Boiler Safety Controls and Switches

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

To prevent burner operation in the absence of sufficient combustion air (correct)
To increase fuel flow to the burner
To reduce the airflow in the windbox
To regulate the temperature of the burner

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

It turns off the burner if there is a high airflow purge
It interrupts or completes the circuit based on combustion air pressure (correct)
It regulates the fuel flow based on the windbox temperature
It controls the fan speed to maintain air pressure

What happens if there is insufficient air pressure in the windbox when the forced draft fan is not operating?

The switch activates a high airflow purge
The switch triggers a low-fire start sequence
The switch opens and prevents burner operation (correct)
The switch closes and increases fuel flow

How does the spring in the Low Combustion Air Pressure Fuel Cut-Off Switch impact its operation?

It opens the switch when there is inadequate air pressure (A) Signup and view all the answers

What triggers the flame safeguard controller to shut the SSOVs in response to low combustion air pressure?

Opening of the switch due to insufficient air pressure (D) Signup and view all the answers

What role does adequate combustion air pressure play in the operation of the Low Combustion Air Pressure Fuel Cut-Off Switch?

Allows the diaphragm to counteract the spring force and keep the switch closed (D) 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 only when the air and fuel are in their low-fire positions (A) Signup and view all the answers

Why is a proven high-fire pre-purge required for burners using mechanical draft?

To clear combustible gases from the furnace before ignition (D) Signup and view all the answers

What can happen if excessive fuel flow occurs during main burner ignition?

A furnace explosion may occur (D) Signup and view all the answers

In a boiler, what is the role of the modulating motor?

To maintain the correct ratio of air and fuel (A) Signup and view all the answers

Why is a proven purge period required prior to the ignition cycle for burners using mechanical draft?

To clear combustible gases from the combustion zone and flue passages (A) Signup and view all the answers

What is the significance of a differential pressure switch in a larger boiler?

It closes at maximum airflow to start the purge timer (D) Signup and view all the answers

What happens if the fan becomes mechanically uncoupled in a system?

The purge switch opens (C) Signup and view all the answers

Why is it important to have adequate combustion air for burners?

To ensure safe and proper combustion (C) Signup and view all the answers

What is the purpose of having larger combustion air openings per kW input for natural draft burners?

To provide sufficient air for combustion (A) Signup and view all the answers

Why must combustion air openings not have screens with a mesh size smaller than 6 mm (1/4 inch)?

To prevent obstruction by dirt, debris, and frost (A) Signup and view all the answers

In what scenario can natural draft burners spill combustion products into a building interior?

In cases of extreme air starvation (A) Signup and view all the answers

"CSA B149.1 and CSA B139 stipulate requirements to prevent what dangerous outcome related to burners?"

Carbon monoxide poisoning and death (A) Signup and view all the answers

"What is the purpose of having ventilation air openings alongside combustion air openings?"

To provide additional fresh air for ventilation (C) Signup and view all the answers

"Why are manual air dampers or louvres not permitted in combustion air openings?"

To avoid interference with burner operation (B) Signup and view all the answers