Fine-Tuning Spraygun Performance
A finisher isn't getting a nice fan pattern from his gravity-feed gun. Others help troubleshoot, and discuss the equipment's air-supply needs. December 15, 2005
Question
I recently bought an Astro gravity sprayer. I just sprayed lacquer and it seemed I couldn't get the material to flow out. Temp and humidity were perfect, so it wasn't that. No matter how much I increased the flow knob, I still couldn't get a nice wet surface. I then switched back to my old CH HVLP turbine sprayer and material went on much better. It seemed the fan spray pattern on the Astro wasn't even - more on top and bottom of fan than in the middle. I've read great things about the Astro sprayer. What did I do wrong?
Forum Responses
(Finishing Forum)
From contributor H:
Your gravity feed gun should handle lacquer very well. You did not mention the viscosity reading of the product. A Zahn #2 reading of 26 or 28 seconds should flow through a 1.2 or 1.4 mm fluid nozzle very easily. A thicker or slower product could have an appearance of being dry. If you choose not to reduce, you could use a larger fluid nozzle, needle and corresponding air cap.
Make sure the fluid adjustment needle at the back of the gun is all the way open and provide 35 to 45 psi to the gun. The uneven fan pattern could be caused by dirt, but you said it was a new gun. I would pull the trigger without air and see if fluid is flowing. If you have a fan pattern adjustment knob, set it about halfway.
From contributor B:
Take out the little plastic strainer where the cup screws onto the top of the gun..
From contributor R:
Is the cup venting correctly?
From contributor J:
You definitely have a problem. Check to make sure your cup is vented. Sometimes
the hole gets clogged and causes exactly what you described.
From contributor B:
Thanks for taking the time to give me advice. I tried some test pieces today using the tips from above and the results were better. Does anyone know if the Fuji 4 stage turbine HVLP sprayer would give me better results?
From contributor A:
1. What size compressor?
2. What N/N set?
3. What gun pressure (with pulled trigger)?
The Astro gravity gun should blow away most turbine guns with the exception of an Accuspray #10. That's if you have enough air supply.
From the original questioner:
My setup is a 4hp 25 gallon Sears comp that is 9.0 cfm at 40 and 7.0 at 90psi. Tip on
Astro is the 1.3mm. Having previous experience with the Campbell Hausfeld HVLP sprayer, I believe the warm air definitely is a plus when spraying NC lac on most days. But the CH sprayer is getting old and I thought I'd try a gravity gun. Having done so, I now believe a pressurized cup with a turbine is the way to go. The Fuji appears to be a step up from the CH sprayer and I've heard nothing but great things about it. Anyone have opinions on this?
From contributor D:
I don't think it will give you better results. I also think you would be better served by investing that money into a better compressor that can run that gun at its peak efficiency. Plus, the compressor will allow you to do other things better and use a wider variety of guns, but that is just my opinion. I bought a 4 stage turbine 4 years ago and although it did lay down a nice finish, for the price I paid I wish I had stuck the money into a bigger compressor at the time.
