# condensation in compressed air tank



## bstickler92 (Apr 15, 2010)

i'm not sure if this is the right place to ask but i'm trying to think of ways to keep condensation out of a metal compressed air tank. it says i should destroy it in 2016 for this reason. would a packet of desicant(sp?) inside the tank take care of this or would a more expensive in line air dryer do the trick? btw, it's a 5 gallon vehicle mounted tank compressed by a 12v compressor so it will be used by me quite a lot once i finish the system. so back to the question. waterproofing the inside of a compressed air tank.


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## mosquitomountainman (Jan 25, 2010)

I don't think there's anything you can do except drain it often. The water in the tank is a byproduct of compressing/decompressing the air. External filters and water separators will only work on the air pumped to the outside of the tank. Any dessicant you use will be saturated very quickly and be worse than nothing at all.


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## horseman09 (Mar 2, 2010)

I'm shooting from the hip here, but it seems as though you could rig some sort of an external dryer. Hmmm. Maybe layers of desicant in a 5 gallon bucket on the intake? In other words, pass the inlet air through the closed dessicant bucket. ??

I don't know if this is recommended or not, but I tilted my new compressor on its back and squirted some of 10W-30 mixed with some Kerosene into the drain plug -- leaned it back and forth to coat the inside. I still get condensation, of course, but time will tell if the oil treatment prevents it from rusting out.


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## longtime (Nov 22, 2009)

I run my compressed air through a big heat exchanger (old heating coils 8'X1'X1' almost 96' total length 3/4 finned copper tube) then through a 360 deg. loop with drip legs before it goes into the tank. I drain both drip legs daily. As a result I get very little moisture out of the tank when I open the drain. The inter-cooler cools the air enough that almost all the water condenses before the tank.


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## bstickler92 (Apr 15, 2010)

i like the oil on the inside idea because i'm pretty sure it's not painted inside. it's a harbor freight tank so there's no drain plug, just one half inch hole near the top of the tank


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## GreyWolf (Mar 17, 2010)

mosquitomountainman said:


> I don't think there's anything you can do except drain it often. The water in the tank is a byproduct of compressing/decompressing the air. External filters and water separators will only work on the air pumped to the outside of the tank. Any dessicant you use will be saturated very quickly and be worse than nothing at all.


I agree, draining the tank often is about all you can do. The tank itself will have condensation form inside it so even external dryers such as those found in sealed refrigeration equipment will not work.


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## NaeKid (Oct 17, 2008)

See if you can locate a B-Pressure welder (person, not just the machine) near your home that can drill the tank and weld-in a petcock that will allow you to drain the moisture from the tank after each use.

Putting oil into the air-tank is a double-edged sword. It can help air-tools stay lubricated, but, that same oil can get into your tires (if used to fill tires) and coat the inside. Depending on the type of oils used inside the tank, it could help wear-down the strength of the rubber-compound inside the tire itself (also known as dry-rotting). If using a motor-oil (most have detergents, ATF and diesel motor oil have higher amounts of detergents), the detergents will eat away the inside of the tires the same way that brake-fluid eats away paint and non-DOT approved rubber hoses.


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## horseman09 (Mar 2, 2010)

Grey Wolfe, it seems as though the dryer should prevent condensation in the tank because if the intake air is free of moisture, then there would be no moisture to condense.


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## NaeKid (Oct 17, 2008)

horseman09 said:


> Grey Wolfe, it seems as though the dryer should prevent condensation in the tank because if the intake air is free of moisture, then there would be no moisture to condense.


The problem comes from the compression cycle. There is always moisture in the air - or - the chemical makeup of moisture (hydrogen and oxygen) that when compressed can force the separate molecules to join and turn into water-vapor which, when cooled against the sides of the tank turn to water droplets which then can help oxidize the tank.

There are products (like POR15) that can be swished inside of a tank to help create a barrier against rust - but - if the tank is dinted, it might cause the coating to flake away in that area...


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## GreyWolf (Mar 17, 2010)

Great job explaining that Vance. That is why even with the heat exchanger/heating coil as described above, there is still some moisture in the tank. In a sealed refrigeration unit the dryer and heat exchanger work well because a vaccum is pulled on the lines of the sealed unit removing all the air and that air is replaced by a gas, usually a freon type gas, which produce much less condensation/moisture in the lines. 

The coating sounds like a good approach and seem like they would work reasonably well. Perhaps if the tank does get dented you could simply recoat the interior of the tank as a precaution. I've never used any of these coatings myself and am not sure if that would work or not. With my luck the oil option would work 99% of the time just fine but that one time I needed something to spray perfectly droplets would come out.


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## allen_idaho (Oct 21, 2009)

NaeKid said:


> See if you can locate a B-Pressure welder (person, not just the machine) near your home that can drill the tank and weld-in a petcock that will allow you to drain the moisture from the tank after each use.


I am a welder. And this would be one way to go. But the easier thing to do would be to drill and tap a hole. Then just screw one in. As long as you get a good seal, it would work perfectly.


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## bstickler92 (Apr 15, 2010)

i like the idea of por 15, if i can get some, it sounds like the best thing to resist corrosion inside


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## mosquitomountainman (Jan 25, 2010)

I'd still install and use the drain plug/petcock.


