🔍 Key Concepts

• How to distinguish fire-tube vs water-tube boilers by looking at where the water is and where the hot gases are • What makes a boiler Scotch marine (shape, furnace location, tube arrangement) • What single-pass vs two-pass gas flow means inside a boiler

💭 Think About

• First, decide if the water is mainly in the big outer shell or in the small tubes shown. What does that tell you about fire-tube vs water-tube? • Next, trace the path of the flame and hot gases in the illustration. How many distinct times do the gases travel the full length of the boiler shell? • Finally, compare what you see to a coil-type forced-circulation boiler. Do you see tight coils of tubing, or a large cylindrical shell with straight tubes and a furnace?:

✅ Before You Answer

• Verify whether the hot gases are inside the tubes or outside them • Verify whether the gases change direction once (making two passes) or not at all (single pass) • Verify if the overall look matches a Scotch marine boiler: horizontal cylinder, internal furnace at one end, return tubes inside a single large shell of water