Fleetwood V8-368 6.0L VIN 9 FI (1982)
Paint: Technical Service Bulletins
Paint - Increased Paint Transfer Efficiency
NO.: 91-1-65
DATE: July, 1991
GROUP: 10
CORP. NO.: 161701R
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
eificiency).
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
Bessam-Aire
26881 Cannon Road
P.O. Box 46478
Cleveland, OH 44146-0478
(216)439-1200
Can-Am
Can-Am Engineered
30850 Industrial Road
Livonia, MI 48150
(313) 427-2020
Devilbiss