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## NaeKid (Oct 17, 2008)

allen_idaho said:


> I am a welder. And this would be one way to go. But the easier thing to do would be to drill and tap a hole. Then just screw one in. As long as you get a good seal, it would work perfectly.


If he has the kind of tank that I have visualized in my mind's eye, the tank-walls might be 16G to 14G material and to do a drill-tap on it and put in a plug would be asking for troubles. If it is a heavier-wall tank (maybe in the 3/16" variety) I wouldn't question the strength of the drill-tap.

You could be very right that it would work, but, from my experience a welded in bung would be better.


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## NaeKid (Oct 17, 2008)

bstickler92 said:


> i like the idea of por 15, if i can get some, it sounds like the best thing to resist corrosion inside


I believe that in the USA, POR15 is available in many of the automotive part stores. If you can't find it locally, you can order it online for shipment to your door. To get you started - visit POR15.com


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## allen_idaho (Oct 21, 2009)

The average compressed air tank is built with a wall thickness of 5/16" in the United States.


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## NaeKid (Oct 17, 2008)

I agree that the tanks that are mounted to a compressor (home / shop / industrial) are all built with heavy-wall construction, but, based on bstickler92's quick description of the tank (_it's a harbor freight tank so there's no drain plug, just one half inch hole near the top of the tank_), so I did a quick-search on the Harbor Freight website and got three possible products on screen that _might_ just be one of the tanks that he has ..

Harbor Freight SearchTerm - Air Tank

If the two cheaper tanks starting at $25 are 5/16" wall - I'll purchase a couple of them for my own OnBoardAir systems that I have planned - that is a freakin' awesome price :2thumb:


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## bstickler92 (Apr 15, 2010)

NaeKid said:


> I agree that the tanks that are mounted to a compressor (home / shop / industrial) are all built with heavy-wall construction, but, based on bstickler92's quick description of the tank (_it's a harbor freight tank so there's no drain plug, just one half inch hole near the top of the tank_), so I did a quick-search on the Harbor Freight website and got three possible products on screen that _might_ just be one of the tanks that he has ..
> 
> Harbor Freight SearchTerm - Air Tank
> 
> If the two cheaper tanks starting at $25 are 5/16" wall - I'll purchase a couple of them for my own OnBoardAir systems that I have planned - that is a freakin' awesome price :2thumb:


the one i have is the yellow 5 gallon, it fits perfectly on the rear wheel well of my jeep and i have added a few things, i might get a second tank and connect the two. i'll post a pic of it in a little bit


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## bstickler92 (Apr 15, 2010)

i am planning to add a quick connect fitting directly above the valve that is going up. ok, so here's the tank as it is:


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## NaeKid (Oct 17, 2008)

Would your Jeep happen to be a YJ (I have a couple of them) or CJ? I can't imagine being able to mount a tank of that size on the wheel well of my LJ.


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## bstickler92 (Apr 15, 2010)

i have a 1995 yj with the 4.0. she's a work in progress so i try to keep myself busy. i've got 2.5" lift springs sitting in the garage ready for a nice weekend


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## bstickler92 (Apr 15, 2010)

so 3 of the connections are leaking , i thought it was just where it went into the tank but i sprayed soapy water and there were bubbles everywhere. i used teflon tape on the threads but i took it all apart, the tape was gone from where it was where the parts were threaded together. any suggestions on sealing it?


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## NaeKid (Oct 17, 2008)

You probably just need to crank-down harder on the connections with a pipe-wrench. It looks like you are using gas-pipe (and fittings) so the only other option that I can think of would be pipe-dope (found in many hardware stores).


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## bstickler92 (Apr 15, 2010)

the pipe is black iron pipe, i got it at lowes in the plumbing section. and what is pipe dope?


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## NaeKid (Oct 17, 2008)

Pipe dope: http://en.wikipedia.org/wiki/Pipe_dope


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## bstickler92 (Apr 15, 2010)

thanks, i was wondering why the connections were tapered, i'll see if i can find a pipe wrench around here somewhere. if i crank it down really hard, will teflon tape work just as well?


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## NaeKid (Oct 17, 2008)

:dunno: I have never tried teflon-tape on black-iron connections, so, I don't know for sure. I have only used teflon-tape on precision-cut threads (like the brass fittings on quick-connects for air-lines) and I know that it works well there as long as you don't put on too much or too little.


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## bunkerbob (Sep 29, 2009)

No, tape is as you said Naekid for non-tapered threads. Get a bottle of thread sealer(dope) with teflon, this one doesn't seem to dry up like the one without teflon. I've had a bottle for about 10 years, great stuff, will also work with propane and natural gas, just don't use very much. It is inert and will take high temp and pressure also. I have even used it on plastic threaded pipe, makes it go together easier. Remember don't use very much.


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## sea_going_dude (Dec 7, 2011)

bstickler92 said:


> so 3 of the connections are leaking , i thought it was just where it went into the tank but i sprayed soapy water and there were bubbles everywhere. i used teflon tape on the threads but i took it all apart, the tape was gone from where it was where the parts were threaded together. any suggestions on sealing it?


Put at least 3 or 4 rounds of the tape on the threads and do not stretch the tape, just enough to keep it in place while you put the pipes together.


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