk2 on the other hand sorts all the above and is far more superior


    Would that about 75lt be based on medium, large or maybe an XXL or worse bought off ebay that's void city :p Then of course
    the diver is overweighted, inexperienced and as has been mentioned maybe at 30m. Biggest cause of rapid ascents by
    a long way is an inexperienced diver failing to respond quickly enough with often a minor change in depth. In these
    circumstances sorting it or having a seriously bad day is measured in seconds, so yes a Mk2 will make a difference.
     
  5. Wibble

    Wibble Fish don't talk
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    If the diver presses the dump. However, they'll probably be exceedingly flustered and heading "starfish" like to the surface (ISTR PADI teach this for uncontrolled ascents -- it's in the books).
     
  6. Tel

    Tel Super Moderator
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    Or if they've been taught properly, they'll be doing inversion recovery, manually dumping gas, driving down
    in a forward roll and while messy, recover neutral buoyancy at almost the same depth as when it went wrong.

    However if it's going wrong big time and uncontrolled would you want a valve that's the same or better :p
     
    Dave Whitlow likes this.
  7. JasonP

    JasonP Member

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    The volume of the average human body is apparently about 75 litres. So 150 litres a minute is a lot. No idea how much air there is sloshing around a drysuit with someone in it, but it can't be a lot in comparison

    Sent from my LG-H990 using Tapatalk
     
  8. Wibble

    Wibble Fish don't talk
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    Doubt you could get 20 litres in a drysuit that fitted. Obviously at 30 metres this is 80 litres.

    Or doesn't it work like that? Never studied gas dynamics.

    In any case the gas will be evenly distributed around the suit, so in order to dump it all you'd have to be almost vertical, etc.

    I do wonder if 75 vs 150 litres/min makes any real difference given that the problem is moving the gas around the suit, not out of the chuff.
     
  9. Dave Whitlow

    Dave Whitlow Well-Known Member

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    What planet is this happening on? Glad it isn't the one I'm on :)

    I use a 1.5l suit bottle and have done two 50m dives from the same bottle and it wan't even half empty.

    Where does all this gas I need to dump come from? Perhaps the same bit of the imagination that requires my bailout planning to assume 75l/minute!
     
    Nick Ward likes this.
  10. Nick Ward

    Nick Ward Active Member

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    how many BARs ;) ?
     
  11. Dave Whitlow

    Dave Whitlow Well-Known Member

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    usually over 150 bar, depending what remains in the cylinder I decant from, which means at least 225 litres are available.
     
  12. becky9

    becky9 Diving bore!

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    Its not 80 litres, the litre is unit of volume, its still 20 litres but at 4ata. If you rapidly take it to the surface it would become 80 litres, and anywhere in between it would become proportional to the depth (boyles law anyone???)

    The depth in this isn't going to impact the volume unless you make a rapid, rapid ascent. x
     
    Wibble likes this.
  13. jb2cool

    jb2cool Moderator
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    If you only have space for 20 litres then you can’t ever have more than 20 litres period. Yes it’s true that 20 litres at 30m has 4 times more gas molecules in it than 20 litres on the surface but whilst it’s at 30m it’s still only 20 litres. If you ascend that’s a different matter then the 20 litres would start expanding with the reduction of ambient pressure.

    Why are we still talking about this? If he wants a mk2 dump then it’s his suit and his money, good luck to him.

    I myself had a shitty old high profile Apeks dump on my last two suits and didn’t die once.
     
    phantomlurker and JohnL like this.
  14. phantomlurker

    phantomlurker Member

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    Right, valve changed even without a tool, thankfully it hadn't been sealed in!
    Hopefully no leakage when I go to see the helicopter next weekend...

    On another note, anyone wanna buy a dump valve?! :whistling:
     
  15. Tel

    Tel Super Moderator
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    It's ok can give it an extra nip on the day :)
     
    phantomlurker likes this.

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