What it explains: How siphon-feed airbrushes draw paint upward without a pump
The Venturi effect is a principle of fluid dynamics: when a fluid (liquid or gas) flows through a constricted section, its velocity increases and its pressure drops. Airbrushes use this effect to draw paint into the air stream.
In a siphon-feed airbrush, compressed air flows at high velocity through a narrow passage near the nozzle. This creates a localized low-pressure zone. Since atmospheric pressure in the paint bottle is higher than this low-pressure zone, paint is pushed upward through the siphon tube into the airstream, where it atomizes.
The same principle operates inside all airbrushes. It’s part of how paint is drawn from the cup into the nozzle assembly, even in gravity-feed designs.
Understanding the Venturi effect helps diagnose siphon-feed problems: if paint isn’t siphoning, the low-pressure zone may not be strong enough (too-low air pressure) or the siphon tube may be blocked or too short.
Related: Siphon Feed · Atomization · PSI
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