SEPARATION OF CREAM. 143 



matic governor on it, the speed is usuallj' quite uniform. Where 

 steam-turbine machines are used, the speed of the machine is 

 more Hkely to vary with the different amounts of steam pressure 

 on the boiler. With turbine separators it is very essential to 

 keep an even steam pressure. Some turbine separators have 

 a safety-valve attached to prevent too high speed. 



The reason why the prevention of a variation in speed is so 

 essential is that a slight variation in the speed has a compara- 

 tively large effect upon reducing or increasing the centrifugal 

 force. The centrifugal force generated in a machine varies 

 according to the diameter of the bowl, and according to the 

 speed of the machine. The greater the diameter of the bowl, 

 the less speed of velocity is required in order to get a certain 

 force. The centrifugal force varies in direct proportion to the 

 diameter of the bowl; that is, if the diameter of the bowl be 

 doubled, then at the same speed, the centrifugal force has been 

 doubled. The centrifugal force varies in quadratic proportion 

 to the speed of the machine; that is, if the speed of the sepa- 

 rator is doubled, the centrifugal force is increased four times. 

 From this it will be seen that speed is a great factor in deter- 

 mining the centrifugal force generated. It is not a good plan 

 to have the diameter of the bowl too large, for the following 

 reasons : A large bowl is more likely to be thrown out of balance ; 

 it is harder to keep on the bearings; and it is heavier and more 

 unhandy to handle. For these reasons it is better to lessen the 

 diameter of the bowl and increase the speed. This, of course, 

 is true only to a certain limit. 



Steadiness in Running. — Smooth running of a separator is 

 one of the first essentials. If a machine runs roughly, there 

 will not be good separation, and it is dangerous to run it. The 

 bowl itself is likely to jump out, or burst. The causes for 

 unsteadiness in running are many. It may be due to a bent 

 or sprung spindle; the machine not standing level; changing 

 covers to bowls; using clamps which do not fit the bowl cover; 

 unclean, worn-out bearings; condition of the bowl, and con- 

 trivances inside the bowl ; and dented and rusty bowls. Occa- 



