Thread: Air compressor - a bit more technical

You are correct a 9cfm air tool run at that higher pressure will drain a normal compressor in seconds... go check out a crash repairs comp they are huge, typicaly 10-20hp 3ph 3 stage pump with a 200-500ltr tank!
Most continous use tools dont need to be run at 90psi, run a air grinder at 90psi and it will scream... more psi = more speed. Intermediate use tools run at higher pressure like nail/staple guns and rattle guns.

Lt/min is what the pump can push at a certain pressure, FAD is what it says... what the pump can supply in free air no back pressure.(ie tank with fully open outlet valve)
The higher FAD pump given the same hp/watt drive motor should mean a more efficient pump.
Most overate the cfm the truth is 240v@10amps will give a max limit of about 9-10cfm(3hp motor).
Some run the pump at a higher than normal rpm to gain cfm... the pump wont last long as heat kills them.

Belt drive Vs direct... 3 reasons I can think of
1. belt drive is better as the drive motor is isolated from the pump so vibration is not transfered. A compressor pump causes a fair amount of vibration... electric motors dont like vibration.
2. Most quality belt driven comps have heavy pulley on the pump to act as a flywheel futher reducing vibration, slow reving revving pumps pulse the input shaft with every compression stroke.(sit on a idling Harley Davison and you'll get what I mean)
3. And this pulley acts as a cooling fan(has blades for spokes) pushing air across the cooling fins on the pump... cant say I've seen a cooling fan on a direct drive?.

Another reason belt-driven beats a direct drive... if the magic black smoke is freed from the motor, it's a simple matter to replace. Direct drive motors tend to be either proprietary or expensive. Especially the cheaper "budget" compressors. It go PHOOM? Buy another, it's cheaper than repairs.

Many of us have been here..... A 50l direct drive compressor with a 2.5HP motor will probably claim 10cfm but deliver around 6 - 7 cfm free air... If you try and drive a 10cfm-rated spraygun it will run continuously, get very hot, and not deliver enough air. To achieve 10cfm free air, you'll need a 3HP belt drive that will probably claim 16cfm. These are around with single phase motors. Good luck.