🔍 Key Concepts

• Purpose of an air cock (air vent) on a boiler when raising steam from cold • What condition inside the boiler makes continued venting of air no longer necessary • Sequence of steps when warming up and cutting in a boiler to the steam line

💭 Think About

• Think about what the air cock is actually removing from the boiler at the start of raising steam and what replaces it over time. • Ask yourself: at what point is the mixture of air and steam in the boiler no longer mostly air, and pressure/flow conditions are stable enough that venting is no longer needed? • Consider which event happens earliest in the startup sequence: steam forming and venting air, lighting all burners, cutting the boiler into the line, or closing the economizer drain.

✅ Before You Answer

• Identify the primary function of the air cock during a cold startup (what problem is it preventing?). • Determine which step in the startup sequence comes first in time among the answer choices. • Verify at which step it becomes safe to stop venting air without risking trapped air or water hammer in the boiler.