Tuesday, August 19, 2014

Inline Desiccant Air Dryer

Build an inline desiccant air dryer for my shop to use for painting and sand blasting

Difficulty Level (Easy, Medium, Hard, Insane):

The most difficult part was by far to figure out how it works and then getting all the little pieces to put it together. The second hardest part was to weld all the parts together so they're air tight but let's start at the beginning.

I built a sand blasting cabinet about two years ago in preparation for my cucciolo restoration. Last year my neighbor found out about it and since he's restoring a mustang he asked me if he could use my sand blaster. This wasn't an issue during the winter but I've found out that during the summer the humidity clogs up the sand. In my research I learned that an air dryer  would/should solve the problem.

There were lots of small cheapo air dryers out there and then there were some more heavy duty versions such as the first picture below. Since I didn't want to spend over $250 for one of these including about $100 for two filters and $40 for the proprietary (#2 below) desiccant tablets I figured I'd try to build one myself.

As for drying agents (desiccant) inside, there are basically three common types:

1. Silica gel
2. Proprietary tablets
3. Activated alumina

Since #1 and #2 are very expensive AND #3 can be re-generated in an oven at 400 degrees for a few hours I decided to buy 10lbs on ebay for $40 bucks.

It was actually quite hard finding parts/materials for this project and I ended up using an old telepost I had lying around for the main pipe.

The way these dryers work is by filtering the air first, then slowing down the air speed in the large tube and run it through the activated alumina which adsorbs the moisture (adsorb = water sticks to the porous alumina), then runs it through a post-filter and out to the sand blaster or paint gun.

The dryer from princess auto or harbour freight
Diagram of the inline dryer
The package I got from ebay
The view into the top of the pipe
After I welded the top and bottom flange to the pipe
A close up of the welded flange
The spacer at the bottom keeps the desiccant from touching the condensated water at the bottom
After it was painted
First step done and painted
A close-up of where the intake filter attaches to the dryer
After the intake and post-filters were installed
I added a secondary silica gel air dryer as a gauge of when the activated alumina is saturated. The blue silica gel turns pink when it's saturated; that's how I know the activated alumina is no longer removing any air
The pipe that brings the dry air back down lower so it's easier to plug in tools
After the return pipe was installed
Close-up of the intake filter and the exit coupler
I had to make some custom gaskets for the top and bottom flange for which I attached a scalpel knife to my Swiss compass and cut circles out of modeling clay
Close-up of the cutting of the first layer of modeling clay
The two gasket "molds" ready for pouring of the polyurethane rubber
After the polyurethane rubber (reo-flex40 from smooth-on) was poured into the molds
Close-up of one of the gaskets after it was "poured"
16 hours later, the custom rubber gaskets were ready
Placing one of the gaskets on the top flange
After it was all done and installed on my shop wall ready for many hours of dry air
Measuring tape
Grease pencil
Angle grinder
Ear muffs
Safety glasses
Drill press
Rolling pin
Oxy/Acetylene torch
MIG welder
Screw drivers
Tap & die set
Adjustable wrenches
Channel lock pliers
Needle nose pliers
Bench top grinder
Bench top belt sander
Metal scribe
Center punch

One telepost
9" by 9" piece of 3/16" scrap metal
Three 1/4 NPT pipe nipples
Two 1/4 NPT elbows
Two air filters ($40 each)
Assorted scrap metal
2ft of 1/2 black pipe
5lbs of activated alumina ($40)
Polyurethane rubber (reo-flex40 from smooth-on)
Eight 5/16-18 bolts (3/4" long)
Black paint
Pipe sealant




Works great so far