RATOSIGHT METER-The ratosight meter is attached to the front of the evaporator shell in the feed inlet line. (Refer to fig. 15-5.) It is used to measure the flow rate of the feedwater enter-ing the evaporator shell. The ratosight meter is a variable-area meter of the tapered tube and float type. A metal float is suspended in a vertically tapered glass tube and moves axially with the water flow. (The flow is vertically upward.) The weight of the float, minus its buoyancy in the fluid, is balanced by the drag force of the fluid upon the float. The float rides at a height that will maintain the balance of forces and permit stable operation while the ratosight measures the liquid flow rate. To prevent excessive scale buildup, the feedwater flow rate through the meter should be set at three times the distillate flow rate as measured by the water meter.

DISTILLATE PUMP.-The distillate pump moves distillate formed within the evaporator to storage tanks or to waste water tanks. It is an electric motor-driven, centrifugal pump with connections for a seal cooling water line, vent, and pressure gauges. The distillate pump is mounted on a plate that is attached to the evaporator assembly. If the distillate pump should stop during normal evaporator operation, the distillate sterilizer heater will be automatically de-energized to prevent burnout due to lack of distillate flow through the sterilizer.

DISTILLATE STERILIZER-The distillate sterilizer is mounted above the evaporator assembly. (Refer to fig. 15-6.) The sterilizer consists of a shell fitted with inlet, outlet, and vent connections. A six-element, 440-volt electric immersion heater is located within the sterilizer shell. The heater heats the distillate flowing through the shell to the required 170F outlet temperature, which is high enough to kill harmful bacteria.

DISTILLATE COOLER.-A distillate cooler is mounted above the evaporator assembly. The distillate cooler is a shell and tube type of heat

Figure 15-6.-Distillate sterilizer.

exchanger containing a vent and a drain fitting. (The shell and tube heat exchanger was discussed in chapter 7, "Engine Cooling Systems. ") Hot distillate from the sterilizer is piped through the distillate cooler shell and is cooled by cold seawater flowing through the tube bundle.

SALINITY CELLS.-Three SALINITY CELLS in the plant continuously monitor the purity of the distillate. One cell is located in the discharge line of the distillate pump, and the other two cells are located in the distillate cooler outlet line. All of the salinity cells are read on a salinity indicating panel. Two of the cells-one located in the discharge line of the distillate pump and the other in the distillate cooler outlet line-also con-trol the three-way solenoid-operated trip valve. Additional information on salinity monitoring and indicating will be provided later in this chapter.