It is important to trigger the gun in order to avoid an uneven coat at the beginning and end of a stroke. Triggering is the technique of starting the gun moving toward the area to be sprayed before the trigger is pulled and continuing the motion of the gun after the trigger has been released. You should avoid too much overlapping on each pass of the gun because an uneven coat will result. The rate of the stroke should produce a full, wet, even coat. Once the job is started, it must be completed without stopping. Spray Gun Adjustments 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. Spraying Pressures 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. SEALANTS AND SEALING PRACTICES 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. TYPES OF SEALANTS The physical conditions   surrounding the seal govern the type of sealant to be used. Some sealants are exposed to extremely high or low temperatures. Other sealants contact fuels and lubricants. There- fore, it is necessary to use a sealant that has been compounded for the particular condition. Sealants are supplied in different consistencies and cure rates. Basic sealants are classified in three general categories—pliable, drying, and curing. Pliable Sealants Pliable sealants are referred to as one-part sealants and are supplied “ready for use” as packaged. They are solids and change very little during or after application. Solvent is not used with pliable sealants. Therefore, drying is not necessary. Except for normal aging, they remain virtually the same as when they were packaged. They easily adhere to metal, glass, and plastic surfaces. Pliable sealants are used around access panels and doors and in areas where pressurization cavities must be maintained. Drying Sealants Drying sealants set and cure by evaporation of the solvent. Solvents are used in these sealants to provide the desired application consistency. Consistency or hardness may change when this type of sealant dries, depending on the amount of solvent it contains. Shrinkage during the drying process is an important consideration. The degree of shrinkage also depends upon the amount of solvent it contains. 14-44