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# Belt Driven Blowers

I was asked to repost this piece on estimating the length of a belt used on belt-driven blower assemblies, so here it is.

Sometimes we need to get a rough estimate on the length of a belt that is to be used on a belt driven blower assembly. This can easily be done if we know the diameter of the drive and driven pulleys and the center-to-center distance between the two shafts.

The following diagram shows D, R1 and R2, which represent the distance between the two shafts and the radius of the drive and driven pulleys.

Since the pulley is only in contact with about half of each pulley, we can use the sum of half the circumferences of the pulleys to estimate this value. The circumference of the pulley is given by 2(3.14)(R), so we can estimate the portion of the belt in contact with the pulleys to be:

(0.5)2(3.14)(R1) + (0.5)2(3.14)(R2)... OR

(3.14)(R1 + R2)

To this we add twice the center-to-center distance between the shafts, or 2D. The total approximate belt length is then:

2D + 3.14(R1 + R2)

Example: Consider a belt driven blower assembly that has a 4" and a 6" pulley. The two shafts are 12" apart. The approximate length is:

2D + 3.14(R1 + R2)

2(12) + 3.14(2 + 3) = 24 + 15.7 = 39.7.

To be on the safe side, be sure to have a 39" belt and a 41" belt in addition tot he 40" belt as calculated.
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