Single action refers to how you work the airbrush. Each control on a single action airbrush operates a separate spray variable.
Like the photo shows…
Twist the knob out and it stays there until you twist the knob back in or out further. This keeps the paint flow steady. Steady paint flow makes it very easy to repeat what you just did.
Scientists and researchers love these airbrushes because of the steady paint flow.
Resetting the airbrush whenever you remove the needle is imperative. Remember, the needle ALWAYS controls the airbrush’s paint flow rate. The knob conveniently adjusts the needle in or out.
Normally this small problem isn’t a big deal. You occasionally forget and have to trouble shoot why your airbrush won’t spray anything. No problem.
Just make sure that whenever you remove the needle that you reset (screw in) the fluid adjustment knob. No big deal.
Single action airbrushes have their place. If you’re a researcher or scientist, if you need something simple and don’t mind the few pitfalls, or if you’re just plain stubborn, you have my blessing. Go get one.
But most people, despite the few added headaches, should still use double action airbrushes. Most manufacturers make adjustable parts that mimic all these benefits, then you can have the best of both worlds.