164 SEPARATION OF CREAM 



3. Speed. All modern machines have a device by which their 

 speed can be determined. Most speed indicators consist of a 

 little wheel, which, when pushed up against the spindle of the 

 separator while running, turns around and permits the calcu- 

 lation of the speed of the separator. If the wheel on the speed- 

 indicator makes 10 revolutions during ten seconds, the machine 

 turns 1000 times during the same time. During one minute the 

 separator will run six times as many revolutions, or 6000, as ten 

 seconds is one-sixth of a minute. Most speed-indicators are so 

 adjusted as to turn one revolution for every 100 revolutions of the 

 machine. The higher the speed, the more thorough is the sepa- 

 ration. Nearly all machines are balanced to do the best work at a 

 certain definite speed, varying with different machines, and 

 indicated in the directions for operating. It is essential that the 

 machine should be brought up to speed gradually, and no milk be 

 allowed to flow through it until after it has acquired its full speed. 



During the run, all machines are likely to vary more or less 

 in speed, owing to different causes. Pulleys are likely to slip 

 on the shaft, and belts are likely to become loose, and thus 

 cause variations in the speed. The steam pressure may get low, 

 and cause all of the machinery in the creamery to run more 

 slowly. This cause, however, is not a very common one where 

 belt separators are used. If the engine has an automatic gov- 

 ernor on it, the speed is usually quite uniform. Where steam- 

 turbine machines are used, the speed of the machine is more likely 

 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 or velocity is required in order to get a certain 

 force. The centrifugal force varies in direct proportion to the 



