I posted this article at West Coast Airbrush in the WCA Forums, General Airbrush Forum.
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I'm going to talk about compressed air. I've included links to websites that I used for research and of course outright plagarized.
When I started airbrushing I would have never imagined I would some day have to set up a compressed air system to supply over 18 artists with air. You learn real quick about "cubic feet per minute" and "pounds per square inch" and what each airbrush requires ..........that 60 gal Campbell Hausfeld I bought at Home Depot just isn't going to do it!!! Neither is the Ingersol Rand 60 gal with a 100% duty cycle.
I know, I know, you're saying "I just started airbrushing and I'm on a budget!"
Well, there is a light at the end of the tunnel.........be patient, read on........get an education first...........you may learn something you'll need later on down the road.
A reliable source of compressed air is probably the single most important piece of equipment we purchase, next to the airbrush of course.
Using an airbrush to paint shirts Full Time is probably the most demanding on a small compressor......compared to painting small illustrations, or even larger automotive illustrations.
Heavy bodied t-shirt acrylics work best being sprayed at higher pressures (psi) 50-80psi.
This means that the Volume of air or Cubic Feet per Minute (CFM) a compressor puts out is what we are concerned with.
Notice I didn't say anything about Horse Power(HP)?
Compressor manufacturers know consumers understand "Horse Power" .......the bigger the number the BETTER , therefore they advertise compressors with the big HP numbers.......and Boy! have they been pushing those hp numbers to sell compressors!.......
...at least until lately. A class action suit against the large compressor manufacturers has resulted in a bit more honesty in advertising.
Horsepower (hp) is the name of several non-metric units of power. As far as compressors are concerned, HP is only the measure of power for the electric motor that runs the pump. It has nothing to do with CFM or PSI.
I'm not going into the technical electrical engineering aspect here and I'll keep this simple:
By textbook definition a 15A 120 volt circuit is able to provide 1800 watts or 2.412 HP. But electric motors are not 100% efficient.........so 2hp is about it. There is also a "Service Factor" number that compressor manufacturers use to boost their HP ratings.......I won't get into that.........
So if you see your local hardware store selling a 5hp compressor that runs on a 120 volt outlet.............you know thats a flat out lie.
That 5hp is really "Peak Developed HP"(with that Service Factor thrown in)......the actual "Running Motor HP" is probably more like 1.75hp. It simply can't be more than 2hp. Any good qualified electrician that remembers his schooling can tell you that.
HP is really not of any concern to us anyways. It can be a guide in the purchase of a compressor but not something you should rely on.
This guy does a great job for those of you interested in the technicalities:
CFM or Cubic Feet per Minute is what we as airbrushers need to see.
More importantly CFM and pressure (PSI).
In fact, remember this:
CFM always needs to be justified by a pressure (PSI).......thus:
4.5cfm @ 90psi, or 2.15cfm @ 20psi. etc. If psi is not stated with the cfm number then they are probably referencing it as "free air".......that is air at 0psi.
A compressor might show a CFM rating of 3cfm for example, but reading the fine print will tell you that it generates 3 cfm at a much lower pressure rating than the pressure you may require.
Always check the psi............300cfm @ .5psi i think is a house fan!.....thats not going to power an airbrush!!!
I know, I know, your sitting there saying, "Come on Gary, this is like Christmas morning, when are you going to tell us how many CFM our airbrushes need?"
Okay kids here goes! Ready?..........Its a tiny bit more than 1/2 cfm at 60psi!!!
That can go up to almost 1cfm if you like to work at 80psi.
To determine the size of compressor you need it's recommended that you take the total air (cfm) required and multiply that by 1.5.
This will give you the total CFM needed to run a single airbrush.
So .55cfm x 1.5=.825cfm (almost 1cfm). This also allows your compressor a 50% duty cycle.
Basically, each artist you have will need about 1cfm @ 60psi to each run a single airbrush.
Don't confuse this with the number of airbrushes you have connected to your manifold........you can only operate one gun at a time.
If you have a Maverick artist that insists on painting at 80psi thats gonna change your CFM requirements...
Lucky for us most compressors will supply plenty of air for a single artist, maybe 2 or three working at the same time.
