Pulley reduction question?

[PipeOrganGuy]

Hi, I’m new to this group so bare with me... I’m a Pipe Organ builder in Houston, TX. I have a blower motor from 1926 and the armature scraped the stator and burnt out the winding. My problem is the old brush motor ran at 1135 rpm and a new motor runs at 1740. (Single phase, 230 volt, 3hp) I have the room to reduce the speed by belt, but unsure of the size of pulleys. I’ve ordered a 3.65” pulley, double V-belt for the motor, and a 5.65” for the blower. Is this the right size? Where would I look for the right formula to calculate the difference? I divided 1135 by 1740 then multiplied that by the 3.65” pulley to get the 5.65” However I might be way off base on that guess work. Thanks for anyone’s input on this matter.

 

[scarecrow55]

Yes, you are correct in your formulae. The blower shaft will be reduced in speed by the pulley dia ratios.
If the blower was close coupled before, it may not take the new load on the shaft from the belt. You'll have to check the shaft & bearings will take this new "overhung" load

 

[PipeOrganGuy]

Thanks for helping me. I installed the motor, belt drive, and the Church has an Organ again. The speed was close enough to the same because the tuning of the pipes didnt change. Thank God, thats an all day affair to tune over 3,000 pipes. The bearings were fine, thats the first thing I looked at before concidered belt drive. All is well! Thanks again!