When purchasing liquid spray equipment, choosing the best technology for your application is key.
Wendy HartleyBecause many factors come into play when making this decision, it helps to understand the advantages and differences between air spray, airless, and air-assisted airless technologies.
Air Spray
Air spray uses a low-pressure fluid stream that is mixed with compressed air at the aircap to atomize material in a controlled manner. It’s used to apply low- to medium-viscosity fluids for products requiring a high-quality, Class A, or decorative finish.
Due to changing requirements for environmental regulations, different versions of Air Spray technologies have been developed:
- Conventional is the traditional form of air spray technology and delivers the highest finish quality and production speeds. To achieve these advantages, it uses a lot of air, resulting in low transfer efficiency.
- High Volume, Low Pressure (HVLP) was developed for EPA-regulated areas. To meet the regulation, the amount of air used is limited to 10 psi at the aircap. The result is a low-velocity pattern with good finish quality and higher transfer efficiency than Conventional.
- Compliant technology is commonly referred to as Low Volume, Medium Pressure (LVMP) and was developed to meet European standards. This requirement means that the air pressure cannot exceed 29 psi at the air inlet. This allows an aircap design that delivers high finish quality while achieving transfer efficiency equal to or better than HVLP.
There are three options for supplying fluid to an air spray gun:
- Pressure-feed guns are usually fed through a hose from a low-pressure pump or a pressure tank. This option is used in industrial applications that need to move large amounts of fluid through the system.
- Gravity feed guns have a cup mounted above the gun’s centerline, and gravity enhances fluid flow. They are best suited to jobs using smaller quantities of fluid, like touch-up or repair.
- Suction feed guns have a cup mounted below the front of the gun. Air flowing from the aircap creates suction, drawing fluid from the cup to the fluid nozzle. This option is used for handling small amounts of fluid, frequent small-volume color changes, and low production rates.
Airless
Airless spraying uses a high-pressure fluid supply for atomization without the use of compressed air, only fluid pressure. It’s used for medium- to high-viscosity fluids, delivers a lower finish quality, and is ideal for speed and transfer efficiency.
Airless spray atomization is created by hydraulic force pushing material through an orifice. As the fluid exits the orifice, friction between the fluid stream and the atmosphere breaks it into small particles. The tip size and pressure determine the material flow rate. High pressure creates a complete pattern; therefore, the higher the material viscosity, the more pressure is required.
Air-Assisted Airless
Air-assisted airless uses a high-pressure fluid supply for atomization and compressed air at the cap for pattern control. It’s used to spray medium- to high-viscosity fluids and delivers a finish quality better than Airless, but not as high as Air Spray.
Air-assisted airless spray atomization is created by hydraulic force, which is less than airless, so it atomizes the center of the pattern. A fluid tip determines the pattern size and fluid flow rate. Air is then applied to help fill out the pattern. An aircap completes the spray pattern and eliminates tails.
Air-assisted airless solves many problems that arise with high-viscosity and high-solids coatings, as well as issues associated with heating and using higher fluid pressures to atomize more viscous materials. Many waterborne materials require the higher fluid pressure of air-assisted airless. The lower pressure and the air assist create finer atomization for a finer finish than airless.
Summary
Overall, each spray technology has advantages and disadvantages. Air spray is best for products requiring a high-quality, Class A or decorative finish, but it has a low transfer efficiency rate. Airless has a higher transfer efficiency rate and is often used for protective, rather than decorative coatings. Air-assisted airless offers high production levels and a relatively high-quality finish. Determining your production-line requirements will help you identify the spray technology that best fits your application.
Wendy Hartley has been a Worldwide Product Manager for Graco industrial equipment since 2004. With 20 years of experience, she has become an expert in manual and electrostatic applicators, spray packages, and plural component manual systems. At Graco, she has launched well over 20 products used in factories worldwide, with a commitment to continual improvements that address manufacturers’ ever-changing needs. Hartley also earned a Master of Business Administration (MBA) from the University of Minnesota. Visit https://www.graco.com.
