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Different Kinds of Incorrect Spray Patterns

If your spray pattern test is conducted and shows a correct, even, elongated oval without excessively pointy or ends or a noticeably bulging center, then all is well and you do not need to clean or adjust your spray equipment. However, any deviation from this “ideal” pattern requires you to work at bringing the spray pattern closer to the necessary benchmark, as follows --

•    If the spray pattern resembles the upper part of an exclamation point (without the dot – a rounded oval at one end, trailing off into a thinner point or even a sharp point at the other), oriented either way (point down or point up), then you have what is known as a top-heavy or bottom-heavy spray pattern.

To analyze, switch the air cap around by 180˚, and shoot another pattern onto the paper or cardboard. If the bulging end and the pointed end have changed places – that is, if a top-heavy spray pattern is now bottom-heavy, or vice versa – then the problem is some kind of debris in the wing ports. Clean the air cap in solvent and carefully ream out the wing ports with a wooden toothpick.

On the other hand, if the spray pattern does not change after rotating the air cap through a half-circle, part of the fluid nozzle hidden behind the air cap must be encrusted or filled with old paint, and requires cleaning.

•    If the spray pattern resembles a peanut or a barbell, with bulging ends and a constricted “waist” at the middle, then this is a split spray pattern. The first thing to check is air pressure, which might be too high – reduce the air pressure and shoot another pattern. If this does not correct the problem, then the nozzle is probably the wrong size for the paint viscosity, and a smaller nozzle opening is needed. Measure viscosity again, then place a correctly sized nozzle into the spray gun and shoot another test pattern.

•    If the spray pattern is an elongated diamond shape, with a bulging center and ends that taper away into sharp points, then this center-heavy pattern can indicate either excessively thick material is being sprayed, or the air pressure is insufficient. Try increasing air pressure, and if this does not work, either thin the paint or use a larger nozzle opening as appropriate.

•    A curved or crescent-shaped pattern is caused by one thing only -- one wing port is blocked and the other is open. You can determine which wing port is blocked by the direction of curvature – if the wing pattern curves to the left, then the left wing port is clogged, while a curve to the right indicates a congested right wing port.


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