Belt (Mechanical)

Introduction
Belts are used for transmitting power between two shafts. Belts will be of two kinds, flat and vee belts. Belts are running over the pulleys which are mounted on two shafts. Belts are used when the distance between the shafts is large. Gears are used when the distance between the shafts is small.

Types of Belt Drive
Open Belt drive

Cross Belt drive

Compound Belt drive

Open Belt drive
Open Belt drive consists of two pulleys A and B in fig 2. Driver pulley is the pulley which is keyed to the rotating shaft. Driven pulley is the pulley which is keyed to the shaft and to be rotated. Here Driver pulley is pulley A and Driven pulley is pulley B.

The driver pulley A pulls the belt from the lower side and delivers it to the upper side. Thus the tension in the lower side of the belt will be more than the tension in the upper side. Lower side is called as tight side and the upper side is called as the slack side.

Velocity Ratio :
Velocity ratio is the ratio of the velocity of the driven to the velocity of the driver.

Let N1= Speed of the driver ;  d1= Diameter of the driver

N2= Speed of the driven ; d2= Speed of the driven

Length of the belt passing over the driver in one minute = circumference of the driver X no. of revolutions per minute