CHAPTER IV 

 THEORY OF TRANSMITTING POWER BY BELTING 



IN developing the theory and formulae on which the 

 horsepower and tension tables on pages 91 to 94 are based, 

 Mr. Barth took as his starting-point the investigations of 

 Frederick W. Taylor, which are discussed in Chapter II. 

 In considering these formulas and in using the tables which are 

 calculated from them, certain facts must clearly be kept in 

 mind: i. The pulling power of a belt depends, among 

 other things, upon the tension in the belt when it is at rest, 

 called, in what follows, the initial tension. Upon this initial 

 tension depends, in part, the tensions in the tight and slack 

 strands of the running belt; that is, the values h and fe in 

 formula (2), in the previous chapter. 2. That a belt in service 

 stretches and thereby decreases the initial tension. This 

 stretch is rapid at first and decreases in amount with the age 

 and use of the belt. 3. That a belt whose initial tension is 

 allowed to fall below a predetermined figure will, at a given 

 velocity of belt, fail to transmit the desired horsepower. 

 4. That excessive unit tension in a belt will cause it to stretch 

 rapidly and will increase the maintenance and other charges 

 relating to the belting. 5. As a corollary to the foregoing, 

 heavy belts, at moderate tensions will give, all things con- 

 sidered, better service than light belts at high tensions. 6. 

 From the standpoint of belt maintenance, it is desirable to 

 equalize as far as possible the intervals during which belts 

 running at different velocities and transmitting different 

 horsepowers will fall to the minimum allowable unit tension 

 and require retightening. 7. That belts that are readily 

 accessible, such as machine belts, can be taken down and 

 retightened more easily than can belts in inaccessible loca- 



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