Flat belt pulleys are used in transmission systems that are driven by flat belts, typically high-speed, low-power applications in textiles, paper making, and office machinery such as computer printers. Flat belts are also used for conveyors. Compared to plied belts of equal horsepower, flat belts are thinner by 25% or more, which allows flat belt pulleys to be smaller than V-belt pulleys. Flat belts are also less expensive than belts used in a serpentine belt pulley. One safety factor is that in overtorque situations, the belt can slip, preventing damage to equipment other than the belt itself. Flat belts require flat pulleys and flat pulley idlers. They do not necessarily require grooved flat belt pulleys. A flat pulley idler can also be used for the back side of a conventional V-belt. Flat belt drive pulleys apply motive power to the belt.
Flat belt pulleys and flat belt idler pulleys can have a molded crown, which helps to center the belt, prevent rubbing against the outside flanges, and provide support under the center of the belt, where there is the most stress. The crown also helps to keep the belt on the flat belt pulley (belts tend to move to the tightest position). In some cases, a flat belt drive includes a tracking sleeve or other mechanism for keeping the belt on the flat pulley. Specifications for flat belt pulleys include belt width, outside diameter, bore size, hub diameter, and hub projection. Tension on a flat belt is usually set by adjusting the distance between pulleys to stretch belts by a small amount, such as 2%.
Standards for flat belt pulleys are maintained by the International Organization for Standardization (ISO) Technical Committees 41 (pulleys and belts) and 101 (continuous mechanical handling equipment). In the National Electrical Manufacturers Association (NEMA) publication, Motors and Generators (MG 1), Section 14.7 mentions flat belt pulleys.