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Paint & Body DIY Tech - Spray Gun Basics

Jeremy Schneckloth | Writer
Posted November 1, 2006
Photographers: Courtesy of SATA

Understanding the Controls

Basic SetupMost spray guns have three basic controls that will allow you to adjust your spray gun for optimum performance on your projects. These controls are the fluid adjustment, the fan control, and the air micrometer.

The fluid adjustment is the control that will allow you to adjust the distance that the fluid needle will travel back, away from the fluid tip, with each pull of the trigger. By setting this control all the way open, you are allowing the full amount of fluid that the fluid nozzle opening will allow. To set the fluid adjustment, start by unscrewing the fluid control almost completely. Next, pull the trigger back to the fully open position and screw the fluid control in until you feel a force from the backside of the trigger. Setting the fluid adjustment in this manner will allow full fluid volume to exit your spray gun.

The fan control, commonly found on the side of the spray gun body, adjusts the amount of air distributed to the different drillings or air passages in the air cap. The air passages that are located around the fluid nozzle are the atomization air passages. The airflow from these drillings helps draw material from the gravity cup and also disperse and atomize the fluid. The air passages that are located on the horns of the air cap help to squeeze and shape the fluid into an elliptical spray pattern. With the fan control adjusted fully pen, air will be distributed to both atomizing and horn passages in the correct ratio. This provides your spray pattern, which is called flat spray. When you start to turn the fan control in or close it, it will begin to restrict the air traveling to the drillings of the horns of the air cap. Once you have turned the fan control knob fully closed, you will have what is called round spray.

The air micrometer r air adjustment valve is the last of the ontrol knobs commonly found on a spray gun, although not all spray guns have integrated air adjustment. The air micrometer is used to adjust the air volume and pressure that is delivered to the air cap of the spray gun. This should be used for final, small adjustments to the air pressure. Normally, the air micrometer should remain in the fully open position to reduce the amount of restriction and pressure loss within the spray gun. Whether adjusting pressure at the spray gun or controlling from a wall-mounted filter or regulator, the anufacturer's guidelines for operating pressures should always be closely followed.

Using the Controls to Create the Perfect Spray PatternNow that you know all of the controls on a spray gun and their basic functions, how do you make them work together to create the perfect spray pattern for the object to be painted? Let's start with the fluid control knob and the fan control knob, which constitute the simplest part of the setup procedure. You'll want the fluid control knob adjusted to fully open, full fluid delivery as described above. You'll also want to start with a similar setting for the fan control knob: fully open, full fan. By doing this, you've allowed for full fluid delivery and the proper ratio of air to be distributed for proper fan size and atomization. You'll also want to ensure that you have the proper air pressure and air volume supplied to the spray gun as per manufacturer recommendations.

The next step is connecting the spray gun to the air supply and putting fluid in the cup. When choosing your air supply hoses and fittings, you want to use large-diameter fittings and air hose to supply sufficient air volume to your spray gun. Air volume, or cfm (cubic feet per minute), is very important with today's spray gun technology. Most spray gun operating instructions will list the cfm which is required by that spray gun. Once the air volume is delivered to the spray gun, it is then measured in pressure (psi). All spray guns will have a recommended operating pressure.


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