CENTRIFUGAL SEPARATION 75 



be firmly screwed to the bowl to prevent leaking. In the case 

 of machines with suspended bowls the cover forms the bottom of 

 the bowl or in some cases, the bowl may consist of two nearly 

 equal halves which screw together, a rubber ring furnishing a 

 tight seal. Most bowls also carry a central tube through which 

 the milk enters, flows to near the bottom and then is released 

 for distribution and separation. 



Experience has shown, that the efficiency of separation suf- 

 fers when the milk is allowed to enter the separating space of 

 the bowl by continuously passing through the innermost layer 

 of milk, which represents the cream layer. This causes a con- 

 stant mixing of the fresh milk with the cream layer. To avoid 

 this the intake of the milk is so arranged that the inflowing milk 

 passes into the neutral zone of the milk layer outside of the cream 

 layer without passing through the latter. This is accomplished 

 by compelling the milk to flow through an umbella-shaped disc 

 at the bottom of the bowl or through properly located slots in 

 the central tube or other similar devices in the center of the bowl. 



The bowls of the earlier separators were hollow in their in- 

 terior. In order to cause the milk to circulate with the bowl im- 

 mediately upon its entrance, these bowls were equipped at their 

 periphery with one or more wings extending radially to near the 

 cream layer. In the newer separators most of the bowls carry 

 a series of internal contrivances which not only assist in subject- 

 ing the milk promptly to the circular motion, but increase the 

 skimming efficiency of the machine further by exposing the milk 

 over a longer distance to the centrifugal force and by facilitating 

 the return of the fat globules to the cream layer. 



Of these internal contrivances the cone-shaped discs of the 

 Alpha separator are the oldest and best known. These tin discs 

 are slipped over the central tube of the bowl and rest on top of 

 one another. They leave a small space open around the central 

 tube for the gathering of the cream. The upper surface of each 

 of these discs is spotted with small projections, for the purpose 

 of keeping the discs at a slight distance from each other. These 

 intervening spaces divide the milk, in its passage from the center 



