How to make your own CO2 air system for under $200

[mrblaine]

The cylinders you get filled are gas. Liquid CO2 requires refrigeration or cryogenic tanks. CO2 is compressed to a higher pressure in the cylinders yielding more stored volume.

All of the Co2 cylinders I've had filled over the years for tire use are not gas but liquid and the cascade system used has the dip tubes in place so only the liquid is transferred. The typical head pressure to keep Co2 in liquid form is roughly 8-900 psi depending on temperature.

I think you've confused O2 and Co2. Co2 in liquid state at room temperature is readily available at any welding or industrial gas filling station that I've ever been to and that is several here in SoCal and across most of the western states when we've had to get refills on our support trips.

Nitrogen is the one that is filled to very high pressures in steel cylinders for the higher volumes. I've heard tell of 6000 psi cylinders and I investigated it briefly for PCP but my local place doesn't handle them.

LOX is one of those that can't be fully contained in liquid form. It will continue to boil off no matter what you do to try and contain it so it has to be vented. If you ever look at a video of the space shuttle, the vapor you see is the LOX being vented. Co2 will stop boiling off into a gas at the pressure mentioned above. That's why dual gauges don't work with one showing tank pressure and the other showing regulated pressure. The Co2 continues to maintain the 8-900 psi in the bottle as it boils into a gas until the liquid is gone.

In case you aren't confused and only have experience with beverage industry, some of them do use only the gaseous form of Co2 but that is a fairly specialized industry and not what we typically encounter when we get a bottle filled for tires.

 

[Jeepaholic]

I figure if I get 3 trips out of it (12 tires total filled) that should last awhile. I only get a chance maybe once a month. I have a big air compressor at home, so I will be draining the co2 from the tires and refilling with normal air once I get home. Strictly for airing up for the trip home. I didn't see much on a nitrogen system, or places to fill up with nitrogen, or how many tires a 10lb tank could do.

 

[mrblaine]

Nitrogen maintains in the tire slightly better than compressed air. It distributes heat more evenly too. That is why race cars run it. We build a couple hundred N2 generators a month for a much better cause. Draft Beer.

Nitrogen and all compressed gases at the pressures we see in tires are not capable of being exceptions to Boyle's law which states that for a given volume at given temperature, all gases will have the same pressure. Nitrogen only maintains in the tire better than the diffusion rate for the other gases like O2 and Co2 and then only ever so slightly since compressed air is mainly nitrogen so the difference would be the smaller percentage of the other gases. Not to mention that it is next to impossible to get a tire filled with pure nitrogen. You would have to pull a vacuum to evacuate all the air out or run dual valve stems and flush the tire through one while you filled with nitrogen on the other. That never happens.

The main reason race cars run nitrogen is convenience. Their portable carts have a place for nitrogen tanks so that's what they use. We have had this discussion ad infinitum on the 'net since folks have been using alternate gas sources for filling tires. During one of them we finally had a guy who worked the trailer for Goodyear at a Nascar race tell us all they use for the initial fill is dry compressed air. Key being they used a dryer on it. That means they were filling the tires with about 78% nitrogen.

The aircraft world uses it in tires to slow down the increased flammability with compressed oxygen since their tire pressures are much higher and rubber burns in the presence of oxygen. No need to accelerate that.

 

[mrblaine]

I figure if I get 3 trips out of it (12 tires total filled) that should last awhile. I only get a chance maybe once a month. I have a big air compressor at home, so I will be draining the co2 from the tires and refilling with normal air once I get home. Strictly for airing up for the trip home. I didn't see much on a nitrogen system, or places to fill up with nitrogen, or how many tires a 10lb tank could do.

There is absolutely no need to change the Co2 out for air. I've been using Co2 exclusively to fill tires for at least 18 years and it just isn't a problem. We have always filled up at the end of the trail and driven home and I have done nothing except check pressure once in a great while if the tire looked low and filled it up. My Jeep on the trailer has sat for several months at a time at 8 psi and when I check the tension on the straps that hold them down to the trailer, they only need one click on the ratchet mechanism to get back to where they were when we put it on the trailer. I have more issues with temp than I do with a particular fill gas.

 

[mrblaine]

I thought I remember @mrblaine telling me something about nitrogen use in tires... Wish I could remember what he said though.

Nitrogen for use in tires on passenger cars is snake oil. None of the claims made are valid, and they all try to overlook Boyle's Law of Gases which isn't possible. Not to mention that the average tire is already filled with 78% nitrogen.

 

[mrblaine]

Question for general knowledge about gases. Does anyone know the "distillation" process by which they extract the common gases out of the air we breathe?

 

[mrblaine]

Nitrogen is much cleaner, non corrosive and it escapes the tire slower. You still have to watch the asphyxiant aspect but it does dissipate back into the atmosphere much faster.

