Ways you can use a spare air tank other than as scuba redundancy

[brandon429]

instead of buying the refill tank, what if I pick a weekend we felt like diving in the pool and simply rented an 80 cf tank as if we were going to dive normally for a couple days and refill from that...how many 3.0 cubic foot refills you think i'd get off a 80? I wasn't thinking it was mathmatically 26 as I was thinking equilization would come well before the end of the tank, just guessing how many fills off a rented 80?

 

[mike_s]

instead of buying the refill tank, what if I pick a weekend we felt like diving in the pool and simply rented an 80 cf tank as if we were going to dive normally for a couple days and refill from that...how many 3.0 cubic foot refills you think i'd get off a 80? I wasn't thinking it was mathmatically 26 as I was thinking equilization would come well before the end of the tank, just guessing how many fills off a rented 80?

you need to check your math... you'd only get one 3.0 cf fill (or actually slightly less as the tank equalized, and you add 3cf volume to the equalization, it'll likely never reach 3cf from the "tank fill adapter".

after that initial fill, the volume filled will go down each time.

I've never filled a spare air before, but I think you can fill them direct. maybe you can get it to 3000psi and 3cf that way off a compressor/bank system.

 

[brandon429]

thanks for the reply, 3 goes into 80 26 times is what I was thinking, why would I only get one refill in a 3 cf tank from an 80 cf tank? couldn't I at least get ten refills or so before the big tank's pressure drops below 3000 psi, at which point the smaller tank wouldn't get full refills any longer...we were guessing about 10 full/complete refills, tell me if you agree to that guess. The techs at spare air business said I would get several refills from a standard diving tank, but I didn't know enough about the pressure specifics to quiz them I just assumed they weren't lying. When you buy the spare air kit you get a refilling adapter meant to hook up to a standard diving tank, I was assuming this would be all I would need to refill off a standard rented tank, when would I need to use that bank system you are talking about?

 

[mike_s]

thanks for the reply, 3 goes into 80 26 times is what I was thinking, why would I only get one refill in a 3 cf tank from an 80 cf tank?

heh.... you can't do math with pressure that way.


think of it this way. each time you breath on a tank, the pressure goes down over time as you breath. that's because each time you remove a small amount (say .5cf).

have you had the Open Water course yet?

couldn't I at least get ten refills or so before the big tank's pressure drops below 3000 psi,

the big tank (AL80) will drop below 3000psi on the FIRST FILL. Sorry, but that's just the laws of Physics.

Go google Boyles Law, Ideal gas law, and other pressure laws.

at which point the smaller tank wouldn't get full refills any longer...we were guessing about 10 full/complete refills, tell me if you agree to that guess. The techs at spare air business said I would get several refills from a standard diving tank, but I didn't know enough about the pressure specifics to quiz them I just assumed they weren't lying.

yeah you might get several, but not 26 that you came up with in the first above sentence.... (several is 3 or 4 ).

When you buy the spare air kit you get a refilling adapter meant to hook up to a standard diving tank, I was assuming this would be all I would need to refill off a standard rented tank, when would I need to use that bank system you are talking about?

forget I mentioned the bank system..... that would be if you were filling direct at a shop off their compressor/bank system. (and not using the tank transfer adapter).

So if you want to see how many fills you get, here ya go...
Someone else can check my math and see if I made a mistake. (I duplicated my formula for the rest of the dives, so if there's a mistake it will duplicate itself)

This is for 15 fills.

Let's assume you use an 3000psi AL80, which is really 77 cubic feet, to start with and an empty 3.0cf Spare Air rated for 3000psi.

seeing that you're adding volume to your starting base pressure of 3000psi, you're never going to get 3000psi in that Spare Air by doing a transfer fill.

Anyway, here is what I came up with. (I think it's right.) I'd attach it via Excel spreadsheet, but the attachment feature of SB has been broken for some folks for over a year

Fill # | AL80 start PSI | AL80 CF | Total capacity (of both) | resulting PSI | Spare Air final volume CF
1| 3000 |77 | 80.00| 2888| 2.89
2| 2888| 74.11| 77.00| 2779| 2.78
3| 2779 |71.33| 74.11| 2675 |2.67
4| 2675 |68.66| 71.33| 2575| 2.57
5| 2575 |66.08| 68.66| 2478| 2.48
6| 2478 |63.61| 66.08| 2385| 2.39
7| 2385 |61.22| 63.61| 2296| 2.30
8| 2296|58.92| 61.22| 2210| 2.21
9| 2210|56.71| 58.92| 2127| 2.13
10| 2127|54.59| 56.71| 2047| 2.05
11| 2047 |52.54| 54.59| 1970| 1.97
12| 1970 |50.57| 52.54| 1896| 1.90
13| 1896 |48.67| 50.57| 1825| 1.83
14| 1825 |46.85| 48.67| 1757| 1.76
15| 1757|45.09| 46.85| 1691| 1.69

 

[brandon429]

unbelievably helpful, I totally see what you mean by no complete fills. Based on our discussion I may send it back upon arrival, I was hoping for better refill potential from the little rascal. Anyway, this is what I was trying to replicate, if I could only pay $200 bucks (200 was all I paid brand new, from a NY dive shop, not 300!) to be able to do this any time I wanted then it would have been worth it:

YouTube - spare air filmed with the oregon action cam in hawaii honolu

 

[brandon429]

I did get open water padi about 12 years ago on grand cayman. I had forgot pressure specifics or the values/formulas for it all in not using it over the years but I was only concerned about breath-holding and sinus equalization for my pool diving idea...I wasn't even going to mess with charting because the depths are maybe 5 8 ft max the whole time...just bare bones diving real simple. I was thinking all in all if I could get 8-10 mins and simple refills it'd be worth it, if not then it's not worth it. If anyone wanted these for legit uses leisurepro diving has them for only 189, the 3.0 ones, I noticed many people thought they were costing me 250 or three hundred, price must have dropped since these first came out...

 

[mike_s]

now do you see why everyone was telling you it was a joke to buy?

don't send it back... PM WhalyerKyle and get his address. He's got a good way of disposing of air tanks.

that way we could at least get some more entertainment out of this thread.



(nite all... I'm going home)

 

[Deefstes]

I'd love to see a Spair Air explode!

 

[elan]

Each time you "fill" the spare air from the large tank it will be "less full". The pressure will equalize each time. "Full" is at 3000 psi, next filling will have less pressure.

Yes I think buying a portable compressor would easily solve this problem

 

[elan]

instead of buying the refill tank, what if I pick a weekend we felt like diving in the pool and simply rented an 80 cf tank as if we were going to dive normally for a couple days and refill from that...how many 3.0 cubic foot refills you think i'd get off a 80? I wasn't thinking it was mathmatically 26 as I was thinking equilization would come well before the end of the tank, just guessing how many fills off a rented 80?

Mathematically - unlimited number of fills. But keeping in mind discrete nature of air I think until you have 1 molecule left in the 80cuf tank and it's willing to move to more comfortable and nice spare bottle.
Another question though is how full the bottle will be.