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Paint sediment is one of the most common hidden causes of poor atomization in gravity-feed spray guns. Many painters first suspect air pressure or gun quality, but the real problem often starts inside the cup. When pigments, metallic particles, fillers, or flattening agents settle at the bottom, the gun receives material with uneven solid content. The result is an unstable flow rate, heavy droplets, edge spits, and fan pattern distortion.
A gravity-feed system depends on smooth material movement from the cup outlet into the fluid passage. When sediment collects around the cup neck, filter seat, or fluid inlet, it restricts delivery. The needle may still open correctly, but the paint column entering the tip becomes inconsistent. This inconsistency changes droplet size during each trigger pull. In production refinishing, that shows up as dry edges, coarse texture, mottling, or sudden dark spots in metallic basecoat.
Before loading the gun, mix the material thoroughly according to the product data sheet. Stir from the bottom of the mixing cup, scrape the corners, and do not rely on a quick shake. For coatings used in LVLP Spray Gun Surface Polishing work, material uniformity is especially important because lower air consumption leaves less margin for breaking up heavy solids. If the paint is not fully suspended, the atomization cone becomes unstable even when pressure appears correct.
Filtration is the next control point. Use a strainer mesh that matches coating viscosity and solid size. Too coarse a filter allows dirt and sediment flakes to enter the nozzle. Too fine a filter slows flow and can starve the tip during long passes. After straining, do not let mixed material sit too long in the cup. If delay is unavoidable, lightly agitate the cup before spraying, but avoid introducing bubbles.
During pattern testing, watch the fan edge carefully. A clean air spray gun pattern should be even from top to bottom, with no heavy tails or random specks outside the main spray zone. If scattered droplets appear only after several seconds of spraying, sediment may be moving gradually into the fluid tip. Stop immediately, empty the cup, clean the filter area, and inspect the tip seat. Continuing to spray will push contamination deeper into the nozzle assembly.
Metallic and pearl colors require extra attention. Heavy particles can settle quickly and create color travel across the panel. For horizontal panels, this may produce cloudy patches; on vertical panels, it can create streaking. A Tight Connection at the cup thread and lid vent also matters because air leakage or poor venting can interrupt gravity flow and make sediment problems appear worse than they are.
Cleaning procedure determines whether the problem returns. Flush the cup channel, fluid passage, needle, and air cap immediately after use. Do not simply rinse the cup and leave residue around the outlet. In LVLP Spray Gun Surface Polishing applications, I use a soft brush for the cup neck and inspect the fluid tip under light before reassembly. The needle must seat cleanly, and the nozzle must be tightened without forcing the threads.
Finally, confirm a Tight Connection during reassembly and spray a short test pattern before the next job. If the fan is still coarse after cleaning and filtering, check paint viscosity, air cap damage, and tip wear. Sediment control is not only a cleaning habit; it is a process discipline that protects atomization quality, color accuracy, and final surface texture.
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