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Wet Compressed air for sandblasting
Old 07-06-2004 09:22 PM
Smokstak Smokstak is offline
 
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I have just starting sandblasting a bunch of parts and my air supply is way too wet. I have two cyclone air separators in the line between my air compressor and my blast cabinet but it’s still too wet. Now what do I do? How can I get very dry air without spending an arm and a leg? – Joseph

Could the location of the separators have anything to do with it? I have a bank of four separators located right off my compressor and I have never had that happen. I don’t know if the quantity of separators or their location might make a difference. Just a thought. – Allen

Try this: With a full tank of air, drain the tank of any water. Let the tank sit at rest for 30 minutes and then drain again. Clean and dry both water separators. Don't forget, you will still have water in the air hose. Dry it as best you can. Preferably, hang the hose and let the water drain out and dry. If you can, add another water separator at the blast cab. Let us know what happens. By the way, do you live in a very humid area? – Jim

As said previously, make sure your receiver is thoroughly blown down (drained) and ditto for your moisture traps. Typically, one moisture trap will be located close to the compressor/receiver, but one is needed at the far end of any hose run as more water will condense in the long hose run. I like to have only a short length of hose from the last moisture trap to the blaster. Make sure that you start out with a dry system and hoses. If your receiver has a slug of water in it or your hoses have pockets of water in them, you may not get the water reduced to an acceptable amount at your tool. Moisture traps that are close together don't add much drying as the moisture doesn't condense in the short distance between them, thus is passed on down the line to condense. Long hose or pipe runs condense additional water. Low spots in the hoses or pipes form pockets of water that may overwhelm the moisture traps as your work time accumulates. Have your final trap close to your work. This may help. -- Kid

I had the same problem when I got my cabinet. What I ended up doing was running 150 feet of 3/4 copper air line from the compressor to the cabinet. Then I went and bought a DeVilbiss 3 stage air drier system that is used in body shops. It has a pre-filter then charcoal and then desiccant. I have no water in my air. Another thing is that you need a large air compressor. I have a 7 H.P 2 stage. If it's too small it will run constantly and heat up the air and create a lot of water. Before I did all this I could only blast for half an hour until my cast parts would turn rusty. Now I can blast all day if I want. The desiccant lasts about 1 year with moderate use. – Rudy

Joseph, I ran into the same problem using a 55 cfm pump @ 120 lbs for blasting. I had a filter and water trap at the compressor and also at the blaster. I ended up adding 50' of hose between them to allow the water to settle a little and it helped. That compressor creates a lot of heat and the water couldn’t separate quick enough. The ideal cure would be an after cooler to speed up the process. Perhaps by using a coil of copper tubing in a bucket with cold water flowing into it? Just a thought. – Randy

(The key solution follows…)
I run my air through one inch black pipe with traps at the beginning and end like that shown in the TIP book. I don't usually have any problems unless the humidity is high for days and I do a lot of blasting. -- Paul

The coil of copper in a cold bucket works amazingly well. It is slightly more complicated than just coiling the tubing in the bucket. I built one in a 55 gallon drum and I can sandblast in extremely humid weather. If anyone is interested I can draw a sketch of mine. – Roger
Are we drying air or making whiskey? – Patrick
Same principle - removing condensation - just one difference though - one is more palatable than the other! – Andrew

I live in Central PA and I have never thought it was overly hot or humid here. Then again I am a boiler operator in a power plant so what do I know about hot or humid, everywhere other than work feels air conditioned to me. But, the compressor is upstairs in my shop and I do think it might be a little warm up there for it. I am toying with the idea of running some copper coils thru a window air conditioning unit, it seems like a win-win situation to me, dry air and A. C. in the shop. – Joseph

I’ve been reading about refrigerated air driers and I think it will work. A coil in front of the cold output side, a separator, then a pass in front of the condenser or hot output side to warm the air up a little so it doesn't sweat in the lines, then another separator, and one near the cabinet. I am also going to bring the compressor down stairs, this will make it easier to service anyway. I have always hated changing the oil on the ledge that it is currently sitting on. When I decided to put it up there it seemed like a great way to save floor space but it has become an enormous hassle to work on. – Joseph

I have used an old 80 gallon tank in line just ahead of the blast cabinet. This allows the air to cool before it goes into the water separator, which is just before the sandblaster. Most of the water stays in the compressor tank, or the auxiliary tank, and the last bit stays in the water trap. I empty all of the drains frequently. This works even on humid days, and it's cheap. The extra air tank also allows a longer duration of blasting before the compressor can't keep up. We have used the coil-in-water idea for cooling the breathing air for the sandblasting helmet on big outdoor jobs. We had 50 ft of 3/8" coiled in a cooler with disconnects on both ends. Fill it with 5 gallons of water and a bag of ice and it's like air conditioning, you never want to take the helmet off. Good luck! -- Al

Most of these posts have touched on the problem. Hot air holds more water than cold air. The harder you work your compressor, the hotter the air. Four water traps at your compressor won't help much because they only begin to work as the air cools. The fix: use an adequate compressor, pipe air lines in black pipe (safer than PVC and it doesn't sag). Incline pipe slightly (4" in 50 ft is OK) to drain water away from compressor. Set water trap at least 50 feet away from compressor. When you tee off your lines tee up and elbow down to water trap so the water in the line passes by to the drain leg at the end of the system. Desiccant and refrigerated driers are great too expensive. I've seen some effective systems in body shops where they ran a coil through an old refrigerator. – Dick

Many valid points have been made above and this thread hit close to home where I have a DeVilbis 6.5hp, 17cfm, two-stage compressor on an 80 gallon tank. I used ¾ inch iron pipe to run a sloped air-line across the ceiling of my shop to the bead blast cabinet. At the bottom end of the line as it comes down the wall, I placed a drain valve. Above that, there is a T, which goes into a dryer and then the regulator. After the regulator, another T runs through the wall to a valve and spigot outside for sand blasting. Off that same T, a line goes into the bead blast cabinet via the foot valve. It all works in Florida! You can’t get much more humid than in Florida. Keep the compressor, dryer and line drained! The air is cooled as it passes through the iron pipe and then water is caught in the vertical riser and then any mist is finally caught in the dryer. This may not be dry enough to spray paint with, but I’ve never had a problem blasting with glass beads. – Harry

See my sand and glass bead blasting story at: http://old-engine.com/abrasive.htm

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