232 bar vs 300bar

[Scuba fryd]

Hi this probably has been discussed menny times here but I can't relly finde any good answers. (also I hope I post this the right place since it's my first post)
Well I am going to start sidemount diving and I am looking at squba tanks I am moving to sidemount because I am 15 years old and not that strong to carry 2 12 liters on my back so I coche sidemount.
I dive drysuit so I am thing about steal tanks but I am not sure if I shuld go with 7 liter 300bars or 10 liter 300bar it cost aproxemently the same for 300 or 232.
My worry is trim with it be hard to lay falt how muche do they wheigt and air because 10 liter if I can't get 300bar 232 is stikke good but 7 liter 232 bar is not that much. So is it a good ider with 300bar to have as muche as possebel. (we have a 300bar pump at my culb no problem there) so all I need to know is do 300bar wheig more and how much more do they weigh. And are they balanced or do one part flot and one doesn't.
I really hope u can read this since I am dislexcic and English is not my first language.

Kinde regards Albert

 

[Alekseolsen]

Not a sidemount-diver myself, but I do know of several cave-dive instructors that dive 7L 300 bar tanks sidemount with drysuit, in other words, I wouldn't worry about trim for the tanks.

 

[Edward3c]

I have 12Lt 232 and 300bar cylinders. there displacement is pretty much identical, but the 300s have around 3.5Kg more mass.

Additionally, the available gas isn’t linear above, say, 250bar (someone will come along and give the exact figure), so you don’t get an extra 68bar of gas – more like 45. If, or when, my 300s fail their test I’ll not replace them.

 

[RainPilot]

• First biggest problem is getting real 300 bar fills, if your club does these then it seems that problem is not an issue.
• Second concern is the weight, with 300 bar tanks it is very easy to get overweighted, especially if you dont need much weight to start. With a drysuit you can compensate by having more buoyant undergarments, but once your tanks are part of your weighting, that means you can never remove them while diving. Not necessarily a big deal, but it is a factor to consider. If you are only doing sidemount in open water due to back considerations, then you shouldn't ever need to remove your tanks so thats not a big deal
• Trim is not a concern specifically, my 7L 300 bars trim out pretty much perfect as is.

 

[Scuba fryd]

how muche air do u get from using 7 liter 300 bar
and right now I use a 12 liter steal 232 bar on my single set up and I use 10 kg of led and I want to make it as little as poosbel is I only put 232 bar in a 300 bar tank do they wehig the same?

 

[Wibble]

As @RainPilot said, you will struggle to get 300 bar fills. The reason is you need to let the cylinder cool off and top it off at least once. Most shops won't do this and the best you'll typically get is 270 bar.

For that you'll find the cylinder is a lot heavier. It's generally easier to use a 232 bar steel cylinder which they can overfill and it'll cool down to 230-ish bar.

I've a pair of the fantastic 8.5 litre "Euro" cylinders for sidemounting. Thin, long, and more capacity than 7 litres. Also can be properly filled to over 230 bar. Alternatively use 10 litre cylinders which are smaller and lighter than 12s.

 

[Searcaigh]

how muche air do u get from using 7 liter 300 bar

7 x 300 = 2,100L

AL80 at 200 bar gives you 11.1 x 200 = 2,220L

12L tank at 232 bar will give you 2,784L

I'm going to move this post to another area

 

[Scuba fryd]

7 x 300 = 2,100L

AL80 at 200 bar gives you 11.1 x 200 = 2,220L

12L tank at 232 bar will give you 2,784L

I'm going to move this post to another area

thank u but how muche dive time u get and how much lead do u use I would rather take more air than leaswith me

 

[Searcaigh]

thank u but how muche dive time u get and how much lead do u use I would rather take more air than leaswith me

Bottom time is based on your breathing rate and depth, varies for everyone and you would need to calculate that for yourself.

Same for weight (lead), which would depend on what type of suit you're wearing and type of tanks you're using (Steel v Aluminium).

Lots of variables involved, and you would need to determine what you need using some trial and error over several dives. A competent instructor should be able to give you more personal advice.

Over time with experience, you should be able to use less weight and less air (gas) for dives.

Learn to plan your dives including gas planning and keep a log book with the details.

 

[Miyaru]

thank u but how muche dive time u get and how much lead do u use I would rather take more air than leaswith me

If you want to take more air with you, 300bar tanks come with another consideration: the air compressibility factor.
A 7 liter tank at 300bar contains theoretically 7x300 = 2100 liters of air.
But above ~240bar, the pressure goes up much faster than the actual gas volume in your tank. At 300bar, that deviation is about 10%.
When you use air, compressed to 300bar, make the calculations for 270bar.