Steam-plant draught systems — name the method: The draught produced when a steam jet issues from a nozzle located in the chimney to entrain flue gases and draw air through the furnace is called what?

Introduction:
Draught is the pressure difference that moves air into the furnace and carries flue gases to the stack. Beyond natural chimney draught and fan-based mechanical draught, steam-jet arrangements can also create suction by momentum exchange. Knowing their names and placements is vital in boiler practice.

Given Data / Assumptions:

• Steam jet issues from a nozzle placed in the chimney.
• Objective is to draw (induce) flow of hot gases upward, thereby pulling combustion air through the furnace.
• Steady operation; standard boiler components.

Concept / Approach:
When a high-velocity steam jet is discharged into the chimney, it entrains flue gases and reduces static pressure inside the stack. This creates suction at the furnace and gas passes, hence the name “induced steam jet draught.” By contrast, if the steam jet is directed into the ash pit or furnace front to push air through the grate, it is termed “forced steam jet draught.”

Step-by-Step Solution:

Verification / Alternative check:
Boiler texts list two steam-jet methods: forced (jet in ash pit) and induced (jet in chimney). The described location matches the induced type exactly.

Why Other Options Are Wrong:

• Chimney draught: refers to natural draught from buoyancy, not a steam-jet device.
• Forced steam jet draught: jet in ash pit to force air in, not in chimney.
• Balanced mechanical draught/none: unrelated to a steam-jet system or too vague.

Common Pitfalls:
Confusing “forced vs induced” with “fan vs jet”; focusing on the device position (ash pit vs chimney) removes ambiguity.

Final Answer: