🔍 Key Concepts

• Boiler combustion control systems and how they maintain proper fuel-to-air mixture • The difference between coarse control elements (on/off, major flow changes) and fine trim controls • Which component directly adjusts the fuel/air ratio rather than just total fuel or total air volume alone

💭 Think About

• Ask which option controls the relationship between fuel and air, not just one or the other by itself • Decide which device is typically used for small, precise changes, rather than large operational adjustments • Consider which adjustment a watch engineer would normally "tweak" while watching the stack condition and combustion indicators

✅ Before You Answer

• Verify which choice affects both fuel and air together as a ratio, rather than only fuel or only air • Identify which component is commonly designed for fine manual trimming of combustion, not for major load changes • Check your steam plant knowledge: which control would you adjust while monitoring stack temperature, O₂, and smoke to get near-perfect combustion?