AIR SOURCES FOR AIR BRUSHING
We now come to, what may see, the easy part of the whole air brushing operation….air supply. As has been seen in our discussion to this point there have been a few questions in this area. Anything from the amount and pressure required to the noise level of the compressors.
The most obvious requirements for our air brush are constant air at a pressure required by our type of brush, and free of water and oil. We will look at each of these requirements relative to the supply options we have.
The compressors typically marketed by air brush outfits such as Badger, Paasche, De Vilbiss are a diaphragm type of construction. These fit the requirement of oil free, but can produce a pulsating air flow due to the up and down movement of the diaphragm. This pulsating movement can upset the output of the airbrush by not giving a smooth even coat. In most cases this won’t be noticed when heavier coating applications are involved, however, if you are doing layers of paint in the light misting category the effects of the pulsating may be seen in an uneven application of paint. Although this may be minimal, it will be present. To what degree that bothers you will determine how you want to correct it.
From the producers standpoint these compressors are cheap and easy to build, light weight, oil free and the pulsating effects won’t be noticed by the majority of the consumers. We can get around this by introducing something as simple as a moisture trap. The volume of air in the trap and restriction of the air passing through it will smooth out the pulsations. Fortunately this is an item we need in our air supply. More on that later.
One may consider other compressor options; however, you need air free of oil. Oil will give the same effect as moisture in the air except it won’t dry ad will contaminate your clean prepared surface. Either an oil separator (extra cost) is required, or you need a compressor that doesn’t use oil in the piston area. The photos show two other compressors. The red one produces air pressures up to 125 psig, as will the blue one Mastercraft job. Both supply adequate quantities of air and both have air receivers to reduce the start/stop cycle of the compressor. All plus points, however, the red compressor is oil lubricated, something we don’t want to get into for our application. In this case a type similar to the Mastercraft job can be worthwhile. It has the advantage of doing other small jobs around your shop since it is equipped with a pressure regulator.

Typical oil less diaphragm compressor

Oil lubricated compressor with receiver

oil free compressor with air receiver
Another air supply possibility is a portable air tank, or as we call them here, an air “pig”. This particular one is a 2 gallon size, but other sizes are available. It can be pumped up to 125 psig. The tank is taken to a local air source such as the tire compressor at your local auto service center, filled and taken home. Put a regulator in the outlet and connect your favourite air hose. No sound, no moisture worries, and most likely no oil worries. Not a bad way to go. How long will it last? Depends on how much you spray, but I expect it would have no problem doing a boat. After all, if you pump it to 125 psig you can draw it down to 20psig or less. Plus it’s inexpensive. Some have suggested using a tire. You can do, except you may only get 40 psig in it and its awfully heavy and cumbersome to haul around. The tank has the benefit of light weight and a handle.

Portable air tank
We talked of moisture traps. These are a necessity in virtually all our air brush painting. When we compress air the amount of moisture in a cubic foot of air becomes denser when subject to higher pressures. The dew point of that dense moist air can often be low enough, at room temperature, to allow that moisture to condense out of the air. This results in droplets of moisture being carried into the air stream and into our paint and onto our work. When you look at your work, you will think you’ve got large droplets of paint coming from the brush, when in fact its paint floating on drops of moisture. You may hear a sputter from the brush when this happens. As the paint dries and the moisture evaporates we are left with “fish eyes” on our work resulting in more sanding and respraying. The moisture effect is much more pronounced on hot humid days and lesser so on dry cold winter days.
To over come this one can purchase a commercial moisture separator /filter combination that will work very will. For those who like to improvise, such as myself, you can make your own. You can see mine in the photos. Its an arbitrary length of 1 ½” dia. ABS plumbing pipe (because I had some scraps on hand). I glued caps on each end. (see pictures) The bottom one I installed a screw in cap because I thought I may have to drain the moisture build up. I have never had to up to this point. You put your air supply in the bottom and take your brush supply off the top. Since I use the diaphragm type compressor this acts to mediate the pulsations from the compressor and it serves to entrap moisture that precipitates out of the air as the air expands through the tube. Since I made it up thirty years ago I’ve never had a moisture problem no matter how humid the air gets, and it can get very humid here in the summer.

ABS moisture trap mounted on the side of my spray booth
Speaking of the air coming from the trap, what type of air hose are you using? Most air brush kits come with a heavy braided hose. A good rugged hose, but heavy and stiff when you want something that is light and flexible to feed your brush. I use the light plastic hose that comes with some brushes or can be purchased as an accessory. It is light weight, very flexible and, I find, excellent for bringing air to the brush and giving minimum resistance to movement when painting. (see picture).

A comparison between the braided and light plastic hose.
Anti vibration material
As a side note, some have been concerned about noise from the compressors, a valid point. Even the little diaphragm compressors can do quite a dance when operating. Here’s a tip. I usually try and use stuff before it gets thrown out. I found a couple of tubes of silicone sealant had hardened from lack of use. The first instinct is to chuck them out. Hmm I thought, I wonder what its like if I cut the cardboard/plastic tube off them and see what the contents is like. The result is in the photo. I had couple of sticks of rubbery firm silicone sealant. The blue stick is much stiffer than the white stick. I have a pedestal grinder sitting on the basement floor. Every time I run it, it vibrates and meanders across the floor. I cut off a four disks of the white material and put one puck under each corner of the pedestal. Instant silence and no more wandering, works great. You may want to try something similar with your air compressors.

Rubbery silicone sealing sticks removed from dispensing tubes.

Silicone puck under corner of pedestal grinder.
That about does it for now.
John