Gimme Air
Obviously, an airbrush requires air. Here are some thoughts on that subject. With appropriate thinning, an airbrush will spray paint over a wide range of air pressure . But, without a good source of regulated air, you may not get the results you want from your brush, no matter which one it is. And, I really mean regulated air, so that you can vary the pressure to suit your paint, airbrush, and technique, and maintain it at that level. Something that can be adjusted from 10 to 30psi is fine for most uses, although T-shirt artists who use thicker paint would probably want more pressure.
So, what are your choices?
Some low priced airbrushes come with an adapter for canned air. The canned air is not very effective and gets expensive really fast. Check out this page for more details.
One really nice way to go is bottled CO2 or Nitrogen. There is no noise and you never have to worry about moisture. But, of course, there comes a time when the bottle needs to be refilled, and you will have to lug it some place where they do that. I can’t give you details, because I haven’t really looked into it. But, I have seen it highly recommended many times on the forums.
I think most people use a compressor of some sort. One option is a shop compressor. They can easily handle the requirements of an airbrush. And, you can also use them for other purposes, like filling your tires. But, they tend to be very noisy. They typically have a holding tank, which they charge up and then shut down until the pressure drops to some lower limit. The tank allows you to spray for some time until the compressor kicks in again, and this might be right in the middle of some delicate work. One solution is to locate the compressor some distance from where you are and run the air through a long hose. I understand this can work very well.
Another option is a small, specialized compressor designed for airbrush use. If money is no problem, there are so-called silent compressors. Some of these are based on refrigerator designs, and make very little noise. In fact, you can find instructions on the web to convert your own, if you’re handy. But, most hobbyists probably end up with a small piston or diaphragm compressor. These come with and without tanks, and you can find discussions in the forums on which type and brands are best. My experience is limited, so I won’t get into that. I will only say that I have seen a number of people who have problems with the tiny ones that are housed in a plastic case. I would avoid one of these. They seem to be too marginal for many airbrushes, especially the external mix type of brush that requires more air. Some small compressors come with an adjustable bleeder valve instead of a regulator. This is better than nothing, but a real regulator will give better control.
Moisture separators
Unless you live where it’s very dry, you are probably going to want one of these. In fact, you may need a couple. If you have a compressor that has the regulator /separator mounted right on it, some moisture can still get through. The reason is that a moisture separator only works if the moisture is in liquid form. When air is compressed, it gets hot. You’ve probably seen this if you have used a tire pump. The hot air carries moisture as a vapor, and it can pass right through the separator, only to condense back to liquid further down the line, like in your hose or airbrush. To trap this, you can get add-on separators that fit your hose or airbrush. Another option is to place some metal pipe or other means of cooling the air a little before it reaches the separator.
What do I use?
Being a cheapskate and tinkerer, I don't have something off the shelf. A company I worked for was scrapping a large quantity of small 1/8 hp vacuum pumps, and I snagged one. I found that it would work as a compressor and supply 25psi or so at a reasonable volume. So, I jury rigged the set-up shown below, with an inexpensive tank and other fittings. It works just fine for me. The little diaphragm compressor runs continuously, but it's pretty quiet, and I’m hard of hearing anyway, so I barely notice it. See the section of copper pipe? It’s there to cool the air, and it seems to work.
Postscript
Since doing this page, Badger has sent me a compressor for review. I have torn down the setup shown above and now just use the badger.
Postscript +1 Plumbing
I hate plumbing. Whenever I touch it, something goes wrong. Usually, I have to make two or three trips to the hardware store before I’m done. There are too many standard sizes.
Unfortunately, this is also somewhat true of airbrushes. Most airbrushes, including Iwata, Grex, and Harder & Steenbeck have a 1/8 inch air connection. Badger, Paasche, and Testors, for reasons of their own, have unique sizes. So, a Badger hose won’t fit an Iwata, Paasche, or Testors airbrush without an adapter, and vice versa. Fortunately, adapters are readily available.
At the other end of the hose is another problem. Some Badger hoses have fittings with the same threads on both ends. These will mate with their Propel can adapter, but to connect to a compressor, you need a special Badger adapter to 1/4 inch threads. There may be other variations out there for other brands too. I have only seen this with vinyl hoses
The braided hoses I have seen so far have 1/4 inch connections at the compressor end. And, here is another source of confusion.
There are four different standard thread types in use! These are NPT, NPS, BSPT, and BSPP. If you visit this page, you can read the details.
I believe most airbrush hoses are BSPP.
I believe most airbrush compressors are also BSPP.
And, I believe most shop compressors are either NPT or NPS.
With other parts, like regulators and moisture separators, who knows?
To make this even worse, manufacturer's specs don’t always tell you which one they use.
Again, you can get adapters. But, they can be fairly expensive. I understand you may be able to get away with mixing types in the 1/4 inch size, but never with the 1/8 inch fittings. So, you might want to ask before you buy.
Postscript +2 Need a Tank?
A very common opinion is that an airbrush compressor needs a holding tank to smooth our pulsations in air flow. However, there are many airbrush compressors on the market that don't include one. Does this mean there are lot of unhappy airbrushers with pulsing air? I decided to try and find out.
I connected a 24 inch piece of aquarium tubing directly to the output of my 1/8 hp diaphragm compressor, and attached a barbed airbrush connector to the end. When I turned it on, the air pulsed like crazy. I used it as an air source for my Badger 155 and Paasche H airbrushes. The H is really an air hog, and is probably a worst case. I sprayed some food color on paper towels to see what would happen. You might think I would produce dotted lines. But, in both cases, the airbrushes sprayed normally. I saw no indication of pulsing. None! Both narrow and wide coverage appeared normal.
Having a tank on the output of a compressor cools the air and makes a moisture separator work better. And, a nice smooth source of air is a good thing, and maybe it matters for critical work. But, as far as I can tell, it isn't really that important for most model painting. I suspect that many airbrush users, not having heard that a tank is needed, spray happily away without one with no problems. If your experience is different, please let me know.