The siphon sprayer works much like some HVLP sprayers except the HVLP sprayer has a baffle in it to soften the air more. The siphon sprayer just sprays air past the nozzle drawing paint out of the cup. The gravity feed HVLP works like it sounds. The paint is in a cup above the nozzle and when you pull the trigger the paint just pours out and the air blowing by it makes a mist of it. I have one of those but only use it when I use a two part paint that I need to use every drop. There are some paints, especially automotive paints that once you mix it you have to either use it all or throw away what is left over. This is where the gravity feed gun comes in handy. The siphon sprayer always has a ounce or so of paint left in the cup when it runs out.