GEORGE W. PUTNAM 427 



Tests have been and at this writing are being made on practically every type of pas- 

 teurizing apparatus for the purpose of determining the thermal treatment received 

 by the milk under actual plant-operating conditions and locating any engineering 

 defects in the apparatus preventing proper pasteurization of any portion of the milk. 

 When a comprehensive report based on these studies is issued, detailed information 

 will be available to health officers on the various types of commercial pasteurizing 

 equipment. As defects are encountered in these studies they have been brought to the 

 attention of the equipment manufacturers with the result that they have been cor- 

 rected in much of the new equipment being sold. 



Defects found in commercial equipment which will prevent proper pasteuriza- 

 tion of all the milk may be grouped as follows: (i) dead ends, (2) leakage through 

 valves, (3) foam and splash, (4) defective continuous-flow units, (5) unsatisfactory 

 thermometers. 



The reasons why these defects prevent proper pasteurization and the methods 

 adopted for their correction are outlined below. 



Dead ends. — Dead ends are sections of pipe or other pockets in which the tem- 

 perature drops below that required, preventing the proper pasteurization of the milk 

 held in them. An example of this defect on a vat holder is illustrated in Figure 6. The 

 25 pints of milk in the dead-end outlet pipe {a-a) is entirely outside the zone of agita- 

 tion and heating and remains cold while the main body of the milk in the vat above 

 is heated and held for thirty minutes. The remedy is obviously the installation of a 

 flush-type valve such as that shown in Figure 7, which will eliminate the dead end. 



In the case of in-bottle pasteurizers, means must be provided to insure that 

 every bottle of milk, and every portion of milk in each bottle, receives the required 

 heat treatment.' 



Leakage through valves. — Practically all milk valves will leak to some degree, par- 

 ticularly after they have become warped in sweating on a connection or scored, dent- 

 ed, and worn by usage. Leaky inlet valves permit raw milk to drain into the holder 

 during the holding and emptying period. Similarly, leaky outlet valves permit milk 

 from the holder to escape into the outlet pipe before it is completely pasteurized. In 

 neither case is the leakage subjected to the pasteurizing temperature for the full 

 thirty-minute holding period. Such leakage may be small in some instances, but an 

 amount equal to more than i per cent of the total volume pasteurized has been found 

 in numerous cases. 



The remedy for this defect is obviously to divert the leakage of unpasteurized 

 milk. This can be accomplished by disconnecting the inlet piping after each filling 

 of a holder and the outlet piping immediately after each emptying. In order to elim- 

 inate labor, wear, and tear on piping and fittings and make this operation more 

 positive, leak-protector inlet and outlet valves have recently been developed which 

 are so constructed that any leakage will not pass through the valve but will be drained 

 out at the bottom. 



Figure 8 shows a leak-protector inlet valve consisting of a standard two-way 

 plug valve with a groove in the plug on each side of the discharge opening to carry 

 away leakage. Figure 9 shows a flush-type leak-protector outlet valve for use on a 

 vat holder. When the valve is closed, a leak drain and steam connection are auto- 



' Ayers, S. H., and Johnson, W. T.: US. Dept. Agric. Bull. 240. 1915. 



