My new compressor...

[Mugenlude]

Well, it has been a great week, I picked up some great tools at an auction, and my buddy found this great deal for me.... I got this compressor for $200 delivered! 60 gallon, single stage, 3hp motor... Now I just need to get my garage wired up for 220v. The guy I got it from said the pump was rebuilt recently and a lightened flywheel was installed... he also stated he would do ~15-16 cfm @ 90 psi, going to have to see how that goes though. We wired it up temporarily when he dropped it off, and it ran nice & quiet. He put a new gauge and switch box on it before selling it to me.

It will be nice to replace my current Craftsman 30 gallon oil-free compressor, which is loud as hell!!! The added capacity will be nice too.

 

[Mugenlude]

he also stated he would do ~15-16 cfm @ 90 psi, going to have to see how that goes though.

I'm not so confident on his claim, but either way, I'm trying to search on information as far as improving the CFM of a unit, just wondering if anyone could point me to a good link.

Why am I quoting my own post...

 

[goodfellow]

Judging simply by the platform, I'd say that this unit had at one time a much larger pump. Might even have been a 2-stage unit. The little single stage pump looks a bit undersized, and I doubt you'll get more than 9 or 10 CFM at 90 psi

If it works to your satisfaction, then you got a good deal! Congratulations!

 

[Uncle Buck]

I won't try to speculate on how it will perform, but I would agree that the pump is not original to that setup. I would bet it is still a step up from what you are replacing.

 

[Mugenlude]

Yes, I agree that it looks as if there was a larger pump at one point. Is there a standard for testing CFM?

 

[Mugenlude]

Is there a standard for testing CFM?

Here I am again quoting myself...

Here some info I found to measure the true hp and cfm rating...
http://www.truetex.com/aircompressors.htm

The way to measure true power is to measure the time it takes to pump the reservoir tank of known volume from a known starting pressure to a known ending pressure. Then you can figure the true CFM from the difference in starting and final pressures, times the volume of the tank, divided by the time it took to pump up. You can also time the pump-up cycle from the cut-in to the cut-out pressure, since that's how one usually runs a compressor. These true performance measurements are impossible to fake.

 

[Uncle Buck]

Yes, I agree that it looks as if there was a larger pump at one point. Is there a standard for testing CFM?

There are many engineer type members that I am sure know all about how you calculate CFM and many other things as well, hopefully one of them will be happy to chime in and share. I must say I do not know how, but just wait someone will know the answer.

 

[LoneGunman]

No way in hell will that put out 15 CFM, I'm thinking 9 will be a struggle, still if it's a step up it's a step up.

 

[Mugenlude]

No way in hell will that put out 15 CFM, I'm thinking 9 will be a struggle, still if it's a step up it's a step up.

Yeah, I'm thinking that number is inflated... but like you said, it's an upgrade for me, so I'm happy. Once I get it wired up I'll do some testing as far as CFM goes to see what it actually provides. I'm going to test out my current air compressor tonight to see what I come up with...

 

[billymade]

On the other hand try the compressor with the air tools you want to use; if it keeps up with them, then it works! You can get stuck trying to figure out specs like cfm ratings etc. but real world usage I think is the best way to test something; does it do what you need it to? Then, its a solution to your needs; die grinders and dual action sanders usually **** up the most cfm. If you get the model # and serial # off the sticker on the back (yellow left back) you could probably figure out what it came with originally; cfm ratings too with the original pump.

 

[Mugenlude]

On the other hand try the compressor with the air tools you want to use; if it keeps up with them, then it works! You can get stuck trying to figure out specs like cfm ratings etc. but real world usage I think is the best way to test something; does it do what you need it to? Then, its a solution to your needs; die grinders and dual action sanders usually **** up the most cfm. If you get the model # and serial # off the sticker on the back (yellow left back) you could probably figure out what it came with originally; cfm ratings too with the original pump.

Either way, the new compressor is going to have more capacity than the 33 gallon unit I have now, I really can't see it being a downgrade, unless something is broke! I didn't really NEED a new compressor, but I think it was a good deal, so there it is in my garage.

I glanced at the back this morning as I left for work, and I didn't see a yellow sticker on the back. I did make note of the pump though (Schultz MSL-10 MAX)... here are the specs I found on the unit... regardless of the work the guy preformed, I think he was stretching the number a little

Displacement ---- Max Pressure --- Free Air Delivery @ 90 psig --- RPM
-- 8.5 cfm -------- 125 psig ------------ 5.9 cfm ---------------- 810
-- 10 cfm --------- 125 psig ------------ 6.8 cfm ---------------- 950
-- 15 cfm --------- 125 psig ------------10.2 cfm --------------- 1430

 

[Mugenlude]

So I did some tests on my current Craftsman 33 gallon, 110v, 2hp, Oil-free compressor based on the website I mentioned earlier in the thread... http://www.truetex.com/aircompressors.htm The only thing that throws me with this article is at the end of the example is states...

The error range in our estimate is perhaps about 30 percent (the true value might perhaps be as much as 8 CFM or as little as 5 CFM).

That seems like a pretty high error range to me, not quite sure where 30% comes from either...

Here my results of the testing...

Starting ---- Cut-off ---- Time (sec) --- Calculated CFM ------- +/- 30%
61 psig ----- 146 psig ----- 225 ------ 6.8 cfm @ 61 psig ---- 4.8 to 8.8 cfm
90 psig ----- 146 psig ----- 126 ------ 8.0 cfm @ 90 psig ---- 5.6 to 10.4 cfm
115 psig ---- 146 psig ----- 61 ------- 9.1 cfm @ 115 psig --- 6.3 to 11.9 cfm

My cut off is setup at 146 psi, is this too high? I have an output regulator and gauge which I have turned down to ~105 psi to my tools.

These numbers seem really high to me, can someone else do the same test on their compressor to see what the numbers look like? I setup an excel spreadsheet to do the calculations, all you have to do is insert the tanks size, starting psig, cut-off psig, and elapsed time. I attached the .xls file inside of a .zip file since I can't attach a .xls file...

In the article it mentions this is for single-stage compressors...

Assumptions: We have assumed a single-stage compressor, which is to say, just about anything small or portable; two- and three-stage compressors are somewhat more efficient, and will yield better results, but only become economical in larger sizes. Our proportioning calculations are based on the ideal gas law PV = nRT with isothermal compression (pressure and volume of the compressed air are changed, but the temperature is not, which is the case for cooled compressed air). This method does not account for ambient humidity condensing in the tank, for different ambient pressures, or for heating/cooling of the air; these are relatively minor but not necessarily insignificant factors.

Maybe humidity is where the 30% error comes from, but states that it is relatively minor.

I should probably start a new thread on this...