CFM requirement variability

[LordPsychon]

This is a question that has been vexing me for quite some time. How is it that two air tools of similar make and design have significantly different CFM requirements? For example, the Dewalt air grinder versus the Kobalt air grinder - the former only needs 3 CFM (reportedly) while the latter hogs 7 CFM (again, reportedly). I know that they are not identical quality overall but why would the Kobalt need so much more? The RPMs on both are nearly equal.

 

[Scimmia]

Could be anything from motor size to simply rating them at different duty cycles. Remember, you're quoting "average" CFM requirements.

 

[MacMcMacmac]

See if they are being rated at the same duty cycle. Some will rate as low as 25% duty cycle. The real requirements are 4X the ratings at 100%.