Spray Gun - Spray Gun Overview

Structure and Function

One of the most important tools used in collision and paint repair is the spray gun. Their precision construction and proper care have a great impact on the results of paint application and finish quality. This chapter includes details about spray gun controls, types, and operation.

Pattern Adjustment Screw
When this screw is rotated fully clockwise, air flows only from the center of cap (T) and the spray pattern would be circular. As the pattern adjustment screw is turned counter clockwise, air flows through the angle hole (R) and support hole (S). The spray pattern will gradually become more oval.

Fluid Adjustment Screw
Turning the fluid adjustment screw fully clockwise shuts off paint flow to the gun. Turn the screw counter clockwise to gradually increase to amount of paint that mixes with the air supply.

Air Valve and Needle Valve
As the trigger is gradually pulled, the air valve begins to open and allows only air to flow through the spray gun. Pulling the trigger further operates the needle valve, allowing paint to begin flowing with the air. This two-stage trigger operation improves paint atomization any time the gun is being used.

Spray Gun Air Cap
The air cap has precision-drilled holes that direct high velocity compressed air. These create a suction that draws paint into the gun and discharges it from the paint nozzle (N). The paint is then atomized and discharged through the area (C) by the force of the air and placement of the holes.



Types

Categorized by the paint supply method

Paint Supply Method
Pro and Cons
Gravity Feed System (Cup on Top)

The paint cup is located above the paint gun nozzle. The paint is supplied by gravity acting on the paint and suction at the nozzle tip.
Suitable for detailed and precise paint work because cup angle can be readily adjusted.
The cup’s capacity is generally 500 mL (16.90 fl oz) or less, so the cup requires frequent refilling. Because of the small cup, gravity fed guns are better suited to spot painting rather than large surfaces.
Paint viscosity has little impact on fluid (paint) flow rate.
Gun must be hung by its hook when not in use because the cup on top makes it unstable.
Suction Feed System (Cup on Bottom)

The paint cup is located beneath the paint gun nozzle. The paint is supplied by suction at the nozzle tip alone.
  
Larger paint cups generally require fewer refills, so the gun is more suitable for painting large areas.
Larger paint cup capacity makes the gun heavier.
Paint viscosity does impact fluid (paint) flow rate.


Categorized by the Nozzle Diameter

Diameter
Use
Characteristics
1.0?1.6 mm (0.040?0.063 in)
Topcoat
High atomization performance, relatively thin and homogeneous paint film suitable for topcoats.
1.5?2.0 mm (0.060?0.080 in)
Basecoat
High discharge rate, suitable for basecoats, such as primer surfacer, which tend to have relatively higher viscosities.


Categorized by the Spray Pattern

There are several different spray patterns based on the nozzle diameter and air cap hole etc.

Spray Pattern
Atomization
Paint Film Thickness
Characteristics and Applicable Paint
Tulip Type
High atomization ensures even application of paint coats.
Suitable for dual component paints such as polyurethane paint, which dries relatively slowly and metallic paint which can easily be applied unevenly.
Semi-Tulip Type
For general purpose applications.
Applies a greater film thickness than the tulip type.
Suitable for dual component solid and clearcoat polyurethane paint.
Straight Type
Suitable for slower drying lacquer type paints and metallic paint which can easily be applied unevenly.