Getting EAN32 out of the bank....

[sccs]

Originally Posted by colinicky

Only place in my limited diving that I have seen 32% banked was a few years ago at GoDive ,don't know if they still do or not .
I personally just dump O2 in the tank then air top ,of course the advantage of having 32% on bank is that you do not need O2 clean tanks .

but then the entire bank would need to be o2 cleaned any way so which is cheaper o2 clean the bank or your cylinders?

and come to think of it wouldn't you be back in a similar boat when it comes to refilling the bank? unless you can pump 32% but if you could would u need the bank?

[colinicky]

Unless you have a membrane compressor you would need a J of O2 anyway
In the op it stated :-
" For discussion let's say that the bank is 3 x 47l run at 250bar and cylinder WP is 232bar "

47L means J size anyway so get some "spare" O2 J's & these are already tested & cleaned so were is the problem ?
I am in the process of setting up a bank for our club & that is only for air ,so I just dump the appropriate amount of O2 in & air top .
The only premix I do is a J of 18/45 which I use all the time for my ccr but I can scavange all my J's as I have a booster pump so typically I send J's back with 5bar or less O2 in but unless you are doing a massive amount of fills or you need 200 bar of O2 fills it isn't worth a booster pump IMHO

[japandiver]

Hmmm ... so it seems that we are not sure (yet) how EAN32 is actually removed from the bank despite it being used as the basis for the GUE standard mixes (and as such one of the justifications of the standard mixes).

One advantage of banking nitrox 32 is that it does away with the need to O2 clean your back-gas cylinders and the bank cylinders only need to be clean on installation (since you know what is going in them and the only smeggy compressor they can be connected to is your own). The second advantage is that 100% O2 needs to be handled less frequently - only when you mix a cylinder of the bank or mix a stage. The third advantage is that almost all of the O2 you buy is used since once an O2 cylinder has been drained to 32bar you can simply top-off with air and add to bank.

I am currently PP blending with a booster and the basis behind this question is that the volume of gas use is increasing and, for purely local (Japanese) reasons O2 is now only available at 140 bar 25L - thus PP blending is a pain.

Options are either to bank 32% and then cascade fill and boost or to buy a bigger booster pump. On both cost and safety grounds I'm more included to bank 32 than increase the amount of O2 boosting done but would appreciate any real world experience.

Hugh

[sccs]

Originally Posted by colinicky

47L means J size anyway so get some "spare" O2 J's & these are already tested & cleaned so were is the problem ?

touche but then i personally would fill em with o2

Originally Posted by colinicky

unless you are doing a massive amount of fills or you need 200 bar of O2 fills it isn't worth a booster pump

yea thats the conclusion i came to.

you would need to be doing alot of diving or filling alot of tanks to justify the costs. tho if you can spend that amount of cash knowing that in x mths time you will actually be saving money then its a good investment

[colinicky]

Originally Posted by japandiver

.

for purely local (Japanese) reasons O2 is now only available at 140 bar 25L - thus PP blending is a pain.

Options are either to bank 32% and then cascade fill and boost or to buy a bigger booster pump. On both cost and safety grounds I'm more included to bank 32 than increase the amount of O2 boosting done but would appreciate any real world experience.

With only 140bar & 25L I can understand your reasoning although you will have to do more boosting it will only be 32%

[colinicky]

Originally Posted by sccs

you would need to be doing alot of diving or filling alot of tanks to justify the costs. tho if you can spend that amount of cash knowing that in x mths time you will actually be saving money then its a good investment

I only bought the booster as I dive ccr & the nearest LDS is 1hour+ drive each way so yes I have easilly saved the cost by now

[japandiver]

Colin

Exactly - the advantage of a bank of 32 is that I can use my existing compressor to increase the available pressure of the O2 mix thus reducing the amount of boosting.

Suspect that I will extend my existing (small bank) with as large a bank as I can fit and endevour to use the existing booster. Buying a significantly larger booster is not cheap.

It's at times like this that I wonder if I should revert to the RB ... but keeping a RB alive and maintained with minimal service support has it's own challenges.

May even find that we end up doing more deep air. It's an old subject, but when doing deeper dives without the infrastructure that people take for granted in the UK now, the balance of risk / reward of deep air changes.

Hugh



If we were meant to go underwater we'd have gills!

[Dave1w]

With the three J ish cylinders, did you do the calc on how far you get doing the cascade filling before the highest pressure drops below 232?

Perhaps if you were happy with going down to 200, you could do the math and see how low the last cylinder is, and then get that one topped up and start again.

Do you see what I mean? And if you did the math, could you maybe share it with us?
- OK, I had a quick go at the sums, using 250 in the banks, and going to 200 in the 12 litre, I think it would be something like 5 fills initially (into an empty 12, each time) then top up the lowest to 250 and start again, but woudl need to do this every third fill.

Cheers
Dave

[nickb]

Originally Posted by japandiver

Calling the DIR crowd .... you all use standard mixes based on 32% so surely someone is running a bank of 32% and then sensibly filling from it.

That's the theory, but I'd be amazed if anyone is blending GUE standard gases in the UK by this method.

I reckon you're wasting your time even contemplating this with 3 J cylinders.

[japandiver]

I agree - current (mix) bank is 3 * 50 L at 230. I suspect that to keep the boosting times reasonable I'll be going to 6 * 50L at 250 bar.

Time do some math.

Economic decision appears simple - buy more bank cylinders v. buy bigger booster.

thanks

Hugh