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Thread: removing moisture from air lines

  1. #1

    removing moisture from air lines

    Anyone running an ATC, what are you using to dry the air coming from your compressor? I have been using a cheap desiccant filter up to now. I am thinking about getting one of the Harbor Freight dryers while they are $100 off. I have heard they aren't bad especially for the price. Anyone else using one? If not what are you using and how much success do you have with it? The spindle is too expensive to let water damage it.

  2. #2
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    I bought this Speedaire refrigerated dryer about 16 years ago from Graingers. I think I paid around $500 at the time. It has worked great - I originally bought it for the air supply to my cnc machining centers (Matsuura 510V and Nakamura Tome Slant 1). The air supplied to my ATC spindle (just like yours) comes from this dryer as well. I have no personal experience with the HF dryer, but I expect you can find reviews at some of the other sites.
    David

    20200423_001517_resized.jpg 20200423_001604_resized.jpg 20200423_001626_resized.jpg 20200423_001641_resized.jpg

  3. #3
    We run a hankinson refrigerated dryer with a coalescing oil filter behind it. Compressor has aftercooler and auto tank drain.
    Last edited by Mark Bolton; 04-24-2020 at 4:07 PM.

  4. #4
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    Yes - it definitely helps to drain the compressor tank daily.
    David

  5. #5
    The tank drain on my setup doesnt drain daily its timed (which I dont like). I wish it were setup like some other brands where it runs a tank drain cycle after each compressor cycle as my thought it on a day where we dont use a mile of air the tank drain isnt dumping air every 45 minutes even if the compressor doesnt cycle. That said, we have the auto drain piped throught the floor into a culvert with a very small 1/4" stainless steel tube and the drain cycle is about 5 seconds so every 45 minutes you just hear a 5 second small hiss. Maybe wouldnt keep up if the compressor was running hard in the summer and making a ton of water.

    Local compressor shop that we bought the equipment from said they dont like the cycle drains because the moisture is condensing out of the air in the tank as it cools so purging only at the end of the cycle doesnt perform well in shops with periods of lower usage.

    There have been times when Ive forgot to turn on the tank drain after just a day and the amount of water even with the aftercooler (suppose to pull 80% of the moisure out) is substantial. Same thing with the dryer. The 20% of the water remaining is pretty substantial coming out of the dryer at times.

    Dryer was 1100 or 1200 as I recall but I would have to look it up. Coalescing filter was another 300+. Protecting the spindle, and supplying dead clean dry air to spray station was the aim.
    Last edited by Mark Bolton; 04-25-2020 at 5:01 PM.

  6. #6
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    I have an automatic tank drain with timer (had it for aver 15 years) - but I've never installed it. I prefer to manually drain my compressor tank - it's easy enough to do. I drain when the compressor is cold (hasn't run for several hours or more). This allows time for the air to cool and all moisture to condense to the bottom of the tank. I do have over 150 ft. of 3/4" rigid copper air line between the compressor location and the refrigerated air dryer out in the machine shop, with drain traps strategically located along the line. In addition, the copper line is slightly sloped back towards the compressor tank so that any moisture that condenses in the copper line runs back towards the compressor tank and not forward towards the refrigerated dryer.
    David

  7. #7
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    You actually want the line sloped away from the compressor, so air flow helps the water along.

  8. #8
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    Quote Originally Posted by Wes Grass View Post
    You actually want the line sloped away from the compressor, so air flow helps the water along.

    Nope! Towards the compressor tank. Particularly if you are running an automotive spray booth (as I am here in the shop). Per Ditzler Automotive Finishes (PPG) Ditzler Repaint Manual - Page 6
    "When setting up the compressor and air line, be certain that the pipe is large enough to carry the necessary amount of air to the gun, and when hanging the pipe, be certain that it drains back to the compressor rather than forward to the air transformer (regulator). (See Figure 10)"

    I thought this was common knowledge, but perhaps I was mistaken.

    David

    Air line drain back towards tank.jpg

  9. #9
    Agreed on the pitch if you can. My shop was already plumbed (was a fire station) with black pipe and didnt want to re-plumb so opted to kill every drip of water right at the compressor. Industrial distributor has us run 175 psi through a short stainless flex straight into the dryer. 175 psi mains in the shop and I had a couple filter/reg/separators on the shelf and tossed a 3/4" at the cnc (100ft away) and used a couple more in the shop on other drops and have never seen a drop of water in the bowls or oil in the elements even on the most humid days and with heavy use.

