If a fan has an 8" pulley turning at 850 RPM and the drive is 5", what is the motor RPM?

To determine the motor RPM based on the sizes of the pulleys and the RPM of the fan, you can use the pulley ratio formula. The ratio of the sizes of the pulleys is inversely related to the RPMs.

Given that the fan pulley has a diameter of 8 inches and is turning at 850 RPM, while the drive pulley has a diameter of 5 inches, you can apply the formula:

Motor RPM = (Fan RPM) × (Fan Pulley Diameter / Drive Pulley Diameter)

Plugging in the numbers:

Motor RPM = 850 RPM × (8 inches / 5 inches)

This calculation simplifies to:

Motor RPM = 850 RPM × 1.6 (since 8 divided by 5 is 1.6)

Motor RPM = 1360 RPM

Thus, the correct answer is 1360 RPM. This conclusion aligns with the principles of pulley systems, which state that a smaller pulley will turn faster than a larger pulley given the same power input. In this case, the 5-inch drive pulley causes the motor to operate at a higher RPM as it compensates for the larger 8-inch fan pulley.