I'll check with my gas guru tomorrow but when I worked at the ambulance company, we had a room that was 20' long x 8' deep. They turned it into oxygen cylinder storage and a cascade system for filling the small tanks. There was a concern that if we had a big enough earthquake, all 100 of the M size cylinders could fall over and knock the valves off resulting in an oxygen rich atmosphere. So, they hired a gas engineer to come in and do an evaluation of what size vent needed to be cut into the wall to vent outside air in and inside air out to achieve equilibrium. They cut a 12" x 12" hole in the outside wall and put a screen cover over it.

 

[Jerry Bransford]

Nitrogen maintains in the tire slightly better than compressed air. It distributes heat more evenly too.

The air we breathe is 80% nitrogen so how can that be?

 

[mrblaine]

The air we breathe is 80% nitrogen so how can that be?

It does but only based on the diffusion rate of the Co2 amount in the air we breathe. Since the amount of Co2 in air is fairly small, a pure nitrogen fill would diffuse though the butyl rubber liner slower than just air because the small amount of Co2 in normal air would diffuse slightly faster.

In other words, at the end of a year, a pure nitrogen fill tire might lose 2 psi, a normal air tire might lose 1.85 psi. POOMA numbers but close enough.

 

[Jerry Bransford]

Good info. With the number of times my tires get aired up with CO2/down every year those very small pressure losses over a year are of course insignificant. Ha didn't take too long to figure out the POOMA term.

 

[CommandoJoe]

Question for general knowledge about gases. Does anyone know the "distillation" process by which they extract the common gases out of the air we breathe?

Cryogenic

 

[Jeepaholic]

There is absolutely no need to change the Co2 out for air. I've been using Co2 exclusively to fill tires for at least 18 years and it just isn't a problem. We have always filled up at the end of the trail and driven home and I have done nothing except check pressure once in a great while if the tire looked low and filled it up. My Jeep on the trailer has sat for several months at a time at 8 psi and when I check the tension on the straps that hold them down to the trailer, they only need one click on the ratchet mechanism to get back to where they were when we put it on the trailer. I have more issues with temp than I do with a particular fill gas.

Thank you for that information, seems to be alot of misinformation on the net about co2 harming tires. This will save me the time of "changing the air out" at home.

 

[JP98]

Nitrogen and all compressed gases at the pressures we see in tires are not capable of being exceptions to Boyle's law which states that for a given volume at given temperature, all gases will have the same pressure. Nitrogen only maintains in the tire better than the diffusion rate for the other gases like O2 and Co2 and then only ever so slightly since compressed air is mainly nitrogen so the difference would be the smaller percentage of the other gases. Not to mention that it is next to impossible to get a tire filled with pure nitrogen. You would have to pull a vacuum to evacuate all the air out or run dual valve stems and flush the tire through one while you filled with nitrogen on the other. That never happens.

The main reason race cars run nitrogen is convenience. Their portable carts have a place for nitrogen tanks so that's what they use. We have had this discussion ad infinitum on the 'net since folks have been using alternate gas sources for filling tires. During one of them we finally had a guy who worked the trailer for Goodyear at a Nascar race tell us all they use for the initial fill is dry compressed air. Key being they used a dryer on it. That means they were filling the tires with about 78% nitrogen.

The aircraft world uses it in tires to slow down the increased flammability with compressed oxygen since their tire pressures are much higher and rubber burns in the presence of oxygen. No need to accelerate that.

Hi @mrblaine I wasn't disputing Boyle's law and nitrogen. I was just stating that it held in a tire slightly better than say compressed air or CO2 and it was better at heat distribution. The heat distribution coming from the fact that it being a single molecule gas vs air(78%N, 21%O balance other gases). Wasn't saying that it was the end all be all for tire inflation. I agree with your other statement about Nitrogen tire fill being snake oil. I build nitrogen gas generators and only top my tires off with it if they need it when I'm here. At the house I use my air compressor.

 

[JP98]

Nitrogen for use in tires on passenger cars is snake oil. None of the claims made are valid, and they all try to overlook Boyle's Law of Gases which isn't possible. Not to mention that the average tire is already filled with 78% nitrogen.

I agree it is snake oil for the average Joe. They wouldn't see the benefit at all.

 

[mrblaine]

Cryogenic

Yes. They reduce the temperature of air to a liquid. Then they raise the temperature to the boiling point of each gas and collect the pure gas that boils off. Since that temperate is very cold and the temperature is very specific it makes it easy to get only the target gas and nothing else. It also means that there is zero moisture in any of the gases being boiled off since liquid air is at least a couple of hundred degrees below the freezing point of water which is a solid at those temps.

Any gas collected by that method is clean, has zero moisture, and has a very high purity level.

