Paint Sprayer Operation


How does a paint sprayer work and how does it relate to Bernoulli's effect? Why does the opening of the tube under the paint found near the bottom of the can?


The air supplied to a paint sprayer is blown through a nozzle which is a pipe with a narrow place in it. As the pipe narrows down the velocity of the air increases since the amount of air being passed is the area of the pipe times the velocity of the air.

Due to conservation of energy, the sum of the energy due to velocity and the energy stored as pressure remains fixed. Therefore as the velocity goes up the pressure of the air at the narrowest part of the nozzle becomes quite low, even lower than atmospheric pressure. This is the Bernoulli effect.

The paint sprayer suction tube has one end in the paint and the other penetrating the wall of the nozzle at this minimum pressure point. Atmospheric pressure forces the paint from the reservoir up through the suction tube where it spill out into the path of the high velocity air. The air carries the paint along with it out the front of the nozzle where it is deposited on the surface being painted. If the suction tube did not reach to the bottom of the paint reservoir it could not reach the last of the paint.