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# What Is a Variable Speed Pulley?

Article Details
• Written By: Mark Wollacott
• Edited By: Lauren Fritsky
2003-2018
Conjecture Corporation
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A variable speed pulley allows for pulleys to be used at various different speeds. This means the basic pulley system can be easily adapted for different functions and uses. Such a pulley system only requires one variable speed pulley in order to function.

Etymologically, the word ‘pulley’ is derived from the Medieval Greek and Latin word ‘polidia,’ which is a pluralized noun meaning ‘little pivots.’ The pulley itself is much older than the term given to it by modern English. It is, in fact, one of mankind’s oldest and most simple machines.

Each pulley in a variable speed pulley system is linked together by a chain. Normal pulley systems can use belts, cables and ropes as well as chains, but the variable speed pulley can only work with a strong lubricated chain. There are usually at least two pulley wheels in such a system.

Due to their variable nature, a variable speed pulley is only used in fixed and compound systems. A fixed system keeps the pulley axle in a fixed position. A compound system mixes both the fixed axle and the movable axle system. The compound system produces far more power multiplications than the fixed position one. The main advantage of keeping the axle fixed is that it provides additional stability.

Theoretically, the pulleys in a variable speed pulley system are weightless. This reduces friction when they are operated, which in turn reduces the amount of energy lost. The pulley does not change the work being done, but it does reduce the amount of force needed to make it work. Additional pulleys added to the system further reduce the force needed.

The adjustable or variable speed pulley in the system is spring-loaded. The spring is used to maintain tension so that the machine operates correctly. This alters the rotation of the variable speed pulley’s axle or shaft.

Variation in speed is controlled by the opening and closing of flanges on the variable speed pulley. A flange is a rim or wall used to stop the belt from slipping off the pulley. Variable pulleys still have flanges at either end to keep the chain on the pulley, but have a series of movable flanges that can help the chain move at different speeds. If the chain moves to a smaller element of the pulley, the chain will move at a faster speed, and it will move slower if it moves to a larger part of the pulley.

The main advantage of the variable speed pulley is that it is economical. It allows for various uses without having to change or modify the equipment. It is strong, quiet and has a near-infinite speed range depending on the pulley’s ratio limits.