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…
The button, or trigger, controls airflow. It’s an on/off device. Don’t try controlling airflow or air pressure here. That’s what regulators are for.
Twisting the knob out, counter-clockwise if you’re looking at the back, starts paint flow and increases paint flow until you twist the knob completely out.
Easy to use
The separate paint and air controls make single action airbrushes easier to use than double action airbrushes. This allows you to concentrate on moving your hand instead of concentrating on how far back your finger is.
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.
Dagger strokes are almost impossible to do.
Dagger strokes on single action airbrushes are difficult (most people say impossible) to master. The technique requires a steady change in paint flow while you move your hand. It’s hard to adjust the back end of the airbrush while moving it. You are, of course, completely welcome to try it out for yourself!
The fluid knob must be reset whenever you remove the needle.
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.