CRBAMBRV MECHANICS 297 



Let us calculate the size and speed of pulleys neces- 

 sary to run a separator 6,000 revolutions per minute 

 when the following conditions are known : Size of drive 

 pulley on engine, 16 inches; size of separator pulley, 3 

 inches; size of large pulley on intermediate, 18 inches; 

 size of small pulley on intermediate, 5 inches; speed of 

 shaft, 180 revolutions per minute. 



The known conditions given here are indicated in the 

 diagram above by figures, the unknown by x (Fig. 85). 



The calculation in this problem begins at the separator, 

 where both the speed and diameter of the pulley are 

 known, and ends with the determination of the speed of 

 the engine. 



1. Determine the speed of the intermediate which has 

 a large pulley at one end and a small one at the other. 

 Applying the foregoing rules, the speed of intermediate 

 is equal to: 



6000x3-5-18=1000 rev. per min. 



2. Determine diameter of pulley on main shaft. This 

 is equal to: 



1000x5--180=27.7 inches. 



3. Determine speed of drive pulley on engine. This 

 is equal to: 



180x27.7-^16=312 rev. per min. 



With most engines a great range of speed is possible 

 by regulating the governor. It is better, however, to have 

 the drive pulley of such size as to keep the speed under 

 300 revolutions per minute. 



