air tank

I am just in the process of putting together a setup like this myself so I don't know for sure but I've read in magazine that a five gallon tank should give you approximately 10-15 minutes of airbrushing time. That should give you a rough idea anyways.

Ray

It actually depends on air flow (CFM) not pressure but heylonghair's estimate sounds reasonable.

How much air pressure is currently in the tank?
Lee

the tank has 125 psi in it, and i will not be using it for those big "tons of paint" jobs, i will just be using it for very retricted air flow, but i needed more pressure cause those crappy cans cause my badger to sputter horribly.

I just got back into modeling and tried using an air tank to postpone buying a compressor. I used a 5 gal. tank starting with 125 psi. I was really surprised how fast I emptied the tank - testing before actually painting, clean-up, etc. I had to bite the bullet and buy a compressor. Plus, I'd think you would need a regulator and water trap on the air tank?

i think that im gonna do it anyway becasue i can get a water trap and a regulator at work for a five finger discount. Would a bigger tan last mush longer?

BIG IDEA- would it work if i had the tank filled with co2 instead of air?

QUOTE: Originally posted by nclay BIG IDEA- would it work if i had the tank filled with co2 instead of air?

Nope. It would make no difference at all... (for obvious reasons)...

My first air tank was a modified propane tank with a regulator and a valve stem like on a car. The regulator was on one end of a "T" and the valve stem was on the other. I hooked up an inflator to the valve stem, ( about $30.00 @ Sears) and had an unlimited supply of air. The air brush hose was hooked to the outlet of the regulator. This worked very well except for the noise! I ended up putting the inflator in the closet and put an in-line on/off switch in the cord.

cant you hold more co2 in so mush space compared to air?

QUOTE: Originally posted by nclay cant you hold more co2 in so mush space compared to air?

You CANNOT put CO2 in an air tank!
The air tank would explode like a grenade.

Air tanks are designed for 125-150 psi maximum.
CO2 is around 1,000 psi!

If you want CO2 then buy a 20 lb. CO2 tank and regulator and paint in peace and quiet.

Mike

QUOTE: Originally posted by nclay cant you hold more co2 in so mush space compared to air?

Yes. CO2 is a liquid that becomes a gas when exposed to the atmosphere. A 20 lb CO2 tank will yield air much longer than a 20 lb scuba tank would.

Mike

how much does a 20lb co2 tank cost? and how long would it last?

Holley, so that air compressor filled that tank nicely? cause theres a valve stem on the 7 gallon tank i got that is used to fill it up.

QUOTE: Originally posted by nclay how much does a 20lb co2 tank cost? and how long would it last?

An aluminum 20 lb CO2 tank sells for about $100 online and the gauges would run you another $60-80 I assume.

I know people who use these for T-shirt airbrushing spraying at 60 psi and they last for about 6-8 hours.

I would assume that painting models at about 20 psi would yield about three times that long. That's a lot of models painted.

Mike

Guys, guys...

I think one should start from scratch here, in order to avoid any misconception that might be proven dangerous (not to mention potentially fatal) under certain circumstances...

So let's examine some facts, to begin with:

1. I understand that nclay owns a 20 lt (5 gallons) regular air tank that can stand 8 atm (125 psi) of pressure, which happens to be the maximum pressure (safety-wise) that any regular air tank can stand.

2. Now, given the above, nclay wants to know:

(a) how long would this tank last, filled with air at 125 psi (tank pressure) if a regulated 30 psi output pressure is required?
(b) would he have better results filling his tank with CO2 instead of air?

The answer to these questions follows:

(a) the above tank filled with air at 125 psi, would only last for a few minutes.
(b) filling the above air tank with CO2 instead of air, would make no difference at all (as I've already stated in my previous reply in this thread), simply because at 125 psi CO2 retains its gaseous form, which in turn means that it would yield the same volume of uncompressed gas, as normal air would. (ok, ok, I know CO2 is a bit denser than air but that doesn't count in practical terms)...

3. CO2 is NOT a liquid (as I read somewhere in this thread)!!! It is a gas in its natural form. It liquifies, however, at 75.27 atm (1106 psi) provided that its critical temperature of 31 C (degrees Celsius) is also maintained. (This means that above 31 C, the CO2 cannot be liquified by pressure alone, and at 31 C, 75.27atm pressure is needed to establish an equilibrium of liquid/vapor). And this also goes to show the obvious reason why one cannot use a regular air tank for storing liquified CO2 which needs to be kept at roughly 10 times more pressure (1106 psi) compared to 125 psi that a regular air tank would normally stand before going ...grenade...

