does cfm goes up when the psi goes down?

[phasesonix]

if I have a compressor that does 8cfm at 100 psi, and if i only need 20 or 40 psi will the cfm go up at those lower pressures?

I've looked on the net and from what I've found it seems it does..anyone know for sure?

 

[zzr1200]

Yes....but by how much is a guestimate......

The manufacturers usually state CFM (Cubic Feet per Minute) this is the amount of air that the pump can shift at normal sea level air pressure (ie: 14.7lbs per sq in or 1 bar). As the pressure rises its harder to compress the air in the tank if its a 14cfm pump at 1 bar it is probably managing to compress nearer to 9 or 10 cfm at 125psi (ie: 9 or 10 FAD's). So the compression ratio is curved, the higher the pressure the less cfm's compressed.

Most air tools state required cfm at 90 psi which is another consideration to make.

 

[Shox Dr]

You also have to remember manufacturers state CFM of the pump and not what is available. so reduce that by 25-35% to give FAD (Free Air Delivered)

 

[phasesonix]

Yes....but by how much is a guestimate......

The manufacturers usually state CFM (Cubic Feet per Minute) this is the amount of air that the pump can shift at normal sea level air pressure (ie: 14.7lbs per sq in or 1 bar). As the pressure rises its harder to compress the air in the tank if its a 14cfm pump at 1 bar it is probably managing to compress nearer to 9 or 10 cfm at 125psi (ie: 9 or 10 FAD's). So the compression ratio is curved, the higher the pressure the less cfm's compressed.

Most air tools state required cfm at 90 psi which is another consideration to make.

so you could make a graph with the 100 psi cfm at the top and sea level air pressure cfm at the bottom and psi on the x axis and judge it from that...

 

[eil]

Is cfm higher at lower pressures, yes, as it has less resistance to overcome for the air to flow. Reading between the lines you are trying to make sure that you have enough capacity to feed your air fed mask and hvlp spray gun, if that is so you have to add a bit on top to allow for pressure drops in your filters, pipework, how cold the air is, how moist the air is, the efficiency of the compressor falling when its been running a while etc