🔍 Key Concepts

• Fire-tube auxiliary boiler internal circulation and water level location • Where scale (mineral deposits) tends to form thickest on the waterside due to heat concentration and steam formation • Relative location and function of crown sheet, stays, hydrokineter, and belly plug in the boiler shell

💭 Think About

• Think about which part of the boiler waterside runs at the highest metal temperature in contact with water during normal firing • Ask yourself which area is closest to the flame/gas path and just at or slightly below the normal water level, where boiling is most intense • Consider which of the listed fittings is mainly a support or accessory versus a primary heat-absorbing surface

✅ Before You Answer

• Be clear on the normal water level position in a fire-tube boiler and which part of the shell is just below it • Identify which option is a major heat-absorbing plate or surface exposed directly to furnace gases • Eliminate components that are primarily structural supports or removable plugs, not the main heating surface where intense boiling occurs