Technical data

4.4.2 Gun Adjustments. The flow of air and fluid at the
gun must be adjusted or balanced to obtain proper atomiza-
tion and other desired spraying characteristics.
4.4.2.1 The first consideration in obtaining this balance is
the proper combination of air cap and fluid tip for the
particular material being sprayed as recommended by the
equipment manufacturer and the coating material manufac-
turer.
4.4.2.2 After the air cap and fluid tip have been selected,
there are several adjustments which may be made with the
gun controls to properly adjust the air and fluid relationship.
These adjustments are necessary to obtain proper atomization
and other desired spraying characteristics required for the job
and conditions. The fluid adjusting screw on the gun (Figure
4-10, B) permits restriction of fluid flow relative to the
volume of air being used, but is limited since it puts
additional tension on the gun trigger and tends to discourage
feathering at the beginning and end of the stroke.
4.4.2.3 For pressure feed spraying, adjustment of tank
pressure and adjustment of the atomization air supply to the
gun is more effective for obtaining the proper air to fluid
balance.
4.4.2.4 The air adjustment screw (Figure 4-10, A) can be
changed to spread the atomized fluid out over a greater area,
which, in combination with the increased air flow, is equiva-
lent to reducing the flow of fluid.
NOTE
Do not thin the paint excessively to increase the
flow of fluid.
4.4.2.5 The correct atomizing pressure depends on the
type of coating and the length and diameter of the air line
from the regulator to the gun. The pressure must be sufficient
to completely atomize the material being sprayed but no
greater. For HVLP paint guns, the regulator pressure shall be
adjusted to a lower level to ensure the nozzle pressure does
not exceed a maximum of 10 PSI per Paragraph 4.2.1. An
excessive amount of air may give a split pattern in which the
material deposited is light in the middle of the pattern; too
little air may give a heavy centered pattern. Pressure on the
paint pot is usually adjusted to a range of 25 to 40 PSI but
may vary more widely, depending on the density of the paint
and the elevation of the surface being painted above the
pressure tank. In normal operation, the wings on the nozzle
are in the horizontal position which provides a vertical
fan-shaped pattern for maximum coverage as the gun is
moved back and forth parallel to the surface being painted.
The spray pattern is variable from round to flat with all
patterns in between and can be adjusted to obtain the pattern
which produces the best results.
NOTE
As the width of the spray is increased, more paint
must be allowed to pass through the gun to get
the same coverage.
Figure 4-10. Spray Gun Adjustments
TO 1-1-8
4-11