Part 1: Using Your Own CO2 Gas

Many years ago I bought a Sodastream machine to make soda. I figured I’d save some money, and save having to lug bottles home and return them for the deposit. I drink a lot of soda.

Well, it worked out great, with one exception: it wasn’t cheap. I went a few years using Sodastream’s CO2 bottles and sodamix, annoyed by having to spend hundreds of dollars a year on it, to say nothing of the inconvenience of having to return CO2 bottles to the mall which is ten miles away.

So I started exploring alternatives. First was buying a few paintball tanks for CO2, and an adapter that converts paintball-tank threads to Sodastream threads. I found a local sports shop that would fill the paintball tanks for a few bucks, and I was in business.

Everything was great until the sports shop stopped filling CO2 bottles, and I couldn’t find anyone else to do it anywhere nearby. I was back to spending $30 to refill a couple of Sodastream cylinders every couple of weeks.

The next step was to buy a big tank that I could use to fill my paintball tanks myself. You can also get an adapter hose to connect a big tank directly to the Sodastream machine, but I didn’t like that idea, mostly because it seemed awkward. So I bought a big aluminum tank, and another adapter, this one to connect to the big tank, with a hose to connect to a paintball tank, and a couple of valves. It was all pretty expensive, but it doesn’t take long to make back that money with your savings.

Now I pay about $25 to fill the big tank, and it lasts a year. I have three paintball tanks, which I have to refill about once a month.

So that’s the story. The rest of this post tells how to do it yourself. Another post tells how to make your own sodamix, which frees you from having to buy those expensive flavor syrup bottles from Sodastream.

Starting with Paintball Tanks

You want to get 24 oz paintball tanks. That’s the biggest size that will fit in the machine.

Warning: there are many models of Sodastream machines, and I don’t know if they all take the big Sodastream cylinders, or even if Sodastream still makes the big cylinders. Look at your machine and see if the space where the Sodastream cylinder goes is big enough for a paintball cylinder, which is about 3-1/8″ in diameter. If not, I can’t help you (for now…). But you might consider one of the direct-to-big-tank hoses.

Right now 24 oz paintball tanks are about $25 on Amazon and eBay has them for 2/$45. I suggest starting with two of them.

The adapter you need is $15 – $20 on Amazon, and $12 – $16 on eBay. Get one that comes with an Allen wrench.

Note that the paintball tanks use an o-ring for a seal. I’ve had trouble with them leaking. I sell oversize o-rings for paintball tanks on eBay. If you have trouble with leaks, try those.

You need to adjust the adapter after installing it on a paintball tank but before mounting it on your Sodastream machine. Use the little Allen wrench that came with the adapter. Stick it in the top of the adapter and engage it with the adjusting screw. Tighten the screw until gas escapes, then back it off a bit. If you ever push the button on the Sodastream machine and little or no gas comes out (but the tank isn’t empty) you need to perform this adjustment again.

Getting Paintball Tanks Filled

Some sports shops can fill paintball tanks for you. The chains typically don’t. Don’t worry about getting “pure” food-quality CO2 — it’s all pure. There are endless threads on message boards about this. It is people worrying about nothing. Expect to pay $3 – $5 for a fill.

Like me, you’ll probably have trouble finding a convenient place to get this done. That’s why I recommend biting the bullet and getting your own large-size CO2 cylinder. It’s a big investment but you’ll make back your money pretty fast.

About CO2

Here would be a good place to tell you about CO2 — you need to know the basics to understand what you’ll be doing.

CO2 isn’t like most compressed gasses. When the pressure reaches about 700 lbs it condenses into a liquid, and the liquid form holds way more CO2 than the gas form. You want to be working with the liquid form. CO2 cylinders are rated by their capacity of liquid by weight. A 24-oz paintball tank holds a pound and a half, and a 20-lb cylinder holds, well, 20 lbs. You’re not supposed to overfill the tanks, which means weighing them as you fill them. I’ve never bothered, and never had a problem. The only problem I’ve seen is that it’s hard to get the full weight into a tank.

Because CO2 is a liquid, you need something called a “siphon tube” in your big tank so the paintball tanks will get filled with liquid sucked from the bottom of the tank. Without a siphon tube you’d just end up filling the paintball tank with 700 psi of gas, which isn’t much gas.

When your big tank starts to run out you’ll be getting mostly gas out of it. When you fill your paintball tanks you’ll still be getting 700 lbs of pressure but since you won’t be getting any liquid, the tank will only last for a handful of bottles of soda in your machine. It’s time to get more CO2.

At this point an option would be to use a direct connection from the tank to the Sodastream machine. This lets you use all the CO2 you paid for. More about this later.

It’s important to empty all the gas out of an “empty” tank before refilling it. This goes for paintball tanks and the big tank. You’re only going to be filling it until it get to 700 lbs, and you want the full 700 lbs worth of liquid CO2. If the tank still has 600 lbs of gas in it when you refill it, you won’t get much liquid before it’s “full”.

Be somewhat careful when releasing CO2 to get the tank completely empty. If you do it in a closed space you can die from lack of oxygen. I’ve had the pilot lights on my stove go out after emptying out a big tank in my kitchen. That’s getting pretty well into the danger zone. Now I always empty out the big tank outside.

A note about CO2 and climate change: the CO2 you buy was removed from the atmosphere, and when you use it it goes back into the atmosphere. The net gain of CO2 is zero. Of course like everything else it takes energy to “make” CO2 and that energy likely comes from fossil fuels, but let’s not go there.

Setting Up to Fill Your Own Paintball Tanks

To fill your own paintball tanks, you need a commercial-sized tank, and an adapter.

