Question on compressors & moisture

The warmer the air the more humidity it can hold. 100% humidity at 0 degrees is pretty dry air. 100% humidity at 105 degrees and you can actually see the humidity. Very wet air. When you use a compressor it heats the air up. Gasses that get compressed heat up (its a physics thing). When that warm air cools it can't hold as much moisture as when it was hot. It deposits this excess moisture anywhere it can like the inside of your airline. The further from the compresser the cooler and dryer the air will be. The air line acts like a cooling coil. The moisture trap catches the water that was deposited closer to the compressor and is pushed down the line by the air flow. The best place for a moisture trap would be at the airs coolest point(dryest point) which is close to the airbrush. A tank helps but does not stop the problem. To stop the spitting you need low humidity or a moisture trap. Some people get by  by spraying in an airconditioned space because the AC lowers the temp and humidity. Some get by because they live in an arid location. I lived in Florida and in the winter I could spray with few problems. However in the summer I always had problems. I have bypassed the whole issue by using C02 and a regulator. CO2 gas dosen't contain water vapor so all the problems with moisture are nonexistant.

MikeV wrote:

Bgrigg wrote: Oh Yeah? Sez who? It's the cooling that causes the condensation. Then why is it so hard to breathe in Georgia, Alabama and Florida in that warm, humid air? I personally believe that although an air tank may or may not cause more condensation, the water at least will fall to the bottom of the tank and not be as likely to be carried down the airhose as water is heavier than air. With a compressor without a tank all the moisture goes directly to the water seperator/regulator that the airbrush is connected to.

That's the mold!

Heat alone isn't the problem. That's why people who live in Southern California don't complain about breathing! You said it yourself "hot and humid. It's why there is a saying that goes "It's not the heat, it's the humidity". I live in an area that is pretty hot in the summer (100-110 fahrenheit is not uncommon), as well as very arid, and have had no issues with moisture in the line or tank.  

I'm no expert on compressors and tanks, but if an airbrush at 20 psi can pick up paint from a siphon, then I would surmise that an airhose exiting a tank at 20 psi can pick up water. 

My setup has a regulator at the compressor (100 psi throttled down to 60 psi) and another regulator on my spray booth that I dial as required, or wide open to clean my airbrush. I can't believe that any water (if present) isn't being pulled from the tank!

You are correct that water would fall to the bottom of the tank, but as the air decompresses, condensation can still occur in the air line.  That is why the closer your moisture trap is to the airbrush, the better. 

Bgrigg wrote:

Oh Yeah? Sez who? It's the cooling that causes the condensation.

Then why is it so hard to breathe in Georgia, Alabama and Florida in that warm, humid air?

I personally believe that although an air tank may or may not cause more condensation, the water at least will fall to the bottom of the tank and not be as likely to be carried down the airhose as water is heavier than air. With a compressor without a tank all the moisture goes directly to the water seperator/regulator that the airbrush is connected to.  

I have a small Aztek tankless compressor I use for airbrushing and a 25 gallon tank compressor I use for running air tools.  I have moisture problems with both of them.  For the Aztek compressor, I have a moisture trap at the regulator (which came with the compressor) and another moisture trap at the end of the hose ( I think that one is made by Iwata).  I live in Wisconsin and airbrush in my basement.  I have large humidity and temperature swings throughout the year, but with my current compressor setup, I no longer have moisture problems when airbrushing.

Russ

IYAAYAS wrote:

The 2 biggest factors that affect the air "quality" are the humidity of the air going in and the temperature of your work area.  I've seen a lot of people speed big bucks for an elaborate set up, and then get bent out of shape when they still get moister in their air. Think about it this way, your air comes out of your compressor warm, if you send it to a tank, it will cool and release moister.  If you place a moister trap between your gun and your tank it will help, but you'll still get moister. If you spray inside at room temperature in an air conditioned environment you may only need a moister trap. If you spray outside (garage type area) in relatively low humidity than all you need is a moister trap. If you spray in high humidity an air dryer is the only thing that will eliminate moister. If you spray in a cold area a moister trap will not be able to keep up and you'll need an air dryer. In my opinion an air tank does raise the amount of moister in your set-up, but it's not as big a factor as the quality of air going in.

