What is mean by dual action airbrush and single action airbrush?
Single action airbrushes are activated by simply depressing the main lever. To change the amount of spray you must stop airbrushing and reset the needle adjustment screw. With more dual-action airbrushes, when the user depresses the main lever, only air is released; the second action of drawing back on the main lever releases the paint. This dual-action - down then back - enables the user to adjust the volume of spray simply by manipulating the main lever and without stopping.