drying compressed air

[Patcon]

I have a 60 gal Ingersol Rand 5 hp compressor, when it runs a lot I have some serious water in the lines. I have a Jet coalescing filter in the main line (3/4") about 20' from the air compressor. I am looking into solutions to dry the whole system and to dry the air specifically for painting one of my cars that is coming back from the media blaster. I could use any help or suggestions for what others have done and the results. It can be very humid here in the south and with high temperatures making dry air can be a challenge.

Thanks, Charles

[Darrel]

I am no expert. But I did drive by a holiday inn express 20 yrs ago on my way to a super 8.

The best thing to have is a air dryer mounted away from the compressor allowing the air to cool a little before going through the dryer. One place I worked for had it placed right at the compressor and we still got a little bit of water, but not near as much when the dryer broke down.

My current job doesn't like to spend money and had an auxiliary tank to take care of the machines and then a direct line to the hand tools and blow off lines. It did have one water catch, but had to empty it on the hour every hour. I didn't want to climb up a 12' ladder every time I wanted to drain the water so I reconfigured the supply lines. I plumbed(air hose) to the auxiliary tank directly from the compressor. Then fed everything from the auxiliary to feed the machinery and every thing else. The auxiliary tank basically work as the air dryer condensing the water at the bottom of the tank. Not the right way to it by any means, but I had to work with what I had on the very cheap. There was still water, but it didn't gat past the water trap like it did before. Now I only drain the water once a week at the trap. The compressor and auxiliary tanks get drained every other day. BTW all the lines in the shop were plastic.

[Zedrally]

If your using a compressor, you only have 2 solutions. The inline filter you already have or an air drying system, which for a one off paint job is going to work our very very expensive.

Have you thought about using argon or nitrogen (there may be other gases out there as well, such as bottle dry compressed air ) ?

Certainly cheaper to rent a bottle or 2 or you could wait for a less humid day.

Edited May 23, 2011 by Zedrally

[EScanlon]

Darrel is correct, the further away from the compressor you put the separator the better it will perform. The only other way that I know to keep the condensation down is to keep the compressor pump and tank as cool as possible so the air doesn't get super heated and then it's hard for the separator to work properly.

The separator works by suddenly increasing the volume in the air line, while it maintains the pressure constant. The formula P=VT is the accepted thermodymanic method for determining it's pressure to volume / temperature ratio. With that formula you can see how the temperature drops directly related to the increase in volume. Do it at a temperature close to the dew point and the humidity falls out of "solution" (the air). Do it at too high a temperature and the drop in temperature isn't enough to allow the dew point to be reached.

That and empty your main tank often on humid days.

E

[Mike W]

I have a much smaller Ingersoll Rand which I use with a media blasting cabinet but had the same issue with condensation build up. It would get so bad that I would get water dripping from the hose connector where it attached to the cabinet.

I purcashed a filter / dryer from Campbell Hausfeld, which was a little pricey, but I managed to find it on line at Home Depot for about $80. I installed it close to compressor as that was the most convenient place for my setup, and no more water. This really worked much better that I would have expected.

The only issue that I found with this is that the dryer uses a desiccant and the unit comes with about 2-3 recharges. It starts out blue and needs to be replaced when it turns pink. Given the amout of compressed air that the blast cabinte uses, I was finding that I was going through about 1 recharge every 1-2 days. The replacement desiccant from Campbell Hausfeld was really expensive but I managed to find it in bulk at guess where, Harbor Freight, and I believe that I paid $4 for 8 pounds of it. Problem solved.

Here's a picture of the unit that I purchased.

[Tony D]

What you have when a compressor is done with it's job of making pressure is hot air, at 100% relative humidity. HEAT makes the ability of air to carry water much higher. Air at 120F can hold 2X the water that air at 85F can---with discharge temperatures of 270+F you can see that the amount of water the air can entrain goes up by factors!

Really, regardless of the relative humidity of the inlet air, the air at the outlet of the compressor is ALWAYS 100% saturated air. Unless you are running in Alaska in February and it's like -65F there will ALWAYS be a considerably amount of water to deal with on any air compressor with that much compression ratio (ambient to 125psig).

