Metal Finishing Guide Book


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Page 186 of 843

Wipe off the gun body with a cloth wet with solvent and lubricate the spray gun with a drop of light machine oil each day. TROUBLESHOOTING SPRAY GUNS 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 Fig. 11. Split spray pattern caused foreign matter on the air valve stem or seat, a broken by too much atomizing air pressure and/or trying to widen the air-valve spring, or a bent air-valve stem; check the air spray pattern too much. Remedy valve packing nut to see if it is too tight, the air-valve assembly to see if is tight enough, and the air valve the problem by opening the fluid control knob (D) to the full assembly gasket for leaks; and check to see if the gun is position and turning the spray a bleeder-type spray gun. control knob (C) down to narrow If fluid is leaking from the front of gun, check for the spray pattern width. 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 Fig. 12. Spitting, caused by air bubbles in the the material with thinner. Do not use fluid supply, can be remedied by scecuring metal devices to probe into the air nozzle all fittings and connections. Loosen nut (E) openings. and place two drops of machine oil on the Dried material also gets stuck around packing. Replace the nut and finger-tighten. In aggravated cases, replace the packing. the outside of Remove the air and fluid nozzles (F) and the fluid nozzle clean the back of the fluid nozzle and nozzle tip restrictseat in the gun body using a rag soaked with ing passage of thinner. Replace and tighten fluid nozzle atomized air to with the wrench supplied with the gun. a point at the Replace the air nozzle. Tighten or replace center of the air swivel nut (G). nozzle opening causing an inverted tear-drop-shaped spray pattern Fig. 13. Fan spray pattern (see Fig. 10). This faulty pattern can also be caused by caused by low atomizing air a loose air nozzle, or a bent fluid nozzle or needle tip. pressure or too much spray If dried material is causing the trouble, remove the air material being fed through nozzle and wipe off the fluid tip using a rag soaked the gun. To correct the probwith thinner. Tighten the air nozzle and replace the lem, increase air pressure from air supply. fluid nozzle and/or the needle, if it is bent. 181

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