300bar tanks, dir ?

[ppo2]

Hi.

Im not sure if it belong here, but couldnt find Dir forum under Basic Scuba Discussions.
So i post my question here.

I'm planning to buy "dir"-configurated rig.

Dir Zone (18kg) wing for single tank, apeks ATX50, DS4.
And im not sure about tank choice.
First of all im planning to dive only recreation dives.
I readed from gue site that 300 bar tanks are not recommended, because
they arent good for mixing gases (i will be using only air),
they arent good for boyancy, (i dived with 300 bar, havent noticed any diffrence)
they might effect negatively on your others rig parts.

I'm diving in cold water with dry suit and just started diving a year a go,
almost everyone else in my club have 300 bar tanks.
I cant buy doubles, because i travel a lot by train/bus between citys
and taking one tank is already hard enough and i really want to be able
to make 1h+ dives, right now i can make only about 40-50min with 10 l 200 bar
at about 15 meter deep, but yet i want to have the savest rig i could get...

It would be nice to hear professional opinion on this one.
Should i just chill on this one and go with 12-14l 200 bar tank and hope that i will buy second for a doubles ?

 

[StSomewhere]

Where are you located? Your profile doesn't say (pot calling the kettle black, here). I'm pretty sure the whole Europe vs. USA thing factors into this, since the types of tanks you find are different depending on where you are diving.

What I can tell you is that diving air isn't DIR (the basic recreational gas is EAN32).

 

[scubamickey]

The DIR forum is under Technical Specialties. You can post any DIR question there. Very helpful people, imo.

http://www.scubaboard.com/forumdisplay.php?f=166

 

[ppo2]

im in finland, diving primarily in freshwater, small rivers etc..

 

[Reinoud]

Hi.

First of all im planning to dive only recreation dives.
I readed from gue site that 300 bar tanks are not recommended, because
they arent good for mixing gases (i will be using only air),
they arent good for boyancy, (i dived with 300 bar, havent noticed any diffrence)
they might effect negatively on your others rig parts.

I'm diving in cold water with dry suit and just started diving a year a go,
almost everyone else in my club have 300 bar tanks.
I cant buy doubles, because i travel a lot by train/bus between citys
and taking one tank is already hard enough and i really want to be able
to make 1h+ dives, right now i can make only about 40-50min with 10 l 200 bar
at about 15 meter deep, but yet i want to have the savest rig i could get...

It would be nice to hear professional opinion on this one.
Should i just chill on this one and go with 12-14l 200 bar tank and hope that i will buy second for a doubles ?

One of the main disadvantages of 300 bar is the fact that 300 bar is not 1.5 times 200 bar.
Normally if you calculate the amount of gas in your tank you use the 'ideal gas law' (I'm not sure if that's how it is called in English). That means that you can multiply the volume of your bottle with the pressuse to get the amount of gas in it. 12 liter times 200 bar makes 2400 liters of gas.
But when the pressure gets higher, another law comes in effect: the VanderWaals forces. Without going into too much detail, it means that the pressure will rise more than the amount of gas.
The effect is that a bottle with 300 bar does not contain as much gas as you would suspect, but closer to 260 bar.
When you start using mixed gas, the problems even get worse...

The result is that gas calculations with 300 bar bottles become *way* more complicated than with 200 (of 232) bar bottles. You might have less gas than you might expect.

For this reason, 300 bar bottles are not considered DIR.