Question 197Steam Plants - Assistant Engineer

The correct answer is B) maintain a positive flow of steam as supplied by the main engine LP bleed system. The first stage heater is typically maintained under a slight vacuum to create a low-pressure environment that allows the steam from the main engine's low-pressure bleed system to flow into the heater and transfer its heat to the feed water. This vacuum helps ensure a positive flow of steam into the heater, rather than relying on the condensate pumps to force the flow (which would be the case if there was no vacuum). The other options are incorrect because they do not accurately describe the primary reason for the vacuum in the first stage heater. Option A is incorrect as the vacuum is not primarily to guarantee feed water flow, but to enable the steam flow. Option C is incorrect as the vacuum is not to avoid the use of condensate pumps, but to facilitate the steam flow. Option D is incorrect as the vacuum is not to force the use of the main condenser as the drain cooler.