To use a spray gun, you need a source of compressed air. Figure 14-39 shows two types of air compressorsa portable unit and a stationary unit. Both types are commonly used. The portable unit consists of an electric or gasoline engine, compressor, storage tank, automatic unloader mechanism, wheels, and a handle. The stationary unit consists of an electric motor, compressor, storage tank, centrifugal pressure release, pressure switch, and mounting feet. In addition to the standard spray equipment, special types have been developed for the occasional or small touchup job. There are many types avail-able. Figure 14-40 shows one that consists of a self-contained power unit with an attached spray bottle (container). The essential features include the power unit with a push-button spray cap on the top and on the bottom, and a screw lid that attaches to the container. A dip tube extends from the bottom of the power unit into the sealant. The power unit contains the propellant.

The air regulator (transformer) is used to regulate the amount of pressure to the spray gun and to clean the air. The air delivered to the regulator always contains some oil from the compressor, some water caused by condensation, and many particles of dirt and dust.

Air regulators are equipped with a pressure valve and pressure regulating screw to regulate the pressure delivered to the spray gun. They also prevent pressure fluctuations. The air must pass through a sack or cleaner before it leaves the regulator. This cleaner is contained in the long cylindrical part of the regulator and should be drained daily. Air regulators are also equipped with two gauges. One shows the pressure on the main line while the other shows the pressure to the spray gun.

Proper spray gun technique reflects knowledge of the equipment and experience. The spray gun should be held so the spray is perpendicular to the area to which the finish is being applied. You should ensure that the prescribed gun-to-work distance is maintained.

A distance of 6 to 10 inches from the gun to the work should be maintained when you are spraying epoxy-polyamide and polyurethane finishes. The gun should be held 8 to 10 inches from the work for lacquer and 6 to 8 inches for enamels. For a narrow pattern, the gun is held at the farther distances (10 inches for epoxy-polyamide and polyurethane, 10 inches for lacquer, and 8 inches for enamels).

A distance of less than 6 inches is undesirable because the paint will not atomize properly, and an orange peel will result. A distance of more than 10 inches is equally undesirable. Dried particles of paint will strike the surface and cause dusting of the finish. Examples of correct and incorrect spray gun techniques are shown in figure 14-41.

The distance the spray gun is held from the work is important; however, there are other factors to consider. The manner in which the gun is held and operated is also important. See figure 14-41. You should move your arm and body with the gun to keep the spray perpendicular to the surface. Avoid pivoting and circular movements of the wrist or forearm. These may bring the gun closer to the surface.

Figure 14-41.-Correct and incorrect methods of spraying.

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.