You can then get your tank filled at any compressed-gas place. There are lots of them, often with “welding supply” in the name. Expect to pay about $25 to get a tank filled. Some places will do it while you wait, some want you to come back later to pick it up. The sizes of tanks that you’ll be dealing with get refilled, and you get the same tank back; they aren’t done on an exchange basis like the really big tanks.

I recommend a 20-lb-capacity aluminum tank. It’s a nice size and not too heavy. You want one that has a standard CGA320 valve and a siphon tube. (A siphon tube sucks the liquid CO2 out of the bottom of the tank — without one you’ll end up filling your paintball tanks with (not much) CO2 gas.) I bought mine from http://www.beveragelements.com, and recommend them. A new 20-lb aluminum tank with a siphon tube costs $126 plus shipping; they also sell on eBay and have the same thing for $139.90 with free shipping. Sounds like a lot? It’s cheaper than ten Sodastream tank refills, and how long would it take you to go through that many?

A note about cylinders (tanks) and pressure testing. Tanks (including paintball tanks) have a date stamped on them — a two digit month and a two digit year, separated by some sort of symbol. The date is when the cylinder was last pressure tested. It is “good” for five years from that date, after which it is supposed to be recertified. If the cylinder certification has expired, the gas place is supposed to refuse to refill it. I don’t know if they actually check, and I also don’t know how one goes about getting a cylinder recertified.

Certification testing (also called hydrotesting) is why I don’t recommend buying used cylinders. You’re likely to get a cylinder that has expired or is about to expire, and you then might have trouble getting it filled.

Now you’ve got a big tank full of CO2 and you need to be able to fill your paintball tanks. What you need is a paintball tank fill station. Search for that on eBay and you’ll find one — they start at about $30. You want something that fits on a CGA320 valve and has a hose connected to something that screws to a paintball tank. You don’t want anything made for scuba tanks.

Some “fill stations” have gauges; most don’t. You can add a gauge if you want. I think they help, even though they don’t tell you how much CO2 is left, until the liquid CO2 is gone. The fill station consists of valves and fittings, usually 1/4″ pipe thread. You can buy more fittings, and gauges, to add to it so long as they have the right threads. It’s most useful to have a gauge between the two valves.

A good source for the parts you need is McMaster-Carr. To add a gauge, buy one each of “0-2000 psi 2″ gauge” 32255K7, and “1/4″ high-pressure tee FxFxM” 50925K197. It should cost about $30 plus shipping. Once you get the parts, separate the fill station fittings in the right place and put it back together using Teflon tape.

Filling Paintball Tanks Step-by-Step

To fill a paintball tank, screw your adapter onto your CO2 cylinder, first making sure all the valves are closed. Open the main valve on the C02 cylinder, which shouldn’t make anything happen.

In the next step you will be screwing the paintball tank (which has brass threads) onto the adapter (which has aluminum threads). It is very easy to cross-thread the tank/adapter connection, which will ruin the adapter. The tank should screw onto the adapter smoothly. If it binds, even a little, back it off and try again,

Now that you have been suitably warned, screw a paintball tank onto the adapter at the end of the hose, and screw down the knob to open the valve on the paintball tank. Now, open the adapter valve furthest from the CO2 cylinder. That should let any CO2 left in the paintball tank escape. This is important because you want as much room for CO2 liquid as possible, to get a complete fill.

Close the valve you opened in the last step, and open the other adapter valve. Liquid CO2 should rush into the paintball tank. It will be cold and heavy. Wait until nothing more is happening, and wait another few seconds just to be sure. Close both adapter valves, then unscrew the valve on the paintball tank to seal the tank.

You’re almost done. Before unscrewing the paintball tank from the hose adapter, you need to let the remaining CO2 out of the hose. To do this, open the outer valve on the adapter and let the gas from the hose escape. There will be a lot. Finally, unscrew the paintball tank from the hose adapter, and you’re done.

It takes a lot less time to do than it does to explain.

Directly Connecting a Big Tank

There is another kind of hose you can buy, which connects from your large CO2 tank directly to your Sodastream machine. This is useful for getting the rest of the CO2 out of your tank once you’ve used all the liquid CO2. The hose has a CGA320 connector on one end (to connect to your tank), and a fitting on the other end that srews into your Sodastream machine where you ordinarily attach Sodastream cylinders, or paintball tanks with a paintball tank adapter as described earlier.

It is also a way to connect a big tank to any Sodastream machine that doesn’t have room for a paintball tank, which I think is true of most newer machines.

If you want to skip the whole paintball-tank thing, you need a CO2 cylinder without a siphon tube. If you have a siphon tube in your tank, you’ll get liquid CO2 instead of gas, and that will not work. Remember: with a siphon tube you get liquid (until the liquid is gone), without one you get gas. The Sodastream machine wants gas.

To find the hose you need, search on eBay for “sodastream co2 tank adapter hose”. You don’t want a “fill station” for this. Some of them have a quick-connect at the Sodastream end, which is very convenient. I paid about $25 for mine. Note: the quick-connect fitting uses tiny o-rings, which tend to come out. If they do, stuff them back in — there are two of them, one on top of the other. It’s hard to get them in place, but it can be done with some fussing.

I’ve noticed that the o-rings tend to swell in use. Let them sit overnight and they’ll go in much more easily. If you lose the o-rings, they are 6mm ID and 10mm OD. You can get them from McMaster-Carr, item number 9262K166. Slightly smaller ones might go in more easily: order 9262K576.

So far I don’t have a lot of experience doing this, and it hasn’t been going well. The button in the Sodastream fitting that releases the gas appears to require a lot of CO2 pressure to activate. Under about 450 lbs you can’t get any CO2 out of it. Maybe there’s something wrong with my adapter, or maybe it’s just designed that way. In any case if you want one of these hoses to get the last bit of CO2 out of your tank, you may be disappointed.