Quick Scuba Tank Question.

[leadly]

I've scrolled through all the topics in here but can't find any info.....however it is late and I am tired, apologies if this has been asked before...

 

I've ordered, but not yet collected a 3litre scuba tank from Go Dive, how many times would that likely fill my 48ci tank?

 

Cheers

 

Rich

[Tommikka]

1 hour ago, leadly said:

I've scrolled through all the topics in here but can't find any info.....however it is late and I am tired, apologies if this has been asked before...

 

I've ordered, but not yet collected a 3litre scuba tank from Go Dive, how many times would that likely fill my 48ci tank?

 

Cheers

 

Rich

Theres a fill calculator linked here:

https://www.scubatoys.com/paintball/scubafills2.asp

 

However the minimum scuba size is an 80. (Which ought to be about 11 litres)

So that’s not going to give you your answer 

But it will illustrate that ‘number of fills’ isn’t an exact science, what matters is preservation of the scuba pressure for as long as possible to enable usable fills

In the calculator select ‘aluminium 80 @ 3000psi’ and ‘47ci

Then run each of the 4 options of refilling when at 0, 400, 750 and 1000psi

Only take the results of column one

(the other two columns are to demonstrate using multiple scuba cylinders and cascade filling in stages)

Every time you fill the two cylinders attempt to equalise, but you should stop as soon as possible 

Assuming both your scuba and playing cylinders are 3000psi cylinders, if you have an empty playing cylinder and fill to the maximum then you won’t have a 3000psi fill:

 

You begin with 4 litres at 3000psi plus approx 1/2 litre at 0psi.  You then share out that 4litres into 4.5 litres which is a larger capacity and a slightly lower pressure.

Therefore you achieve zero fills of 3000psi (but the reduction is negligible and the gauge looks like it’s on 3000psi

Let’s pretend it became 100psi less over the extra 1/2 litre (first fill = 2900psi

You go al Rambo and suddenly find yourself at 0psi

Take the scuba’s 2900, drop by 100psi and your second fill is 2800psi

You have had zero 3000psi fills, but manage to get 10 fills in excess of 2000psi
 

The first trick is to never let them equalise, only draw off as little as possible that you could get away with:

For example fill the playing cylinder to no more than 2500psi, the scuba remains over 2500 for much longer so you manage to get multiple 2500 fills before the source scuba drops that low

 

The second trick is to always top up as soon as possible.  This way you are not taking out 0.5l of 2500psi.  What you are ideally doing is topping up a few hundred psi at a time

 

If you can remember mathematics then you might manage to reverse engineer the calculator and make it work for your 4 litre scuba

Because it starts with an 11litre scuba there’s more capacity to maintain the pressure as it is drawing to a relatively smaller playing cylinder (22 times)

 

In your case the scuba is about 8 times the capacity of your playing cylinder.Not a big drama as it’s pressure you’re after, but the bigger the difference in capacity the more to go around 

[leadly]

Thanks for the reply. 

 

So I'm better off topping up the tank that connects to my RIF little and often, makes sense to me!

 

The reason I asked was just to make sure the 3litre tank will be sufficient to last me long enough for a decent "setting up" session and a couple of top ups on a game day. I live about 2 miles from my local go dive so getting a refill isn't an issue.

 

Portability and space saving is higher on my list than overall capacity as I will only be using the gun in anger at most, once a month.......which will probably be even less once my wifes maternity leave finishes in March! 

[Tommikka]

2 hours ago, leadly said:

Thanks for the reply. 

 

So I'm better off topping up the tank that connects to my RIF little and often, makes sense to me!

 

The reason I asked was just to make sure the 3litre tank will be sufficient to last me long enough for a decent "setting up" session and a couple of top ups on a game day. I live about 2 miles from my local go dive so getting a refill isn't an issue.

 

Portability and space saving is higher on my list than overall capacity as I will only be using the gun in anger at most, once a month.......which will probably be even less once my wifes maternity leave finishes in March! 

Yes - little and often is key

Pressure is more important than overall capacity, and as you say ‘portability’

 

 

 

You won’t want to drag around a large scuba cylinder everywhere, but a smaller scuba is practical enough to take to the staging and you will be able to easily top up more often

 

Its going to be suck it and see for a while and take a notebook to record the pressures at each fill.  You can then refine your regime to see what works for you

 

 

A large scuba gives more capacity but a 15 litre cylinder at 100psi is no use, the benefit of a larger capacity is the relative difference between source and destination means the source can cope for longer at maintaining as close as possible to its original capacity for longer 

[Monkman]

Very handy info thanks...I've bought a 7 litre tank with my new MTW.  Just need to wait for lockdown to be over so I can get it filled. 

[leadly]

Go dive are open to fill by appointment if you have one near by!

 

 

Ah, think it might just be a Derby shop!

[Tommikka]

2 hours ago, Monkman said:

Very handy info thanks...I've bought a 7 litre tank with my new MTW.  Just need to wait for lockdown to be over so I can get it filled. 

Not exactly for your purposes, the following is a list of approved hydro test centres.  Many are dive shops, and as they test cylinders may provide fills

 

(There will be other dive shops etc that can handle fills and may handle cylinders for testing but will operate as middle men with test centres)

 

 

https://www.sita.org.uk/idest/idest_members.php