Boilers and Burner Safety Controls

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

To prevent burner operation in case of insufficient combustion air (correct)
To control the temperature inside the boiler
To regulate the fuel flow to the burner
To start the burner operation

How is the Low Combustion Air Pressure Fuel Cut-Off Switch triggered to shut the SSOVs?

By decreasing the windbox air pressure
By interrupting or completing the burner limit control circuit (correct)
By increasing the airflow purge switch
By turning off the fuel valve

What happens if the forced draft fan is not in operation according to the text?

The low combustion air pressure switch opens, causing the flame safeguard controller to shut the SSOVs (correct)
The fuel valve supervisory switch activates
The low-fire start switch turns on
The burner operation continues normally

What is the function of the High Airflow Purge Switch?

To prevent burner startup sequence if unsafe conditions exist (B) Signup and view all the answers

What role does the flexible diaphragm play in the low combustion air pressure switch?

It interacts with a switch that interrupts or completes the burner limit control circuit (A) Signup and view all the answers

Why does the low combustion air pressure switch have one side of the housing open to atmosphere and the other connected to the windbox?

To ensure adequate air pressure for safe combustion (C) Signup and view all the answers

What happens if the windbox pressure drops below the safe minimum?

The burner shuts down. (A) Signup and view all the answers

What is the importance of the low-fire start switch?

To prevent ignition if air and fuel are not in low-fire positions. (A) Signup and view all the answers

What is required by the CSA B149.3 Code for any appliance over 300 kW input?

Proven low-fire start. (D) Signup and view all the answers

How does a high-airflow purge switch contribute to safety?

Ensures air changes in combustion zone before ignition. (A) Signup and view all the answers

What proof of airflow is required during a purge according to the text?

Variable frequency drive (VFD) contact closures. (D) Signup and view all the answers

Why is it important to have limit switches on combustion air dampers?

To ensure the purge timer starts at high-fire position. (B) Signup and view all the answers

What does a differential pressure switch connected to the forced draft fan do at maximum airflow?

Closes to initiate purge timer. (B) Signup and view all the answers

In what scenario does the text mention a risk of a furnace explosion?

If excessive fuel flow occurs during main ignition. (C) Signup and view all the answers

'Proof of airflow' mentioned in the text serves to ensure what aspect of burner operation?

'Proper purging before ignition.' (D) Signup and view all the answers

'High-low start switch' mentioned in the text is primarily responsible for what function in boiler systems?

'Ensuring safe lighting at low-fire.' (C) Signup and view all the answers

What happens if the fan in a burner becomes mechanically uncoupled according to the text?

The airflow decreases (D) Signup and view all the answers

Why is it important to keep combustion air openings unobstructed?

To ensure proper burner operation (A) Signup and view all the answers

What is the minimum mesh size for screens placed on combustion air openings?

1/4 inch (D) Signup and view all the answers

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

To avoid snow blocking the opening (A) Signup and view all the answers

Which type of damper can be used to shut off the combustion air when the boiler is off according to the text?

Fully automatic damper (C) Signup and view all the answers

What is the percentage of ventilation air openings required in relation to combustion air openings as per CSA B149.1?

10% (B) Signup and view all the answers

What happens if natural draft burners experience extreme air starvation according to the text?

They spill combustion products into the building interior (B) Signup and view all the answers

Why should care be taken to ensure no water lines are run in the path of cold fresh air?

To avoid freezing of water lines (A) Signup and view all the answers

What type of switch must be installed when combustion air is supplied by mechanical means?

Airflow-sensing switch (D) Signup and view all the answers

Why should heavy oil lines be protected from cold air according to the text?

To avoid freezing (C) Signup and view all the answers