🔍 Key Concepts

• Function of an air cock or vent on a boiler drum • What happens inside the drum when a boiler is filled, emptied, and lighted off • Why trapped air in a boiler is dangerous or undesirable

💭 Think About

• Think about each operation (filling, emptying, and generating steam) and ask: in which of these situations do we need to let air in, and in which do we need to let air out? • Consider what would happen to the boiler if air could NOT escape while water is entering the drum, or if air could NOT enter when the boiler is draining. • Ask yourself whether this fitting is usually designed for just one of these operations, or is it commonly used whenever air needs to be controlled in or out of the drum.

✅ Before You Answer

• For each option, decide: does this action require admitting air or releasing air from the drum? • Verify which direction the air cock is normally used for during boiler filling and lighting off. • Check whether the same fitting is commonly used in practice for more than one of the listed purposes.