I am not sure what gun you are talking about but if it is typical of guns for spraying automotive paints, the upper knob controls the pattern (atomization air) and the lower knob controls the fluid flow through the nozzle. I generally run both of mine nearly wide open all the time. If you are using the correct tip size for the viscosity of material (assuming suction or gravity feed), there really is little need to mess with the fluid knob. Likewise, the air knob controls the pattern and usually you don't mess with that either. Some like to "fine tune" gun adjustments but I have never found the need to do anything along those lines. You need to be measuring the air pressure right at the inlet to the gun, not at some wall mounted regulator perhaps many feet away. Tee in a pressure gage right where the air hose connects to the gun. You should be able to read the gage to the nearest 2 or 3 psig. If your gun is an HVLP type, the design pressure should be indicated right on the gun itself or the instructions that came with it. It may be anywhere from about 15 psig to 50 psig. If your gun is pre-HVLP, most enamels are best sprayed at 40 - 60 psig. The manufacturer's tech sheet for the paint will indicate the best pressure. Using whatever regulator you have, adjust it while holding the gun trigger open to the appropriate pressure. You don't need any paint in the gun to do this. If you have anything like my arrangement, you'll have perhaps 50 feet of hose between the regulator and gun. There will be a significant difference between the pressure back at the regulator and the pressure "at the gun". It is the pressure "at the gun" that counts. The "keep pressure below 50 psi" is a little confusing to me. Is it possible that you are using a pressure-fed gun...e.g. the paint cup is under pressure? If so, there should be a separate regulator for the cup pressure, which is usually kept down around 10 or 12 psi, depending on tip size and material viscosity. It sounds to me like you do not have enough atomizing air pressure. Check it out with the method above. Since you bought the gun at an auction, you probably don't know its' history. It may need a good cleaning, especially if you are getting spattering. Try completely disassembling it and verify there is no hardened old paint anywhere. Clean all orifices with a toothpick. If it is an old gun, you may have internal leaks where there shouldn't be any. Seals and gaskets may need to be replaced. In any event, check the pressure at the gun first. Stick with the manufacturer's instructions for mixing. They usually know best about how to use their products. Rod
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