Considering twin 10ltr tanks

[Tech Diver]

Hi

Im currently using a 12ltr 300bar tank and im going to be doing my padi nitrox also advanced nitrox and was thinking of purchasing twin 10ltr (232) tanks but what difference will i see will i get alot more air ?

thanks in advance

 

[AzAtty]

Yes, you'll get more breathing gas. How much depends on the actual pressure to which you fill the tanks. You'll also find that your weighting will need adjusting, and your balance will be different.

 

[pescador775]

Hard to say how to advise since you don't identify the country. A 300 bar tank is a heavy monster and too high pressure for partial press mixing of NITROX. However, if you have premixed gas and a booster available should be less of a problem. "Should be" but maybe not depending on what press gas is banked and whether a booster or compressor can jam the final pressure. A pair of 200 bar, 10 liter might be nice depending on weight and buoyancy.

If you plan on buying a pair of 232 bar Fabers also plan on staying on the bottom permanently. Negative buoyancy will be about 30 pounds.

 

[nickjb]

pescador775 once bubbled...
....

If you plan on buying a pair of 232 bar Fabers also plan on staying on the bottom permanently. Negative buoyancy will be about 30 pounds.

Faber twin tens will be about neutral when empty and 12 lbs negative when full. You will still need your lead.

Twin ten fabers are fairly common over here, but twin twelves are far more common. A little extra gas and they slightly longer so you can rest the weight when you sit down (especially on a rib)

Maybe wait until after your course. Have a chat with the instructors

 

[pescador775]

Nick's comment is the kind of thing that sometimes makes life hard for me. Understand, 'Tech diver' is talking about buying "232 bar" tanks (Faber). These are high pressure tanks, not the kind you are familiar with. They have the buoyancy of a boat anchor. My advice stands.

 

[nickjb]

I'm fairly familiar with faber '232 bar' tanks. I have one or two strapped to me on most dives. They are, by far, the best selling tank in the UK.

Over here 232 bar is 'normal' pressure and 300 bar (as tech diver already has) is high pressure. The 300 bar tanks are pretty negative the 232 bar tanks are not. Faber do a wide range of tanks and you might be able to find some with the buoyancy characteristics you describe but Faber lightweights are the ones most dive shops sell. They are about 11kg (24 lbs) each

There is a handy bouyancy calculator here:

http://www.subaqua.co.uk/cgi-bin/cylinder-buoyancy.cgi


PS for a pair of 10s to be 30 lbs negative they would have to weigh about 40lbs EACH out of the water.

 

[Hoppy]

My twin 10's are Faber 232's and have the bouyancy characteristics Nick described.

Cheers
Hoppy

 

[pescador775]

Please refer to my original post. If you guys would identify the country of origin straight up it wouldn't be so difficult to analyze your problems. In the US, these (Faber) tanks are rated 3300 psi or 3498 psi. They are negatively buoyant.

PS: I did finally figure out what 'blighty' is.

 

[pescador775]

Techdiver, you asked about differences between a single tank and doubles. The buoyancy issue has gone away so it is time to mention that double tanks have quite a lot of drag. This becomes noticeable when swimming in current. Otherwise, the doubles may exhibit better balance under most conditions.

It appears that the 232 bar (3360 psi) tank is the same or similar to tanks sold in the US but rated @ 2640 psi. US DOT (Dept of Transportation) regs require that the min. burst pressure be 2.5 X the working pressure. It is my understanding that Euro laws require that this number be only 2.0 X. Hence, the higher allowed working press in other countries. In the US, some divers fill these 2640 psi tanks to 3000 or higher.