4. A 20 lt (5 gallons) dedicated CO2 tank at 75.27 atm (1106 psi) would last a lot longer than, say, an equivalent 20 lt (5 gallons) scuba diving tank which can hold up to 3 cubic meters (3000 lt or 750 gallons) of air at 200 atm (2900 psi). That is, the above CO2 tank would last 10 to 15 hours, compared to the equivalent scuba diving tank which would last only for a couple of hours (provided that, in both cases, the output pressure would be regulated at 30 psi).

5. As far as safety is concerned, if I were to use CO2 for powering my airbrush, I would go for nothing less than a heavy duty industrial type CO2 tank and regulator, and I'd always keep it securely fastened to a wall. Any compressed gas cylinder is to be considered as a potential rocket. Should the cylinder fall down accidentally and the neck or valve is damaged, the cylinder would behave and act like a steel balloon with its neck untied. I believe you've got the picture, no need to say more on that...

6. Now, about the cost... A 20lb CO2 tank costs about 130 - 150 US$/Euros to purchase or 50 - 60 US$/Euros per year to lease. A regulator costs 50 - 70 US$/Euros, but they don't lease those. You would also have to spend 20 - 30 US$/Euros for each refill.

CONCLUSION: Hmmm... This all sums up for CO2 to not being so simple nor so cheap a source as one would initially think, don't you agree? I mean, purchasing an air compressor might be proven as a substantially cheaper solution in the long run. Not to mention running out of CO2 on Saturday evening... Think about it... On the other hand, the CO2 tank method is quiet, it provides constant pressure, no surges, or declining pressure as the tank bleeds dry. No need for a water trap, especially in the summer. It is also self-contained, no need to plug it in, it can be carried from one place to another very easily, it is clean, quiet, and reliable. Provided, of course, that common sense is used at all times.

Come to think of it fellows, this thread turned out to be pretty "technical" after all, following nclay's simple initial question about his air tank's capabilities and potentials... Anyway, I believe that it doesn't do any harm going back to the gone-but-not-forgotten college stuff from time to time (even if College goes back a long time ago; some 25 years in my case...)

You should also bear in mind that I don't major in this stuff. I get my bread on the table being an attorney at law...

Good advice there George.

My mistake about CO2 being a liquid. I assumed that since it had weight it must be in liquid form in the bottle.

There is no perfect solution to provide air for an airbrush, so all possibilities have to be weighed to come to a conclusion.
You are correct in that CO2 in the long run will be more expensive than even a silent compressor, but that would depend on how much it is used. If you only run an airbrush a total time of an hour per week at 20 psi then a 20 lb. CO2 tank will last somewhere in the neighborhood of 12-15 weeks.

That would work out to about $15-20 every 3-1/2 months for the tank refills, which is real cheap. If you airbrushed a lot more than that then a silent compressor may be the better bet although the cost up front is going to be anywhere between $250-$1000 depending on the model of compressor.

By the way, I am picking up a used Jun-Air 1/2 hp compressor on Saturday so I will have the Rolls Royce of silent compressors and a quiet 45 dB sound level.

Mike

The valve stem worked fine for me. In the worst case you would have an inflator for tires if it didn't work. As long as you have a regulator between the tank and your airbrush, you would have an unlimited supply of fairly low pressure, SAFE, air. Happy spraying!

QUOTE: Originally posted by MikeV My mistake about CO2 being a liquid. I assumed that since it had weight it must be in liquid form in the bottle.

Hi, Mike...

Well, not a mistake really. For, you see, CO2 does happen to be in liquid form in the CO2 cylinder (although, "dry ice" would be more proper a term to describe CO2's status in the tank). Anyway, what I really wanted to point out was that CO2 must NOT be treated as just-another-liquid-in-a-bottle stuff, but rather as a liquified gas that's kept in a tank under EXTREME pressure conditions, thus avoiding any potentially hazardous misconception on the subject.

