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Thread: My painting setup - understanding CFM

  1. #1
    Join Date
    Jun 2020
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    Default My painting setup - understanding CFM

    Hi guys, have been reading on here for a while learning what I can. I have a small compressor setup which I only want for painting one panel at a time.

    I have...

    Compressor - 24 ltr | 2.5 hp | 9.5 cfm
    Hose - 10 Meter | 10 mm | 21 Bar
    Filter - 10 Microns | 12 Bar
    Hose - 20 Meter | 10 mm | 21 Bar

    Inline Water Trap
    BenBow Inline Regulator
    Gun - ANI F1/N | 7.77 cfm

    All connections are BSP 1/4 inch XF High Flow | 35 Bar


    From what I understand the CFM is most important. My compressor is small but its rated at 9.5 cfm so by the time the air has passed through all the lines and fittings do I have enough CFM at the gun for my 7.77 cfm gun?

    My other question is when spraying, my compressor will start at around 100% full and turn on when it reaches around 70%. At this point should I stop spraying until it turns off or is it ok to continue and its providing enough CFM?

    I am debating weather its worth me buying a new compressor as its money I don't really have and and I am only doing a panel at a time here and there, however I do want the best finish possible.
    Previous attempts have been fine but left with moderate orange peel which I sanded and buffed out no problem however it would be nice to achieve a better finish.

    Also is the moisture trap at the gun still needed if I have the wall mounted filter 10 meters from the compressor?

    Thanks

  2. #2
    Join Date
    Nov 2005
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    Default

    I have...

    Compressor - 24 ltr | 2.5 hp | 9.5 cfm
    Hose - 10 Meter | 10 mm | 21 Bar
    Filter - 10 Microns | 12 Bar
    Hose - 20 Meter | 10 mm | 21 Bar

    Inline Water Trap
    BenBow Inline Regulator
    Gun - ANI F1/N | 7.77 cfm

    All connections are BSP 1/4 inch XF High Flow | 35 Bar


    From what I understand the CFM is most important. My compressor is small but its rated at 9.5 cfm so by the time the air has passed through all the lines and fittings do I have enough CFM at the gun for my 7.77 cfm gun?

    My other question is when spraying, my compressor will start at around 100% full and turn on when it reaches around 70%. At this point should I stop spraying until it turns off or is it ok to continue and its providing enough CFM?

    I believe that the tank size is as (if not more) important than the CFM because a larger tank allows you to run your gun longer before you see a pressure drop. Your tank size is quite small but you could give it a try on your first panel to see how it works out. Personally I'd probably either add another tank to increase the air volume or purchase a different compressor.

    I am debating weather its worth me buying a new compressor as its money I don't really have and and I am only doing a panel at a time here and there, however I do want the best finish possible.
    Previous attempts have been fine but left with moderate orange peel which I sanded and buffed out no problem however it would be nice to achieve a better finish.

    If you start with this small compressor and you're happy with the result that's all that matters but you may be able to produce a better job with more air capacity.

    Also is the moisture trap at the gun still needed if I have the wall mounted filter 10 meters from the compressor?

    Another problem you can run into using a small compressor is it could generate enough moisture that it can outrun your filter. Again test it on your first panel to see if it rains on your work.

    Let us know how it works out for you.

  3. #3
    Join Date
    Nov 2013
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    olympia,wa
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    Default

    just adding a couple of things to what len said,
    the cfm rating can be confusing, and some compressors are hard pressed to actually deliver what they claim. compressors are rated for cfm at a specific pressure. matching that to the gun's consumption at it's given pressure is where the confusion usually happens.
    it's doubtful that small compressor would keep up with continuous spraying, but you're only doing panels so it might work out.
    when you empty the tank enough to cycle the compressor on, you should look at your gauge on the gun and see where it's at. you can continue to spray until the gun pressure starts to fall off. (or maybe stop just before that happens.) you can see the pressure on the gun gauge as it relates to the tank pressure to see where that point is.
    the point is, as long as you are able to maintain pressure at the gun inlet, the required cfm is available.
    i never spray without the extra trap at the gun. it's extra insurance for little cost, especially if you're using an undersized compressor. len was spot on that small compressors like that work harder and produce more moisture. that is why the water traps are so important.
    the extra tank is a great idea, as it extends the time before the compressor kicks on, but also remember it will take longer to fill. longer run times make more heat/water to deal with.
    as far as the orange peel goes, it's more a function of the gun, paint viscosity, and technique more than the compressor. more practice will improve that aspect. or maybe a better gun. i'm not familiar with that particular gun so i don't know how it sprays. sometimes though, changing the inlet pressure can help atomize the paint better, which helps it lay out smoother.
    b marler

