Technical HVLP paint gun - clearcoat problems

First, my compliments on the quality of your work. I do have somewhat of a different opinion though about the importance of a compressors tank size......and the water separation issues often caused by mounting a water separator right next to the tank or on the tank. You didn't mention that but I feel that most people using a small compressor and small tank will have that scenario.

The problem is that a compressor expels hot compressed air that contains moisture. That air needs to cool somewhat before it reaches the spray gun. A large tank gives somewhat of an opportunity for that to happen, and thats one reason they have drains on a tank. Anyone who has ever drained a large compressor tank has seen how much water they can remove from the air. Its also best to have a water separator mounted some distance from the compressor and one just before the gun as well. I went to extremes on my system and actually use two 80 gallon tanks and a homemade condenser. Compressor pumps/compresses air and it goes about 15 ft then thru a copper tube condenser with a fan blowing on it. Continues thru the condenser and enters about mid level into an 80 gal tank. Moisture drops to bottom of tank and air rises and exits top of tank. Flows 15 feet back to main compressor tank and sheds any left over moisture as it enters tank. Then exits that tank and p***es thru a water separator/filter and into paint building. As pipe runs along the wall, a second industrial water separator with a 3/4 inlet/outlet should get any water that might remain. Overkill......probably, but I'm kinda **** about some stuff.

I installed a separate oiless compressor to supply breathing air. I was surprised at how hot the air was coming from it. I did not want to breathe that hot air. So I added a way to cool the air before it went into the hose and on to my lungs. Everyone should place their hand against their compressor tank and feel how hot/warm it is after pumping up. Might be surprised.

Point simply is that I don't question your expertise, ability, or results.......but I think that one of the biggest problems some people have is that their systems don't remove moisture or oil, and I think their tank size and water separator placement is something they need correct before they start experimenting with problems and results. This is meant to be a positive comment, so please take it as that as I enjoy your posts.

 

This Months issue of Hot Rod magazine has a pretty good article on spray gun designs and HVLP as well as Reduced Pressure guns and their uses.

 

True that! Condensation in the air lines is the enemy on air tools and especially painting equipment. Compressor with auto water valve in the bottom of the tank, 60 feet of copper, 2 drops with automatic valves, an electronic air cooler, regulator for shop tools and then a dedicated line to a desiccant dryer and paint gun regulator on my mixing bench. I add oil to the tools daily, not to the lines. Overkill? Yes. Water in my lines? Nope.

 

My son bought a nice place with an existing shop. Guy was a builder and had built the place as his own personal valhalla. Finished inside with A/C and a bathroom. Got divorced and then the new owners ended up divorced and my son bought the place. One of the things it came with was a 60 (or 80?) gallon compressor in a storeroom. It had a screwin drain plug in the bottom, but no valve. My son decided to pull the plug and install a drain valve in it. When he unscrewed the plug, water began spewing out and it flooded the storeroom and made its way out into the main shop. When it was done gushing out, it took a while to push all the water out and mop up. Apparently no one had ever drained it.



Billie..........is that an old pay phone on the wall? Man, you need to look into some of the newer technology.

 

Makes his cheap friends pay to call home!

 

I have a water filter that takes a roll of toilet paper in it. Put a new roll in it every time I paint a car. Never had a water problem. I do have drain legs at the end of all my air runs ,which are pitched down toward them.

 

My experience is all in Bakersfield CA where the humidity ranges from zero to just above zero. Never had the condensation problem. Moved to north Texas where the humidity ranges from 100% to almost 100% . So far my 60gal tank that came on the compressor plus a copper serpentine heat exchanger like shown above, heat rejecting, sloped to liquid traps copper piping, HF dryer has been working well here.

 

Your starting line gun requires 30 psi at the gun, when the trigger is pulled, to get 10 psi at the cap. Years ago I used one of those Sears portable compressor and could paint a car but it was slow going. If your regulator at the gun is reading 40 psi plus when you pull the trigger you’re pushing too much pressure, couple that with low fluid flow, and too fast hardeners/reducers, and you gun too far from the surface and you end up with rough/dry paint.

I suggest you open the fan control knob all the way as well as the control knob next to the inlet at the bottom of the handle. Plug in you air and pull the trigger, adjust the the pressure at the gauge to 30 psi. I use the needle adjusting knob to control the material flow.

As far as shooting clear, read your data sheet. It will indicate the amount of reducer that you may add to your mixed product (usually 5 - 10%). If you’re not shooting in a temp controlled booth your hardener/reducer selection is critical. If it’s warm to hot out (my rule of thumb is 70 degrees and up) I use a slow hardener and reducer. Lower temps I use medium hardeners and reducers. I almost never use fast hardeners/reducers, etc.

As it’s already been said, practice setting up and shooting some product. Can you get good results with inexpensive guns? Absolutely, it just takes practice… with that said shooting clear with an Iwata LPH-400-LV (low pressure low volume) is nice… you still have to have the right product and gun set up. BTW, the Iwata uses 16psi at the gun to push 10psi at the cap. This gun also takes a few minutes to get used to it because it puts out a soft pattern and you may slow down your gun speed thinking you’re not putting out a good product.

 

See, this is why I turn to the HAMB when I have tech questions. Lots of information & advice to digest here!
For those who asked:

• I do have a regulator at the gun. I leave my tank regulator wide open & control pressure at the gun. I've been running around 40 psi on the regulator with the trigger pulled; I re-read the manual for the gun & it specifies 29 psi, so I've been running too much pressure.
• I have a filter/dryer mounted about 20 feet from the tank. I also use a disposable filter at the gun (before the regulator so as not to affect pressure).
• I think my technique is not horrible....before switching to HVLP I was able to pull off some pretty nice paint jobs. Not as nice as Willys36, but not bad either. If I do a small job,(say a bumper or a dashboard) I can get a very good finish, it's on the larger jobs (like an entire car) where it goes sideways. Of course practice makes perfect & I probably don't practice enough....

Tonight I cleaned up my old compressor & found the ratings on a sticker. 7.2scfm @ 40psi, 5.6scfm @ 90psi. I believe the Starting line gun calls for 13 cfm. Honestly, it's been so long since I looked at the tank stickers I forgot the volume was that low. I knew I was on the low side of the volume requirements for the HVLP gun, but didn't realize I was THAT far off the mark. Oh well, I was due for a new compressor anyway. Maybe some new hoses too.

Once I color sand & polish my paint looks pretty good. But all the extra work is pretty hard on an old guy.

Thanks to all.

 

And those outputs were when it was new! Probably less now. Nevertheless, they seem kinda low for a 5hp power input?

When I recently replaced just the pump on my approx 30 year old setup, I immediately noticed an increase in output as evidenced by the vastly reduced time it took to pressure up and automatically shut off. Same tank, motor, controls etc, just the pump changed and some pipework to make fit.

Chris