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Dumping Air

Discussion in 'General Scuba Diving' started by Chris Handzel, May 20, 2011.

  1. Chris Handzel

    Chris Handzel Member

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    Very daft question, however im new to diving and techniques, however what I want to know is there a way to stop myself going into a quick ascent? ive tried dumping air and getting rid of air out of me, is there a more controlled way.
     
  2. Flyingspanner

    Flyingspanner Well-Known Member

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    Correct weighting is most important.
    Do a proper weight check with an almost empty cylinder.
     
  3. Steppenwolf

    Steppenwolf Well-Known Member

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    Seconded. During the early days of my diving I found that buoyancy control towards the end of a dive got increasingly difficult with those blasted aluminium tanks. I prefer to use steel ones but if only "alis" were available (like my forthcoming Turks & Caicos trip next week), I will make sure to do a proper weight check with an empty tank.
     
  4. Chris Handzel

    Chris Handzel Member

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    Thats great advice thank you, Im off diving a few times in Tunisia so ill can have try at the weighting side of things!
     
  5. big si

    big si Well-Known Member

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    Anticipate when the lift is going to happen and start dumping its a fine art just like balancing on a seesaw, its just a practice thing and being weighted correctly. also if your over weighted you will need more air in the BCD to keep you bouyant at depth which will expand at a faster rate as the volume is larger on an ascent, so will create a problem as you will not be able to dump fast enough. My guess is you could be over weighted if your new to diving if your using the same amount of weight that you used on your OW as most instructors over weight pupils instead of teaching proper bouyancy from the start.
     
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  6. puddle fish

    puddle fish Well-Known Member

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    All of the above and Also check you are actually dumping air from BCD/drysuit look for the bubbles note how fast they are coming out. you may need to change position slightly to dump air more efectivly.
     
  7. Suggsy

    Suggsy Banned

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    Nearly but not factually correct. The rate of expansion is NOT dependant on it's volume. What I'm guessing you mean is that the greater the volume of gas, the even greater the volume to manage as gas expands inversely proportionally to it's volume. The speed of this expansion is the same, regardless of volume.
     
  8. big si

    big si Well-Known Member

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    Now thats a good point if the rate of ascent was the same speed for 1lt of air or 10lts of air, it then would expand at the same rate but usually the larger volume of air creates more lift making the ascent faster so the air would be expanding faster as the presure is being released quicker.
     
  9. Major Clanger

    Major Clanger P-Plated Meg Diver

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    Apropos of nothing, does temperature vary the rate of expansion? At uni I left thermodynamics to those that couldn't do electronics.
     
  10. big si

    big si Well-Known Member

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    :giggle:

    Temperature has an effect on the molecular structure of air when it is warm the spaces between the molecules are further apart making air less dense, when it is cool the molecules are closer together making it more dense. As air is warmed it expands but the expansion will cause the air to cool as the molecules move apart as it becomes less dense.
    If the air was heated in a closed container the tempurature would rise creating presure but only if the heat was constant.

    I think thats somewhere along the right lines, Suggsy will be along shortly to give a more precise answer. :balanced:
     
  11. Bobco

    Bobco Active Member

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    Chris,
    Stick with the correct weighting posts, get yourself as neutral as possible, this takes time and effort but do it. The more you have to put in, to compensate for being over weighted, the more that need to come out when you ascend. And remember that there is a time lag in the effect of dumping and adding air. All this just takes practice, like everything, the more you dive the easier it will become.
     
  12. Jenkins

    Jenkins Friends, Romans, countrymen, lend me your ears.

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    As others have said do a proper weight check, carrying extra lead will mean you need extra air to compensate. The more air you have in the system the more rapidly you will need to dump in order to control the ascent speed so being overweighted won't do you any favours. That said it is VERY important to ensure that you do have sufficient lead to comfortably stay down and hold a safety stop at the end of the dive.

    Again repeating others, can you see/hear bubbles venting as you ascend? You may need to adjust your position in the water to make sure your dump valves are at the highest point. If using a drysuit you may need to make adjustments to your undersuit to ensure the valves don't clog with clothing and can dump properly - some undersuits are really bad at this.

    As you are learning it's also easier to ascend up a fixed (so solid, rather than bobbing) line or a rock feature as it gives a clear visual reference and combined with your computer will make maintaining a slow ascent easier. Worst case scenario you can also grab hold and hold yourself down whilst you "catch up" with dumping air, ideally though try to use it as a mental crutch rather than a pysical aid.

    Remember there is no rush in ascending and 18m/min is a MAXIMUM not target ascent rate, taking your time on ascent will mean you have time to correct and minor bouyancy errors before a rapid ascent develops.

    Also as others have said, try to anticipate ascending/descending. Remember with your fin pivots how it takes a moment for adding/removing air to influence your bouyancy? Well the same happens with ascent/descent, so little and often is far more adjustable and effective than adding/dumping lots of air at once - and learn to accept that it will take a moment for your adjustment to take effect. Also use lung volume and your fins (stop kicking! or swim gently upwards) so make fine adjustments or help to slow you whilst you adjust the air.
     
  13. Suggsy

    Suggsy Banned

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    I thought PADI had amended their max ascent rate to 9m/min??
    To help control your drysuit, try and keep the amount of gas inside to a minimum and ensure your dump valve isn't blocked by loose clothing.
    The best tip I can offer is to dive, dive, dive and practice, you'll get there eventually. Even better if you can dive nitrox.
     
