Metal Finishing Guide Book


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Page 220 of 903

TROUBLESHOOTING SPRAY GUNS Fig. 11. Split spray pattern caused by too much atomizing air pressure and/or trying to widen the spray pattern too much. Remedy the problem by opening the fluid control knob (D) to the full position and turning the spray control knob (C) down to narrow the spray pattern width. If fluid is leaking from the needle packing nut, check for a loose packing nut or dried-out packing. Tighten the nut until leaking stops, or replace packing, if required. If air is leaking from the front of the gun, check for foreign matter on the air valve stem or seat, a broken air-valve spring, or a bent air-valve stem; check the air valve packing nut to see if it is too tight, the air-valve assembly to see if is tight enough, and the air valve assembly gasket for leaks; and check to see if the gun is a bleeder-type spray gun. If fluid is leaking from the front of gun, check for a worn or damaged needle or fluid nozzle, dirt in the fluid needle seat, and a broken fluid control spring; check to see if the fluid packing nut is too tight, and if the wrong size needle is being used. FAULTY PATTERNS AND HOW TO CORRECT THEM Dried material in a side port of a spray nozzle restricts passage of air through the port on one side resulting in full air pressure coming from the clean side of the part in a ���C��� or fan pattern in the direction of the clogged side (see Fig. 9). This situation can be remedied by dissolving the material with thinner. Do not use metal devices to probe into the air nozzle openings. Dried material also gets stuck around the outside of the fluid nozzle tip restricting passage of atomized air to a point Fig. 12. Spitting, caused by air bubbles in the fluid supply, can be remedied by sceat the center of the air nozzle opening causcuring all fittings and connections. Loosen ing an inverted tear-drop-shaped spray patnut (E) and place two drops of machine oil tern (see Fig. 10). This faulty pattern can on the packing. Replace the nut and finalso be caused by ger-tighten. In aggravated cases, replace the packing. Remove the air and fluid noza loose air nozzles (F) and clean the back of the fluid nozzle, or a bent fluzle and nozzle seat in the gun body using a id nozzle or neerag soaked with thinner. Replace and dle tip. If dried tighten fluid nozzle with the wrench supplied with the gun. Replace the air nozzle. material is causTighten or replace swivel nut (G). ing the trouble, remove the air nozzle and wipe off the fluid tip using a rag soaked with thinner. Tight- Fig. 13. Fan spray pattern en the air nozzle and replace the fluid nozzle and/or the caused by low atomizing air pressure or too much spray needle, if it is bent. material being fed through A split spray pattern ��� heavy on each end of a fan the gun. To correct the probpattern and weak in the middle ��� is usually caused lem, increase air pressure by (1) too much atomizing air pressure; (2) attempt- from air supply. 215

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