Pulley: Definition, Types, Uses, and Examples

What is a Pulley?

A pulley is a wheel that carries a flexible rope, cord, cable, chain, or belt on its rim. Pulleys are used singly or in combination to transmit energy and motion. Pulleys with grooved rims are called sheaves. In belt drive, pulleys are affixed to shafts at their axes, and power is transmitted between the shafts by means of endless belts running over the pulleys.

One or more independently rotating pulleys can be used to gain a mechanical advantage, especially for lifting weights. The shafts about which the pulleys turn may affix them to frames or blocks, and a combination of pulleys, blocks, and rope, or other flexible material is referred to as a block and tackle.

The Greek mathematician Archimedes (3rd century BCE) is reported to have used compound pulleys to pull a ship onto dry land.

The earliest evidence of pulleys comes from the twelfth dynasty (1991–1802 BC) and ancient Egypt in Mesopotamia in the second millennium BC.

In Roman Egypt, the hero of Alexandria identified the winch, one of the six simple machines used to lift weights. Pulleys are assembled to form a block and to handle it to provide a mechanical advantage for applying large forces.

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To transmit power from one rotating shaft to another, the pulleys are also assembled as part of belt and chain drives. Plutarch’s Lives recalls a scene where Archimedes proved the effectiveness of the compound pulleys and block-and-tackle system by using one to pull a fully laden ship as if it were through the water Was gliding.

What are the uses of pulley?

The original primary use for pulleys was to make it easier to lift heavy items. A pulley is a simple machine made with a wheel and a rope, cord, or chain.

Pulleys can be found everywhere to help make tasks easier. In addition to lifting things, pulleys can be used singly or with many pulleys working together to transport people or things. They can also be used to provide power from one shaft to another.

Examples of Pulleys in Everyday Life

Examples of pulleys include:

  • Elevators: Elevators work via a powerful electronic pulley system. In fact, elevators make use of a system of several pulleys and counterweights to provide the lift system with both power and safety.
  • Wells: Old-fashioned “wishing well” style water wells use the simple pulley system to hoist the bucket out of the well.
  • Exercise equipment. Most weight-lifting exercise equipments use pulleys to control the angle at which weights are lifted while keeping the weights themselves in a dedicated location. This makes the process of weight lifting safer and more effective for the user than free weights maybe if used improperly.
  • Construction Pulleys. Construction pulleys are some of the most basic and common pulleys, good for viewing the basic functioning of this simple machine. These pulleys consist of a wheel track that can be raised to great heights, fitted with chains or rope attached to hooks.
  • Theater Systems. In theaters, curtains and fly systems operate using a system of multiple pulleys. These pulleys are located high above the stage where the audience cannot see them and operated from the side of the stage to raise and lower curtains and pieces of scenery during a theatrical performance.
  • Cargo lift system. A cargo lift system that allows for items to be hoisted to higher floors is a pulley system.
  • Blinds on windows. Blinds on windows operate using a pulley system to move the blinds up and down. You pull the cord on the blinds and the pulley system causes the blinds to open or close.
  • Flagpoles. Flagpoles use pulleys to hoist the flag up or to bring it down. You pull the string on the pulley and the flag runs up or down the pole.
  • Crane, Bulldozer, Escalators utilize pulley systems to function.
  • Garage doors, Sailboats, Engine, extend ladders, Rock climbers, all Use pulley system to work safer and more effectively.

These are all examples of pulleys. A cable system makes it easier to lift or move objects. Pulleys are required to move and lift very heavy or large objects. The simple principle behind pulleys makes them one of the most effective tools out there.

How does a Pulley Work?

A pulley is a simple machine that consists of a rope and a grooved wheel. The rope fits into the groove in the wheel and pulling the rope turns the wheel. Pulleys are commonly used to lift objects, especially heavy objects. The object lifted by a roller is called a load.

A pulley with a wheel allows you to reverse the direction of your lifting force by pulling down on a rope (looped over the wheel) and lifting your weight. With a two-wheel pulley, you reduce the force you use to lift the same weight. You lift the weight at half strength.

The more wheels you have, and the more times you loop the rope around them, the more you can lift.

How do Pulley Work

A pulley is just a grouping of one or more wheels over which a rope (or a sturdy chain for heavier objects) is looped. Scientists call these “simple machines” because they allow humans to multiply the forces that allow us to lift a heavy weight. Using a roller greatly multiplies the strength of your physical exertion.

A pulley with a wheel allows you to reverse the direction of your lifting force by pulling down on a rope (looped over the wheel) and lifting your weight.

With a two-wheel pulley, you reduce the force you use to lift the same weight. You lift the weight at half strength. This is known as the Mechanical Advantage (ME) and your two-wheeled pulley gives you an ME of two.

