544 Farm Mechanics. 



687. Size of Belt for Transmission of Given Horse-Power. 



In order not to over-strain a good two-ply leather belt 

 it ought not to be subjected to an effective tension of more 

 than 40 pounds per inch of width. On this basis the width 

 of belt for a given number of horse-power will depend 

 upon the speed of the belt. Suppose the* driving pulley of 

 an engine is 9 inches and that it makes 350 revolutions 

 per minute, developing 3 horse-power. What width of belt 

 would be required ? This may be calculated from the fol- 

 lowing equation. 



3 X 33 000 

 0416 X . 75X350X46 = 3 ' 001 inehes ' Width of belt 



In this case 3 is the number of H. P., 33,000 is the 

 number of foot-pounds in one H. P., 3.1416 x .75 x 350 

 gives the velocity of the belt in feet per minute and 40 

 is the effective tension to which the belt may be safely 

 subjected. From this solution a general equation for cal- 

 culating the width of belt for any H. P. may be stated as 

 follows, 



No. H. P. X 33, 000 

 Width of belt = 



D = circumference of driving pulley in feet. 



No. rev. = number of revolutions of driving pulley per minute. 



Some belt manufacturers allow a strain of 60 pounds 

 per inch of width for a two-ply leather belt as safe but 

 it is in the direction of economy to have the belt stronger 

 than is really necessary, as it will wear enough longer 

 to pay. 



688. Condition of Belt It is very important to keep the 

 belt in a good, soft, pliable condition, as a flexible belt 

 will not only transmit power with less loss but it will wear 

 much longer. If for any reason belts have become hard 

 and stiff, they should be softened with neatsfoot oil. Xew 



