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Old 09-07-2007, 12:30 AM
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snowjeep snowjeep is offline
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Upgrading shop compressor-help

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.
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Old 09-07-2007, 02:31 AM
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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.
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Old 09-07-2007, 01:38 PM
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Originally Posted by snowjeep View Post
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
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.
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Old 09-07-2007, 02:39 PM
barnard barnard is offline
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Get a 60 Gallon tank
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Old 09-07-2007, 04:02 PM
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chesterlawn chesterlawn is offline
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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.
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Old 09-07-2007, 07:45 PM
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Restrorob Restrorob is offline
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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.
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Last edited by Restrorob; 09-07-2007 at 07:53 PM.
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Old 09-07-2007, 11:04 PM
olyman olyman is offline
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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---
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Old 09-07-2007, 11:46 PM
twj721 twj721 is offline
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what ever you get be sure it is a 2 stage compressor a lot better than a single stage
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Old 09-08-2007, 03:47 PM
topsites topsites is offline
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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.

Last edited by topsites; 09-08-2007 at 03:56 PM.
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Old 09-08-2007, 04:07 PM
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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 .
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