If steam is admitted to the shell side of a feedwater heater before the tube side flow path is opened, what happens to the pressure inside the trapped liquid?

• A. Pressure Rises
• B. Pressure Falls
• C. No Change
• D. System Venting Occurs

Answer: (A)

Introducing steam into a closed shell that contains trapped liquid raises the pressure inside that liquid. With the tube side flow path not yet opened, there is nowhere for the liquid or steam to flow out, so the shell-side volume becomes essentially a closed container. As steam enters, it exerts pressure on the liquid and the shell walls; the liquid (being nearly incompressible) transfers that pressure throughout the trapped region, causing the pressure to rise. This pressure buildup continues until venting or flow paths are opened or the steam supply is removed. That’s why the correct outcome is a rise in pressure.