5-1. Pneumatic Tools. Pneumatic tools look much the
same as electric tools, but they are driven by
compressed air. When some sort of air compressor is
available in the field, these tools can be used for a vast
variety of jobs that otherwise would be impossible to do
or would take too long to do by hand.
5-2. Safety Precautions. When operating or
maintaining air-driven tools, observe the following
precautions to prevent injury to personnel:
Inspect the air hose for cracks or other defects.
Replace the hose if defects are found.
Before connecting an air hose to an air outlet,
open the shutoff valve momentarily to expel any
Never point the hose at another person.
Stop the flow of air to a pneumatic tool by
disconnecting, adjusting, or repairing the tool.
Paint Guns. The use of a paint gun permits a
fast and effective means of applying paint.
Description. Figure 5-1 shows the basic parts of
a typical paint gun. Though the specific locations of
some parts may differ from type to type, the guns are
generally the same and the parts serve the same
Operation. The spray gun operates on
compressed air supplied from a compressor. The flow
of paint, is controlled by a needle valve when the trigger
on the spray gun is actuated.
Use. The correct use of a paint gun involves
setting the spray pattern, painting at the correct
distance, and using the correct technique in the stroke.
Setting the spray pattern. The spray
pattern is variable from round to a vertical, flat, oval
pattern, with all patterns in between, as shown in figure
5-2. The vertical fan-shaped pattern gives maximum
coverage as the gun is moved back and forth parallel to
the surface being painted. The fan is vertical because
the wings on the nozzle are horizontal, as shown in
figure 5-3. To adjust the spray pattern from circular to
fan, proceed as follows (see figure 5-4):
To adjust the spray width, turn the
spray width adjustment right for round, and left for fan.
As the width of the spray is increased,
more material must be allowed to pass
through the gun to achieve the same
coverage on the increased area.
To increase or decrease the amount
of material, turn the material control screw right to
decrease flow, and left to increase flow.
Distance for spraying. Depending on the
desired width of the spray pattern, the gun is held six to
ten inches from the work. If all other adjustments are
correct, greater distance will result in dry spray or
dusting and excessive overspray. Holding the gun too
close to the work will result in coatings which are too
heavy and will have a tendency to sag or run.
Stroke technique. The technique of
proper stroking requires maintaining the same distance
between the gun and the work, the same speed, and
keeping the gun as near to a right angle to the surface
as possible throughout the entire pass.
Distance. The natural tendency for
spray painters, particularly when tired or in an
uncomfortable position, is to arc or wave the gun, as
shown in figure 5-5. This practice must be avoided at all
costs, because it causes a thicker coating to be applied
in the middle of a stroke than at the end.
Speed. Maintain a constant speed
through the pass. If the motion is slowed at any point
and the paint output is not changed, an excessive
amount of paint will be deposited, causing it to run or to