Learn about Pulleys

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Pulleys are simple devices for increasing mechanical advantage in a wire, chain or rope system. A pulley consists of a wheel with a specialized rim that rotates on an axle and carries some type of cable or chain. Typically, systems use multiple pulleys, since a single fixed pulley provides little mechanical advantage. As the number of pulleys increase, however, the more system efficiency decreases, since each pulley loses a certain amount of force due to friction.

Pulleys are widely used in marine, shipping and nautical applications; they also find use in various pieces of industrial equipment and machinery. A specialized pulley system known as a block and tackle is very common to sailing vessels and fishing ships, as it enables operators to lift extremely heavy loads with minimal force. A block and tackle consists of at least two fixed and two moving pulleys, each group of which is set in the same block. The number of pulleys directly corresponds to the mechanical advantage, and therefore the ratio of required strength to load weight. The more pulleys that are used, however, the more rope is needed to move any given weight.

For modern industrial uses, pulleys are generally distinguished by belt type. There are timing belt, flat belt, round belt and V-belt pulleys, each used for the corresponding belt type. Timing belt pulleys, for example, contain notched teeth spaced to mesh with the teeth of the matching belt; on the other hand, flat belt pulleys do not contain notches, since they are used with flat, smooth belts. V-belt pulleys contain an angled belt track to match the V-shaped belts that pass through.

Pulleys can be made from a variety of materials, including an extensive range of plastics, wood and metals. Steels and aluminum alloys are regularly used in industrial pulley manufacture; many pulley designs incorporate multiple materials in order to wed strength with proper resistance characteristics.