SKIMMING EFFICIENCY OF THE SEPARATOR 91 



be lessened and more fat is lost in the skim milk. Nothing is 

 gained by running the machine faster than the required speed ; 

 excessive speed does not materially increase the skimming effi- 

 ciency; on the other hand it augments the pressure on the 

 bowl and on other parts of the separator, and beyond certain 

 limits the bowl may collapse, or it may jump the castings, or 

 it may increase the friction sufficiently to cause the spindle 

 and the bearings and bushings to heat and wedge, in which 

 case the bowl may come to a sudden stop warping the spindle. 

 For these reasons each machine is accompanied by directions 

 in which the proper speed of the separator is specifically stated. 



The speed of the bowl varies considerably Avith different 

 makes of separators. Since, at a given speed, the centrifugal 

 force increases with the increase of the diameter of the bowl, 

 separators with wide bowls do not require as high a speed to 

 develop the desired separating efficiency as separators with a 

 narrow bowl. Thus the relatively large-diameter bowls of the 

 De Laval type require only from five to six thousand revolu- 

 tions per minute, while separators with bowls of the tubular 

 type, long and narrow, must be run at about 17,000 revolutions 

 per minute. 



In the case of the hand separator the proper speed is given 

 in terms of number of turns of the crank. This varies with dif- 

 ferent machines from 45 to 60 turns per minute. The exact 

 number of turns required is usually indicated on the crank of 

 the separator. 



When the proper speed has been attained it should be 

 maintained uniformly throughout the separation. Running the 

 separator at uneven speed causes incomplete separation. 



Control of Speed of the Separator. In the case of the hand 

 separator, as used on the farm, the operator can make sure of 

 giving the separator the proper speed by timing himself. All 

 he has to do is to count the turns of the crank per minute, by 

 the watch in his hand. By doing this occasionally he soon 

 learns the necessary rapidity of motion to run the machine at 

 full speed. Unfortunately this is not usually done and expe- 

 rience has amply shown that the general tendency of the oper- 

 ator is to overestimate the amount of work he puts into the 



