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Multiple Pulley Power Transfer

  1. May 18, 2008 #1
    I would like to drive two identical devices off of 1 power source. I would like to use two independent but equal sized V-belts, a double stacked pulley on the drive shaft and a single pulley on each of the device shafts. If the power source has a rating of 36HP @ 3600 RPM, what is the maximum HP rating of the identical devices @ 1200 RPM? The drive pulley/device pulley would have a ratio of 1 to 3. I've looked for an equation or explanation of how to solve for this but have not been successful. Any assistance would be appreciated.

  2. jcsd
  3. May 18, 2008 #2
    HP = power X time = work done
    so if you slow the speeds 3600/1200 you donot gain more work
    as it takes longer

    but you do gain power 3 times the power but at a cost of speed
    minus the friction losses
  4. May 18, 2008 #3


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    That's all incorrect, sorry ray.

    Power = torque x speed

    So (neglecting friction), if your pulley ratio is 1:3, you will increase the torque by 3 times, decrease the speed by 3 times, but power transmitted will remain the same.

    With 36hp being developed at your drive shaft, you'll never get more than this at your 'device shafts'.
  5. May 19, 2008 #4
    Thanks for the responses. So the power stays constant, torque increases and speed decreases. So the two devices would have a max HP of 18 each (not accounting for drive train losses)? Is there a way to take advantage of the increase in torque at the device shafts?
  6. May 19, 2008 #5


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    Exactly. Be careful not to underestimate your drivetrain losses with belt/chain type systems.

    Taking advantage of the torque increase is exactly what you do when using a lower gear on your bike, or in a car. How this can be applied to give advantage to your 'device' depends entirely on what your application is, and what you're trying to do.
  7. May 19, 2008 #6
    I had anticipated 80% efficiency in the belt drive system. I plan to drive two backward curved centrifugal fans. Will driving these types of fans be more more advantageous than driving another type of device?
  8. May 20, 2008 #7


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    It depends entirely on what you want to do. Driving centrifugal fans will be a pretty poor solution if what you're trying to do is compress air to inflate car tyres, yet they could work quite well for shifting contaminated air out of a spray paint booth.

    What's your application?
  9. May 23, 2008 #8
    I don't need pressure - I need to continuously move a large volume of air. I'm essentially creating a wind tunnel for experimenting with aerodynamics.
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