CHAPTER L 



TRANSMISSION OF POWER 



Not all machines can be so placed as to be driven directly 

 by the motor, and so there must be some means of transmit- 

 ting the power to the machine. 



Belting. One of the most common forms of transmitting 

 power from one rotating shaft to another is by belting. In 

 this case the power is transmitted by the friction between the 

 belt and the pulley, producing rotation. While transmit- 

 ting power a belt is under greater tension on one side, the 

 "tight side," than on the other, or "slack side." The actual 

 force transmitted is equal to the difference in the tension of 

 the "tight side" and the "slack side." The power trans- 

 mitted depends also upon the speed of the belt or the distance 

 the force travels in a given time. 



Horsepower of Belting. In installing a power plant of 

 any sort in which belting is used, it is necessary to determine 

 the size of belts which will transmit the desired amount of 

 power. A formula quite generally used in estimating the 

 horsepower of leather belts is as follows : 



V x w 



H. P. 



1000 

 where H. P. equals the horsepower; V the velocity of the belt 

 in feet per minute; and W the width of the belt in inches. 



If the speed of the driving pulley, which furnishes power, 

 and its diameter be known, V may be easily obtained by 

 multiplying the circumference of the pulley in feet by the 

 devolutions per minute. A belt should seldom travel more 



320 



