Originally Posted by John McGraw

I absolutely disagree with the notion that either a refrigerated or desiccant dryer is overkill. In any compressed air system, the air inside the pipe will be completely saturated. That is to say, that the air inside the line will be at 100% relative humidity at all times. All the good advice about nice long runs and metal pipe to help condense water out of the air line, is very good advice, but the fact remains that the air is still going to be at 100% relative humidity, unless you introduce a process that drops more moisture out. You might ask why this is important, so here we go.

Assume that the temp of you shop is 80 degrees, and therefore the air lines and the air inside them are all 80 degrees, and the air is at 100% Relative humidity. As soon as that air passes through an air tool, a blast cabinet nozzle, or the nozzle of a spray gun, that temperature will drop dramatically, and moisture will condense to whatever moisture level equates to 100% humidity at that temp. This will leave little drops of moisture in your blast stream, or in the paint you are shooting. It is not at all uncommon for the temp at these points to drop to 40 degrees F, or even lower. When I use air tools for an extended period of time, I have to wear gloves, because the tool gets so cold!

Keep in mind, that relative humidity, is exactly that, RELATIVE. It is a measure of how much moisture air can hold at a given temperature. As the temp goes up, air can hold way more moisture, and as the temp goes down, it can hold way less. When the temp goes down, the moisture has to fall out of the air stream, until it reaches the saturation point (100%).

What a refrigerated air dryer does, is to drop the temp to just above freezing, to drop out the excess moisture, and then when the air warms back up to 80 degrees, the temp drops to less than 2% relative humidity!

This makes it almost impossible to condense moisture out inside an air tool or nozzle.

I have both a refrigerated air dryer and a desiccant dryer in my shop. The Hankinson refrigerated dryer drops the dew point to about +40 degrees F in most of the shop, and then I use the desiccant dryer for the painting regulator, and it drops the dew point to -40 degrees C on that line. Air used for painting can never be too clean, or too dry. Most commercial paint shops use this same level of dryness, and for good reason.
The desiccant dryer is kind of a pain to regenerate, as I have to bake the desiccant in the oven until it turns blue again, to drive the moisture out. Fortunately, this dryer is large enough, and with the already dry air from the refrigerated dryer feeding it, I only have to regenerate about twice a year. The refrigerated dryer is very low maintenance, as it automatically drains out the water as it accumulates. I pull the moisture trap off once a year to clean it, but otherwise it is zero maintenance. If you keep an eye on Ebay and Craigslist, you can find a clean, used 10-15 CFM unit for a few hundred dollars, and it is money well spent.


Regards, John McGraw

Originally Posted by Roger Walling

I have black iron in my shop for over 40 years and except for an occasional cleaning out the drain valves because of small rust particles, I have never had a problem. Besides that, black iron is easy to modify the system for additional outlets.

Originally Posted by Robert61

.... the fitting broke popped me once and flailed around a few seconds while the pressure bled down from the inside hose. It may be easy maybe neat and won't rust but DONT DO IT. Jmo

Originally Posted by Robert61

White pvc as you use for plumbing. My friends compressor is outside. He hooked it to the inside via a rubber air line. As o.o was changing the pressure switch the pvc adapter he used to screw the air line in broke. I hadn't even paid any attention to it being pvc until it broke. I replaced it with a metal fitting.

Originally Posted by BB767

I used Tansair:

http://www.ecompressedair.com/access...g-systems.aspx

in my old shop. It's powder coated aluminum pipe, uses compression fittings on the joints. It can be bent easily with a conduit bender to help the installation.


I have an auto drain on the compressor that you can vary the length and frequency of the auto bleed for moisture removal. The whole system has been in use for 11 years now with no problems. I do no paint work. The main air valve is turned off every night.

Thomas

Originally Posted by Railroadman

The blast cabinet will be using a lot of air so 1/2" line to that? What about going to the rest of the shop, for air ratchets, etc? Is 3/8" adequate for those? The inlet on the tools is only so big, and the pressure will be whatever I set it at, so it would seem I don't need 1/2" to all 4 corners of the building. Or am I wrong?

Originally Posted by Railroadman

Wow, NOTHING is simple, is it?

The compressor itself has a 1/2" outlet. Does going up to 3/4" gain me anything or does that initial limitation affect the whole system?

I was considering making the part from the compressor to the blast cabinet out of 1/2" iron pipe with verticals, like GTR1999 shows in post #26. Then using the RapidAir hose in either 1/2" or 3/8" downstream of that. Thoughts about that concept?

I will add that this is for a hobby application, not commercial production. Unless my son is in town or a buddy is over, it's a 1-man operation (me) and if I'm blasting I won't be using an impact gun and vice versa.

You mention the pump scrolling up to meet demand. I was hoping the 60 gallon tank would be a hedge against instant pressure drop. The compressor output is listed as 18.1 CFM at 90 psi, while the blast cabinet says it takes 9.1 CFM @ 90 psi. In theory that sounds like it should work, but there are a lot of 90 degree bends in that pipe setup in the pic so maybe not.

Later tonight I'll look on that RapidAir flow calculator you suggest. In the meantime, does this post's additional info change any of your recommendations?

Thank you!