Sometimes the routine "quick" clean of the spray gun and nozzles, hoses and hoppers between each color change is not enough to completely prevent powder contamination.
Although you may clean between each color change by back washing or purging the spray gun, cleaning hoses etc. it is still possible to experience contamination from powder deposits in internal crevices, inlet or outlet tubes of the spray gun or pump fittings.
Powders can be extremely sensitive to cross contamination (depending on the powder) and even the smallest amount of powder can have a detrimental impact on your final finish.
Below are images of common gun cleaning practices...
followed by images showing a more thorough cleaning...
These methods don’t have to be as frequent but it can be good practice to get familiar with the complete tear down of all components of your coating system that come in contact with powder. This includes but is not limited to, gun and pump internals and the pickup tubes of hoppers and box feed systems. It is also a good idea to have multiple hoses for various colors.
The internals from the gun and pump are easily cleaned with the use of acetone or alcohol and a Q-Tip. Bristled bottle cleaner brushes are useful when cleaning pickup, inlet and outlet tubes.