CFM question

[bayzoo]

Hi,

I’m trying to understand CFM figures - if a manufacturer quotes a compressor can deliver 14cfm at 150psi, will this CFM be less at 90psi, the pressure at which many air tools run at?

I understand actual CFM (FAD) the tool gets is different from what it sucks in which is the figure most manufacturers quote.

Thanks.

 

[Spark plug]

Think of it like this 1 bar is atmospheric pressure at sea level, so if you want 1 cfm at 1 bar out of your compressor you need to put 1 cfm at 1 bar in, this is FAD ( free air delivery)

But if you want 1 cfm out at 7 bar you need to put many multiple cfm’s in at 1 bar.

So the higher the pressure the lower the cfm.

 

[bayzoo]

Thanks, I think I get it. I will need to brush up on my physics though.

It is a bit of a minefield though considering manufacturers quote figures based on perfect unrealistic conditions.

I suppose that’s why I keep hearing buy the biggest and highest output compressor you can afford/accommodate.

 

[Spark plug]

What is it you intend to run from a compressor?

 

[bayzoo]

I’m looking to get a plasma cutter in the future, and when I get the space I’ll be doing car restoration so an air hammer would be useful as well as an impact wrench as well as other equivalent tools. I’d also like to do light blasting on small car parts but I know you’re better off with much higher CFM abilities than I previously quoted so that’s more of a dream!

Although I see a YouTuber seemed to use the SGS cabinet successfully with a Wolf Dakota 100… think it needs 10 CFM.

 

[R Kraft]

Hi,

I’m trying to understand CFM figures - if a manufacturer quotes a compressor can deliver 14cfm at 150psi, will this CFM be less at 90psi, the pressure at which many air tools run at?

I understand actual CFM (FAD) the tool gets is different from what it sucks in which is the figure most manufacturers quote.

Thanks.

CFM at a lower pressure should be higher.

 

[Spark plug]

Apart from the shot blasting, I don’t think your being too unrealistic at 14 cfm, the worst offenders for consuming air tend to be spiny tools, like grinders, sanders and die grinders.

You also have to take in to account the duty cycle of the tool, say an impact wrench will run for say, max 30 seconds per minute but a sander can run non stop for 15 minutes non stop.

 

[bayzoo]

Apart from the shot blasting, I don’t think your being too unrealistic at 14 cfm, the worst offenders for consuming air tend to be spiny tools, like grinders, sanders and die grinders.

You also have to take in to account the duty cycle of the tool, say an impact wrench will run for say, max 30 seconds per minute but a sander can run non stop for 15 minutes non stop.

That works for me - I’ve got an electric grinder anyway; a die grinder would useful so I’ll park that with the shot blasting dream…

 

[Spark plug]

That works for me - I’ve got an electric grinder anyway; a die grinder would useful so I’ll park that with the shot blasting dream…

A die grinder will work but only for a minute or two before you have to stop and wait. But blasting is more like 10 or 20 seconds before it’s time to put the kettle on.

 

[bayzoo]

I’m in the market for a new place, if/when more houses come back on the market at semi realistic prices I’ll be asking to see thee CU’s to see if they have 3 phase… though I could be waiting a while.

 

[not done it yet]

I don’t think (m)any specs use anything other than air at atmospheric pressure.

The main discrepancy is when compressor adverts state the volume of the compressors cylinder(s) (air displacement) rather than the real volume of air that is delivered to the receiver (FAD), which will be rather less than the former sensible rating.

The latest ’hype’ seems to be to include the receiver volume as though it is the most important factor when choosing a compressor - all it does is take attention away from the displacement v FAD issue.

 

[brightspark]

I’m in the market for a new place, if/when more houses come back on the market at semi realistic prices I’ll be asking to see thee CU’s to see if they have 3 phase… though I could be waiting a while.

dont hold your breath ive only been in a dozen houses in over 50 years working that had 3 phase

 

[R Kraft]

I haven't ran across that rating, the smallest one that I have is rated 4.0 SCFM @ 90 PSI .
It provides 90psi to a tool that consumes, 4 CFM.
They don't mention FAD on any of my compressors, is that some sort of an European standard ?

 

[not done it yet]

I’m in the market for a new place, if/when more houses come back on the market at semi realistic prices I’ll be asking to see thee CU’s to see if they have 3 phase… though I could be waiting a while.

We had a 3 phase supply when I was growing up. A farmhouse.

I run my five 3 Phase machines from the single phase supply (not all at the same time) without any problems. A great deal cheaper (and easier) than having a 3 phase supply to my home.

 

[not done it yet]

I haven't ran across that rating, the smallest one that I have is rated 4.0 SCFM @ 90 PSI .
It provides 90psi to a tool that consumes, 4 CFM.
They don't mention FAD on any of my compressors, is that some sort of an European standard ?

Lets‘s not muddy the waters with false claims. Do tell us the power rating of your compressor motor, for a start.

If your tool is actually requiring 4 cfm, that is almost certainly the volume at atmospheric pressure, not 6 Bar . The 90 psi is simply analagous to the voltage required in your household wiring - not the actual power of anything plugged in. It just means that the tool would not perform at, say, 50psi.

If your tool (please enlighten us as to its identity) were to really require 4cfm measured at that 6 Bar, you would almost certainly have a very large compressor - likely in the region of 8-10kW (11-14 HP). And that is your smallest?!? What is your largest?