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  1. #1
    Join Date
    Jul 2010
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    Default air compressor water trap

    I want to fit a water trap/regulator (like the one pictured) to my compressor to do some painting... can i mount it to the compressor , or do have to wall mount it and run some hoses ?.
    Ken.
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  2. #2
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    Don’t put it on the compressor. You want it as far away from it as possible so the air cools as it runs through the lines and more potential for water vapour to condense out.

    Having said that I have mine on a 2M line after the compressor and never had an issue.

  3. #3
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Hi Guys,

    Quote Originally Posted by neevo View Post
    Don’t put it on the compressor. You want it as far away from it as possible so the air cools as it runs through the lines and more potential for water vapour to condense out.

    Having said that I have mine on a 2M line after the compressor and never had an issue.
    I agree ! Mine is about 10 Mt away on the end of a plastic hose. It collects very little water but then again it doesn't see a lot of use.
    Best Regards:
    Baron J.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    I have those regs/traps at the ends of two arms of my reticulated comp air network. One is on the a 12m from the compressor, adjacent to where I spray as well as near where use a Plasma cutter, and the lube/coolant mister connection for my lathe. The other is on a 8m from the compressor on my mill to reg the air pressure for its lube/coolant mister.

  5. #5
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    Mar 2011
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    I have one on my tank, never had a problem with water in the lines. Don’t spray heaps but I have sprayed a couple of trailers and other random stuff inc about 30sqm of timber for the last carport I built and haven’t had any signs of water ingress into finish with the reg on the tank.
    Drain the tank and reg (if the reg isn’t self empty type) before you spray and it’ll be fine.
    In theory the ideal place for it is toward the end of the hose, in reality it makes no appreciable difference.

  6. #6
    Join Date
    Apr 2019
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    Adelaide
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    If its a one of spray job then it might be worth buying an inline filter 'sock'. These contain the water absorbing crystals. Cannot recall where I saw them or how much. Other wise as said above, put the reg/separator a little way from the compressor and maybe higher so that condensed water can run back into the tank.

  7. #7
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    Mar 2014
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    Quote Originally Posted by BaronJ View Post
    Hi Guys,



    I agree ! Mine is about 10 Mt away on the end of a plastic hose. It collects very little water but then again it doesn't see a lot of use.
    It is surprising how little water comes out of a compressed air system. At work we have a 40ish CFM screw compressor with a 500l tank and refrigerated dryer, and in 8-10 hours we would be luck to get 1/2 a cup of water out of the system.

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    At 20ºC the most water air can carry (100% humidity) is ~17.3 mg/L
    Assuming a 50% humidity that converts on ~8.6 mg/L which typically what shows up on my "outside my shed" moisture sensor.
    Inside a shed, air carries more water as it's warmer, hot works release water, as do humans so depending on temp I typically see between 8 and 12 mg/

    Half a cup of water is about 125g so that translates to 14500 L of pumped air or 508 cubic ft.
    At 40 CFM that means you should get 1/2 cup water after just 12.5 minutes of pumping.

    If compressor is pumping for any more than 12.5 minutes total during those 8-10 hours then water is either not getting to your dryer or is getting past the dryer.

    Working the other way - how long does the compressor operate for in total over those 8-10 hours?

  9. #9
    Join Date
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    Adelaide
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    dont the water separators only take out water in its liquid state but not that which is in gaseous form? i.e. most of the water goes out the spray gun? Never really thought about it in detail.

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Mk1_Oz View Post
    dont the water separators only take out water in its liquid state but not that which is in gaseous form? i.e. most of the water goes out the spray gun? Never really thought about it in detail.
    The amount extracted depends on the water removal process.

    The water filter/reg as shown in the pic by the OP uses a bronze/brass membrane witch catches fine droplets and they drip into the small chamber below, this doesn't do that much for water as vapour.

    Cooling coils and refrigerated air dryers work by cooling the air so it cannot hold as much water.

    Water coming out of a compressor is quite hot so it can hold large amounts of water.
    eg at around 60ºC as much as 130 mg/L
    Of course it cannot make water out of nothing, there has to be water in the air to begin with.

