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I'll be moving to a small flat very soon, and I'm afraid a standard compressor will be too noisy, both for my girlfriend and the neighbors.

So I've been considering using a Co2 tank instead of a compressor. It should be completely silent, and moisture free. With a good regulator, I should be able to control the pressure well enough.
I found some people online who seemed to use a similar setup with success, but the information I got was pretty scarce.

It should be safe, as I calculated that a small Co2 that completely emptied in the room (through a leak of constant airbrushing) shouldn't change the air composition significantly, and that's assuming no air flow (obviously I'll work in a well ventilated area), so I'm not too worried.

At the moment, my main concern are:
- Volume: obviously, the larger the tank, the longer I can use it between refills. But I'd love to have an idea of how much air I'll be using. Normal compressors often say how much air flow they can provide, but that doesn't tell me much about how much air we usually use when airbrushing. Does anyone have some figure? Something like a given volume of air consumed per unit of time, when using a standard airbrush at common pressures.
- Density: Co2 is denser than air. I suppose the spray pattern won't be affected in any significant way, but I was wondering if it might have consequences I can't foresee.

Has anyone used Co2 for their airbrushing and could give me some info?

Well I can say that my little tanked hobby compressor lasts from a full tank until the compressor kicks back in for...

45 seconds,
35 seconds, or
19 seconds

Spraying at my typical pressure for fine detailing, regular spraying and high pressure spraying respectively.

The tank is 3L, cut out is 4 bar and cut in is 3 bar. Room temperature is roughly 16C and I don't have a hygrometer. Using the ideal gas law you can ball park the mass of air required to spray for those durations and back calculate how much time you'll get spraying from a tank of arbitrary size and pressure.

Great, thanks a lot for the data, that's very useful.

Assuming an ideal gas, a drop of 1 bar in a volume of 3L corresponds to a volume of 3L at 1bar (at the same temperature). So you're basically shooting 3L of air during the posted times, which would be ~9L/min at your highest setting.
I saw many compressor rated for an air flow of 0.81 cfm. Assuming cfm = cubic feet / minute, that's 22L/min, which seems to make sense with the figures I calculated.

A 5lbs Co2 tank (the smallest common size) would be ~2.5 cubic meters of Co2, which is 833 times the 3L that you used.
In other words, it could provide with about 8 hours of regular spraying (8 hours of holding the trigger down).

It looks like even the smallest tank could last me a while.

Remember that the tank needs to be above the pressure you want to spray, so you might not be able to use all the 2.5m^3, that's why my compressor kicks back in at 3bar (roughly 43 PSI). But from the sounds of it you should get a decent amount of spraying out of it still.

Good point.

I think the Co2 is liquid inside the tank.
The vapor pressure of Co2 at room temperature is 57bars. So this should be the pressure inside the tank until all the liquid evaporates.
Assuming that a full tank contains only liquid Co2 (probably not exact in volume, but pretty accurate in mass), and with a ratio of 10 between the gas and liquid phases' densities (ratio of 500 at 1bar, so ~10 at 57bars), I should be able to extract 90% of the Co2 before the pressure starts to drop, and then it should decrease linearly. And should reach 3 bars when ~98% empty.

If the above calculation is correct, a manometer before the regulator should allow me to see when the tank has only 10% left.
I'll check online, I'm sure people already figured out smart ideas to check how full a tank is (apart from weighing it of course).

Won't it be really cold?

If you are considering using a CO2 tank from paintball, the output pressure from the tank is appx 850 psi. Your regular must be able to step that down to about 30 psi which is substantial.

CO2 does not regulate as well as compressed air. At at a constant flow, it cools down and tends to liquefy resulting in a higher volume and/or pressure. In a paintball application, guns that use a solenoid valve to route air tend to freeze up and not function as under cold conditions, o-rings shrink and seals fail and thus can't use CO2.

How much CO2 you have remaining is also measured by weight and not volume. You would need to know how much your tank weights empty and when it is full without all the attached apparatus like hoses and regulators. Compressed air (mostly nitrogen and what we are breathing right now) is measured by volume which can be displayed on a guage.

