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Eliminating moisture in air line?

PostPosted: Tue Dec 31, 2019 9:46 am
by Ralph_III
Hello All,
Can anyone offer suggestions to further eliminate moisture in my air line. I will be painting the hood of a vehicle and have the following setup.

Industrial compressor (outside) with 60ft galvanized pipe leading directly to my filter system/hookup. I then have about 50ft or 60ft of air line hose for my spray gun.

1. My end of line filter system is as follows......water separator with drain and then an affordable 3 stage filter system consisting of a Particulate filter, Coalescing filter and a Desiccant filter as pictured

2. I am also utilizing one of those disposable air line filters (red bulb) at the spray gun itself.

Prior to painting I drained moisture from both the compressor and the end of line water separator. I had hoped to turn off the compressor while spraying and then turn it back on while the paint was flashing and prior to second coat (Repeat). I don't think I will have enough air from the 80ga tank to make a complete pass over the hood though so that may not be possible.

Anyhow, I sprayed 3 coats of base coat over a 1ft x 3ft section that I had repaired and primed. I just wanted to check the color and in testing out my new SATA 5000 RP 1.3 gun. The gun laid the paint fine and it matches perfectly. However, when I disconnected the air hose at my filter system I could feel quite a bit of moisture blow out. In addition, a portion of my desiccant beads are already turning pink. I don't think I could even apply two coats on the hood before the beads needed replacing/drying.

Anyhow, I am not sure how much of the remaining moisture the disposable filter at the gun is picking up but I wouldn't feel comfortable apply a clear coat at the moment. Any suggestions?

1. Should I use a different disposable filter at the gun or one of those DeVilbiss desiccant snakes or both?
2. Should I add a second Desiccant filter or Coalescing filter on my filter system?
3. Should I also install a drop down galvanized pipe prior to the filter system with a drain? As it stands, the galvanized pipe from the compressor runs directly to the water separator (which has a drain) and is immediately before the 3 stage filter system.

Thanks for your help.

Re: Eliminating moisture in air line?

PostPosted: Tue Dec 31, 2019 10:35 am
by DarrelK
Trying to eliminate moisture closer to your points of use is problematic. It is much easier to simply loop more rigid pipe up and down allowing for the moisture to crack out long before it gets to those points of use. One thing of concern you mentioned here is that your compressor is outdoors.... to me that introduces more "variables" into your system as temp.s rise and fall throughout the day..... and is that initial 60 foot run underground or just out in the open?

Re: Eliminating moisture in air line?

PostPosted: Tue Dec 31, 2019 2:53 pm
by OldFatBald

* What part of the country are you located and what is your weather currently like?

I have my compressor mounted outdoors, but I am in Nor Cal and the compressor is in it's own little open faced shed on the north side of the garage and is blocked from direct sun.

Re: Eliminating moisture in air line?

PostPosted: Tue Dec 31, 2019 3:37 pm
by '68 Coronet R/T
You should have some sort of drop in your piping before the filtration system.
Here's a picture of a standard pipe layout. This is just to give you idea of how the system should be set up. There are a lot of ways to accomplish the same thing with doing it exactly like this but at least you get the concept.

Notice the drops (drain legs) with valves on them. Any additional moisture should collect there.

Re: Eliminating moisture in air line?

PostPosted: Tue Dec 31, 2019 4:18 pm
by OldFatBald
The reason that I asked what part of the country you are located in, is that dealing with compressed air has many input variables and the volume of condensation that a compressor produces is based on multiple factors including pressuring level, aftercooler factors, intake air quality including relative humidity and the ambient air temp.
Hot and humid air has a higher moisture content than cold air, it will result in more water coming out of the compressor.
Also, if the inlet temperature going in is higher, more water content will be present in the compressed air.

From college days thermo dynamics (many many years ago);

* Air is a compressible fluid - which is the reason NOT to use PVC for compressed air distribution
* Non-compressed air has water in it (along with other stuff) and you need to do something with it (remove it)
* Compressing the air, heats the air.
* Hot air can hold more water vapor than cooler air.

Both the radiator style of piping or an inline expansion tank with an auto drain at the bottom can help remove some of the now cooler excess water and should be placed upstream of your desiccant dryer. I built my inline expansion tank out of a five-gallon air tank placed vertically on the wall prior to my first water separator. The inlet is down low on one side, an outlet on the other side up higher and a $25 auto drain placed at the bottom. One of the gas laws states that Pressure = Volume x Temp, the pressure is basically constant, the volume goes up therefore the temp goes down and holds less water.

