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Old 02-19-2008, 03:03 PM
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Air compressor and CFM

I have a AC that has a 30 Gal. tank...If i plum another 30 Gal tank nest to it, does anything change, besides the fact that i now have 60 gal storage capacity? Like the CFM???? I can't afford to run out and buy a new ac...

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Old 02-19-2008, 03:43 PM
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re:Air compressor

The 2 thing that l would think about is the run time of the compressor, if the compressor it self is oiless(say 10 cfm) she will burn up with hard use in time, second the hose connecting the one tank to the other, don't restict it(bigger is better than smaller) you'll get what ever cfm the pump puts out but it will have a slower response time to build back up, you could turn up the cut out if its not to the max that will help with the start of use and keep your cfm up alittle longer but once again it makes it work harder, my advise would be if you have pump seperate from motor would be buy a bigger compressor pump(18 cfm plus) a 3 to 5 hp 220 volt will run that, l know here just the 60 gal tank is $300 so l just built on top of my old one(cheapier)
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Old 02-19-2008, 03:54 PM
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I got it now

I did a search and found some good info. I bought a 80 gal. ac tank at a auction, no motor or pump, now i will look for a pump, and motor. there must be 50 threads on this, next time i will SEARCH first........Thanks
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Old 02-19-2008, 04:01 PM
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Quote:
Originally Posted by awert
I have a AC that has a 30 Gal. tank...If i plum another 30 Gal tank nest to it, does anything change, besides the fact that i now have 60 gal storage capacity? Like the CFM???? I can't afford to run out and buy a new ac...

No, adding another tank will not change your CFM's, just your storage capacity. It can also lead to exceeding the duty cycle of your motor/pump when it tries to refill double the tank capacity it was designed to run with. Do a search on this forum for 'compressor' and 'oldred' both as he has explained this in previous posts better than I could. Only way to change CFM is to get a larger pump or run the one you have faster which is limited by the design speed of the pump. Just putting a bigger motor on it won't make a difference ie: a 100 hp motor turning 1725 rpm on my compressor will not make any more air than the 5 hp I have on there which turns 1725 rpm as long as the pump speed stays the same, would just make for a bigger electric bill
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Old 02-19-2008, 04:17 PM
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I have my small 5gal compressor plumbed with another 5gal tank, it helps alot when using an impact, now I can actually take 5 lugs off before loosing pressure.
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Old 02-20-2008, 11:14 AM
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All compressors put out less CFM as the PSI increases.
The higher the cut-off is set, the less CFM the pump is putting
out at those ending PSI's.

Set the cut-off lower and it will do better, work less,
and generate less heat.
That's why my new Eaton shuts off at 150, unlike the earlier units
that shut off at 175. They work much better that way.
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Old 02-20-2008, 12:42 PM
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JC, That's a darn good point and if someone has a compressor with an oversized tank that takes too long to recharge they can actually benefit from the lower cut-off pressure. The thing will tend to cut on/off more often but it will make it somewhat easier on the pump and will actually have the effect of increasing the CFM due to not only the what you mentioned but also because the cooler running pump will be more efficient. These reasons are exactly why a 60 gal tank is sometimes a better choice than an 80 gal on some of the smaller pump/motor combos and almost always the better choice when looking at the very common 5 HP single stage outfits.
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Old 02-20-2008, 07:29 PM
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Quote:
Originally Posted by jcclark
All compressors put out less CFM as the PSI increases.
The higher the cut-off is set, the less CFM the pump is putting
out at those ending PSI's.

Set the cut-off lower and it will do better, work less,
and generate less heat.
That's why my new Eaton shuts off at 150, unlike the earlier units
that shut off at 175. They work much better that way.
what is the typical method used to set cut-off?
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Old 02-21-2008, 05:07 AM
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There's a pressure switch somewhere on the compressor.
It supplies the electrical power to the motor.
It has adjustable set screws for on and off settings.
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Old 02-21-2008, 06:55 AM
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Quote:
Originally Posted by jcclark
There's a pressure switch somewhere on the compressor.
It supplies the electrical power to the motor.
It has adjustable set screws for on and off settings.

I would strongly recommend not tinkering with that pressure switch because it can be very tricky and it is easy to get out of adjustment but sometimes not so easy to get back. Some may say that it is as easy to do as simply turning the screw but there is more to it than that and even though it may seem to be doing ok you may end up with a very inefficient set-up or even possibly a dangerous set-up. I have seen this many times on gasoline powered compressors because it is more critical on them than the electric type but even the electric ones should only, if ever, be adjusted by a professional. I have said before and I still believe that those switches should be fixed at their setting and nonadjustable because usually tinkering with them just leads to trouble.
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Old 02-29-2008, 04:54 AM
 
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I felt like I had to adjust mine because I didn't have any data on the surplus compressor, just the information on a sideplate. It's rated at 90cfm @ 100psi. Nothing to show if that's a recommended or maximum pressure. The pressure switch I bought had fairly good information about the settings, so I managed to get cut-in, cut-out and range reasonable. Without the chart that came with the switch, I don't think trial-and-error would ever get it adjusted right. They are not two isolated adjustments.
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Old 02-29-2008, 08:32 AM
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Quote:
Originally Posted by grouch
It's rated at 90cfm @ 100psi. .

That is a pretty good rating...I don't think you'll need much more air for a home shop....
Unless you start sandblasting bridges or knocking up concrete with a jackhammer as a hobby.


Later, mikey...

(see what happens when you leave a decimal point out?)
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Old 02-29-2008, 08:53 AM
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Quote:
Originally Posted by powerrodsmike
(see what happens when you leave a decimal point out?)

That's not a mistake, I am somewhat familiar with his set-up and it really is rated that high! He is the first person I ever heard complain about having TOO MUCH air!
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Old 02-29-2008, 09:39 AM
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Wow...Ok .I'm not disbelieveing it , most folks don't get their hands on a big industrial compressor.


I had a Kaeser 15 HP rotary that made 69 cfm @ 90 psi, but it was so noisy and used so much electricty that i traded it for a 7.5 that makes 32 CFM @90...I have lots of air...



Later, mikey
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Old 02-29-2008, 09:49 AM
 
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Quote:
Originally Posted by powerrodsmike
(see what happens when you leave a decimal point out?)
Hmph. Come in out of a cold, miserable rain to find Mikey pickin' on my postin'. Aight, I'll dig through my journal mess.

No decimal point displaced but I did transpose and scramble the other numbers. It's an "Iowa Mold Tooling Co., Inc. Model No. DA650" -- diesel, air compressor, 6 cylinder, 50 CFM @ 90 PSI. The 15 HP diesel engine was replaced with a 7.5 HP farm duty electric motor. It was originally part of a tank maintenance kit that included a hoss of a 3/4" ratchet and socket set.

You can see where I got the "90" in the first post. I adjusted the cut-off to 100, so that's where that number comes from. Sorry about all the confusion.

C'mon, Mikey, cut me some slack. I'm old, cold and running out of brain cells.

Quote:
Originally Posted by oldred
He is the first person I ever heard complain about having TOO MUCH air!
Hey, you remember helping me through all that cobbling together! I sure won't forget it and think of all your help and advice every time I use an air tool.

I never have to worry about having enough air, now. Even when I ran a sandblaster or a DA, when the compressor kicked in it would catch up and shut off while I was still running the tool. I was able to use both of those tools even when I had the little 20 gallon tank hooked to the compressor. It was a good illustration of the fact that the compressor drives the tools, not the storage tank.

It's just a world of difference from when I relied on that portable, oilless noise-maker. Best thing that ever happened when it shot its little piston through the side of the compressor.
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