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 first stage heater shell permits smooth admission of low-pressure bleed steam from the main propulsion turbine without requiring excessive pressure differentials, ensuring stable regenerative heating across varying operational loads.