    On a very humid/hot day (eg 35ºC and 90% humidity) can hold as much as 35 mg/L

    At 20ºC, air can hold as much as 17.3 mg/L but drop the temp to 0ºC and water condenses out so it can only hold a max of about 5 g/L
    Even at -20ºC air can still a max of about 1 mg/L of water vapour.m

    Desiccator systems work by absorbing water vapour from the air. When my desiccating agent in my water trap is fresh, depending on the starting humidity of the air it can get the air down to around 0.2g/L but that is for very low air flow (3L/min) air flow - the minimum I can have for measurement purposes- as soon as there is working flow it goes up to around 0.5 g/L and it goes up slowly as the desiccator saturates.

  11. #11
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    Adelaide
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    Cheers Bob. So I am correct that the separator/reg combos only take out water suspended in air as a liquid.

    When redoing my air system I will either use an a/c condensor with fan, a long run of copper pipe or an old wall mount a/c that the copper pipe passes through. This will condense much of the water to liquid that can then be caught by the reg/separator.

    For the OP, I painted my rally car in the shed using only the basic regulator/separator connected to the compressor (and close to it). Never had any water related paint issues. However, Adelaide isn't known for its humidity.

  12. #12
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    Quote Originally Posted by BobL View Post
    At 20ºC the most water air can carry (100% humidity) is ~17.3 mg/L
    Assuming a 50% humidity that converts on ~8.6 mg/L which typically what shows up on my "outside my shed" moisture sensor.
    Inside a shed, air carries more water as it's warmer, hot works release water, as do humans so depending on temp I typically see between 8 and 12 mg/

    Half a cup of water is about 125g so that translates to 14500 L of pumped air or 508 cubic ft.
    At 40 CFM that means you should get 1/2 cup water after just 12.5 minutes of pumping.

    Hi Bob,
    For those of us trying to follow along, are there some "mg" typos in your last post?#10

    Assuming the "g" are meant to be "mg" and that a refrigerated dryer cant get below 0C(google seems to say they aim for 3C). Wouldn't that mean the best you can hope for is 8mg/L - 5mg/L = 3mg/L, making the run time more like 40 minutes?

  13. #13
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Stustoys View Post
    Hi Bob,
    For those of us trying to follow along, are there some "mg" typos in your last post?#10

    Assuming the "g" are meant to be "mg" and that a refrigerated dryer cant get below 0C(google seems to say they aim for 3C). Wouldn't that mean the best you can hope for is 8mg/L - 5mg/L = 3mg/L, making the run time more like 40 minutes?
    RE: "g's and mg's"
    Wmoops - too much cut-n-paste

    5ºC air has a max water vapour content of of 6.8 mg/L so @3ºC its about 6 mg/L - but that thats at 100% humidity - in practice it's better than that.

  14. #14
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Mk1_Oz View Post
    Cheers Bob. So I am correct that the separator/reg combos only take out water suspended in air as a liquid.
    Yep.

    When redoing my air system I will either use an a/c condensor with fan, a long run of copper pipe or an old wall mount a/c that the copper pipe passes through. This will condense much of the water to liquid that can then be caught by the reg/separator.

    For the OP, I painted my rally car in the shed using only the basic regulator/separator connected to the compressor (and close to it). Never had any water related paint issues. However, Adelaide isn't known for its humidity.
    Perth and Adelaide are pretty similar humidity levels with Perth maybe a bit more humid in summer and less so in winter but microclimates can make a big difference. My compressor enclosure is outside the shed in a narrow 750 mm wide gap between the shed and fence. It's basically a well watered garden bed in summer plus water runs from the shed roof when it rains. It typically sees 10 -15% greater relative humidity than open air.
    Recently I removed any vegetation needing water from the garden bed and I will shortly disconnect the reticulated from that garden bed.
    I've also added a snorkel to get the main air intake from the bottom to above the enclosure.
    Snorkel1.jpg

    This is my finned copper cooling coil.
    CUpipe1.jpg

  15. #15
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    I’ve also done a few painting jobs with my setup. With the water trap 2-3m on a hose from my compressor and a disposable filter on the gun, I’ve never had any issues with water in my finish spraying 2k base, 2k clear, acrylic or basic single stage paints.

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