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Proceedings of Indiana Academy of Science 



considering, particularly if a large number of pulleys are in operation. 

 For instance, the seven pulleys in this experiment running at 800 r.p.m. 

 required .32 h.p. less when the spokes were enclosed than when they 

 were exposed. Figuring on the basis of one cent per horse power 

 hour, for ten hours per day and 300 days per year, the saving per 

 year would be $9.60, an average of $1.37 per pulley. 



TABLE II.— POWER REQUIRED TO DRIVE SPOKE AND WEB 



PULLEYS 



In considering the air friction losses of the two types of pulleys, 

 one should note that the spoke pulleys used in the experiment were of 

 the type designed to minimize air friction los.ses. Heavier and thicker 

 spokes increase the loss, double arm pulleys greatly increase it, and 

 wide flat armed pulleys, such as the usual wood split pulley, very greatly 

 increa.se it. There is no question as to the economy of enclosing the 

 arms of any wide face and therefore wide armed wood split pulley that 

 is to be operated at high speed. The data of a .'^ingle experiment will 

 verify this statement. 



A wopd pulley 12 inches in diameter with flat 6-inch face and having 

 four flat spokes or arms 4.5 inches wide was mounted on an extension 

 of the motor shaft of a standard one-half horse power A.C. motor sup- 

 ported by ball bearing trunions and weighted so as to be in balance in 

 any position. Concentric with the shaft and attached to the motor 

 frame was mounted a grooved pulley five inches in diameter over which 

 a cord passed to a sensitive spring balance, which gave the torque re- 

 quired to hold the motor in a given position against the armature 

 reaction. 



When the open pulley was driven at a speed of 1,840 r.p.m. the 

 torque was 3.375 lbs. When the pulley was closed with a cardboard 

 disk at each end and rotated at 1,850 r.p.m., the torque was .25 lb. It 

 will be observed that the torque in the case of the open pulley was more 



