DISTILLATE CIRCUIT.-Distillate (dark blue) is formed in the condensing section of both stages of the evaporator. The distillate from the first stage collects in the bottom of the first-stage condensing section in a hotwell-like area (trough) formed by the joint between the evaporator shell division plate and the first-stage collection tray. The distillate passes through a loop seal into a lower trough (or tray) in the second stage. The piping between the two stages contains an orifice plate that controls the liquid flow rate. Equalization of pressure between the stages is prevented by the two loop seals-one for the feed-water and one for the distillate-which connect the two troughs together. This arrangement also prevents premature flashing of the distillate as it enters the lower pressure area of the second stage. The distillate is then pumped out of the second-stage distillate trough by the distillate pump. The distillate pump discharges the water through a three-way solenoid-operated trip valve which, when tripped, will automatically divert the flow of distillate to the bilge if the salinity content reaches a predetermined set point (usually 0.065 epm). When the valve is in the reset (normal) position, the distillate will be routed through a water meter and into an interlocked two-valve manifold. The two-valve manifold directs the distillate to either the potable water system or the reserve feed system. The manifold is interlocked to prevent opening of both valves at the same time. The potable water system can be contaminated with chloride from a shore water source, which may be suitable for drinking but not for boiler feed. The potable water system and the reserve feed system, therefore, must NEVER be cross-connected in any way.

AIR EJECTOR CIRCUIT.-A two-stage air ejector unit (red and pink), using auxiliary steam, is located at the top of the distilling plant. It draws vacuum and maintains the vacuum in the evaporator shell. The air ejector second stage discharges into the air ejector condenser section of the air ejector condenser/seawater heater assembly. The air ejector condenser condenses the steam and vents air and noncondensables (such as CO2 ) to the atmosphere. The condensate, which forms from the steam, drains to either the bilge or the steam drain collecting system through a three-way solenoid-operated trip valve. On some ships, however, the condensate is routed through a loop seal or trap to the seawater heater hotwell.

BRINE CIRCUIT.-Brine (dark green) is pumped out from the bottom of the second-stage shell. A centrifugal pump is used for this purpose.