Bernoulli's Principle
One of the first principles taught to aeronautical engineers is the same principle that makes an airbrush work. Bernoulli's principle describes the relationship between air flow and pressure. Basically, Bernoulli's principle says that when air speed increases, pressure decreases. This combination of blowing air and pressure dropping is the key to airbrush operation.
Air Supply
Air and paint are necessary to operate an airbrush. Professionals and more experienced artists typically use pressurized tanks or compressors. Air cans, which are about the size of a typical aerosol can, are also available. Some airbrushes require the user simply to blow through them. Regardless of how the air is supplied, it is blown through a tube to a nozzle at the front of the airbrush, where it is accelerated and combined with the paint.
Paint Reservoir
A thin tube connects a paint reservoir to the body of the airbrush. This tube intersects with the air flow tube. The speed of the air creates a pressure drop, which causes suction to the reservoir. Essentially, the air sucks the paint into the flow. External atomization airbrushes combine the paint with the airflow after the air leaves the nozzle, while internal atomizers combine before or inside the nozzle.
Lever Action
Airbrushes have a button or lever that controls the flow rate. Single-action airbrushes have levers that control only the airflow rate, while double action airbrushes can control both airflow and the flow of the paint. Single-action brushes can have either internal or external atomization capability, but double-action brushes can have only internal atomization.
Needles
Double-action airbrushes will always have a needle that helps regulate the flow of air and paint through the nozzles. Typically, the needle is retracted to increase the flow and pushed forward to restrict the flow. Single-action airbrushes may have a needle, but many do not, which means they have a fixed flow rate.
