8 LEATHER BELTING 



Nagle curves show the effect of centrifugal tension at the 

 higher velocities. It will be observed that under the Barth 

 practice a belt will transmit considerably less power at a given 

 velocity than it will according to any of the other formulae. 

 It may be argued that for a given horsepower this will call for 

 a heavier belt than it has heretofore been customary to use. 

 This is precisely what it is intended to do. The object of 

 the Barth practice is not to find the smallest belt that can be 

 used for a particular service, but rather to find that belt which 

 under the conditions imposed will transmit the required power 

 at the least expense, taking into consideration the first cost 

 of the belt, the expense of repairs and maintenance and the 

 loss which would occur as a result of belt breakages in work- 

 ing hours. To accomplish this object low tensions are neces- 

 sary, and low tensions mean large belts. 



A belt put on the pulleys under a certain working tension 

 will not maintain that tension for any length of time. The 

 tension will constantly decrease and in time will fall below 

 the point at which it will transmit the desired horsepower. 

 It must, therefore, be retightened at intervals to restore it 

 to its original initial tension. The interval between retighten- 

 ings will vary with the age of the belt. A new belt will stretch 

 rapidly, and probably will require taking up within forty-eight 

 hours. The second retightening may be necessary three or 

 four days later, and the third within a week after that. The 

 intervals progressively increase in length until the period 

 that will elapse between retightenings reaches three or four 

 months. They then will remain practically constant. No 

 belt, however, should be allowed to go for a longer period 

 than six months without having its tension measured and 

 being shortened to restore it to its original tension. 



In connection with their investigations into the subject of 

 belting, Messrs. Taylor and Barth devised a system of belt in- 

 spection and maintenance which would ensure that all belts 

 in a plant would receive attention, have their tensions meas- 



