The flash type evaporator, like all distilling plants, removes salts and other impurities from raw seawater by the process of evaporation and condensation. This is accomplished by boiling the water to convert it to steam, and condensing this steam to form distilled water. The flash evaporator is different from other distilling plants, because evaporation takes place at temperatures well below the normal boiling point of water and without the use of submerged heat transfer surfaces.

In the flash type distilling plant, the temperature of the water is never raised beyond 175 F, and is only raised to this temperature within the last pass of tubes of the saltwater heater. Flash evaporation takes place at temperatures as low as 104F. In addition, no boiling occurs on heat transfer tube surfaces; as a result, the scale formation is greatly reduced and operation at maximum efficiency is prolonged.

The term flash evaporation means that water is converted to steam as it enters an evaporating chamber, without further addition of heat. Flashing at low temperatures is possible only when a vacuum is maintained in the chamber, since the boiling point of water decreases as the pressure in the chamber is reduced. As in other methods of distillation, a portion of the water re-mains behind in the evaporating chamber and is taken off as a concentrated waste (brine).