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Thread: Air compressor sizing

  1. #1
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    Air compressor sizing

    Since I am moving my shop down to my basement I need a compressor. We have a 60 gallon cambell hausfeld in the current shop that puts out something like 10.2 scfm at 90 psi, but one of the cylinders is broken so really it is half of that. I need something that can run a harbor freight hvlp gun, and the pneumatic powered blast gates for my cyclone. I would think that the blast gates use less air than the hvlp. I have an old compressor but i think that the tank is past its safe use. Would it be rediculous to buy a smaller compressor and hook it up to the old compressor? Any sugestions?

  2. #2
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    Quote Originally Posted by Dave Black View Post
    ...Would it be rediculous to buy a smaller compressor and hook it up to the old compressor? Any sugestions?
    Do you mean buy a new compressor to hook up to the old tank, or link two compressors together on the same air lines?

    You can put a small compressor pump on a large tank, although it'll take it a long time to fill the tank. You might also look into just buying a compressor head...something like one of these:

    http://www.eatoncompressor.com/page/page/518643.htm

    http://www.harborfreight.com/145-psi...ump-67697.html

    It's also possible to hook up two separate compressors to the same air system, although depending on where the thresholds are set, you may end up with one running a lot more than the other. If one's set to kick in at 100 psi and the other set for 90 psi, I'd think the 100 psi compressor will end up doing the majority of the work.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
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  3. #3
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    Can you run a line into the basement and get the cylinder fixed? If so, even a smaller tank, just inside the basement (towards the ceiling), gives you at least one drain point. (I would run multiple due to it being lower then the compressor)

    This would drop down the noise and give you a buffer tank.

  4. #4
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    Quote Originally Posted by Vaughn McMillan View Post
    Do you mean buy a new compressor to hook up to the old tank, or link two compressors together on the same air lines?

    You can put a small compressor pump on a large tank, although it'll take it a long time to fill the tank. You might also look into just buying a compressor head...something like one of these:

    http://www.eatoncompressor.com/page/page/518643.htm

    http://www.harborfreight.com/145-psi...ump-67697.html

    It's also possible to hook up two separate compressors to the same air system, although depending on where the thresholds are set, you may end up with one running a lot more than the other. If one's set to kick in at 100 psi and the other set for 90 psi, I'd think the 100 psi compressor will end up doing the majority of the work.
    I didn't explain that very well. The old compressor has a good compressor and motor as far as I know, but the tank is old and probably not safe, I am not sure what the cfm of the compressor is though. It has a 3/4 motor but is very large is size though, so maybe its really bigger than that. My thought was to buy a compressor from home depot that would maybe be 4cfm-ish with a 20ish gallon tank. I am not sure if this size compressor would be sufficient to run a hvlp gun that I have? So if that wouldn't be big enough I could hook the old compressor and motor up (minus the old tank) and T it into the system, I could set up the pressure switch so that if the pressure dropped and the new compressor couldn't keep under higher loads the 2nd compressor would kick in. Also I have read that it is smart to turn the pressure on the compressor down from what they usually come set at. I think it said maybe turn it down to 80 or 90 PSI. If I remember right it was because the compressor would run cooler and would extend the life, I suppose that at a lower pressure the compressor would also run a higher CFM.

  5. #5
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    Quote Originally Posted by Randal Stevenson View Post
    Can you run a line into the basement and get the cylinder fixed? If so, even a smaller tank, just inside the basement (towards the ceiling), gives you at least one drain point. (I would run multiple due to it being lower then the compressor)

    This would drop down the noise and give you a buffer tank.
    I suppose that I should have explained the whole situation on this thread, I have a shared shop with my family across the road from me on my families farm. I am moving my stuff into my basement and so I need a compressor for my basement. The current compressor will stay in the shop on the farm and it can have broken piston, it works fine for what its used for. There is also a much older compressor and tank that is not in use ( the tank on that is the one which is probably unsafe) But to get back to your comment I was thinking about putting the compressor I buy ( and if I use the old motor and compressor in addition) in the garage to help cut down on noise. Would there be problems with water condensing in the lines if the tank is in the garage in the summer heat then the air traveling into the cool basement?