  4. #4
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    Jun 2020
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    Default

    Thank you for the replies. I really appreciate all the help and I have learned so much on these forums.

    Im now considering if I should just buy a new compressor. In my price range I could get one with double the tank size and a slightly higher CFM, would this be a worth while upgrade? Or would it only make a difference If i upgraded to something much larger?

    I was also considering buying exactly the same compressor again and coupling them together, as this would be a cheaper option. In theory this would give me double the tank size and CFM?

    Which of these would be the better option?


    Also, maybe i'm being completely stupid here but when I attach the moisture trap to the line just before the regulator I can only get minimal pressure though the gun, hardly any air whatsoever. Without the trap the airflow is fine and the gun works fine.

    Am I missing something on the water trap? There doesn't appear to be anything I can adjust or move?

  5. #5
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    Nov 2005
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    If you intend on spraying more projects I'd recommend a compressor that puts out at least 13 CFM or more and a tank size of 60 or 80 gallons. You'll have less to worry about when a decent compressor is the heart of your projects.

  6. #6
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    olympia,wa
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    Quote Originally Posted by DarrenLS View Post
    Thank you for the replies. I really appreciate all the help and I have learned so much on these forums.

    Im now considering if I should just buy a new compressor. In my price range I could get one with double the tank size and a slightly higher CFM, would this be a worth while upgrade? Or would it only make a difference If i upgraded to something much larger?

    I was also considering buying exactly the same compressor again and coupling them together, as this would be a cheaper option. In theory this would give me double the tank size and CFM?

    Which of these would be the better option?


    Also, maybe i'm being completely stupid here but when I attach the moisture trap to the line just before the regulator I can only get minimal pressure though the gun, hardly any air whatsoever. Without the trap the airflow is fine and the gun works fine.

    Am I missing something on the water trap? There doesn't appear to be anything I can adjust or move?
    nobody ever said they wish they'd bought a smaller compressor. always get the best one you can fit either size wise or budget wise. adding another small one will just double your trouble.
    i wonder what the flow rating might be on the water trap you're using. might be too small if you can't get pressure at the gun.
    b marler

  7. #7
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    Nov 2005
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    Default YES - What you said!

    Quote Originally Posted by bmarler View Post
    nobody ever said they wish they'd bought a smaller compressor. always get the best one you can fit either size wise or budget wise. adding another small one will just double your trouble.
    i wonder what the flow rating might be on the water trap you're using. might be too small if you can't get pressure at the gun.
    AGAIN, with you! About the time I read he was thinking of "doubling his pleasure" with another like small compressor, I (seriously) thought 'about' exactly what you wrote herein.

    He should be able to land a 5 horse 60 gallon for around $500 or an 80 gallon for near $800. (BE SURE and check electrical requirements on either in your electrical service panel!)

    I think his first filter/trap is set too close to the main outlet of the compressor thus making it less effective!

    Henry

  8. #8
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    Jun 2020
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    Ok thanks guys, Il look into getting a bigger compressor then instead of coupling them together.

    I have a 10 meter hose out of the compressor to my water filter and then another 10 meter hose to the water trap, gun regulator, then gun.

  9. #9
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    Quote Originally Posted by DarrenLS View Post
    Ok thanks guys, Il look into getting a bigger compressor then instead of coupling them together.

