Question 11 1AE01 - First Assistant Engineer

The Correct Answer is C **Why option C ("neglecting to close the shell vent") is correct:** The unit described is typically a type of freshwater generator (such as a vacuum evaporator) which relies on establishing a high vacuum (low absolute pressure) within the shell to boil seawater at low temperatures. When starting up the unit, air must be removed from the shell to achieve this vacuum. This is typically done by an air ejector or vacuum pump, with the shell vent initially open to allow air to be pushed out. Once the vacuum is pulled, the shell vent *must* be closed. If the operator forgets to close the shell vent, outside atmospheric air will continuously leak back into the shell, preventing the vacuum pump or ejector from establishing and maintaining the required low pressure. Therefore, neglecting to close the shell vent results in a failure to establish sufficient vacuum. **Why the other options are incorrect:** A) **Improper operation of the brine pump:** The brine pump removes concentrated saltwater (brine) from the bottom of the evaporator shell. While essential for continuous operation and preventing fouling, the brine pump's function is primarily related to circulation and concentration control, not the initial establishment of vacuum within the shell. B) **Neglecting to latch the dump valve:** If the unit has a dump valve (often related to dumping produced water if quality is low), failing to latch it might affect the quality or disposal of the generated water (distillate). However, the operation or status of this valve is generally independent of the air ejector system responsible for pulling the initial vacuum. D) **Improper operation of the distillate pump:** The distillate pump removes the produced fresh water from the unit. Similar to the brine pump, its function occurs *after* the vacuum has been established and boiling has begun. Its malfunction would affect the production rate or water level, but not the ability to initially draw a vacuum in the shell.