What is Belt and Pulley? - Their Diagram & Working

A Belt and pulley are important mechanisms because power must be transferred from one source of energy to another in a mechanical device. The most common and cheapest form of this transfer is through a belt and pulley.

This power is either gotten from an electrical or mechanical generator to transfer a rotational motion to the application. Pulley is always mounted on a rotary part of the energy source so that power can be transferred through a belt to the device. Thus, serving as a source of power to that device.

Well, in this reading, we’ll explore belt and pulleys, their functions, applications, diagrams, materials, types, and their working principle. We’ll also look at their advantages and disadvantages.

What is a Belt and Pulley (Drive Belt)?

Pulleys can be seen in more than one form as they serve a variety of purposes in the industrial world. First of all, a pulley is a wheel on an axle or shaft designed to support movement and change the direction of a belt or taut cable.

The device helps in power transmission using a cable or belt. In a belt and pulley system, a belt runs along a pulley’s groove so that the power can be transferred either from one pulley to another or from the pulley directly to the application that requires power.

Pulley is also used to guide a cable or exert a force and it changes the direction of force, making pulling down easier than lifting up. These kinds of pulleys may be called “Sheaves”.

Well, a drive element of a pulley system can be rope, cable, belt, or chain. A belt drive is a loop of a flexible material that transfers movement from one rotating pulley to another. Each is held on a shaft.

Some specific types of pulleys are design similar to levers, to lift loads. These pulleys are wheel-shaped with a groove that allows a cord to fit inside the groove.

Talking about power transmission, a belt is the cheapest form. It’s a loop of flexible material used to link two or more rotating shafts mechanically, often in a parallel form. These belts may be used as a source of motion as it transmits power more efficiently.

Functions of Belt and Pulley (Drive Belt)

Below are the functions of a belt drive and pulley in their various applications:

The primary function of a belt is to transfer power (rotary energy) from one source to another. Whereas a pulley that has a groove around its circumference allows a belt to smoothly through it when transmitting rotational motion.

A pulley is designed to attain different diameter functions as it’s used to increase or decrease the speed of the application of its powers.

A specific type of pulley is used to change the direction of the force. This pulley is often seen on heavier applications and they are not used for transmission of rotational motion.

Finally, the function of a belt is to exert force from one direction to either vertical or horizontal direction, depending on the position of the energy source and the position of application it will be powering.

Pulleys that are not used to transmit rotational motion functions as they are used to lift heavy loads. The pulley helps o reduce the amount of force required to lift a load.

Applications of Belt and Pulley

Below are the applications of a belt and pulley:

In applications where belt drives on a pulley, they are used in automotive engines such as cars, trucks, buses, stationary power generators, marine engines, aviation engines, etc.

Belt and pulley are also used in air compressor engines, agricultural equipment, conveyors, etc.

In fact, a belt and pulley are purposely designed for any application that requires a rotational motion from another source. There are tons of machines and equipment out there from larger ones to smaller ones such as winches, treadmills and washing machines, etc.

A single pulley that changes the direction of force is used on cranes, well to lift out a bucket, raise a flag, adjust a window blind, etc.

Below are examples of the application of a belt and pulley:

A bulldozer, it’s used to do its lifting
An extended ladder
Using a crane on a construction site
The working of an escalator going up or down
Opening and closing a garage door
Belts and pulleys in a vehicle
Elevation uses several pulleys in its working
Various fitness or exercise equipment uses a pulley
Curtain at a theater hall uses pulleys, making them easy to pull apart.
A hoisted-up flagpole or when it’s taken down

Diagram of Drive Belt

Belt and Pulley Material

Below are materials often used for making belts:

Leather belt
Cotton or fabric belt
Balata belt
Plastic belt
Rubber belt
A pulley is made of a metal material often made from cast iron, aluminum alloy, etc. The material used is depending on where the pulley will be used.

The most common material for a flat belt is leather, which is made from strips 1.2 m to 1.5 m long, cut from either side of the backbone of top-grade step hides. The leather hair is smooth and hard on the flesh side, while the flesh side is strong.

Cotton or Fabric Belts are made by folding layers of canvas or cotton duck and stitching them together. They are waterproof and suitable for moist climates and environments, making them ideal for farm machinery and belt conveyors.

Rubber Belts are made of layers of fabric fastened with a rubber structure and have a thin layer of rubber on the face. They are flexible but quickly destroyed when exposed to heat, oil, or grease.

Balata Belts are similar to rubber belts but use balata glue instead. They are acid-proof and waterproof, not affected by animal oils or alkalis, and have a 25% higher strength than rubber belts.

Plastic Belts are made from polyester, polyvinyl chloride, silicon, and polyethylene. These belts are suitable for various applications in various industries, such as sawmills and paper mills.

Types of Pulleys

Below are the various types of a pulley and their functions:

Open Belt Drive (Pulley)

In these types of pulleys, the shafts rotate in the same direction. which means, the direction of rotation is the same as the driven pulley. The shafts are arranged in a parallel direction.

The distance between a pulley and the driver will determine whether the upper side will be the slack side or the blow side will be tight.

Crossed Belt Drive (Pulley)

In crossed types of pulleys, the transmitted power is more, but it cannot run faster. This may cause wear and tear to the belt. The shaft rotates opposite to the pulley. To eliminate wear and tear in these pulley types, more distance should be placed between the pulley, and then it should be run at low speed.

Fast and Loose Cone Pulley

In these types of pulleys, there are two pulleys in it, the first one is faster than the other. The fast pulley is mounted on a shaft with a keyed joint whereas the loose pulley runs freely on the shaft. This loose pulley does not transmit any power.

These types of pulleys are suitable for multiple machines that derive power from a single source.

