Air compressor hose size?

Discussion in 'Mechanic and Repair' started by snowjeep, Dec 30, 2009.

  1. snowjeep

    snowjeep LawnSite Senior Member
    Messages: 463

    I have a kobalt 30gal 3hp compressor. I need to replace my 3/8 air hose and womdering if there is any benefit to going larger like 7/16 or 1/2 inch? What can I do to make the air last longer? I just replaced a die grinder I use a lot and went from 5cfm usage to 3 cfm, are there any tricks to help?
  2. DT Lawn Care

    DT Lawn Care LawnSite Senior Member
    Messages: 850

    Wider hose won't keep the air longer, but will allow you to run higher pressure.
  3. snowjeep

    snowjeep LawnSite Senior Member
    Messages: 463

    Anything I can do to make the air last longer? Beside getting new compressor. I set the regulator at 90psi and the tank fills to 155psi. Are those adjustments correct? I can set tank to maybe 165 safely would that help? I am also due for oil change, is there a synthetic out there which is better than they come with from the factory?
  4. DiyDave

    DiyDave LawnSite Bronze Member
    Messages: 1,695

    One thing you can do is to increase your storage capacity. Get a air compressor with a bad compressor, but a good tank, throw the compressor away, plumb the tank into your system, and you will have your compressor run less cycles.
  5. rlitman

    rlitman LawnSite Bronze Member
    Messages: 1,764

    Less run cycles, but a longer run time. With a small compressor, that can overheat the pump (especially on an oilless setup). Probably not the best idea.

    You can save some air, by having better air flow. Its a bit counter-intuitive, but having too constrictive an air flow (like from a long 1/4" hose), will slow down your tools a lot (due to internal pressure losses under flow).

    Your 3/8" hose should be ok for more CFM than your compressor can handle, BUT, restrictions in the hose can be a problem (and a 25 foot 1/4" coil hose connected directly to your compressor would also be plenty to run a die grinder). Do you have a quick release fitting on both ends of the hose? 1/4" quick releases restrict air flow a lot, and its best to only have one between the compressor and your tool (usually at the tool end of the hose). I use a brass coupling to connect hose to my compressor.

    BTW, as you may have noticed, with air powered tools, the better ones have more power, and use less CFM.
  6. DiyDave

    DiyDave LawnSite Bronze Member
    Messages: 1,695

    He said that he has a 3 HP, 30 gallon tank, I doubt that it is oil-less. Granted run times are longer but when the oil is hot, and moving, wear should be minimal. I have been running a 5 hp 60 gallon with a 30 gallon reserve tank for the last 20 or so years. I know anecdotal evidence isn't the best, but hey, it works for me, Que Sera, as the song says.:waving:
  7. rlitman

    rlitman LawnSite Bronze Member
    Messages: 1,764

    You make a very good point.
    Kobalt made both oil bath and oilless in the 30 gallon size range. I had recalled seeing mostly oilless under 60 gallon size in my local stores, but I just looked, and found both types.
    I feel even more silly, for not noticing the question about synthetic oil.
    I guess that answers the question. So, sure, more tank capacity couldn't hurt.

    I personally fill my compressor with Mobil 1 5w30. YMMV.
  8. snowjeep

    snowjeep LawnSite Senior Member
    Messages: 463

    Thanks guys info helped. It is oiled and will change with mobil. I will also remove 1 quick connect since I have 1 on tool end and at tank. I'll start looking on craigs list for a 60 or 80gal 220v. That should solve my problem.
  9. topsites

    topsites LawnSite Fanatic
    Messages: 21,653


    Once a tank reaches 80-90 or so psi it really doesn't help much in terms of volume to crank the pressure up way high,
    I'm not really sure why this is so but I do know very little air actually goes in a container as the pressure goes past 100.
    It's odd how that works, the motor will work its TAIL off to get that last 5-10 psi in there but the bulk of the volume lies
    below 80 psi (and actually if I listen to my truck tire as I'm filling it, that slows WAY down at 50 psi lol)

    The other thing is, especially on smaller 1-stage motor setups if you go much
    past 110 psi you're only risking motor failure, even with a 2-stage motor I'm not so sure.

    In this particular case the only thing that will make the air last longer is a smaller diameter hose,
    however this will result in problems as soon as you get into your high torque applications.
    You might can setup a device with a manifold and two different sized hoses?

    That or get another whole setup...

    What I usually do...
    Is just have to be patient in most cases, deal with it best I can, there are days I have to let the compressor "rest" for
    20-30 minutes because it's got so hot, there are some things that use a LOT of air but the last thing I need is a burnt motor.
    They're not cheap, last time I checked these compressor motors were running well over $100, the first (and hopefully last) time
    I burnt a motor it wasn't much more to just buy another whole setup, which is what I ended up doing.
    So you'll also want to check the oil requirements...
    On mine it takes 30w NON-detergent!!!
    Probably there's a reason for this, such as rubber seals, I suspect detergent oils might affect these in a bad way,
    so check this out and read up on it in your Owner's manual before you stick some Detergent oil in there (even if it is synthetic).
    Now if the Owner's manual says detergent oil (or doesn't mention anything about it) then I would next check for labels on and
    around the compressor, the tank and the motor itself, only after you're sure that detergent oil won't hurt it would I use synthetic.

    Hope that helps.
    Last edited: Dec 31, 2009
  10. DT Lawn Care

    DT Lawn Care LawnSite Senior Member
    Messages: 850

    My Kobalt 60 gal was factory set at 150 psi :laugh:

    Edit: Oh wait are you talking about hose pressure or tank pressure?

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