    I wish it wasn't black pipe but it is what it is.

  10. #10
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    Quote Originally Posted by David Buchhauser View Post
    Nope! Towards the compressor tank. Particularly if you are running an automotive spray booth (as I am here in the shop). Per Ditzler Automotive Finishes (PPG) Ditzler Repaint Manual - Page 6
    "When setting up the compressor and air line, be certain that the pipe is large enough to carry the necessary amount of air to the gun, and when hanging the pipe, be certain that it drains back to the compressor rather than forward to the air transformer (regulator). (See Figure 10)"

    I thought this was common knowledge, but perhaps I was mistaken.

    David

    Air line drain back towards tank.jpg


    I found the opposite advice. When researching before I installed my system I read various documents. Most of them were for large industrial systems but some also included small shop designs. This for example, discusses condensation:

    "...The header should have a slight slope to allow
    drainage of condensate and drop legs from the bottom side of the header should be
    provided to allow collection and drainage of the condensate. The direction of the
    slope should be away from the compressor
    ."

    CAGI (Compressed Air and Gas Institute), cagi.org, Compressed Air and Gas Handbook, Chapter 4: Compressed Air Distribution(Systems),

    I found other references with similar recommendations. It was often suggested to pipe the output to the compressor into a line at least 25' long to allow the air to cool and condensation to form, sloping that line away from the compressor. Ideally that initial pipe should be metal. At the end of the line put a gravity trap (which must be drained occasionally), then continue the compressed air to dryer then the regulator, then the distribution manifold. I use a trap, a water seperator, then a desiccant dryer. (For my plasma cutting I add a second desiccant dryer at the plasma cutter.) I made traps from brass tubing with a drain valve on the bottom (for noise control the air compressor just the in the main shop):

    air_comp_ctrls_IMG_20150124.jpg

    It seems to me the picture with the line sloped towards the compressor would tend to blow condensate towards the dryer and outlets when air was moving, otherwise drain back into the tank. I guess an advantage would be only one place to drain instead of two.

    I guess it depends on what you read.

    JKJ

  11. #11
    I doubt best practices are standardized across the board given changing/advancing technology, and the myriad of different system configurations based on the application demands. It seems to me in most industrial systems now central processing of air is the norm. Send it from the compressor area, to the facility, clean and dry from the moment it leaves that area.

    BarZ Industrial on youtube did a nice 3 part series on a large install they did a while back https://youtu.be/T2soRICBvRg. They drain back to the compressor.
    Last edited by Mark Bolton; 04-26-2020 at 11:03 AM.

  12. #12
    Quote Originally Posted by John K Jordan View Post
    ...
    I guess it depends on what you read.

    JKJ
    I believe it depends more on what you build. Simpy put, you have to either live with water in the system, keep it from entering, or remove it. The slope of horizontal lines assists with the latter. Lines should slope toward the device(s) provided for water removal.

    If you have a auto-drain at point-of-use, then slope lines toward that (and away from compressor/dryer/receiver) If you have a receiver auto-drain, then slope them toward the receiver. And, it is possible to do both (horizontal lines with a high point in the middle).

    To the OP's original question, you can typically find three common methods of drying compressed air: refrigerated, desiccant, or membrane. There are others, but I think you'll find them a bit unique and pricey for home shop use: i.e compress the air to very high pressure (2000psi?), pass thru an intercooler, then thru an expansion valve to 'refrigerate' it, drain the water, and then of course, compress it again before use. Its been a while, but IIRC, this was applied to a system making 3000-5000 SCFM..? Cha-ching.

    In my experience, refrigerated has been the best (driest) for large volume users (100->1000SCFM) - but also most expensive, especially if it breaks. Desiccant works well and is generally affordable in a home shop, but gets very expensive as volumes get above ~50SCFM, and it requires regular attention - something many hobbyists may forget. I'd also recommend a parallel set of desiccant dryers - one in use, one recharging. The good thing about it to me, it has essentially no moving parts to break. I've not spec'd or used membrane-style, they are relatively new - at least to me - so please do your own research. Bottom line, you have to match your air quality/volume needs and budget to a suitable drying method.

    Or, put a filter/drain at point-of-use and live with whatever water gets by (my choice at home, as I go months w/o ever turning on my compressor).

  13. #13
    I made the purchase for the dryer while it was on sale. I will add that and run my smaller desiccant filters after it, right before the spindle. Thanks everyone.

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