Enjoy your brand new ...RR

QUOTE: Originally posted by A-Centauri Well, not a mistake really. For, you see, CO2 does happen to be in liquid form in the CO2 cylinder (although, "dry ice" would be more proper a term to describe CO2's status in the tank). Isn't dry ice CO2 in it's solid form? Mike “Wisdom is the right use of knowledge. To know is not to be wise. Many men know a great deal, and are all the greater fools for it. There is no fool so great a fool as a knowing fool. But to know how to use knowledge is to have wisdom. " Charles Spurgeon Reply Anonymous Member since November 2005 Posted by Anonymous on Friday, May 9, 2003 4:31 PM QUOTE: Originally posted by MikeV Isn't dry ice CO2 in it's solid form? Hmmm... Yes and no. You see, CO2 is characterized by a pretty weird behaviour under the aforementioned pressure conditions. Practically, it can be in gaseous - liquid - solid form ALL AT THE SAME TIME, depending on the temperature, pressure fluctuations and/or other chaotic factors. If it was a liquid (in trivial terms) it would shift its position inside the tank. However, if you hold a CO2 tank on its sides and tilt from left to right you'll notice that nothing seems to move inside the CO2 tank the way a "normal" liquid would. This is mostly because CO2's form in the tank is very close to ice, since CO2 changes its form by sublimation, thus it has no true liquid state. Sublimation is the change from solid to gaseous phase without transition through the liquid. As far as CO2 is concerned, there's also a 4th phase of matter called supercriticality. This phase exists above the critical temperature and pressure of the compound. It is sometimes called a supercritical "fluid". The "fluid" would occupy all of the space in the container and hence it would not slosh around, ie. there will be only a single phase in the container if it is above the supercritical temperature and pressure. Theoretically, liquid CO2 does exist, however, depending on the pressure, adiabatic expansion causes the cooling effect that changes it into dry ice... Holy cow... is this all waaaaaay off topic, or what? Hey, is there a chemist in the house? Reply Edit MikeV Member since April 2003 From: Hayward, CA Posted by MikeV on Friday, May 9, 2003 7:07 PM Man George! I only live 25 miles from the famous Lawrence Livermore Lab. Maybe I could contact them in regards to this. Haha Thanks for the answer, it was informative. Mike “Wisdom is the right use of knowledge. To know is not to be wise. Many men know a great deal, and are all the greater fools for it. There is no fool so great a fool as a knowing fool. But to know how to use knowledge is to have wisdom. " Charles Spurgeon Reply Anonymous Member since November 2005 Posted by Anonymous on Sunday, May 11, 2003 1:56 PM ok, ok, back to the tank now, im curious, i finally finished putting my regulator on and you all were right it lasted me about 15 minutees. if i drilled the pressure relaese hole in the adapter that i purchased from badger would the allow me to have a electric compressor filling the tank non-stop? Reply Edit Holley Member since February 2003 From: USA Posted by Holley on Sunday, May 11, 2003 5:32 PM Drilling the pressure release hole doesn't sound safe. I'm not sure of your set up but if there is a threaded fitting in the tank, you can hook the regulator and compressor to a 'tee' threaded into the tank. Then the tank acts as a surge vessel allowing regulated air to your airbrush while any air from the compressor that isn't used is stored in the tank. If the compressor doesn't have a pressure shut off switch, you will need to monitor the tank pressure to prevent overfilling. I have a 'tee' on my tank with a pressure guage on either side of the regulator to monitor tank pressure and airbrush pressure. I hope this helps. Thanks for not bringing CO2 back up.......whew what a science lesson we got with that! Holley When all else fails, read the instructions! Reply Anonymous Member since November 2005 Posted by Anonymous on Sunday, May 11, 2003 6:57 PM thx holley, i think that im going to try that, what amount of psi needs to be put out by the compressor to successfully fill the tank, will 125 psi or above work? Reply Edit Anonymous Member since November 2005 Posted by Anonymous on Sunday, May 11, 2003 8:04 PM I agree with Holley. Don't ever try to drill a hole in the tank unless you are prepared (as well as properly equipped) to weld a threaded fitting on it. Otherwise, consider the "tee" method to be your best bet. I also think fitting an automatic (properly regulated) shutdown switch to be an absolute necessity in any case. Turning the compressor on and off manually is simply a no-go, if you want to play it safe. You should also make sure that you never exceed 110 - 120 psi of pressure in the tank. Don't worry about "filling" the tank. At 8 atm (110 psi) the tank will be "filled" with air 8 times its nominal capacity... Best of luck... Reply Edit Anonymous Member since November 2005 Posted by Anonymous on Sunday, May 11, 2003 9:10 PM badger tells you to drilla hole in the adapter for your air hose from 1/4 adapter for compressors that do not regulate themselves that will build up to much exsess pressure, but im not sure if it will work because this adapter is after my regulator and it is meant for non-tank, "made for airbrushing" compressors, hey, how much does this automatic shut off switch go for and where can i get one? Reply Edit Holley Member since February 2003 From: USA Posted by Holley on Thursday, May 15, 2003 7:50 AM As long as you have a regulator, your compressor only needs to put up more pressure than you have it regulated down to. The excess will go into the tank. The tank also acts as a surge surpressor smoothing out the air flow so you dont get that 'tat tat tat tat' type of spray pattern. I have used mine with no pressure shut off switch, but I do have a pressure guage on the tank to tell tank psi. It probably would be a safer idea to install a pressure shut off switch, which you may could find from an industrial supply house or maybe even an auto paint distributor, Holley When all else fails, read the instructions! Reply JOIN OUR COMMUNITY! Our community is FREE to join. To participate you must either login or register for an account. Login Register SEARCH FORUMS FREE NEWSLETTER SIGN UP By signing up you may also receive reader surveys and occasional special offers. 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