Compact Spray Gun Selection Criteria

The selection of a spray gun is an important decision to make in the design of a spray system. Matching the gun, air cap, fluid tip/needle and fluid source to the application is of utmost importance. Failure to choose the correct equipment generally results in lower efficiencies, increased coating costs, increased emissions, higher booth filter costs, ets..

To match the spray gun to the application, the following criteria must be known:

Fluid Viscosity

Generally listed as high, medium and low. Manufacturers charts will usually indicate the capabilities of their air caps and/fluid nozzles in terms of viscosity. If one knows the viscosity in centipoise or time in a viscosity cup, it is a simple matter of conversion to the criteria listed.

Fluid Flow

Generally listed in ounces, cc, ml or gallons per minute. Spray gun charts will generally indicate a range of flow rates for a given fluid tip/air cap combination.

Production Rate

Production speed will dictate what the flow rate of the equipment should be. Obviously, a line running a 30 feet per minute with 6 square foot parts will require a higher flow rate than a line moving at 10 feet per minute with 2 square foot parts.

Available Air (psi & cfm)

In most plants, the available air is adequate to supply the necessary air required by a spray gun. Problems usually show up when:

Restrictive quick disconnects are used
Small I.D. air hoses are used (ie. 1/4”)
Air hose longer that necessary is being used.
Compressors too small in size
Keep in mind, Compact spray gun air caps consume 10-20 CFM

Fan Pattern Size

Pattern size is one parameter listed for an air cap. It should be matched to the part being sprayed. Pattern sizes are available up to about 14 inches.

Atomization Required

A “Class A” finish is not required for all applications. Applying a finish to a garden utensil would not necessarily be the same as the hood of an automobile. A stain applied to wood that is to be wiped off would dictate a very low level of atomization. If a lower level of atomization is required, an air cap with a lower CFM ($$$) would be selected.

Atomization type

Conventional Air Spray (Silver)

The air exiting the spray gun is close to the same pressure entering the spray gun. This high pressure air (25-60 psi) results in excellent atomization, at the expense of efficiency. The high pressure hitting the substrate bounces back, preventing some on the spray that is leaving the gun from landing on the part.

High Volume Low Pressure (Blue)

The air exiting the spray gun has been reduced to 10 psi or less at the air cap (if recommended inlet pressures are used). Since less pressure is bouncing off the surface, higher efficiency (less overspray) is achieved. If HVLP is used as a requirement of a governmental agency, the 10 psi limit must be adhered to. Therefore, choosing the correct air cap/fluid nozzle combination is of utmost importance.

Trans-Tech™ (Green)

The air exiting the spray gun has been tuned using a process called “Computational Fluid Dynamics”. CFD allows the air passing through the gun to be used at its maximum efficiency. Trans-Tech™ spray guns achieve the atomization of conventional air spray guns with the efficiency of HVLPl

Fluid delivery system

Suction Feed

Suction feed guns have been around for a century. While they are simple to operate, they are the most inefficient of the group. The range of motion is somewhat restricted since the pick-up tube must remain in the fluid to function.

Gravity Feed

Gravity feed guns depend on gravity (cup is on top) to supply fluid to the gun. As a result, some control of the gun is gained over suction feed. Maximum use of the material in the cup due to gravity is also a plus.

Pressure Feed

Pressure Feed allows maximum control of the required pressures (air and fluid). The source container of the coating is dependent on the amount used during a given time period. Available sources include pressurized attached cups, pressure pots (.5 to 60 gallons) and pumps (both low and high pressure).

Given the above criteria, a competent equipment supplier can match the equipment to the application.

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