V-belt pulleys (also called vee belt sheaves) are devices which transmit power between axles by the use of a v-belt, a mechanical linkage with a trapezoidal cross-section. Together these devices offer a high-speed power transmission solution that is resistant to slipping and misalignment.

V-belt pulleys are solely used for transmitting power between two parallel axels. The most notable difference between a v-belt pulley and other types of pulleys (round belt, flat, etc.) would be the geometry of the groove or grooves located around the circumference of the pulley; these grooves guide and gain traction on a v-belt. The accompanying video offers a comprehensive overview of some v-belt basics, as well as their advantages and variations.

A v-belt is a unique mechanical linkage with a cross-section that resembles an isosceles trapezoid. The v-belt and its complementing pulley create the most efficient belt drive known (sometimes achieving 98% transmission efficiency). V-belts were developed in the early days of automobile innovation to improve belt reliability and torque transmission from the crankshaft to rotating assemblies. V-belts remain a common type of serpentine belt today.

Types of V-Belt Pulleys

Several types of pulleys are used in v-belt transmissions, each with different implementation. Occasionally flat-belt pulleys are suitable when the backside of the v-belt is used to rotate the pulley in the opposite direction of the driven pulley, as commonly employed with ribbed v-belts.

Standard pulleys are pulleys that have traditional dimensions, with one or multiple grooves, which mate with classic, small-engine, and hexagonal-style v-belts.	Image credit: Carlisle Power Transmission
Companion pulleys contain integral spokes which run radially on the pulley. This produces a high strength-to-weight ratio advantageous to fractional horsepower pulleys.	Image credit: Advanced Bearing
Idler pulleys are used solely as belt tensioners in many v-belt drives, but play an important part in maintaining the tension required to drive the transmission. Idlers can interact with either the wedged or flat side of the v-belt since no torque is required to be transmitted to this axle. Idler pulleys reduce belt service life and the efficiency of the drive, but are required in transmissions where the drive needs to clear obstructions, or the driven pulley does not maintain a sufficient arc of contact with the v-belt to transmit torque.	Image credit: Just Commodores
Variable speed pulleys have a variable pitch which adjusts the driven RPM, often within a range that is represented as a percentage. These pulleys are also useful for maintaining belt tension for dynamic loads.	Image credit: Hi-Lo
Step pulleys have two or more non-adjustable grooves which have different pitches located around the same shaft. These pulleys change the speed ratio of the transmission.	Image credit: Unisoft

The following parameters are important when selecting v-belt pulleys.

Belt profile, or the style and sizes of the belt being integrated.

Outside diameter, or the distance across the pulley when measured between groove edges.

Center diameter is the distance or distances between the shafts of the pulleys in the transmission. V-belt transmissions are limited by center distances, which must be no more than three-times the diameter of the largest pulley, lest significant slipping can occur.

Grooves, the grooves located on the pulley, including the number, and angle and width of the flanges.

Pitch diameter, or the diameter of the pulley where the belt is engaged, and is critical to the drives strength-to-weight ratio.

Arc of contact, the degree of which the belt wraps around the pulley.

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