While cooling the air is a great idea, and it will help somewhat, it does not 'DRY' the air-all you end up with is 100% relative humidity air at a lower temperature. If you use an expansion device (air tool, spray gun) that has more than a 40psi pressure drop across it, the JT Effect will chill the air to the dewpoint of the compressed air and cause condensate precipitation. (This is the reference PV=nRT equation---you drop that pressure and you can figure out how cold that air will get, good engineers will devise orifices for impulse devices like cylinders and actuators in a Pneudraulic System so they don't hit that condensation point in normal operation...)

"Condensate Filters" only catch water in the line, they WILL NOT prevent condensation formation at point of use...they only stop previously condensed water in the lines from migrating down the lines to your point-of-use.

The only way to keep that air from condensing is to COOL IT BELOW EXPECTED JT EFFECT POINT. That generally means for home use in warmer climates a refrigerated dryer which chills the air to 35F to drop out most of the water, then rewarms it to 70F for storage in a tank. This way, on a 70F day, using a spray gun you will drop to maybe 50 degrees at the nozzle, you have less than a 30F drop and condensation is not an issue. Harbor Freight now sells cheap refrigerated dryers, if you have a continual high volume use this might be a good purchase. The BEST dew point you will be able to EVER get with a refrigerant dryer is around +35F, and that means it will now be effective for 'instrument grade air' below 65F ambient conditions. That means even if you are using a refrigerated dryer, if you have long lines and the temperature at night drops into the 40's, or below...you can wake up and start your work the next morning and find condensed water in your lines! For a painting job, it's likely overkill anyway, given the volumes of air needed and how long it's needed...

A Second option is ADSORPTION DRYERS---these are twin-tower dryers that can give you almost any dewpoint from +35 down to -110F. They in their simplest form waste about 15% of your air for it's purge cycle, and this makes them undesirable for smaller users at home. They are the standard for dry air industry-wide, though.

Another more cost-effective way for painters is DELIQUESCENT TABLETS. These are self-consumed tablets of lithium chloride, silica gel, or whatever that chemically absorb water vapor flowing along through with the air. Deliquescent dryers usually come in the form of a small vessel open on one end with a bail or screw top. You just open it up, put in the tablets, and then seal it up again--hook up your lines and go. The tablets are consumed in the process, usually a filter is downstream to prevent particles from making their way downstream. You open it up and drain out the residue after painting. I have a couple of older ZEXs and ZANDER deliquescent dehydrator vessels. They work O.K. and are pretty trouble-free. They will give you near Adsorption Dryer dewpoints, with are far more cost effective---especially for people who only need dry air for painting SOMETIMEs. I-R makes a small 'hotdog' dryer like this, you fill it with Silica Gel I believe (check with your local Air Center)... This is probably the best choice for the intermittent painters. Though the Zander units I got were from a paint shop---they just laid in a supply of tablets and filled up before every car. The big advantage is they don't waste air like a purging twin-tower desiccant dryer. Sometimes these are called 'DEHYDRATOR PACKAGES' and look a lot like the Filter Units, but are longer---sometimes 18" long, and about 2-3" in diameter. They take a dehydrator cartridge that you open like a grease cartridge just before installation.

Really, that is about all you can do. If you only cool the air down, you will not stop condensate formation at the gun due to the JT Effect. It has to be somehow dehydrated. What I have found is helpful to cool down the air before it enters your first tank (they do sell aftercoolers dedicated for this purpose, but I'm cheap...) is to grab a couple of old A/C condensers from the front of the car---they are good for 235psi in A/C use, and stacking a couple of them then putting a fan blowing across the whole shootin' match really chills the air down from the hot side of the compressor. You DO NEED AN AUTOMATIC DRAIN TRAP after this aftercooler---you will drop out a LOT of water if you can drop the air temperature from compressor outlet temperature to within 10F of ambient (and you should be able to do it with this setup---if you can't, go get another condenser or a bigger fan!) This will drop the majority of the water out BEFORE it gets into the tank. This makes your vessel last longer as well as you don't have active condensate (sometimes on Oil-Free machines, this can have a Ph of 4!!!) working on the unprotected metal inside the tank.

