Well, got my new compressor pump today, and found myself going DUHHHHH! Its a 36cfm model from the Surplus Center that one of you guy suggested, and it has a 15.75" double A-groove pulley, with a 1200rpm MAX! Now for the DUH part, I dont have a pulley for the AC motor. Nor do I have a clue what size I need. Its a 7.5 horse Lesson with a 1740rpm max with a 1.375 dia. shaft. Anyone have any ideas of how I figure out what size pulley I need for this combo?
Thanks

Stryder

 

36scfm?? What are you going to power with this thing, that must be massive!!!! What size tank????

Search on the net for belt pulleys and find a place, however they are going to want all the dimensions as well...

Good luck...

 

By my calculations, a 10.86" drive pulley should do it.

 

All,
My calcs say 10.86" also. This seems rather large just from a common sense approach?
A 9.05" diameter pulley would get you 1000rpms at the compressor.
Do you have a HP curve for the compressor? Please review your cutsheet for a HP curve.
KingFisher

 

All,
I've been messy around and did some calcs:
A 32 SCFM compressor can deliver 5.3 ACFM @ 90 psig. My inlet conditions were 80F with 50% relative humidity, not ideal.
This compressor is not that big and 7.5 HP should be able to drive it. Was there any recommended HP for the compressor?
KingFisher
PS I've got a 6HP (5Hp with 1.15 SF) that is rated at 9.9 ACFM at 90 psi.

 

I was expecting some amount of paperwork when I opened the box, but it held just the pump. I'm planning on calling and finding out if someone just forgot to put them in. I've had that happen before with stuff from P.A.W. For know, I just have the rating from their web site, which calls for a 7.5Hp for full output. Its rated at 23 cfm@175psi, which figures pretty close to 36cfm at 90psi. Not bad for $500. Thanks for the pulley calc. What is the formula you used? or did you have a chart. Who knows, it might become handy down the road.
Mach, for your info, a compressor this large is necessary for sandblasting. well at least sandblasting for long periods of time. As far as tank size, I have the 60 gal upright from my old comp. and 3 20gal LP tanks (yes, they have been tested) giving me 120gal.
Thanks again!

Stryder

 

That is some serious SCFM...

That is weird on the Acfm at 90 is only 5.3...

All right guys school me...

whats SCFM, ACFM, and the difference..

Sandblasting I understand the cfm requirement...Great idea on the pane tanks...I have one sitting around that is like 50+ gals..on only $100 dollars...although it works better with Pane in it, runnin a diesel...

 

All,
ACFM = Actual cubic feet per minute at a working pressure (90 psi)
SCFM = Standard cubic feet per minute is the volume of air required from the atomsphere to create the actual volume.
Since atomspheric air is not compressed, it will required a larger volume than what is delivered at working pressure. It's confusing and always will be.
Secondly, a 7.5 HP motor cannot deliver more than 12 to 15 ACFM at 90 psi, Sorry! That's just the reality that we live in.
KingFisher

 

All I know is this this will put out a buttload of air. Besides, every air tool I've ever seen is rated for the SCFM of a compressor @ 90psi, not ACFM. Thanks again for the pulley dimension!

Stryder

 

Thanks for the compressor 101...

 

All,
It makes sense that a compressor pump would be rated in "SCFM". Why? Because it is the only constant the compressor manufacturer can relay to the buyer. The compressor manufacturer has no idea what delivery condition the compressor will be used for. Will you deliver air @ 90psi, 100psi, 120psi? All three of these conditions, "ACFM" will render different results from the same compressor but the compressor will move the same "SCFM". Ergo, the manufacturer will publish the only constant, the amount of air the compressor will consume @ "SCFM", that being the atomspheric condition which will feed the compressor.
Good Luck,
KingFisher