The two types of sprayers used for architectural spraying are the airless and the HVLP (stands for: “high volume, low pressure). There is another type of sprayer, the conventional compressed air sprayer, but this type is never used for house painting. The compressed air sprayer generates way too much overspray to be used for house painting, and does not spray standard house paints very well.
The airless sprayer is a high production sprayer which forces paint through a small opening or orifice in the spray gun tip to atomize or break up the paint into a spray pattern. Air is not used at all (hence it is “airless”) to achieve atomization. Airless spraying allows for better atomization of heavier bodied materials. Latex paints spray very well with airless spraying equipment, usually without the need to thin the paint at all. This is the real benefit of the airless, the ability to spray heavier bodied paints without the need to thin them.
Airless sprayers typically spray paint at a pretty good pace – anywhere from .33 gallons per minute to 1 gallon a minute or more.
There are some dangers that come with the high pressures of the airless sprayer, primarily injection injuries. Because the paint is being driven at such high force (usually 2000 psi or so), if the airless operator gets his hand too close to the spray tip he risks being accidentally injected with paint through the skin which causes a horrific injury requiring surgery to clean out the wound and there is the risk of amputation resulting from complications of an injection wound. It is very important for the airless operator to read the owner’s manual of the equipment he is using, to become familiar with the safety procedures necessary for safe operation of the sprayer.
The HVLP is an “air gun” and uses air to atomize the paint, so consequently it does not spray heavier materials such as latex paint as well as an airless. The HVLP is a fine finish sprayer and works very well with oil (alkyds) enamels, varnishes and thin viscosity paints such as shellac and lacquer. The production rate of the HVLP is much less than that of the airless too making it better for trim and doors rather than walls and ceilings. HVLP sprayers are known for the overspray reduction, i.e. the fact that they produce far less overspray than a conventional air compressor sprayer, and probably less overspray than the airless sprayer too. The key to keeping overspray down is to keep the air volume down to only as much as is needed to do the job. Keeping the fan size down is also helpful in limiting overspray too. You can learn more about HVLP spraying here: HVLP Spraying.