# pulley size



## capt.ron (Aug 28, 2014)

i have a hydraulic motor that turn 914 rpms with a 4 1nch pulley i want to change to a motor that turns 760 rpms what size pulley will i need to get the same rpms


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## CluelessNewB (Aug 28, 2014)

capt.ron said:


> i have a hydraulic motor that turn 914 rpms with a 4 1nch pulley i want to change to a motor that turns 760 rpms what size pulley will i need to get the same rpms




( 4 x 914) / 760 = 4.81 

So you probably need to decide between 4-3/4 or 5"


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## eded59 (Aug 28, 2014)

4.8 inches

4.0    x  pi x 914 = 11485 inches per minute

4.75 x pi x 760 = 11341 IPM

5.0  x pi  x 760 = 11938 IPM


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## JimDawson (Aug 28, 2014)

914 / 760=1.202

4 x 1.202 = 4.810, new pulley diameter

This is an approximation and assuming the current ratio is 1:1, based on the information provided.

It would be more accurate if you gave the current motor rpm, and both pulley sizes.


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## CluelessNewB (Aug 28, 2014)

JimDawson said:


> This is an approximation and assuming the current ratio is 1:1, based on the information provided.
> 
> It would be more accurate if you gave the current motor rpm, and both pulley sizes.



I'm confused!

He did give the current motor RPM = 914 and you used it for your calculation! 

Assuming he keeps the same driven pulley size why would the driven pulley size make any difference?


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## JimDawson (Aug 28, 2014)

CluelessNewB said:


> I'm confused!
> 
> He did give the current motor RPM = 914 and you used it for your calculation!
> 
> Assuming he keeps the same driven pulley size why would the driven pulley size make any difference?



I stand corrected, I need to work on my reading comprehension.  I read hydraulic motor as hydraulic pump, thinking that it was being driven by a motor.  :nuts:  So please disregard my idiocy.


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## 12bolts (Aug 28, 2014)

CluelessNewB said:


> So you probably need to decide between 4-3/4 or 5"



Ron, if its that critical you can possibly turn a 5" pulley down to 4.8, or you could make one....

Cheers Phil


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## capt.ron (Aug 29, 2014)

thanks everyone it's not that that important that it be exact just close i am going with 5 inch


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## KBeitz (Aug 8, 2018)

Save this photo. You all might need it some day...


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