Figure 14-42 shows the principal parts of a typical spray gun. The spreader adjustment dial is used to adjust the width of the spray pattern. When you turn the dial to the right, a round pattern is obtained. When you turn to the left, a fan-shaped pattern results. As the width of the spray is increased, more material must be allowed to pass through the gun to get the same coverage on the increased area. To apply more material to the area, you should turn the fluid needle adjustment to the left. If too much material is applied to the surface, turn the fluid needle adjustment to the right. In normal operation, the wings on the air cap are adjusted to the horizontal position, as shown in figure 14-43. This provides a vertical fan-shaped pattern.

Normally, you will be concerned about spray painting lacquer, enamel, and epoxy materials. The correct air and fluid pressures used with these materials vary. There are several pitfalls of incorrect pressures, some of which are as follows: Excessive air pressure may cause dusting and rippling of the finish. Too little air pressure, coupled with excessive fluid pressure, causes orange peel. Excessive fluid pressure causes orange peel and sags. Too little fluid pressure causes dusting.

Learning Objective: Recognize the types of sealants and the procedures used for applying them.

Sealants are used to prevent the movement of liquid or gas from one point to another. They are used in an aircraft to maintain pressurization in cabin areas, to retain fuel in storage areas, to achieve exterior surface aerodynamic smoothness, and to weather-proof the airframe. Sealants are used in general repair work to maintain and restore seam integrity in critical areas where structural damage or paint remover has loosened existing sealants.