View Full Version : Dessicant in air lines?

Dan Hintz
01-05-2009, 4:24 PM
For those running shop air in your air assist lines, do you use a desiccant pack or simply a moisture/contaminant trap? If using a desiccant pack, which one do you prefer?

Mike Mackenzie
01-05-2009, 5:31 PM

We tried them both and quickly decided to remove the desiccant, What we did was to put water traps in-line and that worked very well. We use two one right off of the compressor and one down stream before the laser. We also use a loop method run the air line up to a high point and then back down to the water trap that way the moisture in the line goes to the lowest point the water trap then we go back up to the laser. Eight years with this set-up and not one drop of water in the system.

Tim Bateson
01-05-2009, 5:35 PM
Mike, what was your deciding factor? Was there any pressure differences?

Mike Mackenzie
01-05-2009, 5:47 PM

My decision was based on dealing with the desiccant it seemed to get wet much faster and once it was it has to be dried or replaced. The time to dry it is substantial even though you can bake it it still can take several hours and you can only do this a few times before it becomes in ineffective. The pressure lost had nothing to do with it the water traps you open a valve and drain thats it and you can even get auto draining ones now just be sure to put a bucket near or under the trap so the water has some ware to drain.

Tor Amundson
01-05-2009, 8:41 PM
I use an inline dryer from Harbor Freight:


Got it on a sale day, combined with a coupon, for about $250. Just for safety we also run a basic moisture trap (from Craftsman) just before the valve by the laser, but to date we've never had a drop of moisture to empty from the trap. The lines have been super-dry ever since adding this.

Note: I didn't just buy the dryer for the laser. I'd bought it about a year before I got my VLS4.60 to use with my Miller plasma cutter, so it'd been in service for a good amount of time before I moved it over to lasering duty.

Tim Bateson
01-05-2009, 9:56 PM
Thanks Mike. That's a Serious dryer Tor! :eek:

Andrey Anfimov
01-06-2009, 2:36 AM
If anybody use this Miniature Desiccant Air Dryers <http://www.airdryers.com/rdmd.htm>?
It seems to me very suitable for laser engraving.

Rodne Gold
01-06-2009, 3:27 AM
Some Vapour in air lines is not a real issue , and in fact water is not an issue unless your air assist allows that water to get onto lenses or mirrors. (like pressurising the lens box)
We run 6 lasers and various other air dependant products with simple water traps , and have been doing so for many many years without any issues.

Dan Hintz
01-06-2009, 7:27 AM

While they aren't pressurized, the PLS series from ULS screens their optics at every turn with an air curtain. At the moment I have a basic water/contaminant trap (Craftsman, bought it with the compressor) at the laser, but wondered if I need to up that with an additional desiccant pack. If I decompress a single tank of air (33 gallon), I get a few drops of water from the compressed stream.


Those dryers look about the right size for this application, but I'd like to find something easily obtainable (mail order, local Borg, etc.).


Nice, but way overkill for me :p

Dan Hintz
01-06-2009, 7:37 AM

I meant to mention... that water trap right off of the compressor is probably not doing much for you. You need to give the air a chance to cool and let the water condense before hitting the trap, i.e., let it run through 25'-50' of hose before hitting it.

Dan Hintz
01-06-2009, 8:15 AM
Spent a few minutes searching and found this 3/8" rechargeable one for $82 shipped:

This is the cheapest I found, starting at $95+S/H at the first site Google popped up. They also have 1qt bead refills for $17.

Your thoughts?

Scott Shepherd
01-06-2009, 10:02 AM
Dan, we tried the packs. In the summer, we'd saturate the pack in minutes and it'd be all over.

Finally ended up with a refrigerated air dryer from SpeedAire. No worries at all now. I've seen the moisture trap fill completely up during the summer, and not a drop of moisture coming out of the dryer. Not cheap, but it works very well.

Dan Hintz
01-06-2009, 10:06 AM

During the summer I have a hefty dehumidifier running, which appears to do a really good job. While it's not designed to completely dry the air, I wonder if it would take care of the "saturated within minutes" issue...

Rodne Gold
01-06-2009, 10:13 AM
If your optics get the air assist stream..you MUST make sure you have dry air , the lens is especially prone to problems if it gets water spatter and even worse problems if that water contains any oil.
Mirrors are generally polished steel with a gold plating , so cant really be harmed that much , but the lens and coatings will burn with moisture drops or oil/water.
I suppose it depends on the climate as to what strategy you adopt..non of our machines use the air assist to presurise or blow on optics and I live in a meditteranean climate (wet winters , hot dry summers)

Scott Shepherd
01-06-2009, 10:15 AM
I don't know Dan, I was at my wits end trying to resolve this on the cheap. I'm in a conditioned space, it's an office building, 6 stories tall, and I'm sure the space never gets damp in here at all, but for some reason unknown to me, for about 1 month, I couldn't stop the water from coming out of the compressor. Tried everything and nothing worked. Finally got this dryer and haven't had any issues.

It ain't cheap to give the ULS system what it requires, I do know that!

Mike Mackenzie
01-06-2009, 11:47 AM

When I said right off of the compressor is at least 10-12 ft. We also found that using steel gas pipe for most of the run reduced the moisture as well. Our air setup is run through-out the shop. On the laser we put a coalescing filter, water trap, regulator, and a ball valve.

Bill Cunningham
01-06-2009, 5:51 PM
If you want to increase the the ability of your simple water trap, you can do two things.. 1. fill it with marbles.. the spheres add a huge amount of surface area to collect water. 2. Keep your water trap at the highest working pressure you can. i.e run your regulator downstream from the water trap, and keep your lines above 100 pisg at least (more if you can...much more if you can). Also, Activated alumina is probably your best desiccant for low pressure air systems, it's cheaper and lasts longer than silica gel or molecular sieves. Most commercial low pressure breathing air purification system use it in two units, and dry it in cycles from chamber to chamber with a reverse flow of warm air..