12 



The American Public Health Association 



IS required all the time so that a by- 

 pass should be used and nearly enough 

 steam allowed to pass through this by- 

 pass valve to maintain temperature. 

 The controller will then only have to 

 act on the additional steam required, 

 and may be comparatively small, and 

 when closed does not cut off all steam 

 from the heater. 



All temperature controllers must 

 have a constant steam pressure to op- 

 erate properly ; therefore, it is impor- 

 tant to use at least one efficient steam 

 pressure valve between the boiler and 

 the controller instrument. In many 

 cases where there is a large fluctuation 

 in the boiler steam pressure, two re- 

 ducers can be used to advantage in ob- 

 taining a final constant pressure for 

 the controller. 



(j) Temperature Recording Instru- 

 ments and the Interpretation of Re- 

 cording Charts. The only meanS that 

 the operator of a pasteurizing plant or 

 the health authorities have of knowing 

 the treatment to which the milk has 

 been subjected, excepting by constant 

 testing with the thermometer, are the 

 chart records made by reliable time 

 and temperature recording instru- 

 ments, that have their bulbs placed in 

 such" a manner that the bulb is not in- 

 fluenced by the temperature of the ap- 

 paratus. Instruments sensitive to the 

 changes of temperature and quick to 

 record such changes should be used in- 

 stead of sluggish instruments. .All in- 

 struments should have pins close to 

 the center post that holds the charts 

 from inadvertently rotating, or from 

 being intentionally rotated by hand to 

 produce fake records. 



Temperature recording instruments 

 are not thermometers ; they record 

 temperatures after being adjusted to 

 correspond with a thermometer, and 

 require frequent testing to assure cor- 

 rect records. 



The operator in personal charge of 

 each pasteurizing apparatus should 



have a calibrated thermometer and 

 should be held responsible for the cor- 

 rectness of the recording instruments 

 and of the charts. Each chart should 

 have printed on it a statement certify- 

 ing to the correctness of the chart, to. 

 be signed by the operator, with a place 

 for date and identification mark of 

 the apparatus of which chart is the 

 record. On the chart of the holding 

 tanks there should be a statement to 

 the effect that the pump speed (if a 

 pump is used) has not been accelerated 

 during the run, and that the holding 

 lime has not been shortened. • The op- 

 erators should be held to rigid account 

 for the correctness of the charts on 

 which they have signed the certifica- 

 tions. 



All charts for recording the time and 

 temperature of milk treatment must be 

 set on the instrument dial at a uniform 

 time so that the time elapsed from one 

 treatment to another can be checked 

 and determined. All the charts must 

 show the time of the operation from 

 start to finish. 



The chart showing the temperature 

 record of the milk in an apparatus 

 where the milk is heated, held and 

 cooled in a \at, must show the time, 

 the temperature of the milk when it 

 starts to raise, the time when the milk 

 reaches its high point, the temperature 

 maintained during the holding period, 

 the time when the cooling temperature 

 commences, and the temperature to 

 which the milk is cooled. If the milk 

 is cooled by a separate cooler, the 

 chart on the cooler will record the cold 

 milk temperature, and the end of the 

 holding period which is indicated on 

 the chart as the time of the start of 

 the cooling operation. 



The chart showing the heating tem- 

 perature record of the milk in a con- 

 tinuous flow apparatus, must show the 

 time and temperature of the milk when 

 the heater starts to discharge, the tem- 

 perature of the milk as it is discharged 



