Boiler Safety Controls and Switches Quiz

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What is the main function of the Low Combustion Air Pressure Fuel Cut-Off Switch?

To control the start-up sequence of the burner

To prevent burner operation when there is not enough combustion air (correct)

To regulate the flow of fuel to the burner

To monitor the temperature of the burner

How does the Low Combustion Air Pressure Fuel Cut-Off Switch interact with the burner system?

It adjusts the flame intensity of the burner

It completes or interrupts the burner limit control circuit based on combustion air availability (correct)

It controls the fuel supply to the burner

It regulates the air-fuel mixture ratio

What happens if there is insufficient combustion air in the windbox according to the text?

The flame safeguard controller shuts the SSOVs (correct)

The high airflow purge switch is activated

The fuel valve shuts off

The burner starts automatically

What component of the Low Combustion Air Pressure Fuel Cut-Off Switch is connected to a switch that affects the burner operation?

Diaphragm Signup and view all the answers

When is the switch in the Low Combustion Air Pressure Fuel Cut-Off Switch opened according to the text?

When insufficient combustion air is supplied to the burner Signup and view all the answers

What is the role of the spring in the Low Combustion Air Pressure Fuel Cut-Off Switch?

Moves the diaphragm to open or close the switch based on air pressure Signup and view all the answers

What is the purpose of the low-fire start switch in a boiler?

To ensure the pilot and main burners ignite when air and fuel are in their low-fire positions Signup and view all the answers

Why is a proven low-fire start essential for boilers over 300 kW input?

To ensure safe ignition of pilot and main burners in correct positions Signup and view all the answers

What triggers the high-fire pre-purge in burners that use mechanical draft?

Intermittent or interrupted pilot ignition Signup and view all the answers

Why does the airflow rate during a high-fire purge need to be at least 60% of that required at maximum input?

To sweep clear combustible gases from the furnace before ignition Signup and view all the answers

What device can prove the airflow and purge duration during a high-fire purge?

Calibrated airflow switches Signup and view all the answers

When does a larger boiler with a dedicated airflow-proving switch start the purge timer?

At high-fire position of the combustion air damper Signup and view all the answers

Why might the purge timer count even if the forced draft fan is not supplying air?

Tripping of the draft fan motor Signup and view all the answers

What happens if the fan becomes mechanically uncoupled?

The airflow decreases and the purge switch opens Signup and view all the answers

According to CSA B149.1, what is the purpose of combustion air openings for gas and propane fired appliances?

To provide adequate fresh air for proper and safe combustion Signup and view all the answers

Why do natural draft burners require larger combustion air openings per kW input than power burners?

To ensure proper combustion with sufficient air intake Signup and view all the answers

What is the significance of maintaining unobstructed combustion air openings?

To prevent rodents or birds from entering the mechanical space Signup and view all the answers

Why must combustion air inlets not be located lower than 300 mm above the outside grade level?

To prevent obstructing snow from blocking the inlet Signup and view all the answers

What is the ventilation air opening requirement according to CSA B149.1?

At least 10% of the required combustion air opening, but not less than 6500 mm2 in cross-section Signup and view all the answers

What type of manual dampers or louvres should not be installed in combustion air openings?

Mechanical dampers or louvres Signup and view all the answers

When combustion air is supplied by mechanical means, what safety feature must be installed?

Airflow-sensing switch wired into the burner management system safety limit circuit Signup and view all the answers

Why should care be taken to ensure that no water, oil, or steam lines are run in the direct path of cold fresh air entering from outside?

To prevent freezing of the lines Signup and view all the answers

Why must all burners be interlocked with a fully automatic damper assembly when used to shut off combustion air?

So that burners cannot fire unless dampers are completely open Signup and view all the answers