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  14. Chris Handzel

    Chris Handzel Member

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    Thanks Everyone, great advice from you all. I think more than anything I am over weighting my self and using the weight I used when doing my O/W looking at my diving logg I have been using 12kg, due to my inexperience at my last dive I was at Capernwray and the first dive I did I couldnt get myself on the bottom, I had dumped my air and I was still fair bit from the bottom. At the end of that dive frustrated at myself as I knew my inexperience had not helped, on the dive I enjoyed what I was seeing etc however I was wanting to have a look at the objects on the bottom.
    I was hiring most of my kit I decided to ask at the shop if I could have more weight like 2kg, I was told I was wearing my maximum limit and that I was not allowed no more. I didnt realy know what to do, the first dive was frustrating and I couldnt control my ascent as slow as I wanted, on my 2nd dive I decided to try something weather I was wrong in doing this I dont know, I got two rocks that seemed equal in size and weight and placed in my bcd pockets, sure enough I was able to control my descent, however at the end of the dive I did come up at a better pace but felt I was struggling a little still and I was fighting to come up at the pace I wanted, the equipment I was using had a black arrow on the gauge which told me if I was coming up at a safe pace and managed just on that dive.

    The last dive I did I remember my weight belt wouldnt stop slipping, I remember tightning it a few times as much as I could, I had a great dive buddy who at one stage helped me with it, at the end we used the ledge of the quarry to come up on ascent, the last 8m I think it was I had to keep grip on the side as I could feel myself wanting to ascend fast, eventualy we got to the surface with in guide times, however I remember feeling angry at myself as the dive itself was great and enjoyed the experience but felt I let myself down with the ascent, and I didnt want to spoil it for my buddy.

    Im not sure if I am going to be doing right here, I am thinking of using my BCD weight system completly instead of the belt so not having to concentrate on that slipping, I have heard a few people say that this is ok, but im unsure if this is a good practice or not, and also thinking of coming up with more air than I did so I have more weight to me instead of less to see if that helps!!!!!!!
     
  15. Ellie

    Ellie Non scene GUE diver

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    Why not do a proper weight check at the end of your dive? Have 30 bar left in the cylinder, RELAX and let the air out of your BCD and breathe out as much as possible and see if you sink. Make sure you keep your fins still. I've seen a few divers who claim they need more weight but are kicking their fins whilst trying to sink and working against the downward motion. If you can get down remove 1kg and do it again until you can't get down or add it in 1kg increments until you can. That should tell you the correct amount of weight that you need. You need to be calm, relaxed and try to stay still whilst doing this. Everyone needs different amounts of weight so don't get hung up on the numbers.

    With regards to integrated weight systems, whatever works for you is fine. I hate weight belts and when I dived a single cylinder and jacket BCD I'd put weight in the pouches on the cam band and some in the ditchable pouches at the front. I thought it was great and never used a weight belt again after that. Did someone in the shop really say you weren't allowed any more lead?! Personally if that was the case I'd have just bought some, you need what you need, and uncontolled ascents are not worth not spending a few pounds on some lead.
     
  16. Chris Handzel

    Chris Handzel Member

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    Thats reassuring to know about using the weights only on my bcd in the pouches as it drove me mad with the weight belt, next time I get a chance to get in the water I will have a go at weighting that way, I used more weight as I felt I was bobbing along aswell.
    As for the shop or the hire unit I was told that I had my weight limit, but found it better when I put rocks in my bcd! I felt a bit daft at first when I asked cos I thought to myself is this like as set law etc and should I have known.
     
  17. Suggsy

    Suggsy Banned

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    Are you sure ALL gas had been expelled from your BCD? I'm confused as to why you can be at x depth yet not descend any further? Once you make it below the surface then the only way is down unless gas is added somewhere or youre breathing at the top of your lungs.
     
  18. Chris Handzel

    Chris Handzel Member

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    Its more than likely my lack of experience, the two areas I had problems with was that I couldnt get myself to stay on the bottom and had the feeling I was bobbing around, and when ascending I was losing control of my ascent, with what everyone has said it would seem I am overweighted and or I havent got rid of excess air in my BCD, as far as I remember im certain my lungs were empty however again this may have been an issue and inexperience.
     
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  19. Jenkins

    Jenkins Friends, Romans, countrymen, lend me your ears.

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    Integrated BCD weight systems will have a quick release mechanism so are a perfectly acceptable alternative to using a weight belt, just make sure you cover how to dump lead as part of the buddy check. That said most BCDs won't really cope with more than around 8-10kg so I would suggest perhaps keeping around 8kg on your belt (a lighter belt will slip less) and stick the rest in your BCD.

    Regarding how much lead you need, what suit are you using? Also how big are you?
    FWIW when I did my drysuit course even with 12kg in a borrowed suit I was underweighted, but once I bought my own suit (different undersuit which trapped less air) I dropped to 8kg.

    Really though Ellie is dead right that your best bet is to get to the end of the dive when your cylinder is almost empty and do a proper weight check. It's slow and boring but well well worth the effort - and ideally wants doing again if you cange you suit/equipment configuration.
     
  20. Elvis

    Elvis Banned

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    Also with you do still need one a Rubber Weight belt is much nicer than the webbing ones, no more having to tighen it up when you get to the bottom, no more climbing out it around your kness (if using a crotch strap) or ankles (without).
     

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