I always see postings saying that gravity-feed airbrushes spray finer lines at lower pressures and I have been guilty of saying the same thing, so I thought I would try a siphon-feed airbrush at a low pressure myself as a comparison. The following test was with the same Model Master Acryl thinned 2:1 as I stated in my test of different airbrushes earlier.
I shot these lines at 10 psi and the results surprised me.
Is 10 psi considered low pressure for acrylics or are the claims about gravity-feed airbrushes using less pressure than that? I don’t have a lot of experience spraying at low pressures like this so maybe some of you veterans can shed some light?
Well, I sprayed 9 psi once and got just a 1/8 of a hairline thinner. OK, just kidding. My gauge only reads down to 10 psi and I doubt that my pressure gauge would read accurate pressures at the bottom of the dial. I might be throwing a monkey wrench into the rumors but I’ll be the first to say that I don’t believe a gravity fed airbrush sprays finer. Once the paint gets into the nozzle of the AB it is the thickness of the paint solution and the AB operator that determines how a fine paint line will spray. I doubt a slight increase in pressure, a lb. or two, if necessary, from an air source would make a difference in a fine spray pattern between a siphon feed and a gravity feed AB. Your pictures seem to reinforce the idea, Mike.
I use gravity or well-fed ABs because I don’t like a hanging bottle getting in the way to get close to spraying on my project. I felt a gravity fed brush felt more balanced in my hand as I sprayed. And I didn’t like having to look over and under the bottle or cup while I sprayed. The side mount setup always seemed to get in my way while I worked on a project.
But I could never see a difference in fine spray lines in an AB side cup or gravity feed. I think both types of ABs spray just as fine. The AB operator had more of a difference than the AB itself. I think the difference is like drinking a cup of coke with a straw. It doesn’t matter if the drink is above or below your mouth and I don’t think it take much more “suck” to get the drink in your mouth. And it sure doesn’t take any more pressure to spit the drink out of your mouth either.
I agree that a gravity-feed does not spray a finer line, but I think the argument for them lies in the fact that at really low pressures the siphon-feed may not be able to reliably pick up the paint from the jar below it. I have not tested it in that manner so I couldn’t comment. I also see no reason to ever go any lower than 10 psi as that is some really low pressure and I would imagine you could paint a mural on a grain of rice at that pressure. [(-D][(-D][;)]
The coke drinking part was more of a graphic output then input. I do spray at 10 psi but it is for very small or subtle detail. Next time I’ll start collecting sample of fine lines with my different airbrushes. But they will be will enamel paint. I suppose to get a thin line with enamels I’ll really have to thin down the paint.
My old Aztek siphon feed wouldn’t even spray at 10 psi. It wouldn’t spray at all below about 20, but my Iwata gravity feed will spray on down to no air coming out at all. I feel better about the gravity feeds for that reason. Also, like roosterfish said, I don’t like the bottle bumping and obscuring, and I hated cleaning those siphon tubes and whatnot.
which of the ab that you’ve tried is simpler to clean mike?
ps. my omni 5000 is a cinch to clean. all areas are easy to reach with the brush cleaners or a qtip. for me, that was one excellent feature of the omni that i didnt “try” to find, i’m just blessed to have stumbled upon it.
I would say the Omni 4000 and the Vega 1000 are both the easiest to clean as they are gravity-feed models. The siphon-feed models are not that hard to clean either, they just have a siphon tube that needs to be cleaned on top of what you have to go through with the gravity-feed models. I would say the siphon-feed models only take an extra minute or two over the gravity-feed models in terms of time to clean them.
Of course that is with using the 1/8 oz metal cup with the siphon-feed and not the glass jars. If you have to clean a glass jar and it’s siphon tube and all then it takes quite a bit more time.
Even if the bottom feeder require a lb. or two extra pressure to get the paint into the AB once the paint is there the pressure will be the same in the AB and the thin lines will paint the same. The extra pressure is used just to pull the paint into the AB.
I wonder at what point the siphon-feed will fail to pull the paint up reliably?
Also, who would ever need to go that low in pressure anyhow?
If you can’t paint at 10 psi without overspray then you need to practice a lot more. [;)]
It has bben my experience that when shooting model paint (acylic or enamel), the average minimal effective air pressure is approx 15psi to spray our larger pigmented hobby paints. This is concidered very low as it is! Can gravity feed AB spray at appreciable air pressures lower than 10 psi, sure they can, depends on what type of spraying technique your trying to achieve; for example: finely atomized exhuast stains, fine lines for camo demarcration, etc. For these techniques you’ll have better control of the AB spray pattern with thinner paint and lower presure…gravity-feed AB excel at this. I have used my Iwata HP-CS in this manner on hundreds of models to do intricate camo detail, weathering, shading and etc. A finer spray pattern?, not nessessarily. This will depend on how the airbrushed was designed and what type of media it was engineered to spray. My “hobby-oriented” Paasche-H sprays a finer atomized line than my mega-buck “fine-art” oriented Iwata HP-C. Trying these same techniques with siphon feed AB’s are indeed possible as I found out years ago with my Paasche-VL; however the higher pressure forced me to critically monitor paint volume so as to avoid suddenly blasting the area with paint if my trigger action wasn’t absolutely precise…I had traded a lot of control here. Also a factor ofteen not mentioned with gravity feeds is the more consistant flow of paint due to gravity , as aposed to suction to feed paint to the airbrush. Some paints don’t feed well to bottom feed brushes, but theres no appreciable difference in performance. In this aspect of the two AB designes it is agreeable that gravity feed models uses less paint than there bottom feed brothers and cleans up faster -not nessessarily easier. Practice, skill and experimentation will ultimately answer these very intrinsic questions to help you master any airbrush for you specific needs; gravity or siphon-feed.
I do spray at 10 psi but it is for very small or subtle detail. Next time I’ll start collecting sample of fine lines with my different airbrushes. But they will be will enamel paint. I suppose to get a thin line with enamels I’ll really have to thin down the paint.