3000psi tanks...why?

[Wookie]

And, as has been mentioned before, the tanks used to store air in an air bank are rated - by the same international standards - to the same pressures. Filling a tank is a non-linear task - filling from zero to half full takes a few minutes, cramming the rest in takes a lot longer due to the pressure gradient involved. Imagine - it's quicker to roll down a hill from 200m to 0m over a horizontal distance of 10 metres than it is to roll down a hill from 200m to 195 metres over a the same linear distance. This is why people go skiing in The Rockies, not the plains of Iowa.

C.

I want you to think about this. A compressor puts out a standard flow based on a rated temperature and pressure. It is a positive displacement pump. It is pumping into a closed cylinder. A set number of cubic feet. If that cylinder has 0 cubic feet in it and it holds say 300 cubic feet and it is being pumped into using a 10 Cubic feet per minute compressor, it will be half filled ((150 cubic feet) in 15 minutes (150 cubic feet = 15 min X 10 cubic feet/minute). If you fill it the rest of the way, you are adding another 150 cubic feet with a compressor pumping the same 10 cubic feet per minute. It should take another 15 minutes to fill the cylinder the rest of the way.

Now, there are losses inherent to a compressor (gas escaping past the rings, and out the leaks in the cooling coils), but a well maintained compressor should pump it's rated flow regardless of pressure downstream, or at least close enough that you can't tell the difference with a watch.

Or am I missing something? I keep my priority valves at about 1700-2200 PSI always, so the compressor output is steady across the range of pressure.

 

[gcarter]

Don't worry about getting bigger tanks. Get a good pair of split fins, learn to kick them correctly and you will greatly improve your air consumption.

 

[Token]

Don't worry about getting bigger tanks. Get a good pair of split fins, learn to kick them correctly and you will greatly improve your air consumption.

Hmmm...I see. So split fins are really good, are they?

NOOOOOO....please don't answer that! I KNOW this is an unending controversy....


However I do appreciate all the discussion and expert commentary on this subject. I haven't logged in here for a couple of days and I'm amazed to see I managed to spark such a great discussion. Thank you one and all for your comments.

 

[redacted]

Token

While larger capacity tanks may be your best solution in the near term, as a new diver you should expect to improve your consumption rate as you get more experience. I weigh a bit more than you but have learned to control my breathing and to recognize and avoid those things that lead to higher consumption. I now have little trouble keeping up with those light weights - even donating some of my gas to extend their dives on occasion.

So, for now pay a little extra and rent larger tanks if available. But you may want to hold off buying any larger tanks to compensate for your higher consumption right now. Get more experience and work on reducing your consumption rate - and enjoy.

 

[Hatul]

I think there are two types of issues here. One is how to get deal with what's available today and the other how to improve on what's available. I actually doubt there will be a big breakthrough on the amount of air by increasing pressure. A more promising technology is the rebreather, and there would have to be development in safer units that require less maintenance that can be used by the average diver. With the small number of people diving and the economics as it it, I'm not hopeful.

 

[Druid]

Both cylinder and valve are available in 300 bar. My doubles are 232 and valves 300.

You would probably not get those filled in a UK dive shop, valves should be rated the same as cylinders to avoid confusion.

The cylinder has a rating, that is the limiting factor.

Each valve is fitted with a burst disk that acts as a fuse should the cylinder be severely overfilled. The disc rating is significantly above that of the cylinder service limit.

Many valves will have a rating in excess of the cylinder pressure which lets them be mass produced for many applications. The burst disk is what matches the valve to the cylinder.

Not this side of the pond. I've never seen a burst disk on a valve in the UK, Europe or Egypt, they seem to be a US thing. 300bar valves are DIN only, with 7 threads rather than the 5 threads on 232bar valves - so you can't fit 232 bar regs, or fit the insert to use A clamp regs.

Yes. That was my understanding as well. My point was that I'd never seen a tank rated to 300 bar.

They're not exactly common over here either, although twin 300bar 7litre tanks are quite popular, they make a nice compact twinset for dives in the 35m range. Until recently it was quite difficult to get a 300 bar fill but it's got easier in the last 10 years or so. 300bar cylinders are bloody heavy too so it's quite easy to be overweighted even without any ditchable weight.

 

[turnerjd]

Both cylinder and valve are available in 300 bar. My doubles are 232 and valves 300.

Have I understood correctly you have 232 bar cylinders with 300bar vales on them?

Here in France you cylinder would fail its inspection for that. They might allow you to change the valve to a 232bar one, but I'm not sure what the rules are. Is this legal where you are? Most diving shops that were awake would not fill it, although a lot of them are not equipped with 300bar din fittings, so might not be able to fill the tank either.

This does seem like an accident waiting to happen. With the 7 thread DIN on the tank you need to fill the tank from a 7 thread DIN compressor that will most likely to be capable of filling to 300bar. The possibility of filling beyond 232bar would appear to be quite high I think.

 

[elan]

Have I understood correctly you have 232 bar cylinders with 300bar vales on them?

Here in France you cylinder would fail its inspection for that. They might allow you to change the valve to a 232bar one, but I'm not sure what the rules are. Is this legal where you are? Most diving shops that were awake would not fill it, although a lot of them are not equipped with 300bar din fittings, so might not be able to fill the tank either.

This does seem like an accident waiting to happen. With the 7 thread DIN on the tank you need to fill the tank from a 7 thread DIN compressor that will most likely to be capable of filling to 300bar. The possibility of filling beyond 232bar would appear to be quite high I think.

Yes you can have 232 bar cylinders with 300bar valves on them. Or you can even have 206 or 184bar cylinders with 300bars (This is how I have my double LP108 and AL80 cylinders)

Here fill stations do not care what valve you have, they just look at the neck of the tank and fill to the pressure that the cylinder is certified for. Besides the valve should have a corresponding bust disk, based on the pressure of the cylinder. So if you have a 184bar cylinder you suppose to have a burst disk for a 184 cylinder even if you have a 300 bar valve.

So you can have a 184bar cylinder with a 300bar valve they will just fill up to 184 (legally) or sometimes to 206bar (3000 psi) as some of them have a cut off set for AL cylinders and then do not bother changing it But the latter usually happens only if they know you well, at least here.

At the shop that I get my fills from all the whips have 300bar DIN connectors. So you can fill 5 and 7 thread DINS and Yoke tanks (through an adapter).

 

[turnerjd]

Besides the valve should have a corresponding bust disk, based on the pressure of the cylinder. So if you have a 184bar cylinder you suppose to have a burst disk for a 184 cylinder even if you have a 300 bar valve.

OK I had forgotten that the other side of the pond had burst disks, so there is an extra layer of safety incorporated, making it less of a problem if you accidentally over-blow the tanks. I have only ever seen these in the PADI OW manual from many years ago. I don't know if they were ever really used in Europe. Anybody know?

What is the tolerance of a burst disk? How far over the theoretical pressure do you have to go for them to burst?

Jon

 

[elan]

OK I had forgotten that the other side of the pond had burst disks, so there is an extra layer of safety incorporated, making it less of a problem if you accidentally over-blow the tanks. I have only ever seen these in the PADI OW manual from many years ago. I don't know if they were ever really used in Europe. Anybody know?

What is the tolerance of a burst disk? How far over the theoretical pressure do you have to go for them to burst?

Jon

They are set usually at 5/3 of the rated pressure. AS far as I remember. 5000 for 3000psi (206) cyl and 4250 for 184 bar cyl