How does a Moisture trap work?

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ImpactX

ImpactX

Member
May 4, 2019
636
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Minnesota, United States
I've seen people on YouTube saying they use moisture trap on their compressor over the cotton or desiccant beads. How does a moisture trap work. Idk but I was thinking its just a hollow tube where the moisture and oil collect at the bottom and get purge out? Correct me if I'm wrong.

My compressor comes with the gold filter on the left in the picture. It used a small cotton filter. I change it like once every 6 months. The filter would get soak with moisture and oil and it have corroded and rust inside the tube. I was thinking about taking out the cotton filter and just having it a hollow tube with nothing in it? Will the moisture collect at the bottom and get purge out? There are 3 holes at the bottom. Top hole is incoming air from the compressor, middle hole is for the guage, bottom hole is where it gets purge from the auto set purge. So would my theory work better than having a cotton inside the tube touching to walls and corroding it? Or does having the cotton is better. Maybe thats why hatsan and air venturi are using the cotton inside their filters? I don't know. Someone with experience with these water/oil separator can give your thoughts.

The right picture is the standard gold filter you get from ebay/aliexpress. It is the last defense before the air goes into the tank. 

20220310_134320.1646942061.jpg

 
@ImpactX Are you in the habit of removing the cotton plug after each time you use your compressor to allow it to completely dry out before putting it into the tube to use again?
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Nope. I dont remove it. It is built into the compressor. To remove it i would need to take off the fitting connection. Then take off the cap. Only do it like once 6 month or so. Do not want to keep taking fitting off and on each time I use it as it can cause leaks. 
 
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@ImpactX That’s likely the cause of the rust and corrosion. I have compressor that uses those plugs. After each use i remove the cotton plug, allow it to dry out and either alternate it with another cotton plug, or allow the damp one to completely dry before using it again. I also allow the fitting that contains the filter to dry out as well. If moisture remains trapped and the filter remains damp long-term, imagine what’s being pushed through the filter, line, and into your airgun’s reservoir? You don’t want rusty moisture entering your airgun. 


As for the the part media in your photo. To my understanding the beads are a desiccant material designed to absorb moisture. I believe the black stuff is some sort of activated charcoal. I’ll stop there. I don’t want to speculate and mislead you.


I have a filter that uses a desiccant bead type of media and I understand that it absorbs moisture. I’m really not the best person to explain it so I’ll defer to others with more knowledge of the subject. What I do know is that I tend to follow the manufacture’s suggested maintenance schedule when it comes to compressor parts, fluids, and filtration. There are other members way more knowledgeable than I. Let’s see what they have to say. 
 
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Impact,

The $125 copper-colored water separator, or moisture trap, contains no filter medium and is not recommended to be opened. I'm not sure how it works, there's a diagram explaining how on the eBay seller page, but it clearly works. I check the cotton filter in the small black YH filter, so far, clean and dry. Since my Florida garage gets very humid, during the rainy season, I consider it a must have. WM
IMG_20220226_110144.1646946874.jpg

 
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I believe what you're thinking of is a coalescing filter, though in my mind it's not really a filter as it doesn't have any media. A proper coalescing filter brings air in up at or near the top, and has a pathway causing the air to rapidly change direction, and possibly slow down. In doing so, the heavier water vapor & oil in the air can't react as quickly to the changes, and tend to settle out with gravity's help. They will drop down the cylinder to a purge valve at the bottom, cooling & coalescing (i.e. "coming together") along the way. The now drier & consequently lighter air will escape via another fitting near the top. I've only recently started using one, but from what I've read they can be quite effective when placed between the compressor's output and a desiccant filter (as in the right side of the photo). Another nice thing in addition to their effectiveness, is no media to worry about replacing.

The only ones I've seen for airgunning are made by Toauto, though they also use the name "fasttobuy20208" on ebay: https://www.ebay.com/itm/313595700705 (scroll down to see diagrams). They're available on Amazon & AliExpress, as well, all around the same price.
 
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the way i understand those cheap gold ones is the filter media cartridge pretty much does nothing but force the air 'around' it so it condenses water out on the thick aluminum body, then it pools at the bottom .. the cartridge may help it dry the air some but not much .. that said they are effective to remove moisture, but as mentioned above they need to be set up so they can be broke down and dried out after use or youll wind up with corrosion in them ... and particles getting into your equipment .. the cotton plug little filter that comes with something like a young hen traps particulates shooting out of the compressor ... those need to be broke open and drid out after use to or theyll corrode ...
 
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Just get some 13x dessicant from ebay and change it out every couple months. It's not a "trap" unless there's something to trap it. The cotton isn't great IMO and requires more maintenance. 

1lb of good desiccant will last years. (It's a lot of it) you can also use slices of those cotton filters as plugs at either end to keep the beads from going into the fittings/lines. 
 
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