Air-Drying Systems for Large-Volume Spray Operations

If you're spraying a lot, get serious about a clean air supply. September 14, 2006

Question
I am considering putting in a desiccant air drying system to get rid of contamination in my compressed air. If anyone has experience with this system, good or bad, I would sure appreciate any info.

Forum Responses
(Finishing Forum)
From contributor R:
How much are you spraying? The desiccant dryer is only for water. You need both a water separator and oil filter in front of the dryer and they need to be sized to the amount of CFM you use for spraying. I have filters and dryer from Grainger and it works well for me, but I don't do a lot of spraying (two-three days a month).



From the original questioner:
I have 4 booths working 40 hours a week. We already have the water and oil filters, but we still have a small bit of contamination that is occasionally causing micro-bubbles. Our compressor oil is not the problem, so we are going after the water.


From contributor J:
I use a Sharpe desiccant filter. It has a couple pre-filters also. Works awesome. I don't have a dryer and it keeps up.


From contributor O:
I use an RTI oil and water separator. It solved my problems with air contamination. I change the filters once a month just to be sure. It's a small price to pay for quality assurance. Another thing you can do is put in a compressor that is only used by the spray booth.


From contributor T:
Your description does not make sense. Micro-bubbles are caused by solvent entrapment. They look like tiny pinholes or 7Up bubbles. I think you may be describing fisheyes. They are caused by contaminants and have ring or crater around a small hole or area where the wet coating pulls back into the shape of a pin hole. Water will not typically cause a fisheye. Water will turn a solvent coating white or blush. Oils or waxes will cause a fisheye. So the solution is to find the source of the contaminant. This is why an oil filter or trap is being recommended to you rather than a desiccant. If the source is not obvious and you have a good and working oil filter, look for outside sources of contamination. I've seen orbital sanders drip oil and then sand it into the wood. Once it's in the wood, it will always fisheye. If you still can't lock the contamination down after all of that, you may want to try a fisheye eliminator additive like Smoothie, but I'm not a big fan of adding it unless you have to.


From contributor R:
That big of an operation, you need a refrigerated dryer.


From contributor B:
I agree - if you are shooting more than 50 gallons of material per day, you need a refrigerated system. To add to contributor T's comments on contamination, WD-40 on a grease rag on the other side of the shop can cause it. I have even seen it migrate from a rag in a guy's back pocket and land on a fresh coat of precat - boom, fisheyes. Silicone should be banned from all parts of the wood shop and everything cleaned with toluene to eliminate this possibility.


From contributor Y:
We spent the big bucks on a new Kaeser SM-8 screw compressor with a refrigerated dryer. It's quiet enough to answer the phone standing next to it. The desiccant in our old desiccant dryer was dark blue (wet - on a hot summer day you could spray a continuous mist through an air nozzle). Within a day it was pink again from the (Sahara Desert) dry air going through it. We're a small three man shop with a $7,000.00 compressor sure, it's overkill, but my compressed air worries are gone for good. If you can't afford the whole setup, start with the dryer. A desiccant dryer may help, but a refrigerated dryer will work.