Variable speed drives are needed because many applications are not run at the same speed all of the time, due to the surrounding conditions. Revolutions per minute (RPM) of the driven shaft need to be increased or decreased when there are changes in load conditions, application requirements, or other circumstances.
Variable speed belt drives achieve the versatility needed to maximize application efficiency and productivity while remaining an inexpensive solution. In the most typical installation, a belt connects a variable speed pulley to a driven sheave. The pulley is mounted on a motor shaft and the motor is at constant speed. Thus, the speed at the driven shaft is a ratio of the pitch diameters of the pulley and sheave.