Originally Posted by hduff
I had the chance yesterday to use a friend's Eastwood soda blaster to clean up some vintage auto trim. It did a nice job except for the problems with moisture. I would not want to use it on anything large; yes it would be a PITA.
Moisture in air lines how does it get there? Well let me first explain a little bit of physics. Air that is below the temperature of 32 degrees Fahrenheit can not hold water because the water freezes and falls out. So the opposite holds true: The hotter the air the more water it will hold unless you are in an area that is very dry. In humid areas as the air temperature rises it absorbs more water. Now on a humid day of 80% that means that the air is saturated with water vapor to a percent of 80. Ok so our air compressors take in humid air and compress it by about 9 times. Water does not compress so it winds up in our compressor air tanks and lines. Also compressed air is hot and when it leaves the air compressor it starts to cool and this also causes the water to drop or fall out.
Now with all of that said how do we work around it? Well you can buy one of the high dollar driers that cool the air to below freezing before it enters the compressor or you can buy one that cools the air after it leaves the compressor. These are very expensive but they do a good job. They are actually refrigeration units. I once worked at a shop that had one and it was great. Another way is a trap or filter that uses desiccant. These work good but you have to change the desiccant cartridge from time time and they too are kind of pricey. I have seen some of the high dollars units (thousands of dollars) that contained both desiccant and chilled the air.
I've been at it now for going on forty years and I have fought moisture all along the way. I don't do much blasting any more but I still paint and I use a plasma cutter attached to shop air and the moisture can really create problems in all of these. For years I have used the old standby toilet paper air filter (real cheap) and I usually replace it for every job. I have tried all kinds of traps and made a few of my own and some worked and some didn't. But a few years ago I came up with another idea. I have already posted it in another thread so I just copied and pasted it here:
Now something that you guys may not know is to use an old house steam radiator as a water trap. You can pick them up cheap at building wrecker yards. They can hold a lot of pressure and usually all that is wrong with them is bad fittings and you will change all of that anyway. Plumb it so the air from the compressor goes into the bottom at one end and leaves at the top of the other. Depending on what type you find you may have to drill and tap a hole to accomplish this. You may even have to use a bung and this could be brazed on or silver soldered. Place it so that air can get to both sides and put a water trap down low at the outlet side or end that is farthest away from the compressor, I have an automatic spitter valve on mine. Be sure to slope it about an inch toward the spitter. On hot humid days I put a shop fan on one side of it but I have found that this is not necessary during the winter months. You will be surprised at how much water it collects.
For insurance I still use a fresh roll of toilet paper in the toilet paper filter when ever I paint a car but the steam radiator works great for everything else.
I hope that this helps with the water problem.