1. A belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts.

2. They may be used as a source of motion, to efficiently transmit power, or to track relative movement. Belts are looped over pulleys.

3. In a two pulley system, the belt can either drive the pulleys in the same direction, or the belt may be crossed, so that the direction of the shafts is opposite.

Types of belt drive

• Light drive – Up to 10 m/s

• Medium drive – over 10 but up to 22m/s

• Heavy drive – Above 22m/s

Types of belts

• Flat belt

• V – belt


Circular belt (or) rope

Flat Belts

• Rectangular in cross section mounted on pulleys

• Crowning on the pulley to prevent the belt from running off the pulley


Based on Materials

• Leather

• Rubber

• Canvas

Based on Layers

• Single-ply

• Double-ply

• Triple-ply



Most popular.

• V belt is designed to ride inside the groove of the pulley or sheave

Types of belt drive

• open belt drive

• crossed belt drive

• Quarter turn belt drive

• belt drive with idlers

• compound belt drive

• stepped pulley drive

• fast and loose pulley

Simple belt drive


The shafts are parallel, and the pulleys fastened to the shaft with set screws or keys.

The central planes of the pulleys must obviously be coincident

Cross belt drive


belt drive with idlers


Compound belt drive


Advantages of belt drive

• They are simple. They are economical.

• Parallel shafts are not required.

• Overload and jam protection are provided.

• Noise and vibration are damped out. Machinery life is prolonged because load fluctuations are cushioned (shock-absorbed).

• They are lubrication-free. They require only low maintenance.

• They are highly efficient (90–98%, usually 95%). Some misalignment is tolerable.

• They are very economical when shafts are separated by large distances.

Disadvantages of belt drive

• The angular-velocity ratio is not necessarily constant or equal to the ratio of pulley diameters, because of belt slip and stretch.

• Heat buildup occurs. Speed is limited to usually 7000 feet per minute (35 meters per second). Power transmission is limited to 370 kilowatts (500 horsepower).

• Operating temperatures are usually restricted to –31 to 185°F (–35 to 85°C).

• Some adjustment of center distance or use of an idler pulley is necessary for wear and stretch compensation.

• A means of disassembly must be provided to install endless belts.


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