Upgrading shop compressor-help

Discussion in 'Mechanic and Repair' started by snowjeep, Sep 6, 2007.

  1. snowjeep

    snowjeep LawnSite Senior Member
    Messages: 463

    Porter Cable 175psi, 25gal, 2 stage, cfm @ 90psi 5.1, $484.00 w/shipping or Kobalt 155psi, 30 gal, single stage I think, cfm @ 90psi 5.7, $415.00 w/tax

    Which one and why. Tools used are die grinder, impact gun, cut off tool, air saw.
  2. WhitakerServices

    WhitakerServices LawnSite Member
    Messages: 159

    The cheaper one has the better cfm so I would go with that. I don't think the extra 20 psi is worth the extra $$$. 155psi is plenty to run an impact gun that would handle 99 percent of the bolts you will use it on. Just my opinion.
  3. Breezmeister

    Breezmeister LawnSite Bronze Member
    Male, from South Jersey
    Messages: 1,794

    Personally, I would keep looking, but if I HAD to chose between the two, it would be the Porter Cable @ 175 psi. The only problem I see is the 25 gal tank. Your die grinder will eat that 25 gals up quick.
    ericg likes this.
  4. barnard

    barnard LawnSite Senior Member
    Messages: 618

    Get a 60 Gallon tank
  5. chesterlawn

    chesterlawn LawnSite Senior Member
    Messages: 704

    Unless you are going to do alot of shop work I'd stick with the smaller tank. The bigger tank takes a longer run time to get to pressure for a quick job.
  6. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Maybe this article will help you decide which size/style compressor would best suit your needs.


    In my opinion a 2 stage is the way to go.
    The larger the tank the better to keep up with constant use of grinders/saws etc., A larger tank does take longer to fill/build up pressure but once filled if there are no leaks in the hose/connectors or any piping it will stay full when not in use thus no build up time.

    I have a 2 stage 80 gal. and it keeps up with anything I plug up to it.

    Oh, I also have a small 20/30 gal single stage that will not stay up with my die grinder (steady use) and is only good for 3 to 4 pulls of the trigger on my impact wrench before having to wait for it to build back up.
  7. olyman

    olyman LawnSite Gold Member
    Messages: 3,649

    air die grinders--and air disc grinders--are the hardest on air usage--no matter what brand you buy----and a big da aint much better---been there---got em---
  8. twj721

    twj721 LawnSite Senior Member
    Messages: 619

    what ever you get be sure it is a 2 stage compressor a lot better than a single stage
  9. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    My problem is never the max psi per se, I don't run much past 110 anyhow so anything that's well over that is fine, it's the gallons!

    Here's the thing, once an air line's hooked up there's air volume inside of that line that is fed from one end as the other releases it. As soon as I pull the trigger it draws a solid amount of air from the one end, and even thou the regulator is feeding as fast as it can from the tank, there's TIME involved before that air travels along the line and can replenish itself at the business end, the longer the air line the worse the problem gets...

    There's an initial burst of pressure, and then it drops to a nominal psi...
    In other words, it's what it can sustain that's important, the initial burst can't be TOO high but the nominal can't end up too low!

    If you think of an a/c system in a car, it's the same thing... It's called the low and the high side but it's all one open loop, there's no actual 'break' between low and high, it's just that the compressor is literally sucking SO much out of one end and spitting it out the other that the pressure on one side ends up low and the other end high, but turn the a/c off and the high side feeds into the low so then both sides end up at the same psi, it is a matter of the freon flowing through the lines as psi's equalize, hope this makes sense.

    So even thou we're not supposed to run these tools past 90 psi, within a split second the pressure on the outlet side has dropped and I don't got squat, as things stand with my 27 gallon tank I HAVE to run it at 110 so after that split-second initial burst I have at least 90 nominal so the tool keeps running.

    Of course this isn't good for the tool, but there's nothing doing.

    Now in the tank it's the same thing, when it must suddenly meet the demand of however many gallons / minute these tools suck out, with a small tank that demand results in an immediate loss of pressure inside the tank itself, the larger the tank the less the actual psi loss is felt in the tank. Regulator or not, if your tank loses pressure between squirts of a trigger, the problem is worse than with a larger tank that has more air to feed out before the psi's drop.

    If you were to have too small of a tank combined with say 100-150 feet of air line, your problem would be compounded both by the issue of the length of air line in addition to having too small of a tank, you'd dang near have to turn it up past 120 just to get 90 psi nominal, I really don't think a tool would be keen on that initial 120 psi burst.

    I'd recommend the 30 gallon tank, those 155 - 170 psi won't make that much of a difference, I doubt you'll ever want or need to turn it up past 120, really you're not supposed to push it past 90 at all but I suspect you'll need 100-110 so the tools run for more than a second at a time...

    Your choice.

    MOW PRO LAWN SERVICE LawnSite Bronze Member
    Messages: 1,568

    I have the kobalt it does fine,picked it up in a pawn shop for $200 bucks itz brand new it seems okay i have the digital head .

Share This Page