Cool..... I spray inside, and it's air conditioned. And right now humidity is not a problem here in NC..... although in the summer it is. 

The 2 biggest factors that affect the air "quality" are the humidity of the air going in and the temperature of your work area.  I've seen a lot of people speed big bucks for an elaborate set up, and then get bent out of shape when they still get moister in their air.

Think about it this way, your air comes out of your compressor warm, if you send it to a tank, it will cool and release moister.  If you place a moister trap between your gun and your tank it will help, but you'll still get moister.

If you spray inside at room temperature in an air conditioned environment you may only need a moister trap.

If you spray outside (garage type area) in relatively low humidity than all you need is a moister trap. If you spray in high humidity an air dryer is the only thing that will eliminate moister.

If you spray in a cold area a moister trap will not be able to keep up and you'll need an air dryer.

In my opinion an air tank does raise the amount of moister in your set-up, but it's not as big a factor as the quality of air going in.

LOL- I can just see it! The "revenuers" raid my house because they think my airbrush is a still!

You guys trying to get me in trouble?  

Jon, I was having the same problem here in Atlanta with my old Badger 180 compressor. After about 15-20 minutes of running, it would spit water everywhere.  I ruined a 1/32 Hornet paint job that way when I lived in Rock Hill.  So tonite I ordered a CO2 tank and regulator.  It should be in next week.  I'll have to get the bottle filled at a local welding place but it's fairly cheap at $11 for 20lbs.  I bought the regulator from Dave Monnig @ Coast Airbrush and it is airbrush ready.  I know this doesn't answer your original question, but it is worth considering.

 

E

Oh Yeah? Sez who?

It's the cooling that causes the condensation. If you have a tanked compressor, and don't drain the tank on a regular basis, then the heating/cooling action during the day can on it's own cause moisture to form out of the air.

Your idea of a still's cooling coil proves my point. Without that rapid cooling action, you would get no 'shine at all! I don't think I would want my airbrush hooked up to a cooling coil.

Hot and dry is preferable to cold and humid, but the worst is hot and humid. You rarely hear people in Arizona complain about moisture, yet people on the southern coastline do. 

I believe an airtank lessens the water in an airline as moisture comes from heat which is produced by either the compressor motor or introduced into the system from the air, especially in humid climates like you have there in SC.

I would put my water seperator close to the airbrush and far from the compressor motor to give the air some time to cool. You may even want to try and make an airline out of copper tubing and bend it is circles like a cooling tube on a still for making moonshine. That would cool the air very well.  

Not sure about tank vs. no tank, but I have the little blue D500 and I use a built in (in-line about midway down the 10' hose) moisture trap and I have had no moisture collect in it at all. It's usually about 80-90% humidity every day, but then again I airbrush inside.

Bgrigg wrote:

Jon, The very nature of compressors means that moisture may be "squeezed" out of the air. For this reason a moisture trap is pretty much required, except in regions that are very arid. I feel that the relative humidity is actually a bigger source of moisture than what a hobby compressor like the D500 can put out. IMHO a tank is a storage place for air, and helps settle the air only. Moisture can collect in tanks through condensation, so I'm on the side that says tanks exacerbate the problem. However, the benefits of having an air tank out weight the problems, and I wouldn't be without one! I'm also of the opinion that the length of hose can also cause more trouble, again because of condensation and humidity, and have my moisture trap located as close to my airbrush as possible.

Thanks Bill!  

Jon,

The very nature of compressors means that moisture may be "squeezed" out of the air. For this reason a moisture trap is pretty much required, except in regions that are very arid. I feel that the relative humidity is actually a bigger source of moisture than what a hobby compressor like the D500 can put out.

IMHO a tank is a storage place for air, and helps settle the air only. Moisture can collect in tanks through condensation, so I'm on the side that says tanks exacerbate the problem. However, the benefits of having an air tank out weight the problems, and I wouldn't be without one!

I'm also of the opinion that the length of hose can also cause more trouble, again because of condensation and humidity, and have my moisture trap located as close to my airbrush as possible.