Duty Cycle
Compressors have whats called a "Duty Cycle". Most Compressors (including Silent compressors) are built for a 50% Duty Cycle. If it runs for 15 minutes it has to be off for 15 minutes. Some compressors you may find have a 60/40 duty cycle. But those are typically not the portable models we use.
Undersizing a compressor, will cause it to run over its duty cycle and shorten the pump life.
Pump Life
Compressor pumps are given a rated life in hours of runnning. Generally this is based on the expected life of the pump BEARINGS, not the piston/cylinder. The bearings generally fail before the other components within the pump do. (this rating method may differ for silent compressors).
Interestingly enough silent compressors, oilless, and oil lubricated type compressors all have about the same rated pump life........about 3000hrs.
Silents, 3000hrs
Oilless, 1500 to 3000
Oil lube, 3000 to 4000
Variations occur in pump life when the rpm they are running at varies. Higher rpm= shorter pump life.......it also means a noisy, screamer-of-a-compressor.
Also, lack of maintenance, high ambient temperature, and air intake quality will shorten pump life. So keep your compressor COOL, change the OIL, change the AIR FILTER regularly.
Tank size.
The size of the air holding tank on a compressor will have alot to do with how often it runs.
Although, if you buy a compressor with a pump thats undersized for your application a larger tank will not fix that, at some point the tank will empty and the pump won't be able to keep up.
If you buy the correct sized pump for your application a larger tank or even an additional tank will help extend the time between pump-ups. A compressor with a 5 to 10 gal tank is probably your best bet. If your compressor has a small 2 gal tank you may want to consider attaching another larger tank to it and running off that tank. The additional tank also helps reduce water in your air line.
Its pretty obvious which compressor you should buy if you are looking for long life. If you can find an oil lube type, running at a lower rpm not only will you have years of performance but it won't hurt the eardrums either........although the lower rpm will also mean its cfm output is lower and if you are planning on having more than 2 to 4 artists working at the same time you may want to consider something bigger.
Here's the light at the end of the tunnel................
Most of us work alone or with another artist, so just about any compressor you can pick up at your home improvement center will do. They are very noisy and draw a maximum of amps. The thing to remember about those units is that they are for "occasional home use" not full time industrial use. Okay for the 'moonlighters' but not recommended for a busy mall store. Don't expect to get years of use out of it. Don't expect to make any friends of the vendors near-by.
DO NOT run these on an extension cord. If electricity is not near by then you should run a long Airhose to where you will be working. I've run 200ft of air hose to have a compressor plugged in near an outlet.
Silent compressors are great but we all can't afford the $600 to $1000 price tag for them.
I bought and used a couple of the Thomas Ultra AirPac compressors. Their specs are impressive.
They use what is called a WOB-L piston..........or wobble piston, the piston wobbles side to side in the cylinder as it moves up and down and compresses air, theres no big cylindrical piston with a wrist pin and rings etc. like we see in an automobile.
Thomas Industries invented this and most all oilless compressors use the WOB-L piston, DeVillbiss, Campbell Hausfeld, Speedaire, Westward, Craftsman.
The 1 1/4hp, 3/4hp, 1/2hp Thomas AirPac are the ones I have used. They are not silent but they aren't the screamers made by Campbell Hausfeld (CH). Their modest noise level was easily muffled simply by placing them inside an uninsulated cabinet. The 1 1/4hp is ideal for airbrushing shirts. You can run these on an extension cord (they have low amp draw) which is a cardinal sin with any other compressor............but these ran like a champ on an extension cord.
One thing I can't stress enough is, "Know what your compressor sounds like when it's starting and running PROPERLY."
If you insist on running a compressor on an extension cord it may run fine for a few starts. But you'll begin to notice that it is not starting up as quickly and sounds like its laboring to start.
If you hear a low buzzing sound and then it starts, you know you're in for trouble.
Consider getting rid of your extension cord and buying a long airhose.
The oil type, belt-run pump compressors are available but even they are a bit noisy due to the motors running them at high RPMs. If you're handy with tools you could make yourself a nice pleasant sounding chug-chug compressor by putting a smaller pulley on the motor and getting another belt to run the pump.
But most of us just want to buy a compressor that works and start making money........which is fine.........like I said before just about any compressor you can find at your home improvement centers will work.
Choosing a compressor can be as personal as the type airbrush you prefer.....along with how much you will be using it, restrictions of your location (allowable noise level & electrical source), and other mobility factors.
