Page 4 SB-2-001-H
Internal and External Mix Guns
An external mix gun mixes and atomizes air and
fluid outside the air cap. It can be used for applying
all types of materials, and it is particularly desirable
when spraying fast-drying paints such as lacquer.
It is also used when a high quality finish is desired.
Figure 6 External Mix Gun
Figure 7 Internal Mix Gun
This gun mixes air and material inside the air cap,
before expelling them. It is normally used where
low air pressures and volumes are available, or
where slow-drying materials are being sprayed. A
typical example is spraying flat wall paint, or outside
house paint, with a small compressor. Internal mix
guns are rarely used for finishing when a fast-drying
material is being sprayed, or when a high quality
finish is required.
HVLP (High-Volume/Low-Pressure)
HVLP uses a high volume of air (typically between
15-22 CFM) delivered at low pressure (10 psi or
less) to atomize paint into a soft, low-velocity spray
pattern.
As a result, far less material is lost in overspray,
bounce-back than with conventional air spray.
This is why HVLP delivers a dramatically higher
transfer efficiency (the amount of material that is
actually applied to the part) than higher pressure
spray systems.
Spray a horizontal test pattern (air cap horns in a
vertical position). Hold the trigger open until the
paint begins to run. There should be even dis-
tribution of the paint across the full width of the
pattern (see Figure 10). Adjust with fan pattern
Figure 9 Suction Feed & Gravity Feed System
Components
Figure 8 Air Cap Overspray, Conventional/HVLP
The HVLP spray gun resembles a standard spray
gun in shape and operation.
HVLP is growing in popularity and it has also been
judged environmentally acceptable due to its high
transfer efficiency.
HVLP can be used with low to-medium solid mate-
rials, including two-component paints, urethanes,
acrylics, epoxies, enamels, lacquers, stains, primers,
etc. More recently developed HVLP air caps can
also satisfactorily atomize even high solid coatings.
OPERATION
Suction and Gravity Feed Equipment Hook-Up
Connect the air supply from the compressor outlet
to the air filter regulator inlet. Connect the air supply
hose from the regulator outlet to the air inlet on the
spray gun. After the material has been reduced to
proper consistency, thoroughly mixed and strained
into the cup, attach the gun to the cup.
HVLP
Conventional
(15 pages)
(44 pages)
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