  6. #6
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    Quote Originally Posted by Dave Black View Post
    I didn't explain that very well. The old compressor has a good compressor and motor as far as I know, but the tank is old and probably not safe, I am not sure what the cfm of the compressor is though. It has a 3/4 motor but is very large is size though, so maybe its really bigger than that. My thought was to buy a compressor from home depot that would maybe be 4cfm-ish with a 20ish gallon tank. I am not sure if this size compressor would be sufficient to run a hvlp gun that I have? So if that wouldn't be big enough I could hook the old compressor and motor up (minus the old tank) and T it into the system, I could set up the pressure switch so that if the pressure dropped and the new compressor couldn't keep under higher loads the 2nd compressor would kick in. Also I have read that it is smart to turn the pressure on the compressor down from what they usually come set at. I think it said maybe turn it down to 80 or 90 PSI. If I remember right it was because the compressor would run cooler and would extend the life, I suppose that at a lower pressure the compressor would also run a higher CFM.
    Ah, now I understand. I'm pretty sure the idea of adding the old pump teed to a new compressor would work. Sounds like you have the pressure switch setup already figured out. I haven't read anything about reducing the pressure to extend the life of the compressor, but it seems to make sense.

    On the condensation question, you're going to get condensation however you run the lines. Actually, running through long lines is a good way to cool the air and remove the condensation. Just plan for it by sloping the piping to multiple drops and drains, and you should be fine. In my shop. my compressor is only about 15' away from where I use most of my air. To cool and dry the air before it gets to the end of the hose, I'm running it through about 50' of 3/4" steel pipe, and there are about five water traps along the way. (Still, most of my water collects in the tank, which is a good thing.) This is the first thing it runs through after leaving the compressor...



    The condensation collects in the drops at the bottom of the loop, and is drained out via the ball valve at the bottom right.

    And here's the end of the run where I plug my hoses in. The blue cylinder is a desiccant air dryer, but there's a drain drop before it and a water trap/regulator after...



    Kind of overkill for my needs, but I have really dry air coming out the end of my hoses.
    Attached Thumbnails Attached Thumbnails Air System 01 - 800.jpg   Air System 12 - 800.jpg  
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

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  7. #7
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    Dave

    Check out Burdens Surplus Center for compressor heads at an attractive price.

    https://www.surpluscenter.com/air.asp?catname=air

    The other Larry

  8. #8
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    Quote Originally Posted by Vaughn McMillan View Post
    Ah, now I understand. I'm pretty sure the idea of adding the old pump teed to a new compressor would work. Sounds like you have the pressure switch setup already figured out. I haven't read anything about reducing the pressure to extend the life of the compressor, but it seems to make sense.

    On the condensation question, you're going to get condensation however you run the lines. Actually, running through long lines is a good way to cool the air and remove the condensation. Just plan for it by sloping the piping to multiple drops and drains, and you should be fine. In my shop. my compressor is only about 15' away from where I use most of my air. To cool and dry the air before it gets to the end of the hose, I'm running it through about 50' of 3/4" steel pipe, and there are about five water traps along the way. (Still, most of my water collects in the tank, which is a good thing.) This is the first thing it runs through after leaving the compressor...



    The condensation collects in the drops at the bottom of the loop, and is drained out via the ball valve at the bottom right.

    And here's the end of the run where I plug my hoses in. The blue cylinder is a desiccant air dryer, but there's a drain drop before it and a water trap/regulator after...



    Kind of overkill for my needs, but I have really dry air coming out the end of my hoses.
    what size compressor do you have, do you do much spray finishing?

  9. #9
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    You won't need to worry with the blast gates flow requirements, it will be minimal. Just make sure the system has enough pressure to work them. The spray gun will pull way more volume than the blastgates will ever need to work.

    I'm not sure about the pressure setting you're talking about. Reducing the pressure at the regulator doesnt' really impact the compressor any. It will allow your compressor to cycle on and off to keep the tank at say, 100 psi and if the regulator is at 90 psi your output air from the regulator will be nice and steady. If you can change the operating pressure it would reduce the load on the compressor parts, but not sure about extending the life any. I was always under the belief to size your compressor as close to your actual needs, as oversize in volume and flow wastes a lot of electricity.

  10. #10
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    Quote Originally Posted by Dave Black View Post
    what size compressor do you have, do you do much spray finishing?
    It's a 5 (true) horsepower motor on a pump designed for 7.5 motors, pumping into a 60 gallon tank. It's rated at 19 cfm @ 100 psi. I don't do a lot of spray finishing, but I run a pneumatic sander quite a bit. This compressor fills the tank faster than the sander can empty it. My last compressor wasn't able to keep up with the sander. Like I said, it's overkill to some extent.



    Attached Thumbnails Attached Thumbnails Air System 19 - 800.jpg   Air System 18 - 800.jpg  
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

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