The bigger your Mechanical Advantage, the less force you need to lift a weight.

The more wheels your rope can wrap around, the more weight you can lift. This type of pulley system is often referred to as a pulley system and usually consists of a rope wound around two axes several times.

As you pull on the rope, the lower and upper axes slowly come together, increasing your ability to lift the object.

Material use for pulleys

Pulleys can be made from a variety of materials, including cast iron, cast steel or pressed steel, wood, and paper. The cast material should have good friction and wear characteristics. The pulley made from pressed steel is lighter than cast pulleys, but in many cases, they have less friction and can produce excessive wear.

Types of Pulley

There are three main types of pulleys:

  • Fixed pulley
  • Movable pulley
  • Compound Pulley

1. Fixed Pulley

A fixed pulley’s wheel and axle stay in one place. A fixed pulley changes the direction of the force on a rope or belt that moves along its circumference. A good example of a fixed pulley is a flag pole: When you pull down on the rope, the direction of force is redirected by the pulley, and you raise the flag.

A fixed pulley is a pulley with the drum attached to a single location. While the force required to lift or move an object is no different than lifting it by hand, the fixed pulley allows you to change the direction of the force required.

For example, if you’re attached to a bucket that pulling water from a well, you can pull sideways with a firm pull to lift the bucket more comfortably than if you were pulling a bucket of water up hand in hand vertically. The water bucket still feels like the same weight, but it’s more convenient to lift.

Types of Pulley
Types of pulleys

2. Movable pulley

A movable pulley has an axle in a movable block. A single movable pulley is supported by two parts of the same rope and has a mechanical advantage of two.

A movable pulley is one in which the drum moves as you are moving the load. There is no change in the direction of the force that you need to apply, but the load will “feel” lighter than it is. If you were hauling a heavy hay bale up into the loft of a barn, for example, a movable pulley would make the load feel much lighter, although the direction you are pulling would be the same.

3. Compound Pulley

In a compound pulley system, there is both a moveable pulley as well as a fixed pulley. This means that not only does the load “feel” lighter, but you can also change the direction of the force.

Although this type of configuration makes it possible to move heavy loads very easily, the tradeoff is that considerably more motion is required to do the work.

4. Cone pulley

The cone pulleys is another specialized pulley system that incorporates the basic mechanics of a pulley system while allowing for mechanical adjustments. A cone pulleys are essentially multiple pulleys of decreasing vertical circumference on top of each other, forming a cone shape.

This cone shape allows the pulley operator to transfer the speed of the pulleys’ movements, requiring less work with a smaller circumference, but also producing less work.

Multi-gear bicycles essentially operate on the same system; Cyclists can easily shift between smaller gears that propel the bike at a slower speed, and more gears require more effort but move the bike more distances per revolution.

5. Block and Tackle pulley

A block and tackle are a specific form of compound pulleys that can dramatically reduce the amount of work required to move a heavy object. A block-and-tackle pulleys system consists of several fixed and movable pulses arranged parallel to each other; a Fixed pulley is aligned with fixed and movable pulleys with movables.

Each compound pair is associated with the next pair, and each set reduces the total work required. This pulley system is attributed to the popular ancient inventor and mathematician, Archimedes.

What is Flat belt pulley?

Flat belt pulleys are used in transmission systems that are operated by flat belts, typically high speeds in textiles, low power applications, paper making, and office machinery such as computer printers.

The flat belts are also used for conveyors. Compared to equivalent horsepower plaid belts, flat belts are 25% or more thinner, which allows the flat belt pulleys to be smaller than the V-belt pulleys.

Flat belts are also less expensive than belts used in a serpent belt pulleys. A safety factor is that in high torque situations, the belt may slip, causing damage to equipment other than the belt. Flat belts require flat pulleys and flat pulleys idlers.

They do not necessarily require a flattened flat belt pulley. A flat pulley idler can also be used for the backside of a traditional V-belt. Flat belt drives apply motive power to the police belt.

Types of Flat belt Pulleys

Following are the various types of pulleys for flat belts:

  • Cast-iron Pulleys,
  • Steel Pulleys,
  • Wooden Pulleys,
  • Paper Pulleys, and
  • Fast and loose Pulleys.

1. Cast Iron Pulleys

Pulleys are usually made of cast iron. The rim is placed on the web from the central boss or by arms or spokes. The arms may be straight or curved and the cross-section is usually elliptical. Cast iron pulleys are usually made with round rims.

