gtslabs wrote:
What are the calculations to size a pully if I change the horsepower of
the driving motor on an air compressor? Also will changing the
Diameter without the HP help a compressor run with less effort?

You're thinking backwards. Think of it this way: at its max RPM, the air pump
will deliver max CFM but will take max horsepower. If you want the pump to run
quieter and with longer life at the expense of delivered air, you can decrease
the size of the motor pulley, thus slowing the pump. This will require less
horsepower, so you might want to downsize the motor as well.

Run the air pump slower, sure it "takes less effort" because it's doing less work.

Air pump speed (with a given driven pulley) is proportional to the size of the
motor pulley diameter. Cut the diameter from 5" to 3" and you can go from 5hp to
3hp.

If you have a "real" compressor (Quincy, Ingersoll Rand..) you can call the
company and talk to someone with smarts and experience who can tell you right
out what you want to know.

Grant