I first started using acrylic trim paints in 2004, and am now an authority in the UK on the application of water-based paints with brush, roller and spray. 

 Air Assisted Airless (AAA) for spraying acrylic paint

Graco Air assisted airless, note the two lines coming into the gun

Air assisted airless or AAA may seem like a contradiction in terms. Surely, if it’s airless, why is it air assisted?

In reality, an AAA unit is an airless pump with an onboard compressor that enables it to be an airless pump for walls or larger areas, but at the flick of a switch turns into a very high powered HVLP type unit. I say type because it is not exactly the same. The power, as I said, is better and the finish is far superior.

These units are best just used for trim and fine work in the air assisted mode, occasionally switching to airless. You can spray walls with them in airless mode, but the combination of 2 hoses at the gun (one for air, one for paint) makes it more cumbersome than a standard airless. This is fine for the odd room, but not really a machine for spraying mainly ceilings or walls on a day to day basis.

Full article on introduction to airless spraying acrylic paint published on Traditional Painter