When a cast pulley contracts into the mold, the arms are in a state of tension and are very liable to break. Curved arms yield rather than break. Weapons are near the hub. This slight convexity is known as a crown. The crown centers the belt on a pulley rim while in motion. The crown can be 9 mm to 300 mm in the width of the face.

cast iron pulley
Cast iron pulleys

Cast iron pulleys can be of solid or split type. When it is necessary to mount a pulley on a shaft that is already carrying pulleys etc. or its ends are swollen, the split-pulleys are easy to use. There is a clearance between the faces and the two parts are easily tightened on the shaft by a bolt. A sunk key is used for heavy drives

2. Steel pulley

Steel pulleys are made from steel sheets and have great strength and durability. These pulleys are lighter in weight (about 40 to 60% less) compared to iron pulleys of the same capacity and are designed to run at higher speeds. They present a coefficient of friction with a leather belt that is at least equal to that obtained by a cast-iron pulley.

Steel Pulleys
Steel Pulleys

Steel pulp is usually made in two parts that are tied together. The clamping action of the hub keeps its shaft pulley; Thus, no key is required except in the most serious service. Steel pulleys are generally equipped with interchangeable bushes with shafts of different sizes to allow their use.

3. Wooden pulley

Wood pulleys are lighter and have a higher coefficient of friction than cast iron or steel pulleys. These pulleys have 2/3 of the weight of a similarly sized cast iron pulley. They are usually made of selected maples that are placed in sections and glued together under heavy pressure. They are kept from absorbing moisture by protective coatings of shells or varnishes so that war does not occur.

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Wooden Pulleys

These pulleys are either solid or split with an iron hub with screws or have adjustable bushes that prevent the frictional resistance between them and the shaft from being installed. These pulleys are used for motor drives in which the contact arc between the pulley face and the belt is restricted.

4. Paper Pulley

Paper pulleys are made from compressed paper fibers and are formed with metal in the center. These pulleys are commonly used for belt transmission from electric motors when the distance from the center to the center shaft is small.

paper pulleys
Paper pulleys

5. Fast and loose pulley

Fast and loose pulleys, used on the shaft, enables the machine to be turned on or off. A fast pulley is mounted on the machine shaft, while a loose pulley operates independently.

The belt operates on a fast pulley to transmit power by the machine and is transferred to a loose pulley when the machine is not required to transmit power. In this way, stopping one machine does not interfere with other machines that run by the same line shaft.

The loose pulley is provided with a cast iron or gun-metal bushing with a collar at one end to prevent axial movement. The rim of the fast pulley is made larger than the loose pulley so that the belt runs slower on the loose pulley. The loose pulley usually has a longer hub to reduce wear and friction and requires proper lubrication.

Advantages and Disadvantages of Pulley Drive

Advantages of pulley

  • The main advantage of the use of pulleys is that the effort becomes less as compared to the normal lifting of the weights.
  • It reduces the amount of actual force required to lift heavy objects.
  • It also changes the direction of the force applied.
  • It also provides a mechanical advantage.
  • There is a safe distance between operator and weight, which avoids any disaster.
  • Pulleys are easy to assemble and cost-effective.
  • Although the pulley system contains moving parts, once installed, they require less or no lubrication.

Disadvantages of pulley

  • It makes use of friction while transferring motion hence there are chances of slip.
  • It is not a suitable solution for very high-power transfer at high rpm.
  • Lifting distance increases while taking mechanical advantage.
  • Long-term fatigue and creep break the rope.
  • If the rope usually slipped when it was being pulled to the sides.
  • A comparison with gears is not reliable.
  • A combined pulley system uses multiple wheels and extra ropes to support the weight of a heavy object.

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FAQs.

What is a pulley?

A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that does not transfer power to a shaft, but is used to guide the cable or exert a force, the supporting shell is called a block, and the pulley may be called a sheave.

What are the uses of pulleys?

Uses of pulley:
Pulleys are used in many exercise equipment to function. Pulleys are also used to lift heavy materials in construction, and elevators also use them to function. It is also used in the theater to move curtains. Blinds on windows can be operated with a pulley system.

What are Examples of Pulleys?

Elevators use multiple pulleys to work and by Using the pulley system to lift the bucket out of the well. It is also a good example of pulleys used in many types of exercise equipment, construction, theater, Cargo lift system, blinds on windows, flagpoles, cranes, bulldozers, escalators, garage doors, sailboats, motors, extends ladders, and climbers.

What are the Types of Pulleys?

There are three main types of pulleys:
1. Fixed pulley
2. Movable pulley
3. Compound Pulley
4. Cone Pulley
5. Block and Tackle pulley

How does a Pulley Work?

A pulley with a wheel allows you to reverse the direction of your lifting force by pulling down on a rope (looped over the wheel) and lifting your weight. With a two-wheel pulley, you reduce the force you use to lift the same weight. You lift the weight at half strength.

What is the definition of a pulley?

A pulley is defined as a wheel that carries a flexible rope, cord, cable, chain, or belt on its rim. Pulleys are used singly or in combination to transmit energy and motion. Pulleys with grooved rims are called sheaves.