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pulley rpm math

pulley rpm math

pulley rpm math

(OP)
Please check my math. 3400rpm mtr with 5" pulley connected to a 10" pulley on compressor. We will replace 3400rpm mtr with a 1725rpm mtr. So, either the mtr pulley needs to be enlarged or the compressor pulley needs to be smaller:

(5 x 3.14 x 3400)/(10 x 3.14) = 1700.9 comp rpm
(9.85 x 3.14 x 1725)/(10 x 3.14) = 1700.0 comp rpm
(5 x 3.14 x 1725)/(5.07 x 3.14) =1701.2 comp rpm

tks, paul

RE: pulley rpm math

You need a 1:1 ratio.

Check your torque/power requirements before doing this.

RE: pulley rpm math

You like waving pi around do you? img http://i19.tinypic.com/43cuc6f.gif]

You can leave it out. You have the numbers right.

Don't get too hung up on them.  A few RPM will not make a big difference.  Usually you just go for the closest off-the-shelf size to get you back to where you want to be.

I would caution you to not use a small pulley as below 5 inches starts to be very hard on belts.

Keith Cress
kcress - http://www.flaminsystems.com

RE: pulley rpm math

Also a smaller pulley puts more force on the bearings for same power transmission.  If you go to smaller compressor sheave, do a sanity check whether compressor bearing can handle increased radial pulley force.   

=====================================
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RE: pulley rpm math

(OP)
tks

RE: pulley rpm math

Too much math.

Dm/Dc = Nc/Nm

D = Diameters (motor, compressor)

N = Speed (compressor, motor)

I agree with pete. Go with a 10" pulley for the motor.

RE: pulley rpm math

Or turn the shafts toward each other and use a coupling.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: pulley rpm math

Increasing you motor pulley will keep the dynamic tension on the belt the same. Performance should be good. If you make the compressor pulley smaller, you will doule the dynamic tension on the belt and cut the contact area approximately in half. That gives you four times the chance that the belt will slip.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: pulley rpm math

On second thought, if the compressor pulley has a heavy rim and/or an integral fan, a coupling is contraindicated.

On third thought, you may need to make the larger motor pulley extra light, so the extra inertia won't prevent starting.

On fourth thought, given the extra inertia of the larger motor pulley, even a lightweight one, you may be forced to go to somewhat smaller pulleys and a high torque belt, i.e., you may have to re-engineer the drive.

In which case, a new two-pole motor may be cheaper.  
Why are you replacing the motor?

 

Mike Halloran
Pembroke Pines, FL, USA

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