There are two different style guns that work as High Volume Low Pressure guns.
One style uses a compressor and a 1/4" NPT air hose connection. It does
require a healthy compressor to produce the CFM volume requirements of the gun,
which average around 10 CFM @ 40 PSI. A good inline dryer is also needed with
this type gun.
The most efficient HVLP guns use a turbine and not a compressor. The air
supply hose is aprox 3/4" ID and the turbine supplies warm dry air at low
pressure with plenty CFM (volume).
Like everything else, the guns vary in price and performance. Several tips are
available to apply everything from thin bodied stains to Mulicolor fleck type
commerical latex wall coatings.
When applying latex paints, a good high quality paint is important. The paint
must have very fine ground solids for good performance in this type of gun.
While cheaper paints will work they are both hard on the gun & tips as well as
poor performers with regard to final results.
As has been said here many times, these guns are not for painting homes or
other large surfaces.