Another thing if you pipe the air in hard pipes is to ALWAYS slope the lines back towards the compressor tank so condensate goes back that way...and ALWAYS take the air off the TOP of the line! Even if you have a workstation directly below the pipe---take it off the TOP of the distributor line, then use a 6" standpipe up, and a couple of elbows to make the turn down to the workstation. ALWAYS extend the pipe beyond where your air coupler is, at least 12", so that if any water vapor DOES manage to condense in the lines overnight, it is down at the bottom of a 12" 'condensate leg' that can be drained or blown down in the morning before starting work by simply opening a valve.

There ARE now 'membrane dryers' out there that work by just having water vapor knocked out with special engineered membranes---they tend to be pricier than silica gel dryers, and usually for home use are limited to smaller flows, like 10SCFM. An airbrush might get away with it, but air tools and big body guns won't...

I linked some information at the bottom from the Van-Air site, another was "La-Man Extractor Dryer" they had several interchangeable stages, and the dryers could be piggy-backed so you could take out oil in the first one, then moisture in progressive stages through felt-pad filtration and eventually little dehydrator cartridges. I used these a LOT but have no real contact since my original supply (which I took over at a distributor who stocked them....) dried up (uh..) They seemed to work really well, and I see them out there still to this day.<EDIT> Hey! I found the La-Man website, so I linked it as well, these a neat little dryers and are relatively inexpensive given the alternative!<EDIT> Take a look below for the links to the Van Air Stuff.

I could, as you see, go on and on about this with tricks and crap... I have been supplying compressors and compressed air systems to industry for going on 20 years now, and have worked with air compressors (and compressors of all types) continually either as a technician or Factory OEM Rep/Engineer since 1984.

The LAST thing I will say is DO NOT consider the use of N2 or Argon---not only is is expensive, a dual-stage regulator likely will not keep up unless you have a very expensive one (we used a six-pack of N2 at my last commissioning and they had a hard time finding a regulator to provide 18SCFM at 7psig continually!!!) BUT MOST IMPORTANTLY if you are spraying (even outside) you are blowing massive amounts of non-life-sustaining gasses around. It is ENTIRELY possible that you could get one full breathful of nothing but this gas which would knock you out to the ground almost immediately...should you seize or convulse and the gun stay engaged you then blanket atmosphere the area with this deadly Oxygen-Displacing gas! If you are in a garage with minimal ventilation "Confined Space" protocol would apply, and anybody walking into the space could become engulfed and pass-out / die in short order. This is a VERY serious side effect of using inert gases in high volumes like spray painting. Even welding booths using 'SCF-H' (standard cubic feet per HOUR) of these same gases will require a forced-air ventilation. I don't think this was considered when that suggestion was made---it is a potential death sentence and I would HIGHLY DISCOURAGE this approach.

For the cost of a single T-Cylinder of gas, I'm laying money you will be able to find a suitable dehydrator package for your air line, and be really happy with how it works.

Deliquescent is more popular for 'gas':

http://www.airvacuumprocess.com/Desiccants-NaturalGas.html

Silica Gel has been preferred for 'air' for a while now--this is probably a good choice for your application:

http://www.airvacuumprocess.com/CompressedAirDryers/VanAirMD-35.html

This one is a 'regenerative' style, and is the 'next level up' from what you probably need:

http://www.airvacuumprocess.com/CompressedAirDryers/VanAirMHL.html

HERE IS THE LINK TO THE NEAT LA-MAN DRYERS! WOOT!

http://www.laman.com/extractor.htm

Edited May 30, 2011 by Tony D
Found the Link to La-Man Dryers! WOOT!

