Help me understand my HVLP gun

[ksechler]

Hi, I'm having trouble getting the hang of setting up my HVLP gun.  I sprayed some primer this weekend and wasn't happy with the results.  I'm hoping someone here can help me out a little.  I've watched to usual youtube videos and understand the controls, but because I'm inexperienced I don't think I know what the spray pattern should look like or what adjustments to make to get there.

 

Pressure seems to be my biggest problem.  I understand the concept of HVLP - high volume, low pressure.  Some of the paints I'm using talk about pressure at the cap.  There's no way that I'm aware of to measure this.  Obviously there's a pressure drop in the gun.  I notice, though that when I start to get to lower pressure at the gun (20 psi) the atomization is poor and the paint comes more in large globs than spray.  Obviously this causes  a poor finish.  Can someone explain pressure at the gun vs. cap and give me some pointers about where you are setting your guns. 

 

I also think that my pressure reducing setup may be inadequate.  What are you guys using for pressure regulation?

 

FWIW - I am using a dessicant air dryer, filter and mixing the paint per manufacturer's recommendations.  I'm also using the recommended tip size in my gun.  So I think I'm good there. 

[rcb280z]

The last time I used a HVLP set up I had to thin the material more than what was recommended by the manufacturer. You may have to experiment on thinning your mat. until you get the "finish" you are looking for. Might help to contact the HVLP manufacturer also for advice. I would thin the mat. a little more and then try on an old body panel standing up, vertical. Probably take a few tries at thinning but I think you'll get there.    

 

Im no expert BTW. But I know if it's not thinned right it wont spray right.

Edited October 5, 2015 by rcb280z

[siteunseen]

Mine has a knob at the bottom of the handle for regulating the pressure. A pattern knob on the left side up top. Flow knob on the back up top. I use more pressure but less material flowing.

Get a big ole cardboard box and test spray until you're happy. For me very light coats work best. Tighten the material flow knob.

At the worst, dig out the instructions.

 

Oh yeah, I thin mine about half and half.

Good article on set up,

 

http://www.how-to-build-hotrods.com/set-up-hvlp.html

 

Edited October 5, 2015 by siteunseen

[Patcon]

Site's pictures are good. You aught to be able to hold the trigger for a second to a second and a half and get the pattern on the far right. I have a special cap that I can screw on the front of the gun that tests the pressure at the cap. You really don't need it. I run 25-30 psi, if I remember right,  into the gun to get the atomization I like. I have never really had to over thin any paints I use. Most P sheets will state you can reduce an additional 10%. Do you have the P sheets for your products? I have a 3 ring binder in my shop with P sheets for all the products I use. If I need to, I make notes on those sheets for pressures or additional thinner desired. If you add more pressure the only issue it is likely to cause is using some additional material. I base all my pressures off of how it lays down. I adjust my fan to 10-12" wide for most work, adjust the flow until I get a decent pattern like the pictures and adjust my pressure so it atomizes well. I am using DeVilbiss finishline guns for most things...

[nix240z]

What is the brand and model spray gun that  you are using and which size nozzles?

 

 

for primer I use a cheap HF gun with 1.8 and for paint I use a Iwata's LPH400 1.4

Edited October 6, 2015 by nix240z

[ksechler]

All, thanks for the replies.  I think that my pressure regulation is inadequate.  I ordered a better regulator so I can get a consistent pressure setting at the gun.  I'll find out if that is the issue in a couple days.

[Patcon]

I run 2 regulators. I have a Sharpes dryair system where I regulate down to about 50-60 psi and then I have a small inline gauge at the gun and regulate that down to where it sprays the way I want. Nix's question referring to tip size is important too. Primers don't flow well through smaller tips. The P sheets will also make tip suggestions for their products. FWIW I would think 20 psi is too low...you need to regulate right at the gun because there is pressure loss in the hose...