IDLER PULLEYS 75 



ings will be reduced. This arrangement of machinery will 

 make one-half of the belts drive with the top strand tight. 



The distance between the shafts has considerable influence 

 on the life of belts, and the distances should as a rule be made 

 as great as possible up to reasonable limits. For narrow belts 

 on small pulleys, a good average figure is 15 ft.; for larger 

 belts the center line distance should be from 20 to 25 ft., while 

 for main belt drives using wide and heavy belts the pulleys 



Idler v 

 Pulley 



Movable 



Weight 



FIG. 21. IDLER PULLEY ARRANGED AS A GRAVITY TIGHTENER. 



should be from 25 to 30 ft. apart. If the distance is made too 

 great the belt will have a tendency to flap and injure itself. 



Idler Pulleys. Belts which are run on pulleys located 

 close together are liable to stretch rapidly and thus lose the 

 tension necessary to the transmission of the desired amount 

 of power. For such cases, and also for belts which are 

 required to run for long periods without stopping, an idler 

 pulley which can be moved against the belt to take up the 

 slack and thus increase the tension, will be found desirable. 

 The idler should be located about one-quarter of the distance 



