Air-assisted airless: What is it?

A primer on air-assisted airless finishing and how it works. August 10, 2000

I'm not familiar with the air-assisted airless pumps that are discussed on this board. Are they used with an HVLP set-up (either turbine or conversion) to supply fluid in place of the pot, or as stand-alone systems that aren't compatible with my spray guns?

Air-assisted airless pumps are usually air-operated, positive displacement, reciprocating piston pumps that siphon coatings directly out of one, five, or 55-gallon containers. They require an air compressor for operating both the pump and the gun.

The good news is that there are some systems that can operate on as little as 5 cfm, from a 1.5 HP compressor. That is about one-quarter the amount of air needed for a conversion HVLP gun. They deliver the fluid at a significantly higher fluid pressure, 300-600 psi (typical) to a gun rated for these higher pressures.

The coating is forced through a tip made from tungsten carbide and cut in an eliptical shape, like a traditional spray pattern. The coating atomizes as it escapes to atmospheric pressure. The gun then adds a little bit of air (about 2 cfm) to the ends of the spray pattern, eliminating the "tails" or heavy edges, thereby minimizing overlapping lines or stripes. Thus, the "air assist" of the "airless" process.

In fact, air-assisted airless is the combination of two types of atomization, air spray and airless. What makes them so popular in the wood finishing industry is that they are usually faster, give a better finish without reduction of the coating, and are more efficient than most HVLP guns. They are used predominantly for sealers, topcoats, primers and wiping stains. With a little extra practice you can even do NGRs.

Aside from saving you money in coating usage, the smaller pumps can reduce solvent use for flushing to as little as 16 ounces per color or coating change.

Yes, pumps can be used with HVLP guns as well, and with excellent results. I suggest you try an HVLP gun hooked to a pump as an alternative to the air-assisted airless systems. They are fast, simple, and produce excellent results.