The speed of the driven unit can be varied by as much as ___% using a variable pitch pulley.

• A. 10%
• B. 50%
• C. 5%
• D. 30%

Answer: (D)

A variable pitch pulley changes the speed of the driven unit by altering the effective diameter the belt runs on. As the belt shifts along the conical (adjustable) pulley, it rides on larger or smaller diameters, which changes the drive ratio and thus the driven speed. In practical designs, this range is limited to about 30% to maintain adequate belt contact, proper tension, and to avoid slip or excessive wear. So the driven speed can typically be varied by around 30% with a variable pitch pulley.