A 10" diameter flywheel on a belt-driven compressor operates at 700 RPM. What size motor pulley is required for a 5 HP condensing unit operating at 1,012 RPM?

To determine the required size of the motor pulley for the condensing unit, it’s necessary to consider the relationship between the diameters of the pulleys and the speeds at which they operate. The principle of pulley operation is based on the idea that the product of the speed (RPM) and the diameter of the pulley for both the motor and the driven equipment (in this case, the flywheel on the compressor) must be equal. This principle can be expressed in the formula:

(Diameter of the driven pulley * RPM of the driven) = (Diameter of the motor pulley * RPM of the motor).

In this scenario:

• The flywheel (driven) pulley has a diameter of 10 inches and operates at 700 RPM.

• The condensing unit (motor) operates at 1,012 RPM.

By plugging the known values into the formula, we can first calculate the necessary diameter of the motor pulley:

10 inches * 700 RPM = Diameter of the motor pulley * 1,012 RPM.

Solving for the diameter of the motor pulley, we rearrange the formula:

Diameter of the motor pulley = (10 inches * 700 RPM) / 1,012 RPM.

This calculation results in approximately 6.9