This section will deal with the operation, troubleshooting, and repairing of the submerged tube and the flash type distilling plants that are used by the Navy. For additional and more de-tailed information than is provided by this train-ing manual, consult the manufacturers technical manual for the type of distilling plant installed on your ship.

Distilling plants in naval ships are of three general types: (1) vapor compression, (2) low-pressure steam, and (3) heat recovery. The major differences between the three types are the kinds of energy used to operate the units and the pressure under which distillation takes place. Vapor compression units use electrical energy (for heaters and compressors). Low-pressure steam distilling units use low-pressure steam from either the auxiliary exhaust steam systems or the aux-iliary steam system. Heat recovery distilling units use diesel engine jacket water instead of steam as the heat source. Vapor compression units boil the feedwater at a pressure slightly above atmospheric pressure. Low-pressure steam and heat recovery units depend on a relatively high vacuum for operation.

Vapor compression type distilling units are used in submarines and small diesel-driven sur-face craft where the daily requirements do not exceed 4000 gallons per day (gpd). Since the vapor compression type found on surface crafts is being replaced with the heat recovery distilling units, vapor compression distilling units will not be covered in this manual. Chapter 531 (9580-II) of Naval Ships Technical Manual contains infor-mation on these plants.

The low-pressure steam distilling unit is used in all steam-driven surface ships and nuclear sub-marines. Enginemen usually share responsibility with Machinists Mates for the maintenance and operation of the low-pressure steam distilling plants.

There are two reasons why low-pressure steam distilling units are considered low pressure: (1) they use low-pressure steam as the source of energy, and (2) their operating shell pressure is less than atmospheric pressure.

The three major types of low-pressure steam distilling units are submerged tube, flash type, and vertical basket.

In this section of the chapter we will be discussing only two of these distilling unitsthe submerged tube and the flash type.