Refrigeration & Equipment Engineering

Unit 7 - Power transmission elements

7.4.2.1.Types of flat belt drives

• Open belt drive: Open belt arrangement is employed for transmitting motion between parallel shafts rotating in the same direction. When the centre distance between the two shafts is large, thus the tight side of the belt should be the lower one.
• Cross or twist belt drive: The crossed belt drive is used with shafts arranged parallel and rotating in the opposite directions. A little consideration will show that at a point where the belt crosses, it rubs against each other and there will be excessive wear and tear. In order to avoid this, the shafts should be placed at a maximum distance of 20b. where b is the width of the belt and the speed of the belt should be less than 15m/sec.
• Belt drive with idler pulley: A belt drive with an idler pulley is used with shafts arranged parallel and when an open belt cannot be used due to small angle of contact on the smaller pulley. This type of drive is provided to obtain high velocity ratio and when the required belt tension cannot be obtained by other means.
• Compound belt drive: A compound belt drive is used when power is transmitted from one shaft to another through a number of pulleys.
• Stepped or cone pulley drive: A stepped or cone pulley drive is used for changing the speed of the driven shaft while the main or driving shaft runs at constant speed. This is accomplished by shifting the belt from one part of the steps to the other.