28 LEATHER BELTING 



opposite the velocity of 2500 ft. per minute, for a belt of 

 i sq. in. of cross-sectional area. The total power to be trans- 

 mitted is 27.5 horsepower and therefore the area of the belt 

 to be used is 27.5-1-6.66 = 4.129 sq. in. In the table of relative 

 areas we find under ^ in. thickness of belt, the value of 3.5 

 opposite the width of 8 in. The present SXrg- in. belt is 

 too small for the work it is required to do if it is to be run 

 under the most economical conditions. If its use is persisted 

 in it will be necessary to operate it at a higher tension and to 

 tighten it at more frequent intervals. If we desire to use 

 the same width of belt, which is quite as wide as should be 

 used on a pulley of 9 in. face, we must increase its thickness. 

 The table of relative areas shows that an 8-in. belt | in. thick 

 will have a cross-sectional area of 4 sq. in. and that an 8 

 X-rV m> belt will have an area of 4.5 sq. in. As the former 

 will transmit 6.66X4 = 26.64 horsepower it can safely be used 

 without increasing the tensions given in the horsepower table 

 to any great extent. It might be advisable to tighten the 

 belt at a slightly higher figure than that given in the table 

 as the minimum tension. Assuming the 8X^-in. belt to be 

 chosen, the total tension under which it should be put on the 

 pulleys will be 4X142 = 568 lb., and the tension at which it 

 should be retightened 4X85.5=342 lb., or to be on the safe 

 side, 350 lb. total tension. 