Basically, cool the air prior to your filters if possible and allow for drains such as 68 shows above.

Re: Eliminating moisture in air line?

PostPosted: Tue Dec 31, 2019 6:13 pm
by DarrelK
Yep, all that^^^^^^^^^^^^^^^^^^^^^^^^.

Re: Eliminating moisture in air line?

PostPosted: Wed Jan 01, 2020 1:44 am
by Ralph_III
Hey guys and thanks for the input. Many years ago I actually considered setting up a paint booth and even spoke at length with a SATA tech who was willing to come out to help with my setup (impressive). So I had a good general idea of a proper setup but I just didn't have a proper understanding of the importance each plays. Your input has helped me in this regards.

I was able to examine our compressor and air lines a little more thorough today. So consider the following.

1. The compressor is 80ga and puts out about 25cfm. It is outdoors but under a covered area so the sun never shines on it with exception of a very short period in the morning. I think I can actually spray the entire hood with it turned off. I can then recharge it and drain the lines prior to applying the second coat (etc). This should help with moisture, correct?

2. There are actually two drop downs. Neither had been used in many years so both were full of water. I think this was one of the major issues because there was really no place for the water to collect prior to my filter system. I can utilize them now.

3. I live in Mobile, Al. so humidity during the summer is a way of life down here. It's actually pretty low at the moment due to the cooler weather and clear skies.

4. I can add additional galvanized pipe and vertical tee's with drop downs and drains.

5. I also have a 100ga or 120ga tank myself. Could I expect a significant benefit if I connected this to the system somehow? It would be a pain but if the benefit were significant then I'll do it.

6. I'm still inclined to add a second desiccant filter?

Let me know what you think would be most beneficial.

God Bless,

Re: Eliminating moisture in air line?

PostPosted: Wed Jan 01, 2020 2:03 am
by DarrelK
Ralph....I think I'd start simple here. If two of the drop legs were full of water I would not be surprised if the rest of the system was "siphoning" off that water as the air flow went over them. Just dump em' and try your system. They may be enough to take care of your problem with no more than you have to do here.

Re: Eliminating moisture in air line?

PostPosted: Wed Jan 01, 2020 2:04 pm
by Ralph_III
Thanks DarrelK.

Yes, I am curious to know exactly how much if any benefit the two drop downs will now provide. I'm not overly confident they will completely rectify the issue though.

In case it doesn't, what about installing a DIY after-cooler into the system? I saw an excellent YouTube video where a gentleman is using a transmission radiator as a pre-cooler. Others are doing the same and it can be seen

I couldn't install it on our work compressor but I could install it at the end of the line and prior to my filter system. I could then use a box fan and even hose water to cool the radiator.

If my moisture issue isn't rectified could I expect a significant improvement with the radiator or would you just add more drop downs and a second desiccant filter? What about misting water over our compressor with use of a large warehouse box fan?

God Bless,

Re: Eliminating moisture in air line?

PostPosted: Wed Jan 01, 2020 4:46 pm
by OldFatBald
I agree with Darrel, try your current setup since you have cleaned it.

Make sure that you have drains at the bottom of your loops or drops. The little 1/4" npt quarter turn valves work great. Just make sure to drain them each time you get ready to paint.

I don't think that misting your compressor is going to help as you are dealing with a huge air reservoir - in calcs we consider the surroundings "infinite".

The actual compressing of the gas (air) is where you are generating the heat.

On that air to air intercooler, how large is the tubing? In theory it should help, but you would want to help it with a fan to move the air across it. You also want the air to not have to move through it so fast (small tubing) that it doesn't have a chance to give off its heat. Here's another equation (yea!) Flow (Q) = Velocity (V) x Cross Sectional Area (A), your flow is constant, so smaller cross sectional area (pipe diameter) the velocity goes up.

If it works and you have now cooled the air, you still need to remove the water. Adding a 5-gallon (or whatever) expansion tank immediately after it would give a place to collect the water that has essentially been squeezed out of the cooled air.

You want to remove as much water out of your compressed air prior to your desiccant so that you aren't just replacing the desiccant media too much.

I don't see why a second desiccant filter would hurt as long as it isn't inducing too much of a pressure/flow drop - which it shouldn't. But if you are still having that much water vapor going through your system, you are going to be changing (or drying out) a lot of desiccant material.