Just a question??

[padiscubapro]

Doppler once bubbled...



Closer... did you factor gas compressibility?

I find unless I'm mixing gas by atomic weight, my relationships are off anyway, so it's not science any more but art...

So the selected gas will weight= "somewhere in the region of..."

And don't pick on me... I'm a physics major -- properties of light -- Chemistry came a distant second.

Anyhow, interesting postings guys... you gotta take that one into your local scuba shop !

Picky, piky picky

if my math is correct the compressibility factor for an 21/40 trimix @3000 psi is about 1.05153 so there is 2085 liters of gas instead of 2192, therfore 1789 grams or 3.94 lbs

 

[Doppler]

padiscubapro once bubbled...


Picky, piky picky

if my math is correct the compressibility factor for an 21/40 trimix @3000 psi is about 1.05153 so there is 2085 liters of gas instead of 2192, therfore 1789 grams or 3.94 lbs

Hey PSP: you having a slow day at work too!!

You gotta post the spreadsheet by the way!

Take care... and don't you dive a 'Breather all the time. You have different buoyancy challenges then don't you?!

DD

 

[padiscubapro]

Its not really a concern.. the inspiration uses two 3l steels (approx 600lfg per cylinder)
If I use 10-20 bar of diluent (30-60 liters of gas) thats alot.. I also use about 20 bar of oxygen an hour (approx 60 liters of oxygen an hour)

thats about 1 cuft of oxygen an hour (actually less) and 1 to 2 cuft of diluent for the entire dive..

 

[faye]

Once again we see that if you do one thing wrong, you end up also having to do a bunch of other things wrong in an attempt to work around the problem you've created for yourself.

any one who says that you are doing something wrong, without any flexibility has to have there head looked at.

As for the requiring HE to have a balanced rig, I just see that as too fine a line for something that is as important as bouyancy.
And yes I am going to give her a go this summer on the single bladder thing. I was taught with double bladders and would like to try the single as there are some very good points about diving that way. But I won't throw out the dual just yet. I just hope I don't have to buy alot of HE, I'm only a lowly dive bum;-0 plus I like diving air!=-)

The jab at the founders of philosiphy was just that a jab not and insult.

 

[omar]

well...

I used the tilde to represent approximate. You will notice I tried not use equal signs.

As far as compressibility it will depend on the EOS used and temperature and the size of the cylinder that the gas is going into. At best all EOS for real gas compressibility are only approximations of an infinite Taylor series.

For a general idea on compressibility of mixes look at:

http://www.atomox.com/mixing.html
http://www.atomox.com/Z_factor.html
http://www.atomox.com/gas_volume.html

omar

 

[padiscubapro]

omar once bubbled...
well...

I used the tilde to represent approximate. You will notice I tried not use equal signs.

As far as compressibility it will depend on the EOS used and temperature and the size of the cylinder that the gas is going into. At best all EOS for real gas compressibility are only approximations of an infinite Taylor series.

For a general idea on compressibility of mixes look at:

http://www.atomox.com/mixing.html
http://www.atomox.com/Z_factor.html
http://www.atomox.com/gas_volume.html

omar

Thanks for posting the links.. I forgot about that site.. Its a good reference for people who are unaware of gas compressibility.. and
I agree with you about being approximate approximate.. temperature is a BIG factor.. everthing is referenced to STP..
if 100 liters of gas make that big a difference... The person is really planning the dive wrong.. thats only a bit over 3 cu ft.. if the planned it using 80, its still only 5 cuft per tank...


The only place I used the "=" was for a mole of gas at STP, thats a standard....

As you can see I'm not afraid about mistakes.. I didn't try and hide them.. I could have easily edited my messages, but then everything looks fishy.. just easier to admit the screw up and go on..

Trying to run calcs or picking out table values between my boss look over my back can get a bit tricky..

The thing that fooled me earlier was that the "air" numbers were almost right just a little high 6.23 vs 7.25 by what I noted in the luxfer specs.. I just didn't have time to look over everything.. but once the thread got moving I had to fix it.. I didn't suspect the He component was off by a factor of 10... (had a divide by 10 instead of divide by 100)

 

[cnidae]

This has been the hardest thing for me to decide. Currently I’m diving a dual but I go back and forth whether to go to a single. My current opinion is based on task loading. You look at what tasks can be created wearing a dual and what tasks will be created if a single fails. Deaths are usually caused by a chain of events, if you can stop the chain before another task is created then you’ll be much more likely to survive. As far as DIR is concerned, remember that DIR is an evolving thing and none of it is set in stone. At first DIR was all about the V weights and getting rid of weight belts now they’ve changed to V weights are bad and weight belts good. Who knows in a year DIR may be single bladder bad, dual is good.


JMHO
Safe diving everyone

 

[Doppler]

omar once bubbled...
well...
SNIPPED
http://www.atomox.com/mixing.html
http://www.atomox.com/Z_factor.html
http://www.atomox.com/gas_volume.html

omar

Omar: I've had that site bookmarked for a while because it is a useful resource... I particularly like the "outcome statement" which basically says: When mixing trimixes, add a little less oxygen and a little more helium... Which is the pragmatic view.

Still think this is one of the most intersting threads going right now... even if getting one's buoyancy rarely involved representing functions near their expansion point.

Take care

 

[nradov]

cnidae once bubbled...
At first DIR was all about the V weights and getting rid of weight belts now they’ve changed to V weights are bad and weight belts good.

It would be greatly appreciated if those who do not understand DIR would please refrain from making false statements about it. The rule has always been to have a balanced rig. This has never changed. There has never been a specific rule about V-weights. If we are discussing ocean diving here, there are some combinations of equipment where a V-weight works well and others where using one would leave you without sufficient ditchable weight.
I am curious, though: who has been giving you this misinformation? There are an abundance of DIR "wannabes" out there spreading nonsense so I guess I shouldn't be surprised that so many divers end up unclear on the concept.

Who knows in a year DIR may be single bladder bad, dual is good.

Don't count on it.

-Nick

 

[faye]

You guys are talking about molecular weights as it portains to mixing. Any resources on the net or in paper that are dedicated to the "art " of mixing. I got to get better at this you know