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Troubleshooting - DeVilbiss JGA-504 Service Bulletin

Conventional spray gun
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Heavy top or
bottom pattern
Heavy right or
left side pattern
Heavy center pattern
Split spray pattern
Jerky or fluttering spray
Unable to get round spray
Will not spray
Starved spray pattern
Excessive overspray
Excessive fog
Dry Spray
Fluid leaking from
packing nut
Paint bubbles in cup.
*Most common problem.
Horn holes plugged.
Obstruction on top or bottom of fluid tip.
Cap and/or tip seat dirty.
Left or right side horn holes plugged.
Dirt on left or right side of fluid tip.
Remedies for the top-heavy, bottom-heavy, right-heavy and left-heavy patterns:
1) Determine if the obstruction is on the air cap or the fluid tip. Do this by making a test spray
pattern. Then, rotate the cap one-half turn and spray another pattern. If the defect is inverted,
obstruction is on the air cap. Clean the air cap as previously instructed.
2) If the defect is not inverted, it is on the fluid tip. Check for a fine burr on the edge of the fluid tip.
Remove with #600 wet or dry sand paper.
3) Check for dried paint just inside the opening. Remove paint by washing with solvent.
Fluid pressure too high for atomization
air (pressure feed).
Material flow exceeds air cap's capacity.
Atomizing pressure too low.
Material too thick.
Atomization air pressure too high.
Fluid pressure too low (pressure feed only).
Spreader adjusting valve set too high.
*Loose or damaged fluid tip/seat.
Material level too low.
Container tipped too far.
Obstruction in fluid passage.
Loose or broken fluid tube or fluid inlet nipple.
Dry or loose fluid needle packing nut.
Spreader adjustment screw not seating properly.
Air cap retaining ring loose.
No air pressure at gun.
Internal mix or pressure feed air cap and tip
used with suction feed.
Fluid pressure too low with internal mix cap and
pressure tank.
Fluid needle adjusting screw not open enough.
Fluid too heavy for suction feed.
Inadequate material flow.
Low atomization air pressure (suction feed)
Too much atomization air pressure.
Gun too far from work surface.
Improper stroking (arcing, gun motion too fast).
Too much, or too fast-drying thinner.
Too much atomization air pressure.
Air pressure too high.
Gun tip too far from work surface.
Gun motion too fast.
Gun out of adjustment.
Packing nut loose.
Packing worn or dry.
Fluid tip not tight.
Clean. Ream with nonmetallic point.
Clean. Ream with nonmetallic point.
Balance air and fluid pressure.
Increase spray pattern width with spreader
adjustment valve.
Thin or lower fluid flow.
Spreader adjustment valve set too low. Adjust.
Increase pressure.
Thin to proper consistency.
Reduce at transformer or gun.
Increase fluid pressure (increases gun
handling speed).
Tighten or replace.
Hold more upright.
Backflush with solvent.
Tighten or replace.
Lubricate or tighten.
Clean or replace.
Check air supply and air lines.
Change to proper suction feed air cap and tip.
Increase fluid pressure at tank.
Open fluid needle adjusting screw.
Thin material or change to pressure feed.
Back fluid adjusting screw out to first thread
or increase fluid pressure at tank.
Increase air pressure and rebalance gun.
Reduce pressure.
Adjust to proper distance.
Move at moderate pace, parallel to work surface.
Remix properly.
Reduce pressure.
Reduce air pressure.
Adjust to proper distance.
Slow down.
Tighten, do not bind needle.
Replace or lubricate.
Tighten tip to 15-20 ft. lbs.
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