## Method 1 Pulley Ratio Method

Step 1: determine the ratio of the existing motor pulley and fan pulley by dividing the driven (fan) pulley diameter by the motor pulley diameter.

(Driven (Fan) Pulley Diameter)/(Motor Pulley Diameter) = (Working Ratio)

Step 2: multiply the listed sheaves diameter of the appropriate model payback drive by the derived working ratio to determine the ideal new driven (fan) sheaves diameter.

(Payback Listed Sheaves Dia.) x (Working Ratio) = (Calculated Fan Sheave Diameter.)

Step 3: select the nearest size sheaves from a sheaves selection book. Using the new selected sheaves diameter in conjunction with the new drive listed sheaves diameter and the center to center measurement, size the belts from a belt selection guide.

Note: taking into account the difference between the motor rpm of 1750 and the drive's maximum attainable output of 1600-1700 rpm, the actual new driven rpm may be slightly less than the original by a factor of this difference rpm, however mechanical lockup, if required in emergency situations should return the driven pulley close to the original rpm.

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