[pwd]

The only issue that I found with this is that the dryer uses a desiccant and the unit comes with about 2-3 recharges. It starts out blue and needs to be replaced when it turns pink. Given the amout of compressed air that the blast cabinte uses, I was finding that I was going through about 1 recharge every 1-2 days. The replacement desiccant from Campbell Hausfeld was really expensive but I managed to find it in bulk at guess where, Harbor Freight, and I believe that I paid $4 for 8 pounds of it. Problem solved.

Mike,

You don't need to replace the desiccant when it turns pink. Just sprinkle it out on a cookie sheet and put it in the oven at 350 degrees for 30 minutes and let it bake the water moisture out. It's good as new after that.

[BadDog]

When I set up my air system in my garage, I used black cast iron pipe, with two 6-foot "legs", each with a drain/valve. The first leg is near the compressor, so that the flexible hose/line from the compressor hooks up to the pipe about a foot above the drain/valve. The pipe then goes up and over the side/man door, then about 10 feet, then down the second leg. The top is sloped slightly back toward the first leg. The second leg comes down and has a drain/valve at the bottom, with my Devilbiss filter/pressure regulator about halfway down. I have a 25-gallon 12CFM compressor. I primed and painted several pieces and jambs over a year or so in all different kinds of weather. Then I shot color and clear on the whole exterior one warm June day. The compressor kicked on frequently, though it always kept up. Never had any moisture issues, though I always had some water in the tank at the end of the day. I don't ever recall water ever draining out of the iron pipe or the Devilbiss filter, but the pipe is the way to go to cool the air. Oh, and always vent the entire system after every use. I received advice to leave the system "open" when not in use to help keep everything dry. Seems to have worked for me

[Patcon]

Thanks for all the info,

I did not realize all these posts were added. Thanks Tony for the links. I had decided before I saw these post to add some 3/4" copper line between my first coalescing dryer and the air compressor. I also ordered a Sharpe DryAire 6760 to hook up on the other side of the shop and let it supply my fresh air and my paint gun.

http://www.sharpe1.com/sharpe/sharpe.nsf/Page/Dryaire+Desiccant+System

I am planning on getting an SAS fresh air system. I believe I will be good to go from there. Comments are welcome...

Thanks, Charles

[BadDog]

I bought a Hobbyair with a direct feed hood (positive pressure) and a pack of lens protectors. Relatively affordable, good visibiblity, and comfortable. When I was shooting the color and clear on my car's exterior on a hot summer day in my homemade booth for several hours, it kept me cool and comfortable...

[Patcon]

I have looked at the hobbyair. The air coming from a seperate pump would definately be cooler. Did you have the 40' hose? Were you able to set the fresh air pump far enogh away from the booth to not pick up booth exhaust? Was having an extra hose a hassle? I have looked at the SAS system that has a tap off for the spray gun instead. Only one hose to work with is the upside, downside is very dry air into the hood and air that may not be as cool as outside air. Thoughts?

Thanks, Charles

[BadDog]

I bought the version that had 2 hoods and 2 hoses - my brother wanted to be in on the experience, but the timing didn't work out. I think I put both of my hoses together, and put the pump inside my house (I have a detached garage) in case it rained. My booth was venting (through filters) out a side-window of my garage that was on the opposite side of the garage from my house. I never caught a whiff of anything :-)

To deal with the 2-hose issue, I duct-taped them together every coouple of feet of their length. It's not like my gun's air supply hoise was all that flexible anyway, so it didn't make too much difference to me. Maybe I had to be 10% more mindful of hose movement, but I was already trying to keep the hoses far away from my work as it was :-)

I bought mine from autobodystore.net If you've never been to that site, it's very helpful. Its run by a pro who caters to novices like us :-) Lots of very good advice on there, and he points out some very good reasons for the seperate air supply. Fresh, cool air unheated by my air compressor was a bonus, but I also wanted to make sure I had plenty of air for my gun. I have a 35 gallon compressor that puts out from 10-15 CFM depending on pressure, and it kept up fine with my HVLP gun even when the tank emptied and the compressor kicked on. But having my breathing air seperate from the gun air probably helped make sure that I didn't run out of air for my gun. Very important to have even pressure when spraying metallic paint :-)