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# What is a Tension Pulley?

Article Details
• Written By: Alexis W.
• Edited By: Heather Bailey
2003-2019
Conjecture Corporation
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A tension pulley may be considered one of the most complex forms of all of the different types of pulleys that are used to make work easier for both users and machines. Tension pulleys are belt pulley systems that have at least one pulley wheel, or “block,” that is not in a fixed position. This movable block is placed in a manner within the pulley system that allows it to decrease the amount of tension on the belt that the pulley system is driving.

When the belt is in place or the system is engaged, the movable block is engaged. It moves into a position that places an amount of tension on the belt or chain being driven. The tension engages the belt or chain as well. The tension pulley functions based on the amount of tension placed on the chain or belt.

One of the most simple and common forms of a tension pulley is found within the intricate workings of an automobile engine, in the serpentine belt system. The tension wheel in the pulley system causes the serpentine belt to become engaged. This is the same belt that turns the coil wheel on the alternator, delivering charge to all of the electrical elements of the automobile.

While the circuitry and components of the engine may be intricate and complex, the function of the tension pulley is simple. It just involves placing enough tension on the belt to pull it without slipping. This then engages a number of other components within the automotive system.

Another example of a tension pulley is in a bicycle’s gearing mechanism. There, it is one of the two smaller spindles that comprise the three-spindle gear system located on the rear tire of the bicycle. This tension pulley is responsible for allowing the necessary slack in the bike’s chain to allow for the chain to be moved on the bike’s other pulley system, the cone system.

This system moves the bike chain up and down the alternately-sized gear spindles. This makes the task of peddling the bicycle easier or harder, depending on the preference of the user. The cone pulley system that the gear spindles are arranged in, however, would not be able to perform its function if it weren’t for the function of the tension pulley allowing the necessary amount of tension to be applied to the bike chain.