A Archie Member Messages 2,297 Sep 26, 2008 #1 How would I go about estimating the cfm of my compressor? It's quite old and I can't find any tags that detail it though there's loads of other info on it. Last edited by a moderator: Sep 26, 2008
How would I go about estimating the cfm of my compressor? It's quite old and I can't find any tags that detail it though there's loads of other info on it.
malcolm & Clementine the Cat Messages 9,623 Location Bedford UK Sep 26, 2008 #2 For old compressors the motor markings might be useful - 3hp motor might do 10 to 13 cfm, 1.5hp half that. Last edited: Sep 26, 2008
For old compressors the motor markings might be useful - 3hp motor might do 10 to 13 cfm, 1.5hp half that.
A Archie Member Messages 2,297 Sep 26, 2008 #3 The panel says made in 1969 and all manner of test pressures but no cfm. Motor says 7.5 HP though....
The panel says made in 1969 and all manner of test pressures but no cfm. Motor says 7.5 HP though....
shenion Tool Pack Rat Messages 7,586 Location Stone Mountain, GA USA Sep 26, 2008 #4 If you know the size of the tank, you can calculate the CFM by measuring how long it takes to fill and and the start/end pressures. For example: My tank is 60 gallons (US Gal) 60 gal = 8.022 cubic feet from empty to 120psi is 8.28 bar (atmospheres) so, to fill is 8.022 * 8.28 = 66.389 CF It took 5.1 minutes to fill 66.389 CF / 5.1 minutes = 13.28 CF/minute Not bad as the pump is rated at 9.8 CFM at 90 PSI. Here, the displacement of the pump is not specified, just the actual specs under pressure. My pump is probably near 15 years old. I wanted to see how worn out it was. Turns out it is still good.
If you know the size of the tank, you can calculate the CFM by measuring how long it takes to fill and and the start/end pressures. For example: My tank is 60 gallons (US Gal) 60 gal = 8.022 cubic feet from empty to 120psi is 8.28 bar (atmospheres) so, to fill is 8.022 * 8.28 = 66.389 CF It took 5.1 minutes to fill 66.389 CF / 5.1 minutes = 13.28 CF/minute Not bad as the pump is rated at 9.8 CFM at 90 PSI. Here, the displacement of the pump is not specified, just the actual specs under pressure. My pump is probably near 15 years old. I wanted to see how worn out it was. Turns out it is still good.
A Archie Member Messages 2,297 Sep 26, 2008 #5 Thank you, Malcolm, for moving this! Sorry it went in the wrong place to start with. Shenion, assuming the start pressure is atmospheric and the end is 120 psi, what would be the calculation I would need to do?
Thank you, Malcolm, for moving this! Sorry it went in the wrong place to start with. Shenion, assuming the start pressure is atmospheric and the end is 120 psi, what would be the calculation I would need to do?
andypocock Member Messages 304 Sep 26, 2008 #6 Just substitute the volume of your tank in cubic feet for the 8.022 and change the fill time. Andy
andypocock Member Messages 304 Sep 26, 2008 #7 But.. Couldn't we argue that the pressure is already 1 bar before we start? So the amount pumped in this example is actually 7.28 x the volume which means that shenion's compressor is actually managing 11.45cfm Andy
But.. Couldn't we argue that the pressure is already 1 bar before we start? So the amount pumped in this example is actually 7.28 x the volume which means that shenion's compressor is actually managing 11.45cfm Andy
shenion Tool Pack Rat Messages 7,586 Location Stone Mountain, GA USA Sep 26, 2008 #8 It was at 0 bar in respect to ambient then added 6.28. If you wanted to use absolute pressures, then it would be 1 to 7.28; same thing. That's why I said use the change in pressure. I want to recalculate mine going from 90 to 100 PSI or 30PSI (just over 2 bar) difference.
It was at 0 bar in respect to ambient then added 6.28. If you wanted to use absolute pressures, then it would be 1 to 7.28; same thing. That's why I said use the change in pressure. I want to recalculate mine going from 90 to 100 PSI or 30PSI (just over 2 bar) difference.
A Archie Member Messages 2,297 Sep 26, 2008 #9 ok. So that was a fairly daft question to ask. I shouldve thought about it a bit more! Thanks guys.