SERVICE GUILD: HIGH VOL.-LOW PRESSURE PAINT APPLICATION

Subject: HVLP-HIGH VOLUME LOW PRESSURE PAINT APPLICATION

Model and Year: 1982-91 ALL PASSENGER CARS AND TRUCKS

VOC stands for Volatile Organic Compounds. Most solvents used in automotive refinishing paints are considered volatile organic compounds. Volatile organic compounds react chemically with sunlight and make a variety of pollutants generally referred to as "Photochemical Smog." VOC regulations seek to reduce the amount of VOC getting into the air and thereby limit pollution. One way to reduce the amount of volatile organic compounds being emitted into the air is to increase the transfer efficiency rate of the paint material being transferred between the spray gun and the surface being painted.

Different states throughout the country, such as California, New York, New Jersey, etc., are in the process of writing VOC emission regulations. As an example, the South Coast Air Quality Management District (SCAQMD) in Southern California has a Rule 1151 for automotive refinishing that stipulates that coating applications must be done with either electrostatic application, high-volume, low-pressure (HVLP) spray or "such other coating application methods that are demonstrated to the executive officer to be capable of achieving at least 65 percent transfer efficiency." HVLP spray is defined as "to spray a coating by means of a gun that operates between 0.1 and 10.0 psi air pressure."

What is the difference between the high pressure conventional spray guns now in use and the HVLP spray guns being stipulated in VOC regulations? In the conventional spray gun high pressure air leaves the air cap and rapidly expands. As this air expands, the paint from the fluid tip is blasted apart, sending small paint droplets in all directions at a high velocity. This explosion of paint causes much of the paint to pass or bounce off the surface being painted. Transfer efficiency on conventional spray guns is usually between 20 percent and 50 percent efficiency.

HVLP stands for (H)igh (V)olume (L)ow (P)ressure. HVLP spray guns utilize lower spray pressures upon atomization. The relatively low air pressure causes a much "softer" explosion. The resultant paint droplets are larger and slower. The large volume of air from the air caps can now better control the flight of the droplets. The paint spray tends to move in one direction. Bounce back and paint passing by the substrate are reduced, resulting in increased transfer efficiency. Transfer efficiency of HVLP guns is usually between 65 percent to 90 percent efficient. The amount of savings and transfer efficiency varies with the skill of the painter, gun adjustment, the air pressures, the size of the object being painted, and the viscosity of the paint.

Basically, there are three types of HVLP spray equipment available; turbine units, air conversion units, and spray guns with the air conversion units inside the gun.

The turbine unit is normally a portable or wall-mounted unit that generates a high volume of air at between 3 to 7 psi. Due to friction, the turbine generates heat. The amount of heat generated and the temperature of the air depend on the size of the turbine and length of hose. A large size diameter air hose is used between the turbine and the HVLP spray gun.

Air conversion units are normally portable or wall-mounted units that use high pressure air from an air compressor and then convert it to a high volume of air at a lower pressure set on a regulator. Most air regulators on these units do not exceed 10 psi. A large size diameter air hose is used between the air conversion unit and the HVLP spray gun. These units do not generate any heat, but can be purchased with a heat source.

HVLP spray guns with the air conversion units inside the gun use high pressure air from an air compressor and then convert it to a high volume of air at a preset pressure normally dependent on incoming air line pressure. The spray guns cannot exceed 10 psi no matter how high the incoming air line pressure is. There is no large diameter air hoses or heat to contend with. HVLP equipment that can maintain precise control and maintain close to 10 psi air cap pressure will provide better atomization of materials, especially low VOC paints.

A GM training course on HVLP Paint Application is currently available (Course 22001.42). Please refer to the GM monthly training schedule for more information.

MANUFACTURERS of HVLP SPRAY EQUIPMENT

Accuspray System Binks Bessam-Aire Binks Manufacturing Co. 26881 Cannon Road 9201 West Belmont Ave. P.O. Box 46478 Franklin Park, IL 60131 Cleveland, OH 44146-0478 708-671-3000 216-439-1200

Can-Am Croix Can-Am Engineered Croix Air Products Products. Inc. 520 Airport Rd./Flemingfield 30850 Industrial Rd. So. St Paul, MN 55074 Livonia, MI 48150 612-455-1213 313-427-2020

DevilBiss Graco Inc. The Devilbiss Co. RO. Box 1441 320 Phillips Ave. Minneapolis, MN 55440-1441 RO. Box 913 1-800-367-4023 Toledo, OH 43962 419-470-2169

Lex-Air Turbine Spray Mattson Lex-Air South 230 West Coleman 5874 Buford Hwy. P.O. Box 132 Doraville, GA 30340 Rice Lake, WI 54868 404-454-8417 715-234-1617

Sata Sharpe Mfg. Sata Spray Equipment 1224 Wall St. P.O. Box 46 Hwy. 16&63 N. RO. Box 15042 Spring Valley, MN 55975 Los Angeles, CA 90015-0042 507-346-7102 213-749-4368

Xcel Spray Smith Eastern Corporation 5020 Sunnyside Ave. #207 Beltsville, MD 20705 301-937-4548

We believe the sources listed in this bulletin and their equipment to be reliable. There may be additional manufacturers of such equipment. General Motors does not endorse, indicate any preference for or assume any responsibility for the products or equipment from this firm or for any such item which may be available from other sources.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.