HOW DOES YOUR SPRAY GUN SHAPE UP?
No matter how experienced the sprayer, merely triggering and moving a gun in space will not reveal any of the performance characteristics vital to a top quality finish.
A simple brief static spray pattern will immediately highlight any potential problems before the gun is used on the painstakingly prepared workpiece or vehicle.
1. Ensure that you have the correct air cap, fluid tip and needle set-up on the gun to match the material being applied.
2. Tape up a piece of brown paper—approx. 20" (1/2 m) square—onto the spray booth wall at shoulder height.
Follow the procedure explained below and compare the pattern to our examples.
If your result resembles examples 2-8 then look at the corrective measures before you apply paint to the workpiece.
3. Having set the gun at the recommended inlet or atomizing air pressure, hold it at the correct target distance and spray at the paper WITHOUT MOVING THE GUN.
Normal Pattern – Ready to Spray Intermittent Spray Fan or Fluttering
• Good balance and uniformity
• Symmetrical pattern shape
• Good working height and width
• Uniform distribution of material
(Verify by horizontal spray out)
Banana Pattern
• Air in the fluid passageways
• Insufficient paint in cup
• Fluid tip loose
• Fluid needle packing or packing screw loose
• Cup vent hole clogged
Heavy Top or Bottom Pattern
• Air cap horn hole dirty or damaged
• Test spray pattern, rotate 180° and test again to isolate horn hole location
• Clean air cap thoroughly
• Replace air cap if necessary
• Fluid tip or air cap dirty or damaged
• Test spray pattern, rotate 180° and test again to isolate cause
• Clean both items thoroughly
• Replace fluid tip or air cap if necessary
Single Split Pattern Center Heavy Ellipse
• Too much air for fluid quantity used
• Reduce air pressure at regulator
• Increase fluid flow by changing fluid tip size or opening needle control knob
• Bad air or paint setting
• Viscosity too high – thin with solvents
• Fluid flow too high – reduce
• Air pressure too low – increase
Double Split Pattern
• Too much air for fluid quantity used
• Reduce air pressure at regulator
• Increase fluid flow by changing fluid tip size or opening needle control knob
Ball End Heavy Pattern
• Too much air flow
• Change fluid tip for smaller size
• Reduce flow using fluid needle control
• Reduce fan size using fan control
STATIC PATTERN TEST
Having examined the vertical spray pattern for uniformity of shape and size, now turn the air cap through 90° and static spray a horizontal pattern making sure you trigger for long enough to load the shape with material. Then watch to see the formation of the run-outs of material across the full width of the sprayed pattern.
This will highlight how well the material is distributed throughout the spray pattern. If run-out is more obvious at the center or at the ends then this indicates a problem.
TYPICAL GOOD
PATTERN RUN-OUT
TYPICAL BAD
PATTERN RUN-OUT
THE THREE “C”s OF SPRAY GUN TROUBLESHOOTING — CONDITION, CAUSE, CORRECTION
The information below provides you with a simple and effective method of tracing problems with your gun if it proves troublesome.
Look down the left hand “CONDTITION” column until you identify the problem and you will find the possible “CAUSE” and “CORRECTION” that needs to be taken.
CONDITION
A
Will not spray
CAUSE CORRECTION
No air pressure at gun
Fluid needle adjusting screw not open enough
Fluid too heavy for suction feed
Check air supply and air lines
Change to proper suction feed air cap
Increase fluid pressure at tank
Open fluid needle adjusting screw
Thin material or change to pressure feed
A
Gun spits paint when triggering on and off Incorrect needle fitted to gun
Excessive needle wear
Excessive fluid tip wear
Check tip/needle selection chart and fit correct item
Replace with new needle
Replace with new fluid tip
A
Small air leak from air cap when gun is Air valve contaminated and not correctly sealing Remove valve and thoroughly clean not triggered valves shaft and seating
A
Gun spits paint when triggering on due to Fluid tip not fitted correctly in gun head paint build-up inside air cap between spraying operations Fluid tip/needle leakage
Tighten to correct torque
Check for damage or blockage
B
Slow fluid leak from fluid tip and needle seat Fluid tip internal seat scored, damaged or worn Replace
Fluid needle external profile damaged or worn Replace
Contamination on needle or tip mating surfaces Thoroughly clean preventing good seal
Incorrect fluid tip for fluid needle fitted to gun Check tip/needle selection chart and fit correct item
Sluggish needle
Tight packing
Remove needle and clean or lubricate packing
Adjust
B
Major fluid leak or fluid jetting from fluid tip Contamination on needle or tip mating tip and needle seat
Incorrect fluid tip for fluid needle fitted to gun
Fluid needle stuck or “binding up”
Remove tip and needle and thoroughly clean surfaces preventing good seal
Check tip/needle selection chart and fit correct item
Remove and clean fluid needle shaft
Lubricate needle packing
Loosen needle packing
B
Paint build-up on fluid tip Fluid tip not fitted correctly in gun head
Fluid tip/needle packing worn or loose
Tighten to correct torque
Check for damage or blockage
A
B
K
I
C
G
D
E
J
F
H
CONDITION CAUSE
F
Air leak from fluid needle exit point in top of handle Seal damaged or missing
K
Paint build-up on air cap
G
E
Air cap retaining ring will not rotate
Stiff trigger action
CORRECTION
Replace
Damaged air cap holes
Gradual build-up of bounce-back on gun head
Contamination on retaining threads
Deformed or damaged retaining ring
Replace with new air cap
Thoroughly clean
Soak gun head in solvent to soften paint
Cut retaining ring off of gun (probably replace retaining ring and baffle as well)
Air valve stem bent
Contamination on air valve stem
Replace damaged component
Remove and clean
Contamination on trigger bearing screw Remove and clean
Contamination on fluid needle shaft Remove and clean
Fluid needle packing too tight Loosen packing nut
H
Unable to turn fan control knob on top rear of gun Internal o-ring swollen or broken
H
Unable to get round spray
Paint contamination on threads
Fluid tip or air baffle incorrectly fitted
Air baffle chimney damaged
J
Unable to turn air control valve on handle of gun Internal o-ring swollen or broken
Paint contamination on threads
D
Air valve sluggish or slow to turn on/off when Air valve stem bent trigger is pulled/released
Contamination on air valve stem
D
Air leak from around air valve stem Air valve seal damaged or missing
D
Air valve will not operate (air valve stem will not Air valve stem bent fully slide into valve body) when trigger is pulled
Contamination on air valve stem
I
Air leak from baffle seal
C
Slow fluid leak from needle packing
Baffle seal swollen or damaged
Fluid needle packing worn or loose
Replace o-rings
Remove and thoroughly clean
Remove, check components for damage and refit correctly
Replace air baffle
Replace o-ring
Remove and thoroughly clean
Replace damaged component
Remove and clean
Replace
Remove air valve and replace damaged air valve stem
Remove air valve and thoroughly clean
Replace
Tighten or replace as necessary w w w . d e v i l b i s s . c o m
DeVilbiss has over 100 years of experience and innovation and offers some of the finest
HVLP and conventional spray guns, tanks, cups and accessories in the finishing industry.
Industrial Finishing | DeVilbiss
195 Internationale Blvd., Glendale Heights, IL 60139 | For Your Nearest Distributor Call: 1-888-992-4657 TH1POSTER (6/07)
