Pulley Size calculations

To keep the same RPM, the driven pulley would need to be half the size of the drive pulley.In summary, the person is seeking help with a restaurant exhaust fan that has a 2" drive pulley and a 7 and 3/4 inch shaft pulley. The belt used for this setup is 21/32" in width, but it keeps wearing out quickly. They are considering doubling the size of the drive pulley to solve the issue and are wondering what size to make the driven pulley to maintain the same RPM (around 700-750). The expert suggests that the real issue may be a tight belt or faulty fan bearings, and that increasing the drive pulley would increase the RPM. To
  • #1
marksmithlegends
1
0
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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  • #2
Double. You knew that --- be sure you can get the appropriate belt length.
 
  • #3
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.
 

1. How do I calculate the correct pulley size for my system?

To calculate the correct pulley size, you will need to know the desired speed of the driven pulley, the diameter of the driving pulley, and the center distance between the two pulleys. Once you have this information, you can use the formula: Pulley size (driven) = (Pulley size (driving) x Speed (driving)) / Speed (driven). This will give you the correct pulley size for your system.

2. What is the importance of selecting the right pulley size?

The correct pulley size is crucial for the proper functioning of your system. If the pulley size is too small, it may not be able to handle the load and can result in the belt slipping or breaking. On the other hand, if the pulley size is too large, it can cause excessive wear on the belt and other components of the system. Therefore, it is important to select the right pulley size to ensure the longevity and efficiency of your system.

3. Can I use a different pulley size than the one recommended for my system?

It is not recommended to use a different pulley size than the one recommended for your system. Each pulley size is designed to work with specific speeds and loads, and using a different size can result in improper functioning and potential damage to your system. It is best to stick to the recommended pulley size for optimal performance.

4. How does the number of pulleys affect the calculation?

The number of pulleys in your system does not significantly affect the calculation for determining the correct pulley size. The key factors are the speed and load requirements, as well as the center distance between the pulleys. However, it is important to note that using multiple pulleys can help distribute the load and reduce wear on the belt and pulleys.

5. Is there a rule of thumb for selecting the correct pulley size?

While there is no specific rule of thumb for selecting the correct pulley size, there are some general guidelines you can follow. As a general rule, larger pulleys can handle higher speeds and loads, while smaller pulleys are better suited for slower speeds and lighter loads. Additionally, the center distance between the pulleys should be at least three times the diameter of the larger pulley for optimal performance.

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