Twinsets

[kinetic]

Pierre,

The link I posted above and again here:

http://www.gasdiving.co.uk/pages/misc/kit/cylinder.htm

goes on to discussing mixed gases above 220 bar and does not recommend it for the reason you just mentioned.

kinetic

[Mark]

Originally Posted by [b

Quote[/b] (spike jackson @ Sep. 03 2003,11:12)]However for gas calculations I use my stressed/working rate of 17l/min.

<font color='#0000FF'>You are being a little optomistic there. A figure of 30lpm is probably a bit more like it for the first minute of an emergency.

Regards,

Mark.

[Spike Jackson]

Yes I agree but I am calculating the entire ascent as though I was at the bottom and adding 20 bar reserve - 480 free litres AND at a higher breathing rate.Does that give enough extra?

[Mark Chase]

Originally Posted by [b

Quote[/b] (Pierre Farrugia @ Sep. 03 2003,11:38)]Hello,

I use twin 12's which easily give me 30min at 60m with rule of thirds, then if you go deeper you would stay less due to deco penalty. What I also considered was that with twin 15's you have pleanty of gas but also plenty to carry on back also he cost of which you have to drain more with twin 15's.

Mark,

Do you fill trimix to 250bar? I have read that mixes become unstable over 200bar according to a theory that Daltons law of partial pressure does not remain linear.

Regards

Pierre

My group are doing 40min bottom times at 65-70m with 120 to 140min run times.

To get a 30min bottom time at 60m on rule of thirds your SAC will have to be about 16 which about what my own is so it's not a probelm. Past 30mins things get a bit silly and add 15m to your depth and they get very very silly

Yes we fill to well over 250 bar I had 260bar on my last 65m dive thanks to my garage man. That said some of the divers use 300bar 12s. We havent noticed a problem with mix fills but On a 260bar fill you will probably be at 220 by the bottom of the shot unless you use travel gas on the way down.

The instabuility of gas issue appears to be more theory than an actual problem and I beleive Helium is less afected due to the density of the gas.

ATB

Mark Chase