SERVICE GUILD: HIGH VOL.-LOW PRESSURE PAINT APPLICATION

SUBJECT: REDUCTION OF VOLATILE ORGANIC COMPOUNDS (VOC'S) AND INCREASED PAINT TRANSFER EFFICIENCY THROUGH THE USE OF HIGH VOLUME LOW PRESSURE (HVLP) PAINT GUNS

Most solvents used in automotive refinishing paints are considered volatile organic compounds (VOC's) These VOC's react chemically with sunlight and can produce a variety of pollutants generally referred to as "photochemical smog". The amount of VOC's emitted into the air can be reduced by improving the transfer efficiency rate of the paint during application (by increasing the amount of paint which actually ends up on the painted surface).

New VOC regulations are going into place in various parts of the United States. 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 by 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% transfer efficiency". High volume low pressure spray is defined as "spraying a coating by means of a gun that operates between .1 and 10.0 psi air pressure".

Conventional high pressure guns operate at an efficiency transfer rate between 20 and 50 percent. In the conventional gun, high pressure air leaves the air cap and rapidly expands. As the air expands, the paint from the fluid tip is blasted apart and small paint droplets are sent out in all directions at a high velocity. This explosion of paint causes much of the paint material to pass by or bounce off of the surface being painted.

HVLP guns operate at an efficiency rate between 65 and 90 percent. (The efficiency rate is affected by certain variables: the skill of the painter, adjustment of the gun, air pressures, viscosity of the paint, etc.) These guns utilize lower spray pressures which cause a much "softer" explosion resulting in larger and slower droplets of paint. The large volume of air from the air cap better controls the flight of the paint droplets tending to move the paint in one direction. Bounce back and paint passing by the surface to be painted are reduced resulting in more paint on the surface (higher paint transfer efficiency).

There are three categories of HVLP spray equipment:

1. Turbine Units - Normally a wall-mounted unit which generates a high volume of air between 3 and 7 psi. The amount of heat generated and the temperature of the air depend upon the size of the turbine and the length of the hose. A large diameter hose is used between the turbine and the HVLP gun.

2. Air Conversion Units - Portable or wall-mounted units which use high pressure air from an air compressor and then convert it at a lower pressure set on a regulator. Most air regulators on these units do not exceed 10 psi. A large diameter hose is used between the air conversion unit and the HVLP spray gun.

3. HVLP Guns With Built-In Air Conversion - Use high pressure air from an air compressor and then convert it to a high volume of air at a preset pressure. These spray guns cannot exceed 10 psi and there are no large diameter air hoses or heat to contend with.

A GM training course on HVLP paint application is currently available (course number 22001.42). Please refer to the GM monthly training schedule for additional information.

MANUFACTURERS OF HVLP SPRAY EQUIPMENT

Accuspray System Binks Bessam-Aire Binks Manufacturing Company 26881 Cannon Road 9201 West Belmont Avenue RO. Box 46478 Franklin Park, IL 60131 Cleveland, OH 44146-0478 (708)671-3000 (216)439-1200 Croix Can-Am Croix Air Products Can-Am Engineered 520 Airport Road/Flemingfield 30850 Industrial Road South St. Paul, MN 55074 Livonia, MI 48150 (612) 455-1213 (313) 427-2020 Graco, Inc. Devilbiss P.O. Box 1441 The Devilbiss Company Minneapolis, MN 55440-1441 320 Phillips Avenue 1-800-367-4023 P.O. Box 913 Toledo, OH 43962 Mattson (419)470-2169 230 West Coleman RO. Box 132 Lex-Air Turbine Spray Rice Lake, WI 54868 Lex-Air South (715)234-1617 5874 Buford Highway Doraville, GA 30340 Sharpe Manufacturing (404)454-8417 1224 Wall Street P.O. Box 15042 Sata Los Angeles, CA 90015-0042 Sata Spray Equipment P.O. Box 46; Highway 16&63 North Xcel Spray Spring Valley, MN 55975 Smith Eastern Corporation (507)346-7102 5020 Sunnyside Avenue; #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.