Stepped Cone Pulley

The stepped cone pulley is also known as the speed cone. In these pulley types, there is more than one pulley of different diameters attached to be adjacent to each other. Stepped cone pulley is used in applications that required changing of gear or where the speed of the driven shaft changes frequently like machines. The same belt is used for different speeds attained.

Jockey Pulley

A jockey pulley is used in a steering section of a system. it’s similar to an idle pulley which is used for increasing the angle of contact in a one-belt drive. The function of a jockey pulley is to increase the angle of contact of a belt. This is to help the belt tension is increased and also to offer a high-velocity ratio to the drive.

All the above-explained pulleys are used to transmit rotational motion in one way or the other. Some other types of pulley include:

Complex Pulley System

A complex pulley system has a block and tackle system that contains two or more individual drums. Each of these drums has two or more wheels that rotate on the same axle. A rope is looped back and forth between the drums and pulley to help it multiply so as to accomplish the operations. The complex pulley system is used to move an extremely heavy load.

Compound Pulley

A compound pulley has both fixed and moveable pulleys, making the load feel lighter. With this, the direction of the force can be easily changed, making the system suitable for moving heavy loads. Sometimes, more motion is required for the work to be properly done.

This system is also called a combination pulley system. it’s designed to make heavier loads be lifted with less force. It is often used on a construction site to lift heavy objects like concrete and steel.

Moveable Pulley

The moveable type of pulley consists of a drum that moves while moving an object. There is no change in direction of the force but the object still feels much lighter than it is supposed to. A moveable pulley moves more freely. It’s often seen in an elevator.

Types of Belts

Below are the various types of belts used in different applications:

Flat Belt

Flat types of belts are used where low power and more speed are required. They are rectangular cross-section types and the shaft distance must be between 5 to 10 meters. These belts transmit power by using friction produced between the belt and the pulley.

Finally, the pulley’s rotation in flat belts is in the same direction and the efficiency of the belt is around 98%. However, the belt makes little noise.

V Belt

The v belt types are used where the shaft distance is less than 2 meters. They offer moderate speed and high power, unlike flat belts. V belts are in trapezoidal cross-section. Multiple drives are possible in these types of belts.

Circular Belt

A circular belt is used where the shaft distance is more than 5 meters. It’s a circular cross-section and it is used to transmit high power. Circular types of belts are used on applications that require smaller initial tension and vibration and noise will not be produced.

Timing Belt

Timing belts are popular types of belts that serve alternative purposes. They are mainly used in internal combustion engines to transmit power. They are known as positive drives as they are more reliable and precise.

Some other types of belts include:

Spring belt
Multi-groove belt
Ribbed belt
Film belt
Specialty belt (belt used for transmitting power on the tension side of the loop)
Rolling road (belts used in rolling roads for wind tunnels).

Working Principle

The working of belts and pulleys is less complex and can be easily understood. With the above explanation, am sure you are now familiar with the basics of belts and various types of pulleys including their applications.

Well, a machinery incorporated with belt drive will contain a pair of pulleys attached to parallel shaft. They are connect by an encircling flexible belt that help to transmit and modify the rotary motion from one shaft to the other.

Selection Consideration

Below are things to consider while selecting a drive and pulley for a device:

The source of energy used in transmitting energy.
Center distance between the shaft and pulley.
The speed of the driver and driven pulley.
Power is transmitted through the system.
The layout of shafts.
The flexibility of the belt
Reliability and durability of the belt
How much high tensile stress it can withstand?
Low weight per unit length.
Resistance to wear and fatigue
High coefficient of friction between belt and pulley.
A temperature that can be resisted.

Advantages and Disadvantages of Belt and Pulley

Advantages:

Below are the benefits of a belt and pulley in their various applications:

Low power consumption
Low maintenance cost
Easy to install and dismantle
Simple in construction
Lubrication is not required
Can be easily replaced, due to its low cost.
Power can be transferred vertically, horizontally, or incline.

Disadvantages:

Despite the good advantages of a belt and pulley system some limitations still occur. below are the disadvantages of belt and pulley systems:

Power loss could occur due to slip and creep.
Can’t be used in a very short distance
Speed is limited to some extent
It’s very quiet
Limited operation temperature between 35 to 85 degrees.
They don’t serve long
Chances of breakage are common.
The angular velocity ratio is not necessarily constant or equal to the ratio of the pulley’s diameter due to slipping.

FAQs

What is a Drive Belt?

A belt drive is a pair of pulleys attached to usually parallel shafts and connected by an encircling flexible belt (band) that can serve to transmit and modify rotary motion from one shaft to the other.

What Are The Types Of Belt Drives?
There are seven different kinds of belt drives which include Open belt drive, Closed or crossed belt drive, Fast and loose cone pulley, Stepped cone pulley, Jockey pulley drive, Quarter turn belt drive, Compound belt drive

What Are The Types Of Belts?

There are three types of power transmission belts: flat belt, V belt, and synchronous belt. The Round belts are generally made of rubber, V belts are arguably the most widely used belts in the industry, Flat belts are also used to transmit power from one shaft to another and Timing/toothed belts.

How Do Belt Drives Work?

In the working of a belt drive power is transmitted between at least two pulleys by a belt. One pulley drives the belt (driving pulley) and the other pulley is driven by the belt (driven pulley). In belt drives, the speed is often reduced, so that in these cases the smaller of the two pulleys is the driving pulley.

Is Belt Drive Better Than Chain?

The major difference between belt drive and chain is that chain drives are simply stronger: they can lift more than a belt drive. This makes them the choice for moving heavier doors, so consider them if you’re going with a steel carriage. But this won’t be a factor with lighter door models. Go with a chain drive if you have a 2-car garage door.

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What is Belt and Pulley? – Their Diagram & Working