Educate me about seals please

Colin F

Double Actioner
I’ve been told that through regular cleaning the seals in an airbrush will resist solvents. Normal cleaning meaning a regular spray through and flush, not disassembly. Logic being that the only seal to come into direct contact with the solvent would be the packing seal. This makes sense to me, as I’ve sprayed lacquers for years with no problems.

But I have questions:

1. The only PTFE or Teflon seals found in modern airbrushes are the packing seal, in some cases nozzle seal (like on the back of a H&S nozzle) and I’ve also seen them between a removable cup and body. I’m basing this off of their white color and square profile. All the others are conventional black rubber seals, correct? Head seal, nozzle and nozzle cap seals on cheaper brushes?

2. Since those rubber o-rings are in place to…seal, then why aren’t they quickly chewed up by solvent cleaners or lacquer paints? How can they be isolated? Usually they’re at the base of threads - can’t these thin solvents travel down the threads to the seals and saturate them? If not, then why the need for a seal in the first place?

3. How resistant are these seals to alcohol?

4. Why do some higher end brushes have fewer seals? My GSIs have no nozzle or nozzle cap seals. Better machining of the threads? Closer tolerances?

5. What is the purpose of the seal on the handles of some cheaper brushes?
Hi CFster a lot of questions at one time, but I will try to answer them.
Cheaper generic airbrushes have so many seals because they are not made with the tight tolerance’s of the quality brushes. That is why you often see o-rings on the handles
Ithese are often the same as the one for the head. A spare maybe.
If the rubber o-rings are in contact with solvents over a longer period of time the swell up and cause problems as sticky trigger and needle.
I personally don’t use those kind of airbrushes with solvent paint’s.
Short time contact with alcohol should not be a problem.
The quality airbrushes are made with tighter tolerance’s, therefore need less o-rings. The high end brushes can still sometimes give you sealing problems like bubble’s in paintcup or air leaking between body and nozzlecap. These can be solved by using beeswax or chapstick on the threads.
If I have to give a brush a intense cleaning, I disassemble the whole brush remove all seals and soak only the metal parts of the brush in airbrush cleaner and run them through the ultrasonic cleaner using jewelry soap. The seals are cleaned by hand with water and soap.
That way I make sure none of my seals get in contact with something that would would give me any issues.
I hope this answers most of your questions
Most o-rings used in commercial applications are buna-n also called nitrile. They are pretty good at a broad range of chemical compatibility - to be sure about the solvents you are using, you can look up the compatibility in charts like this:

There are only a few sizes generally used in most brushes - so, I went through and figured out what they are, and ordered the most common sizes in bulk from an o-ring supplier. There are usually quantity discounts, so many only cost a few cents a pop. I don't worry too much about what I use in a brush, and simply change out the o-rings when i start either seeing or feeling any sort of change.

The o-ring used between body and handle is usually there to allow the handle to be aligned in a manner as to sit against you hand comfortably (most common on brushes with handle cut-outs).

Not much to add but my limited understanding is that O-rings primarily prevent air leaks and are not really intended to be in continuous contact with harsh paints/solvents. If they do, there is a limited life span, requiring eventual replacement. That's why it is not advised to dunk a complete airbrush in solvents like lacquer thinner. The Teflon seal, aka packing seal (introduced by Walter Schlotfeldt, founder of Badger in 1964), should last for a very long time as it is truly solvent resistant. It will most likely be damaged mechanically before been affected by solvent.

Long chain Hydrocarbons like 140 weight oil through to petroleum is ok with all but the softest nitrile 45 duro and up and at continuous temp below 65 degC
With the shorter chained H/C lighter fluid benzene ,acetone, thinners, pentane, hexapentane and so on.
Is when only the harder grades of acrylonitrile butiene with its higher content of acrylonitrile can tolerate those solvents. It's the oil plastifiers in the Butadiene that give it's flex and are what those solvent H/C break down and remove from "O"rings leaving behind a harden rubber that is shrunken by the removal of the cut chains of the plastifiers of the Butadiene
Now there are some additives in oil like ATF fluid that is loaded with other things can breakdown that can bring down nitrile as well.