MILITARY MATERIALS EQUIPMENT MILITARY MATERIALS EQUIPMENT | Page 3

Spray Application Processes
Atomization Technology Options
Conventional, HVLP, LVMP (Trans-Tech), Air Assist Airless and Airless are all types of Atomization technology, each has slightly different
operating parameters.
Conventional Air Atomizing
The most established method of air atomizing, used on spray guns for decades. It uses high velocity air jets to produce a very high
atomization power. However; this speed results in low transfer efficiency due to considerable “bounce-back” and overspray. Air
pressure exiting the air cap during use is typically 30 to 60 psi (2 to 4 bar) with typical air consumption of 6 to 25 cfm (170 to 700 l/min).
High Volume Low Pressure (HVLP)
Although not new, this method first became important in the early 1990s when environmental legislation started to be introduced.
It uses larger air volumes (11 to 30 cfm or 300 to 840 l/min) at low pressure to atomize the coating. HVLP has a much higher transfer
efficiency than conventional air atomizing due to the lower air pressures. The droplet sizes produced tend to be slightly larger,
sometimes resulting in a lower quality finish. Officially HVLP is limited by Government Environmental Legislation to a maximum of
10 psi (0.7 bar) atomizing pressure measured at the air cap.
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Trans-Tech (LVMP)
This equipment type was first seen in the mid 1990s and is a mixture of Conventional and HVLP atomization methods. Trans-Tech
makes more energy available for the atomization process but gives a higher transfer efficiency of coating material than the Conventional
air atomizing method. To qualify as Trans-Tech the air cap must be able to transfer at least 65% of the sprayed material to the sprayed
component (BSEN 13966 Determination of Transfer Efficiency of atomizing and spraying equipment for liquid coating materials). Air cap
pressure is typically in the region of 20 to 45 psi (1.3 psi to 3 bar) while using 9 to 20 cfm (250 to 560 l/min) to carry out its work.
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Air Assist Airless
To maximize efficiency, the best features of air spray and airless atomization are combined. This process is called Air Assist Airless.
The pattern is formed by the spray tip and air is used to eliminate tails and adjust the shape. Air Assist Airless provides fast application
of materials, a soft spray that reduces fog, and the ability to penetrate into recesses and cavities. This is especially important in the
wood industry where intricate shapes require a fine finish.
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Airless
Fluid is atomized by high pressure usually 500 to 4500 PSI and pushed through an orifice in the spray nozzle. The shape of the fluid
orifice determines the fan pattern. The particle size is larger than other spray methods so it is not generally used for fine finishes.
Advantages: Airless spray has a high transfer efficiency, allows for high speed production, and provides less overspray.
Fluid Delivery Options
Siphon-Feed
Siphon-feed hookups (external atomization) use vacuum
created at the nozzle to draw fluid from a cup.
Advantages: This fluid cup system offers quick material /
color changes.
Clean Air
Filter
Gun
Air
Siphon Cup
Pressure-Feed
This option uses an external pressure source (pressure tank, piston pump, or diaphragm pump)
to force air and fluid to the spray gun nozzle. Air and fluid are then mixed outside the nozzle
(external mix air caps).
Advantages: This method delivers higher volumes of fluids than other gun set ups, and will
spray a wider range of materials. It also enables independent control of fluid pressures.
Gravity-Feed
On Gravity-feed guns the cup is located above the gun. The force of gravity pushes the fluid
into the gun.
Advantages: This method offers quick color changes and convenience on small jobs or touch-up
applications. Gravity guns are able to use all of the coating – reducing waste.
Gun
Air
Air
Pressure Tank
Fluid
Extractor
Gravity Cup
with Fluid
Air Supply
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