Converting 2x12L to Decanting Bank

[nickbutcher]

A lot of people seem to do this, but it's an expensive option for a dil/air bank. A decent in-test, twinset would fetch a good price on the second-hand market, whilst old, larger gas bottles can be sourced very easily and hold a lot more volume.

I picked-up 5 empty 30l oxygen bottles for £40 each when I switched to a CCR.

 

[Wibble]

How many time can you fill a 3L tank with one bank?

You don't "fill" them, you top them off. I seem to use about 50 bar of both O2 and diluent per dive (depends on the dive, use that as a simplistic guide amount). Thus a 50 bar top-off of a 3 litre cylinder is 150 litres of gas used.

I close the manifold on the twinset bank and will use both sides to get the highest pressure. Assuming the bank's full, this means I'd use 150 litres divided by 12 litres (the cylinder size) = 12.5 bar (≈175psi).

As the bank drops in pressure on one side through use, I'll start to use both sides, top off from the left and then top off from the right.

With 3 litre cylinders you can easily do a dive with only 150 bar (x3 litres = 450 litres of gas)

As a simplistic calculation, starting with 260 bar in the twinset, and ending at 150 bar, i.e. 110 bar, that's about 9 fills per side = 18 fills. (Simplistic - won't be as much as that in reality)

In the summer this lasts me several weeks between bank fills.

The gas I mostly use is air as the suit inflate needs topping off as well as the diluent. I'd buy a 15 litre tank if one came up at the right price.

 

[Jack Hammer]

How many time can you fill a 3L tank with one bank?

Depends on the size of the supply bank and its pressure and the size of the bottle being filled and to what pressure as well as how low of a fill you are willing to accept in your 3L bottle.

You'll quickly find that a small booster will become a good investment in convenience as it will allow you to access a tremendous amount more gas in your supply bottle.

 

[Wibble]

You'll quickly find that a small booster will become a good investment in convenience as it will allow you to access a tremendous amount more gas in your supply bottle.

Would love a booster but they also need a supply gas to run which kind of requires a compressor (even if a garage compressor). Then there's the cost of running it (spares, servicing) on top of the cost of buying one.

But very shiny! Want one, especially in my dream dive RV van!

 

[Jack Hammer]

Would love a booster but they also need a supply gas to run which kind of requires a compressor (even if a garage compressor). Then there's the cost of running it (spares, servicing) on top of the cost of buying one.

But very shiny! Want one, especially in my dream dive RV van!

I mostly run mine off a couple old steel 72s I have laying around. I have access to a few fill stations so no big deal to refill them. As a backup I just use a small .75cfm compressor. It takes awhile but will boost my 3L to a little over 180bar.

 

[broncobowsher]

How will you be getting the banked gasses filled? Figure that into the works as well. Quick bit of info to think of, you will be getting them topped off when they are still at least half full.

After getting the rebreather it was quickly apparent that a booster was soon in my future. The nearest place I could get fills was a little over an hour away. And they did not fill while I waited. So it was two round trips. Over 4 hours on the road. I already owned a shop compressor at home. So I got a booster. Do my home filling.

I have traveled with it. Done parking lot fills. That is where the big twin set is nice, for drive gas. You use a lot of drive gas so I avoid doing parking lot fills any more than I need to. To the point that I own more rebreather bottles that I just fill at home now. Makes long weekend road trips easier. A set of bottles per day.

The parking lot fills are good as in you can do them anywhere. Getting an air fill at any dive shop. That will be drive gas. You don't have to find a shop that has a booster. You could rent a cylinder, go in the parking lot, use it for drive gas, and return it inside of an hour. And you are diving full bottles.

 

[helios]

I can usually get o2 filled on the spot. The bank is just for air to dil/drysuit tank at a moments notice. I have 2x o2 tanks 1x dil and 1x trimix, so I typically always have a full o2 tank on standby.

The 2x12L I can easily get done 15 minutes away if I need to get it refilled. It's really for when the dive shops are closed/weekend diving when I don't have time/ability to get a quick top-up.