84 CENTRIFUGAL SEPARATION 



Its chief advantage is that it protects the separator against sud- 

 den shock of the spindle and bowl which is practically unavoid- 

 able when operated by certain forms of power. This is especial- 

 ly true in the case of gasoline engine explosions. In these belt 

 driven farm separators, the power is transmitted by belt to the 

 tight and loose pulley which is provided with a belt shifter, 

 thence from the short center shaft which is a part of the set 

 drive, by an endless belt to the lower worm wheel shaft of the 

 separator. In the latest type of hand separator the power trans- 

 mission is further equipped with a coil spring belt tightener over 

 which the belt runs and which automatically absorbs shocks and 

 irregularities in speed. 



In the great majority of hand separators which are used for 

 hand power only, the power is transmitted exclusively by cog 

 wheels or by worm wheels or by a combination of both. The 

 transmission mechanism usually consists of one, two or three 

 pairs of wheels. The large cog wheel resting on the crank shaft 

 transmits its power to a small cog wheel, this constitutes the first 

 transmission of power with increased speed. The small cog 

 wheel rests on a second large cog wheel which transmits its 

 power either direct to the worm gear of the lower spindle, or to 

 a third small wheel, to the axis of which is attached a third large 

 wheel which connects direct with the lower spindle. 



The successive multiplication in speed resulting from these 

 transmissions depends on the difference in the number of cogs 

 between the large and the small wheels. Assuming for example, 

 that there are three pairs of cog wheels and in each pair the 

 large wheel has 50 cogs and the small wheel has 10 cogs, the 

 speed is increased by each of the three sets of transmissions five 

 times, or 5x5x5=125. In the above case each turn of the crank 

 shaft yields 125 revolutions of the bowl. If the required number 

 of revolutions of the bowl is 6,500 per minute, then the crank 



shaft must be given ^ = 52 turns per minute. 



It is obvious that the smoothness of running, as far as the 

 transmission is concerned, is dependent on the regularity and 

 state of preservation of these cogs. If the cogs are abnormally 

 worn, or if one or more cogs are broken, the machine slips and 



