How Do I Calculate Pulley Sizes to Maintain RPM in Exhaust Fans?

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SUMMARY

The discussion centers on calculating pulley sizes to maintain RPM in a restaurant exhaust fan. The current setup includes a 2-inch drive pulley and a 7.75-inch driven pulley, with a belt width of 21/32 inches. The user, Mark Double, inquires about doubling the drive pulley size to maintain an RPM of 700-750. Responses indicate that the rapid wear of belts may be due to improper tension or misalignment rather than pulley size alone, and typical exhaust fan RPMs are often around 1350 when using direct drive systems.

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  • Knowledge of belt tension and alignment issues
  • Familiarity with exhaust fan operation and specifications
  • Basic mechanical engineering principles related to rotating machinery
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This discussion is beneficial for mechanical engineers, HVAC technicians, and maintenance personnel involved in the design and upkeep of exhaust systems in commercial kitchens.

marksmithlegends
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can you help?

I have a restaurant exhaust fan with a drive pulley of 2" and a shaft pulley on the fan of 7 and 3/4 inches. The belt that fits this is 21/32" width. The belts keep wearing out very quickly. I think that larger pulleys would solve the problem. If I doubled the size of the drive pulley, what size would I need to make the driven (fan) pulley to keep the same RPM (about 700 to 750)

Thanks for the help!

Mark
 
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Double. You knew that --- be sure you can get the appropriate belt length.
 
marksmithlegends said:
The belts keep wearing out very quickly. I think that larger pulleys would solve the problem.
Mark


I think the real problem here is not pulley size, but that the belt is too tight, or the berrings in the fan have gone bad; and the pulleys are no longer aligned with each other.

700-750RPM for an exhaust fan does seem a bit slow - I usually see them running at 1350RPM, but direct drive. Increasing the drive pulley would, of course, increase the RPM of the fan.
 

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