CO2 "resistant" tubing...

4650 Views 5 Replies 4 Participants Last post by Nordic, Jan 21, 2017

Aqua99

Discussion Starter · Jan 21, 2017

I know this has been discussed to death and I'm not trying to rehash all of it over again. I honestly believe if you have a system that works for you, then you should stick with it. I've always preferred to use one type of tubing from my reg to my bubble counter at the tank, and a more pliable type from my counter to the diffuser. Strictly my own preference.

Just recently, I decided to pose the question to one of the leading manufacturers that I often deal with at work. My concerns were permeability, as well as "brittleness" with prolonged use. I use two of their other products currently and asked how they stack up.

----- I'm posting this with their brand names removed, as to strictly convey what their technicians responded with. I'm not trying to push a specific product. I just happened to find their response interesting, informative, and worded in a way that was easy to understand. -----

"Thank you for your interest in our products.

Please find answer below from our technical team -

OK - for general, low pressure use in conveying C02, the (tubing A) and the (tubing B) are good economical choices. It will become somewhat brittle over time, and there is a level of permeability to most gases due to the plasticizer used in both, inherent in most flexible materials.
The best choice would be (their version of "beverage" tubing), not only is it a polyelfin liner, but since it is cross-linked, there is far less movement of the polymer chains as they are "linked" together. Of course, (bev. tubing) is not nearly as economical as (tubing A), not quite as flexible, but far better performing...

In general terms, materials that are more flexible have greater permeation levels, and through use (and permeation), the polymer chains get "stuck" and will not move as freely - thus, the tube gets brittle. The more rigid the material (usually), the more structured the chains, move out of the way of the gas less easily, and have a lesser permeation. The (bev. Tubing) offers some of the best of both worlds, still rather flexible, but with a good barrier to permeation due to the crosslinked liner."

My "tubing A" and "tubing B" are both PVC. Both are pliable, but the one I run up near the tank feels just like silicone. I essentially get both for free and replace them frequently even if they seem fine.

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PlantedRich

· #2 · Jan 21, 2017

You are correct to approach this subject with care!! We now live in an era where any differing opinion requires immediate attack!
But I also have talked to some techie folks and they agree. Some things we often fail to mention when speaking of CO2 loss through the molecules of the side walls is what pressure we are running. When dealing with our pressure levels, we are far out of what the tech folks think of as pressure. So when asked how much goes out through the wall on a tube with 200PSI you will get a different answer than if you ask how much is lost when the tube dumps into a reactor where the end is close to open!
My spin?
When dealing with 200PSI and running 24-7 for a couple hundred feet, it matters a whole bunch. When dealing with under 50 PSI and dumping it out 6 feet away into a tank of water, it matter more which tubing works for the fittings you have!

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jeffkrol

· #3 · Jan 21, 2017 (Edited)

When dealing with under 50 PSI and dumping it out 6 feet away

Though not generally fiscally important (CO2 being cheap) I think you are being a bit 'generous'..
You can get "measurable" losses at 50psi...

To get a true calculation of permeation losses you have to add in the difference between atmospheric pressure and the the local partial pressure of CO2. Since atmospheric CO2 is in the neighborhood of 350ppm, it's partial pressure at sea level is negligible at 0.03 cmHg or 0.006psi. So the 1psi gauge pressure is actually ~15.7psi (81.2 cmHg) pressure differential driving diffusion. At that pressure the loss baloons from 137 cc/day(270mg/day) to 2160 cc/day (4.25g/day). If you're running a 5 pound tank that means it would self discharge in 18 months, or decrease a ideally 9 month fill interval to 6 months. I don't think that is insignificant. If you're running into a ceramic diffuser, you can expect even higher losses. I'm running CO2 into an very fine airstone located within a reactor underneath my tank. My gauge pressure, measured at the input to the bubble counter is 3.8psi, though I'd expect in-tank diffusers are higher than this.

There are many options with permeablity around 1/50th that of silicone rubber, which bring total loss rate below 100mg/day (<1% total loss for the above scenario).

co2 tubing ? - Aquarium Plants - Barr Report

This usually goes around and around about losing a few $'s per fill..for most .
Multiple tanks and a central distribution being an "exception"

Getting tubing the really "fits' is probably a better objective..
On a personal note, and admittedly not cheap recommendation, though it will be a few months b4 I determine if it "hardens"
Tygon Fuel Line 1/8" ID X 1/4" OD.. The yellow stuff..

Low permeability, good fit to the fittings I've used (3 different bubble counters, barbs, atomizers) and an oddly pleasant color..

YMMV

Is it worth it to most? Probably not..

Silicon tubing is probably the only not recommended tubing except as the "last mile" using glass fittings..

So the 1psi gauge pressure is actually ~15.7psi (81.2 cmHg) pressure differential driving diffusion.

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Aqua99

Discussion Starter · #4 · Jan 21, 2017

Good catch! I should have posted my original question.

"Hello. Could you please give me any info on your Excelon SL and RNT tubing with regards to pressurized CO2?

I plan to use both in a system I'm setting up due to their unique specs, but have concerns with permeability and brittleness with prolonged use.
Pressures would likely not exceed 3psi, and the tubing in question is 1/8ID-1/4OD."

I keep meaning to bring a digital gauge home from work and read the actual pressure downstream of the needle valve while the flow is dispensing to my diffuser. Both of my systems in use right now are set between 12-15psi on the low side gauge, with downstream pressures expected to be be a fraction of that.

You are definitely right. I think given our relatively low pressures and short runs, there is little need to be concerned at all.

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Aqua99

Discussion Starter · #5 · Jan 21, 2017

Btw- I did purchase 50' of the tubing they recommended just to see how it handles. It would be nice to get something with permeability on par with something like the tygon mentioned above (4040/1100 I think), but slightly more flexibility for ease of use.

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Nordic

· #6 · Jan 21, 2017

Well, even the fancy tubing should get hard over time. it is one of the downsides of flexible synthetics. Most of the stuff that goes wrong on even luxury vehicles is down to shrinkage and drying of plastics and rubber o-rings etc.
My take on it would also be to buy whatever fits and is cheaper and do a regular replacement. But, thanks for sharing, and I hope you will report back further down the line to report how well it held up.

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