 

[JP98]

I'll check with my gas guru tomorrow but when I worked at the ambulance company, we had a room that was 20' long x 8' deep. They turned it into oxygen cylinder storage and a cascade system for filling the small tanks. There was a concern that if we had a big enough earthquake, all 100 of the M size cylinders could fall over and knock the valves off resulting in an oxygen rich atmosphere. So, they hired a gas engineer to come in and do an evaluation of what size vent needed to be cut into the wall to vent outside air in and inside air out to achieve equilibrium. They cut a 12" x 12" hole in the outside wall and put a screen cover over it.

The difference between the oxygen rich atmosphere that you were trying to prevent and the asphyxiant gas rich atmosphere that I was talking about is that too much oxygen becomes a fire/explosion issue. The nitrogen or CO2 rich environment can cause asphyxiation and death without the victim knowing it. CO2 can cause loss of consciousness at 20,000 ppm and die at 30,000 ppm. That doesn't take a lot in a small space. Nitrogen dissipates back into the atmosphere faster than CO2 due to the fact that the atmosphere is made up of 78% nitrogen and the natural balance is always fighting to maintain that. I maybe should have stated that I was comparing nitrogen & CO2 in the post as to nitrogen dissipating quicker.

 

[mrblaine]

Thank you for that information, seems to be alot of misinformation on the net about co2 harming tires. This will save me the time of "changing the air out" at home.

Co2 in the presence of water can form carbonic acid. It is particularly harmful to steel due to the interaction with the ferrous portion of the alloy. If you run high moisture in the tires, have unprotected steel rims, and use only Co2 for inflation, you may bring about the conditions where you could have an issue. It would be rare and uncommon for that to happen and the carbonic acid is only harmful to the parts containing ferrous material enough to cause concern.

I have changed out my tires on the rig many times breaking down the bead locks and not once have I seen anything that looked different inside the rim or tire that would be a concern and these are tires and rims that have only been filled once to seat the inner bead with compressed air and the rest of the time, years typically, run with Co2.

You can dig around on the 'net and find lots of info on carbonic acid and where it is a problem and make up your own mind.

 

[JP98]

Liquid N2 requires refrigeration, liquid CO2 does not... If you've ever refilled a paintball tank (co2) the supply bottle will have a siphon tube to ensure you are getting liquid from the bottom of the tank rather than just gas from the top - for those that don't have a siphon tube people turn the tank upside down to ensure liquid co2 fills smaller bottle.

@CommandoJoe I'm apologize for not being more clear on my statement. The high pressure cylinders are a Case II storage of CO2 which is high pressure holding the CO2 in a liquid form. Cryo is a Case IV where it is held in a liquid state via refrigeration which allows for lower pressure storage. CO2 gas has a critical point of 88F @ 1,080 psi where it can no longer stay in the liquid form. So it has to stay above 1,080 psi or turn to gas above the 88 degrees.

 

[mrblaine]

The difference between the oxygen rich atmosphere that you were trying to prevent and the asphyxiant gas rich atmosphere that I was talking about is that too much oxygen becomes a fire/explosion issue. The nitrogen or CO2 rich environment can cause asphyxiation and death without the victim knowing it. CO2 can cause loss of consciousness at 20,000 ppm and die at 30,000 ppm. That doesn't take a lot in a small space. Nitrogen dissipates back into the atmosphere faster than CO2 due to the fact that the atmosphere is made up of 78% nitrogen and the natural balance is always fighting to maintain that. I maybe should have stated that I was comparing nitrogen & CO2 in the post as to nitrogen dissipating quicker.

I understood what you were comparing. I'm just one of those that has been around far too much bullshit when it comes to compressed gases to take much at face value. I'm lucky that I have some engineer type folks as very good friends who I use as a resource when I don't know something myself. When I worked at the ambulance company there was a common story about being careful with O2 because you could saturate a patient's clothes with it and cause them to spontaneously combust. The next one was that O2 is flammable. I would hold a lit cigarette in front of the valve on one of the small bottles and open the valve to show them that O2 doesn't burn, it supports and enhances combustion but does not itself combust. There was always about half the group watching that would turn and run when I cracked the valve open.

 

[JP98]

Co2 in the presence of water can form carbonic acid. It is particularly harmful to steel due to the interaction with the ferrous portion of the alloy. If you run high moisture in the tires, have unprotected steel rims, and use only Co2 for inflation, you may bring about the conditions where you could have an issue. It would be rare and uncommon for that to happen and the carbonic acid is only harmful to the parts containing ferrous material enough to cause concern.

I have changed out my tires on the rig many times breaking down the bead locks and not once have I seen anything that looked different inside the rim or tire that would be a concern and these are tires and rims that have only been filled once to seat the inner bead with compressed air and the rest of the time, years typically, run with Co2.

You can dig around on the 'net and find lots of info on carbonic acid and where it is a problem and make up your own mind.

@Jeepaholic Blaine is correct about the water and CO2 forming carbonic acid and that is where you can run into trouble. If you are running CO2 regularly like blaine and do not introduce moisture, say from an air compressor, you will be more than fine.