You will want to use co2 tubing for co2 or you will leak quite a bit of co2 through the airline tubing. I think co2 has smaller molecules or something because it escapes through the pores of standard airline tubing. Co2 tubing is more dense which you will see by how stiff it is. Feel free to use either but you'll have to refill co2 more often with airline tubing. Co2 also degrades airline tubing making the leak problem worse

 

I prefer the silicone tubing because it doesn't get real hard over time like standard airline vinyl tubing does, and it isn't nearly as stiff and hard to work with like CO2 vinyl tubing is. I tested some really cheap silicone tubing for CO2 leakage several years ago, and found none at all. I'm sure it does leak more than vinyl tubing does, but it is still way less than I could detect.

 

Unknown about CO2 but just as airline tubing silicone all the way. The standard stuff cracks, hardens, leaks at connections etc.

 

Some depends on what you want it to do and how long you want it to last versus how expensive you want to go.
I talked to the tech dept at US Plastics when ordering and they say it doesn't matter at the super low pressures we use and for something as simple and harmless as CO2. For higher pressure or something dangerous or difficult, they would have choices but not for most of our uses.
If you are sticking to under 50 PSI, none will leak any amount beyond theory. If you are using it to carry high pressure, you certainly DO NOT want to use airline tubing. But some depends on how you feel. Airline normally lasts a few years, depending on how much light and UV exposure it gets and then it does get brittle and may break or leak. For my use, this is not a problem as I look at the fittings and tubing ends every few months anyway and I can spot when tubing is getting hard. I have a big roll of tubing and when it gets hard, I run a new line for a few cents. If I used expensive stuff that would resist UV and last a few years longer, I might not change it with so little thought. None of my tanks are assumed to have CO2 running for 5-10 years so going with cheap and easy works far better for me than searching out and paying for something I don't need.
So the question becomes whether you want to pay more for "forever" tubing or less for quick and easy to find stuff.
If you are using it to go from a solenoid/needle valve setup to a reactor, there will be precious little needing to go through the molecular structure of the walls when the end is pretty close to open.
If you want a really fully trained and qualified answer to which is better, call one of the plastic companies and ask for tech service.

 

How can I tell what the pressure would be?

I believe the pressure is behind the regulator, valves,etc...

When it gets to the airline tubing, its only releasing like 1 bubble per second.

I'm not sure what type of pressure that would be but I don't think it would be much would it?

 

Found this on another forum.

http://www.coleparmer.com/techinfo/t...tingTubing.htm

CO2 permeability (cc.mm/cm2.sec.mmHg) x 10^-10) (lower number = better)

FEP @5.9
PTFE @ 6.8
PVC @ 6.8
Nylon @ 20
Viton @ 79
Polypropylene @ 90
Tygon Fuel @ 100
Polyethylene @ 280
Tygon Lab @ 360
Vinyl @ 360
Polyurethane (clear and aqua-tint) @ 395
Norprene @ 1200
Gum Rubber @ 1311
Tygon Pressure @ 2700
Tygon Ultra-chem resistant @ 4840
Silicone @ 20,132

As you can see polyethylene is a good choice. For a while I was using vinyl from HD, but now have what I think is flexible PVC. All in all, beats silicone.

End quote:

Ok, so I don't know what pressure they are talking about. This might not apply if my application is under low pressure.

 

http://www.plantedtank.net/forums/2...-planted-tank-faq/107312-pressurized-co2-just-thought-id-share.html#post1056450

 

We can easily make things too complex to really care or we can get down to what works. The chart above makes this all sound really difficult so I like to get down to asking what works. Since the above post mentions Cole-Parmer and that silicone is the worst tubing to use, I wanted to do a bit more checking as the above info is complex but leaves out some things that I feel matter. Like what temperature and what pressure. Those have always seemed to be the primary questions on choosing tubing as I rarely work with any serious chemical hazards.
So if you want to get some simple info that is reasonably easy to read, I suggest trying this.

Go to the Cole-Parmer site:
Chemical Compatibility Database from Cole-Parmer

Scroll down to get the rating for silicone as it is the material mentioned as the worst. Then scroll down to set it for using either CO2 dry or wet or check both as the rating comes back the same.

Click "results" and you may find the same as I did. The rating for the worst tubing (silicone) is this:
B = Good -- Minor Effect,
slight corrosion or
discoloration.

We can make life hard or we can make it simple. For me, if the worst is still rated GOOD, I think I can live with using most any of the better rated types! But then it is still just a matter of personal choice as to which you want to use but I recommend using what is cheap and easy until I get better information.

:wink2:

As to the question of what is low or high pressure it is all depending on who and what we are talking about. Steam lines may be a couple thousand PSI but for me, if it reads on the low pressure gauge, I'm for calling it low?

 

As was mentioned earlier, pressure likely has a lot to do with permeability of a specific material. With my particular setup, cerges reactor, the maximum pressure within the tubing is slightly greater than the water pressure in the reactor. I have not specifically determined the exact pressure, but it is definitely under 10psi. Likely closer to 5psi.

Now if you were running a ceramic diffuser then I could maybe see some cO2 leaking thru the tubing at 30psi.

 

Just from personal experience, silicone tubing ballooned a bit when using it at 40 psi with one of the higher pressure atomizers. At lower working pressures, like 20 psi or so, there was no ballooning.

 

That is where I see we tend to get things confused at times. We can all see that there are different types, sizes and thickness of tubing. And with logic we can see that some will last longer or fit better on the particular fitting we have. So we do need to choose one that works with what we have.
But when the folks who make all kinds of tubing post a website so we can look and see what works best, I like to go with their advise as it seems far more reliable than most any posting on any forum. Cole-Parmer makes tubing and they do have the website that says even the worst tubing (silicone?) is rated good with no major problem.
What that info tells me is that the loss of CO2 through the walls is a figment of overactive thinking on forums! It can happen but not in our tanks and the way we use it.

 

For our uses where the distance from co2 to tank is minimal I think we are counting fractions of a penny. Personally I right now have both vinyl and silcone running to different setups and sometimes I switch from one to the other and I don't notice any real difference. The silicone is easier to attach to the diffuser. If I'm using stiffer tubing I heat up the end and then attach.