1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Air Compressor Question

Discussion in 'Other Tools' started by dancom, Feb 22, 2016.

  1. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    More accurately, this is an air compressorS question.

    Anyone using more than one air compressor working on a single air system?

    Sandblasters, die grinders and such have pretty hefty demands for air.

    I have a 17 gallon Craftsman that can make about 6.5 CFM at 90 psi, but struggles with the sandblaster running. Sandblasting cabinet requires "5 to 15 CFM." Seems like a large range, but in any case, a friend donated me a second air compressor. It's an old 2 cylinder thing, around 15 gallons, that has a 1-1/2 horsepower 4 pole motor on it. (No CFM specs anywhere to be found.)

    What are the rules for working them together? Do I need check valves? I am entertaining the idea adding some additional air storage in the form of a recently expired 100 lb propane tank. That would give me around 60 gallons of tank + any lines.

    Dan
     
  2. John Noon

    John Noon Well-Known Member

    Likes Received:
    588
    Trophy Points:
    113
    don't use a propane tank the particular laws in Canada regarding modifying air storage tanks or making one without certification in place are very short. In case of accident you have one option "Plead Guilty" opening up all sorts of lawsuits for anyone that may get injured from a failure. Oh and household insurance will find a way of not paying out any claims so you would be on the hook for the full amount.

    Air compressors in parallel will need valves to dump pressure right before a manifold also backflow prevents so as not to place any extra strain on the compressor during start up.
     
  3. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
  4. John Noon

    John Noon Well-Known Member

    Likes Received:
    588
    Trophy Points:
    113
    well that was fast. usually takes me a couple of minutes to find those documents.
     
  5. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    Hi John,

    What is the reason for the valves?

    My thinking is the two compressor tanks are plumbed together and act as one tank. Either the pressure in that combined tank is low and the compressors start up or it is enough to open their respective switches and they shut off. No compressor should see any pressure higher than the highest of the two pressure switches dictate. It's unlikely that they will start at exactly the same.

    There aren't many clear answers on the web about this.

    Dan
     
  6. John Noon

    John Noon Well-Known Member

    Likes Received:
    588
    Trophy Points:
    113
    You want the pressure to be dumped after it shuts off. This reduces the stress on the compressor during startup and If memory serves you do not want to be back feeding a compressor either.
     
  7. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    I found this video that makes some sense of it. (until the guy hooks up the extra 7 hoses! LOL)


    This is effectively what I want to do.
     
  8. John Noon

    John Noon Well-Known Member

    Likes Received:
    588
    Trophy Points:
    113
    the key to what he was doing is having matched compressors and for the limited use probably never find the need for pressure dumps. They are on the compressor separating the piston from the tank typically so you may actually have them and they make that little pfft sound when the compressor shuts off.
    Or you may not have them, if you are not running them 8-12 hours a day you may never notice any problem. If the breaker kicks off during start-up then that is from the extra load of having the compressor exhaust above atmospheric pressure and loading up the motor
     
  9. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    His point of common coupling is before the regulators. If you couple them after their respective regulators, the a check valves should be used. This prevents damaging the regulators with back pressure.

    Got it.

    Thanks,

    Dan
     
  10. John Noon

    John Noon Well-Known Member

    Likes Received:
    588
    Trophy Points:
    113
    That makes sense, it has been a few decades since I played with pneumatics.
     
  11. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    I'll do some experimenting...with full body armour of course. LOL
    I'll post what I have learned.

    Dan
     
  12. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    I have both my old compressors running in tandem.
    [​IMG]
    The one on the left is a 1.5 horsepower (mystery CFM) with a 14.5 gallon tank.
    The one on the right is a 1.0 horsepower twin cylinder 6.5 CFM@90 psi and 17 gallon tank.
    Pressure switches are both set to 120 psi. From the tanks I run through ball valves and into the 5 port manifold.
    If I just want the extra capacity, I can switch one compressor off and let the one that's running fill both tanks.
    Also, on the manifold, I have extra ports for adding another additional tanks.

    I can run the die grinder or sand blaster continuously with this setup. Mission accomplished.

    Dan
     
  13. Icho-

    Icho- Staff Member

    Likes Received:
    152
    Trophy Points:
    63
    That's pretty cool Dan. I don't remember the specs of my compressor but it is not enough to continuously run my sand blaster. I've also noticed that after a while I have to let the compressor catch up it I'm using a larger die grinder. Some day I'd like to upgrade.
     
  14. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    970
    Trophy Points:
    113
    I was contemplating going down to the store and dropping $800 on an 11.5 CFM, then the washing machine crapped (ka-ching) out, was needing new tires (ka-ching) etc. So I reckoned I could improvise something. I had the one compressor for years and looked after it. I swapped a kitchen knife for the other. With a bunch of plumbing they work like a single unit with the CFM and extra storage that comes in handy. Maybe when I sell a few more knifes I can get a new one and put those compressor motors to use. Hmmmm.

    Dan
     
    Last edited: Apr 3, 2016
  15. Icho-

    Icho- Staff Member

    Likes Received:
    152
    Trophy Points:
    63
    I like you attitude. Lol
     

Share This Page