    I have a 10 meter hose out of the compressor to my water filter and then another 10 meter hose to the water trap, gun regulator, then gun.
    You could PIPE your air for better performance. I usually recommend coming from the compressor to the wall, up the wall, around the room then drop down past the regulator with a T to the regulator and a drain at the bottom of the T so help drain the water before it gets to the regulator. I've been using "good" PVC pipe for years with no issues. If you purchase a compressor try to get one that has a valve at the bottom of the tank for easy draining, I have a hose rolled up at the bottom of my compressor and installed a lever type valve for easy draining.
    Last edited by Len; 07-28-2020 at 06:15 PM.

  10. #10
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    Quote Originally Posted by Len View Post
    You could PIPE your air for better performance. I usually recommend coming from the compressor to the wall, up the wall, around the room then drop down past the regulator with a T to the regulator and a drain at the bottom of the T so help drain the water before it gets to the regulator. I've been using "good" PVC pipe for years with no issues. If you purchase a compressor try to get one that has a valve at the bottom of the tank for easy draining, I have a hose rolled up at the bottom of my compressor and installed a lever type valve for easy draining.
    Hi Len,

    Thanks for the reply. After reading this some weeks ago i began researching into pipe set ups for my property. This seems like a great idea for me as I use the compressor tools for so much more than just spraying.

    My compressor is location in the shed at the end of the garden, I then have a 15 meter run along a fence to the house and then a 20 meter run down the side of the house to the front where the drive is.
    This is where I would like to put my filter mounted on the wall so I can easily just plug in a tool and hose whenever I need to use something on the driveway.

    Currently I am having to wheel the very heavy compressor down the side of the house each time and it just puts me off doing jobs.

    Oh I also purchased a new compressor with a much larger engine and a 100 litre, so 4 times the size as the previous. I know that,s still not massive but was an upgrade within my budget.


    Now I have a few questions I'm hoping someone can answers as after lots and lots of research I still cant find conclusive answers.

    In my country I basically have two choices available to me...

    1. Aluminium piping by prevost
    2. Nylon piping my john guest

    Both are available in different diameters and I have already calculated which one I need for my required CFM etc.

    As The pipe will somewhat be exposed to UV and the elements will this be OK or will it effect performance? They will be shielded in a way as I will hide them as much as possible running alongside the fence and house however still exposed.
    The aluminium has an epoxy coating which it says is corrosion resistant, i'm not sure if that means as in outside use or as in oils etc.
    The Nylon I assume is a type of plastic and so would withstand the elements regardless?

    So which material for pipe should I choose for my situation?

    My design won't be in a loop fashion, rather a straight line from the back to the front. I know I need a slight slope to allow water to drain and I know I need to install drain drops etc or as you mentioned a T type junction.

    Is this viable not being in a loop and do I need to add anything in between the end of the pipe and the hose going to the compressor to stop air flowing backwards?

    Lastly my compressor has 2 outputs to enable 2 tools to be used at once, would it make a difference if I connect both of these to the pipe system or just one?


    Any help is so appreciated, I have been reading on the web forever and have found no real answers!

  11. #11
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    It's not necessary for the pipe to be in a loop as long as you control the moisture that gets generated. As the moist air condenses it should run into the low areas and be drained. I like collecting it back in the compressor so I tilt the pipe so the water runs back but that's not a rule and it can be collected anywhere prior to your filter/regulator.

    As far a pipe material goes it can be made of anything as long as it can take the pressure. Aluminum is popular and so is PVC (plastic) pipe but you want to make sure that it can handle well over 200 PSI. The number of air outlets shouldn't effect performance as long as your tool usage is withing your compressor's CFM output.

  12. #12
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    Sep 2020
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    Hi Darrent,
    If you haven't changed your compressor, you might look around your town/area for used ones. As long as the tank is solid, the motor/pump are working well and nobody has modified the motor to pump pulley ratios, these things tend to work for ages. I have no idea how old mine is...I've had it for nearly 40 years and it was old when I got it. You might look on eBay, also.

    In the past some of the best places to look were old gas stations that were being converted to self-serv or just closing. You might also keep your eyes open for tire centers, auto centers, body shops, etc that are closing, being sold or being remodeled.

    Good luck!

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