General question - loop volume and buoyancy

jepuskar

Ok, I just had my first pool dives on a couple units last weekend and have I have been soaking the experience in...not quite obsessed yet, but getting there...it wasnt a class, but just an experience.

Please feel free to slap me if I'm wrong on these points/observations..but if you are going to slap me atleast help me.

1) Your loop is just like your BC...the more air in it the more it has an affect on your buoyancy..meaning injecting more gas into the loop is going to increase your lift in the water column.

2) If #1 is correct that would mean that if you are nuetrally buoyant and not changing depth...if oxygen is not being injected into your loop to keep your setpoint than you will become negative. Less loop volume means not as much lift...keeping in mind no adjustments to the BC and constant depth.

3) When ascending, besides venting the BC/drysuit...you can exhale out of your nose to lower the loop volume as the gas in it expands. Exhaling out of the mouthpiece is ok as well. If you have an OTS CL than as you exhale you pull the dump cord to let the gas escape.


Do I have the correct understanding?

Thank you.

Jason

dave t

1 yes true but you will only need to add gas (diluent) as you descend to compensate for the increase in pressure that will colapse the lung. we practise a skill called "minimum loop volume" to minimise among other things the effects of buoyancy

2 yes but more importantly if no 02 is added you will die!.if o2 is added to match metabolism the volume will stay the same.

3 Its always better to use your mouth to dump as you ascend, you get better control

HTH

Dave

jepuskar

Hi Dave and thanks for responding...

The point of number two is that it is another way to identify an issue with your system and well, just for my own understanding.

Why is it easier to control your ascent using venting from the mouthpiece instead of your nose?

Thanks,

dave t

You will loose buoyancy if no o2 is added and you are metabolising whats in the bag but to notice it you will have to maintain a perfect constant depth, pretty hard to do in open water (may be better in a cave) Far better to watch your po2 displays!

Its better to use your mouth as you can get rid of gas without having to breathe it first, everything that comes out of your nose must first be breathed in. I am not saying you cant use your nose, in my opinion its easier to use your mouth

Dave

hoppyinca

I agree, MONITOR PO2 DISPLAYS; however, cruising along at a constant depth, a decrease in bouyancy is an indicator that you should be adding o2... or have a leak...

I would have to disagree a little with the second comment... kinda a throw back to tech OC, but...

any gas that I am taking out of my system be it for bouyancy, lift bag deployment, etc SHOULD be breathed first, that way I can get some use/ benefit out of it before it is gone. by no means a hard and fast rule, just food for thought...

my 2 cents...
hoppyinca

dave t

Agreed but there may also be a time when you dont want to breathe it, if your only skill is nose dumping you will have to breathe in the crap before getting it out the loop. sometimes using the OP valve may not be convenient. Also dont you find that if you use mouth dumping the breather tells you when to get rid of gas? maybe thats just me being lazy

didnt understand your comment on OC tech, can you eleborate?

Dave

onetime

I agree about mouth dumping the loop pretty much tells you when it needs to come out. Additionally letting the gas slip from the corner of your mouth doesn't obstruct vision as much as purging from the nose and doesn't dislodge the mask.

As far as the "OC tech" comment I suspect he means that with limited gas supply you want to make use of it before getting rid of it. After all you carried it all that way and then to just release it in the water is a waste. May as well get some fuel for the body before letting it go. Of course that doesn't take into account being at the wrong depth for the mix.

dave t

Ah right, thanks for that. Its about 12 years since I dived OC I sort of forgot about conserving gas!!

jepuskar

My point about losing buoyancy if O2 is not being injected was to ensure I am understanding loop volume and how it relates to everything else. It wasn't meant to infer you dont have to look at your PPO2 displays.

Gobfish1

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Steve G

Apparently not the only gay diver in the village

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