312 THE SPRAY PROCESS 



and continuous flow through the spray nozzles and the deep stuf- 

 fing boxes enhance the tightness of the seal. The hardening of 

 condensed milk on the plungers is prevented by an open pot water- 

 seal which completely merges the stuffing boxes, the water serving 

 to both cool and lubricate the packing and to prevent its being hard- 

 ened by absorbing condensed milk. While the pump is in operation 

 a small stream of cold water is allowed to run into this water pot 

 and to -overflow through a suitable opening. 



These pressure pumps should also be provided with proper 

 relief or overflow valves, so as to avoid the danger of excessive 

 pressure and variation in the spray, in case several of the spray 

 nozzles should become clogged simultaneously. 



At the finish of the run of milk, a quantity of water should 

 be pumped through these high pressure pumps and pipes and it 

 is advisable to allow the pumps and pipes to stand full of water 

 when they are not in use, so as to loosen and remove remnants of 

 condensed milk,- preventing their accumulation in the cylinders and 

 avoiding difficulties incident to plugging, and clogging. 



The pressure used at which the milk is forced through the 

 spray nozzles varies from 800 to 3,500 pounds per square inch, 

 the usual range of pressure employed fluctuates between 2,000 and 

 3,000 pounds. The multiple nozzles with the fine openings require 

 less pressure to secure the same atomizing effect than when fewer 

 or one large nozzle, is used. 



Hot Air Intake and Discharge. The heated air enters the 

 drying chamber at points varying with different types of cham- 

 bers. Where the spray issues forth from nozzles located all on 

 one side, the heated air often is admitted through a slot located 

 directly under the spray nozzles and the air travels in the same 

 direction as the spray and mixes with it. 



In desiccating chambers in which the spray nozzles are in- 

 stalled on all sides, the heated air may enter near the bottom in 

 the center of the desiccating chamber, pass up through and mix- 

 ing evenly with the spray that issues from all sides toward the 

 center. Or the heated air may enter at the top and pass downward 

 with the spray. Or it may enter at the periphery at various points 

 near the top, in the form of a cyclonic current moving spirally to- 

 ward the center, and escaping in the center through the top of the 

 desiccating chamber. 



