How to Choose the Right Atomizing Spray Nozzle

Q. What parameters do I need to know to find the correct atomizing spray nozzle for my liquid coating applications?

A. Atomizing spray nozzles atomize fluids with compressed air to create fine sprays in a variety of patterns for a variety of uses. Their most common uses include marking, painting, coating, cooling, dusting, lubricating and cleaning parts and products. Different types of atomizing spray nozzles deliver better results for some of these tasks over other tasks.

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While it is challenging to sift through the many types of atomizing nozzles, you can narrow down the right nozzle type for you and your application with a few basic questions:

Are you using a pressurized liquid feed?
In cases where a pressurized liquid source is unavailable, you will need a gravity or siphon-fed nozzle. While this removes the complexity of having a liquid pump pressurizing your liquid, there are some drawbacks. Siphon height limitations will require your liquid source to be fairly close to your nozzle. Siphon-fed nozzles are also hard to turn off and on, making them best suited for applications that require continuously spraying a low viscosity liquid at a low gallons per hour (gph).  

What is the viscosity of the fluid you are using?
Another deciding factor between nozzles is the viscosity, or thickness, of the liquid it will need to spray. Different nozzles are compatible with different viscosities, measured in centipoise (cP). For example, two mainstream nozzle types are internal-mix nozzles and external-mix nozzles. They function just as the name states: internal-mix nozzles mix the compressed air and liquid source inside the nozzle and external-mix nozzles do the same outside the nozzle. Because internal-mix nozzles need to mix liquids, they typically cannot spray liquids at viscosities over 300 cP. As external-mix nozzles do not need to atomize fluids inside the nozzle, they can handle liquids well above 300 cP.

What is your required liquid flow rate in gallons per hour (gph)?
If you have a process requiring the application of a set volume of liquid, you can narrow down your correct nozzle based on its maximum flow rate. As a general rule, external-mix nozzles inherently dispense more liquid than internal-mix nozzles, as the former have fewer restrictions on the liquid flow. For applications requiring higher gph, a liquid-only atomizing nozzle will provide an increase in gph. That said, using liquid-only nozzles will increase your droplet size.

What droplet size are you looking for?
Fine droplet sizes are vital to many atomizing nozzles applications. Benefits of small droplet sizes include even coatings and liquid conservation. Internal-mix nozzles excel at providing the smallest droplet size possible. External-mix and liquid-only nozzles produce larger droplet sizes, but increase gph.  

Should you use a No-Drip option? 
Nozzles equipped with a No-Drip option positively shut off liquid flow when their operators shut off their compressed air supplies. This benefit is especially welcome in coating applications, where an errant droplet of liquid would mar an otherwise smooth, even coating. Operationally, it also allows precise control in rapidly turning the liquid flow on and off to provide up to 180 bursts of liquid per second.