It isn't a vacuum fed it is pressure fed. The handle is hollow and hold the paint. The vacuum part comes when you suction the paint from the can into the handle. You then close that port and pump up pressure to the handle with an attached pump. You then push a trigger that allows the paint to flow from the handle to a specially designed roller so you can apply the paint to the wall.
In my personal experience they are a waste of time. You will spend more time setting it up and then tearing it down and cleaning it all than you would if you just used a roller pan and standard roller. The standard roller takes seconds to put on a frame and when you are done you put the roller into a trash bag, grab and remove in one easy step, the roller is in the trash and you are clean and paint free. if you use a disposable pan liner you dump the extra paint back in the can and throw the liner away. With the pump style you have to clean the roller or buy special ones with holes for use with the thing. you have to disassemble it and clean each section and flush all of the paint out of it.The paint you applied to the wall with it will be dry before you get done cleaning it.
Put the money you would have spent on a pump type paint roller or power roller towards a higher quality paint and you will be better off in the long run.
