Minnesota Boiler License Practice Exam

What is draft on a boiler in operation?

1. Flow of gases through the boiler

2. Difference in pressure between atmosphere and furnace

3. Difference between atmospheric pressure and breeching

4. Measurement of airflow rate

The correct answer is: Difference in pressure between atmosphere and furnace

Draft on a boiler in operation refers to the difference in pressure between the atmosphere and the furnace. This differential pressure is crucial for maintaining proper airflow through the boiler system. It helps to ensure that combustion gases are effectively drawn out from the combustion chamber, allowing for efficient operation and safety. By creating a negative pressure in the furnace area, draft enables atmospheric air to be drawn into the boiler for combustion, while also facilitating the expulsion of exhaust gases. In this context, understanding draft is vital for ensuring adequate ventilation and prevention of backdraft, which can lead to safety hazards. The ability to manage draft influences combustion efficiency and can also affect the boiler's operational stability. Factors affecting draft include design characteristics, fuel type, and the stack height. Other choices, such as the flow of gases through the boiler or a direct measurement of airflow rate, do not capture the essential relationship of pressure that defines draft. Similarly, the concept of draft is not solely about the pressure difference between atmospheric pressure and breeching, as that would not fully encompass the role of draft in maintaining operation within the confines of the boiler system.