A slight vacuum is maintained in the shell of the first stage heater shown in the illustration. The primary reason for the vacuum is to __________. SG-0025

Correct Answer: Option C — maintain a positive flow of steam as supplied by the main engine LP bleed system

Maintaining a slight vacuum in the low-pressure feed heater shell, referenced to the main condenser, ensures a positive pressure differential that continuously draws and flows extracted LP turbine bleed steam into the heater without stalling.