Pressure feeding air spray guns is where a spray gun is attached by hoses to a remote pump or pressurised paint tank to deliver paint to the spray gun instead of using a paint cup attached directly to the spray gun.
There can be many benefits of using a pressure fed spray gun over a traditional siphon or gravity feed spray gun. One of the most obvious benefits is the weight reduction by removing the paint cup from the spray gun. Using a pressure pot or eight double diaphragm paint pump to deliver paint to a pressure feed spray gun means you are able to spray paint continuously for longer as the need to stop and refill the smaller paint cups attached to your spray gun is removed.
A pressure fed air spray gun can also be used at literally any angle which is not possible with gravity feed or suction feed spray guns because the paint cup on the spray gun will either leak or at extreme angles paint will not enter the spray gun.
There is a difference between pressure feed only spray guns and regular suction or siphon feed spray guns to be aware of. Good-quality brand name suction feed spray guns can almost always be used when attached to a paint pressure pot or double diaphragm paint delivery pump. Inferior quality, cheaper siphon feed air spray guns may not operate satisfactorily when attached to a pressure pot or double diaphragm paint pump as leaking may occur due to low quality fluid needle and nozzles and sometimes it is difficult to achieve satisfactory atomisation with the lower quality atomising air cap's on cheaper siphon feed air spray guns.
On the other hand, it is generally not possible to use a spray gun that has been designed as a dedicated pressure feed only spray gun. This is usually due to the fact that the atomising air cap on dedicated pressure feed only spray guns has much larger compressed airports and usually extra atomising air ports all of which are designed to atomise much higher volumes of paint streaming from a pressure feed spray gun. It is generally not possible to achieve these flow levels of fluid using a siphon fed spray gun.
An easy check to see if your siphon feed spray gun may work attached to a paint pressure pot or double diaphragm pump is to test the spray gun attached to your pressure tank or pump with water. If there is no leakage from the nozzle of the siphon feed spray gun with 5 to 10 PSI of fluid pressure you may be okay. Generally inlet fluid pressure should be kept lower than it would be for a pressure feed dedicated spray gun otherwise it will be difficult to achieve adequate atomisation.
The Anest Iwata W200 pressure is a popular high quality pressure feed spray gun.