If you are going to try to use a tank, I highly recommend using compressed air and not CO2. You can buy a compressed air tank from a paintball shop for $45. You still have the issue of regulating the output pressure down from 850 psi though. The tank is already regulated down from 3000 or 4500 psi to 850 and you would need 1, possibly two more regulators to drop it down to a working pressure for an airbrush.

CO2 and CO (carbon monoxide) are different in terms of harm but care must be taken with all compressed gasses. Unless you have a huge bulk tank (5 feet tall and 150 pounds) and it falls over knocking off the valve, there is no real concern with the amount of CO2 shot out by the airbrush

In summary, CO2 is not a good choice. Compressed air is better but still no substitute for a compressor. Airbrush compressors are not the noisy beasts you might see in an industrial setting. Most of the ones I have used are no louder than a TV at regular volume or a hair dryer on low.

Sidenote: Is your compressor really that loud? Mine is a bit noisey but not louder than running a TV at less than normal levels.

You could also soundproof your compressor by sticking it in a wooden box, put felt stickers (those ikea thingies to put on chairs and tables to protect the floor) on the feet and on the bottom of the wood box.

That should seriously silence the comp.

Klaus von Groehm wrote:
You could also soundproof your compressor by sticking it in a wooden box, put felt stickers (those ikea thingies to put on chairs and tables to protect the floor) on the feet and on the bottom of the wood box.

That should seriously silence the comp.

If you do that make sure it doesn't overheat.

Thanks everyone for the replies.

A normal compressor could still be an option for me, especially since I would shop for the most silent one, and I could try to put it on a rubber mat to lower vibration transmission. But the noise, while acceptable, would still be annoying (can't airbrush if someone's sleeping next door, probably not if the neighbors are sleeping). A co2 setup seems more compact, and completely silent.

I wasn't too worried about the tank/air getting too cold, as I haven't seen anyone complain about that when airbrushing with co2. But again, the information I found wasn't extensive. Also, the bigger the tank, and the lower the airflow, the less it will be an issue. Most people I've seen use co2 were using pretty big tanks, so maybe they didn't have any issue, but I would with a tiny tank.

@Rickfactor: I don't follow you on the compressed air vs co2. Your point was that co2 is hard to regulate because it cools down a lot (because of a high pressure gap between the inside/outside of the tank). But from what you're saying, compressed air is actually compressed to much higher pressures inside the tank, so that there would be an even larger pressure gap. Also, nitrogen will cool down more than co2 for the same pressure drop. To me, it looks that pressure regulation should be even worse.

@Rickfactor: I don't follow you on the compressed air vs co2. Your point was that co2 is hard to regulate because it cools down a lot (because of a high pressure gap between the inside/outside of the tank). But from what you're saying, compressed air is actually compressed to much higher pressures inside the tank, so that there would be an even larger pressure gap. Also, nitrogen will cool down more than co2 for the same pressure drop. To me, it looks that pressure regulation should be even worse.

You considered an air tank? Silent, cheap, easy to refill and way less hassle.
Something like this perhaps.

PourSpelur wrote:
You considered an air tank? Silent, cheap, easy to refill and way less hassle.
Something like this perhaps.

This is ideal and could be filled with your normal compressor during a time when noise for a few minutes would not be terrible. You should be able to get a 3-5 gallon and fill it from 135-150 psi and that would last a good while and these tanks are not that expensive. And, regulators are easy to find for these.

When I used to do A LOT of airbrushing, I had a Badger Silent 1 compressor. Weighed a ton, but compared to this a refrigerator was extremely loud. Alas, I gave it away just about 5 years ago and use normal compressors now.

I have a 10lb CO2 tank setup for home-brew beer and it's no issue getting it down to 12-16psi using the standard regulators used for beer and soda dispensing. Getting the tank filled can be annoying, but most places just do an exchange rather than refill if you bought a tank from them (they'll have a supply of indestructible old steel tanks).