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. A pulley is always mounted on a rotary part of the energy source to transfer power through a belt to the device. Thus, serving as a source of power to that device.
In this reading, we’ll explore belts and pulleys, their functions, applications, diagrams, materials, types, and working principles. We’ll also examine their advantages and disadvantages.
Let’s begin!
Learn about chain belts with this detailed guide!
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.
A 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 designed 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 they transmit 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 move 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 a vertical or horizontal direction, depending on the position of the energy source and the position of the application it will be powering.
Pulleys that are not used to transmit rotational motion function as they are used to lift heavy loads. The pulley helps to reduce the amount of force required to lift a load.
You should also learn about engine drive belts with this detailed guide!
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 pulleys 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, 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
- Curtains at a theater hall use pulleys, making them easy to pull apart.
- A hoisted-up flagpole or when it’s taken down
Learn about bearing with this detailed guide!
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 depends 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.
You should also learn about flat belt fulley with this detailed guide!
Types of Pulleys
Below are the various types of pulleys 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 lower 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 pulleys are used in applications that require changing of gears 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 idler 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 be 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 pulleys 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.
Learn about The Difference Between Timing Belt And Timing Chain with this detailed guide!
Compound Pulley
A compound pulley has both fixed and movable 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 movable type of pulley consists of a drum that moves while moving an object. There is no change in the direction of the force, but the object still feels much lighter than it is supposed to. A movable 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 trapezoidal in 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 in applications that require smaller initial tension, and vibration and noise will not be produced.
Learn about transmission systems with this guide!
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, I am sure you are now familiar with the basics of belts and various types of pulleys, including their applications.
Well, machinery incorporated with belt drive will contain a pair of pulleys attached to parallel shafts. They are connected by an encircling flexible belt that helps 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 can it 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.
You should also learn the sysmptoms of a bad serpentine belt with this detailed guide!
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
- It can be easily replaced due to its low cost.
- Power can be transferred vertically, horizontally, or on an 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 and 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.
Learn about Conveyor with this detailed guide!
Conclusion
The drive belt, also known as a serpentine belt or V-belt depending on the type, plays a vital role in the operation of various engine accessories like the alternator, power steering pump, AC compressor, and water pump.
A properly functioning drive belt ensures smooth and efficient engine performance. Regular inspection and timely replacement are crucial to prevent sudden breakdowns and maintain overall vehicle health.
FAQs on Drive Belt
What is a drive belt?
A drive belt is a rubber belt that transmits power from the engine’s crankshaft to auxiliary components like the alternator, AC compressor, power steering pump, and water pump.
What are the types of drive belts?
- V-belt – Narrow, wedge-shaped belt used in older engines.
- Serpentine belt – A long, flat belt that snakes around multiple pulleys in modern engines.
- Timing belt – Although not typically called a drive belt, it also drives engine timing components.
What are the signs of a failing drive belt?
- Squealing noise from the engine bay
- Cracks or fraying on the belt
- Accessory failure (e.g., dead battery, overheating)
- Visible wear or looseness
How long does a drive belt last?
Most drive belts last between 60,000 and 100,000 miles, but this varies depending on vehicle use and environmental conditions.
Can I drive with a broken drive belt?
It’s not recommended. A broken belt can cause immediate loss of power steering, cooling, and battery charging, potentially leading to engine damage.
What causes a drive belt to wear out?
- Age and heat exposure
- Contamination from oil or coolant
- Misaligned pulleys
- Improper tension
How can I maintain my drive belt?
- Inspect regularly for cracks or fraying
- Ensure proper belt tension
- Replace according to manufacturer recommendations
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 drives and chains 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.