What Is a Serpentine Pulley?

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  • Written By: Jeremy Laukkonen
  • Edited By: A. Joseph
  • Last Modified Date: 18 November 2019
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A serpentine pulley is a component that can be used to transfer the mechanical power from a source, such as a motor, to another device. To facilitate this transfer of power, a serpentine drive belt can be passed around two or more pulleys. When the drive pulley turns, the serpentine belt transfers that motion to accessory pulleys. A serpentine pulley can be smooth or have a number of grooves, depending on the amount of slippage that is permissible in any given system. Some systems have both smooth and grooved serpentine pulleys, in which case the belt will have one grooved side and one smooth side.

The three main serpentine pulley types are used to provide motion to a system, to power accessories or to provide tension. Drive pulleys typically have the heaviest construction of the three and often include a harmonic balancer in automobile applications. Accessory pulleys can be either smooth or grooved and exist to use the motion of a serpentine belt to power various devices. Tensioner pulleys typically are needed to ensure that the belt does not slip. Depending on the configuration of a system, a tensioner pulley might also be either smooth or grooved.


Grooves typically are added to create additional gripping strength between a serpentine pulley and belt. The number of grooves on the pulley, which can range from three to six or more, are matched by an equal number of grooves on a belt. The grooves on a serpentine belt fit into those on a matched pulley, so the comparative surface area of contact between the two is greatly increased over a smooth belt. This can allow a belt to have greater gripping power without needing more tension. Most serpentine belts tend to have one smooth side and one grooved side, though others have two grooved sides.

The primary advantage of a serpentine pulley over V-belt pulleys or other pulleys is the complexity of the systems that can be created by using them. Either side of a serpentine belt can be used to drive accessory pulleys, which can result in snake-like designs. In this way, it is possible for a single serpentine belt to be routed around pulleys for many accessory devices, which can save a great deal of space when designing a system. This can be particularly important in applications where space is at a premium, such as automobile engines. In other cases, the increased simplicity of design might be desirable because of cost issues.


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