143 Questions
EASY What happens if the main flame is not established within 10 seconds?
The BMS shuts the pilot and main SSOVs and goes into safety shutdown and lockout
During the run period, what happens if a permissive opens?
The BMS conducts a post-purge of the furnace
What is the purpose of the safe start check?
To look for a flame before the ignition period begins
What happens during the standby stage?
The controller is ready to begin a burner startup
What happens if there is power at any of the fuel SSOV terminals during the safe start check?
The controller returns to standby mode
What happens if the low-fire proving switch is not closed during the ignition trials?
The ignition sequence is terminated
What is the purpose of the pilot trial for ignition period?
To prove the pilot flame
What happens during the initiate stage?
The power quality is determined
What happens if a burner safety limit opens during the run period?
The BMS performs a safety shutdown and lockout
What is a safety shutdown?
A built-in feature of every programming controller
What is the primary function of the pre-ignition interlocks in a boiler's programming controller?
To check permissives and allow startup
What is the purpose of the purge counter in a boiler's programming controller?
To ensure a safe purge cycle
What happens if the pilot flame is deemed inadequate during the pilot trial for ignition period?
The burner system is locked out and shut down
What is the primary factor that determines the specific sequence of operation for a boiler's programming controller?
All of the above
What is the purpose of the high airflow step in a boiler's programming controller?
To prepare the furnace for ignition
What is the function of the airflow sensing devices in a boiler's programming controller?
To sense airflow and ensure proper combustion
What is the final step in the typical sequence of operation for a boiler's programming controller?
Lighting the main burner
What is the term for the period of time during which the pilot flame is established and proven to be stable?
Pilot trial for ignition period
What happens if the pilot does not light within 15 to 90 seconds?
The primary controller waits for 5 minutes and then retries ignition.
What is the purpose of the 5-minute wait before retrying ignition?
To allow the furnace to naturally purge.
What happens if the pilot is not established on the second attempt?
The primary controller goes into safety shutdown and lockout.
What is the purpose of the flame detector in oil-fired boilers?
To detect the main flame and signal the programming controller.
What happens if the main flame goes out during the run period?
The burner goes into safety shutdown and lockout.
What is the purpose of the permissives in fully automatic boilers?
To satisfy certain conditions before startup.
What is necessary to reset the primary control after a lockout?
Turning off the power to the boiler.
What happens if the number of main flame failures in a call for heat cycle reaches 5?
The primary controller performs a 5-minute natural draft purge.
What is the purpose of the programming controller in oil-fired boilers?
To control the fuel oil pump and draft fan.
What is the purpose of the boiler pressuretrol or aquastat?
To signal a call for heat by closing when the water temperature or steam pressure drops below the desired set point.
What must be closed for the boiler ignition sequence to initiate?
The main electrical disconnect switch or breaker
What is the purpose of the purge period in the boiler startup sequence?
To purge the furnace of combustible gases
When does the programming controller begin counting the purge?
When the combustion airflow reaches at least 60% of the high-fire airflow
What happens when the purge period is completed?
The programming controller returns the combustion airflow to the low-fire position
What is the purpose of the flame detector?
To sense the pilot flame
What happens when the steam pressure or hot water temperature rises above the set point of the operating control?
The programming controller de-energizes the SSOVs
What is the purpose of the post-purge period?
To cool down the boiler
What must be satisfied for the boiler to start?
The on-off switch and the operating control
What is the purpose of the oil pumps in an oil-fired boiler?
To satisfy the low fuel pressure cut-off switch
What happens during the run period?
The flame detector supervises the main burner flame
What happens when a condition that can cause unsafe burner operation is detected?
The controller closes all SSOVs and locks itself out.
What is indicated directly on the controller during a safety shutdown?
An alarm light, an alarm horn, or an expanded visual display.
During the INITIATE period, what can cause a safety shutdown and lockout?
If an AC line power error occurred or power quality problems persist for over 4 minutes.
What is required for all fuel-fired boilers?
A burner management system.
What happens when an operating control opens in an automatically fired boiler?
The burner shuts off but the BMS does not lock out.
What happens when the main flame is established in a natural draft gas-fired boiler?
The ignition transformer is de-energized.
Why does the primary control system restart when the boiler steam pressure or water temperature drops?
Because the operating control is closed.
What is the purpose of a safety shutdown and lockout?
To leave the burner in a safe condition.
What must an operator do to reset the programming controller after a safety shutdown and lockout?
Press the reset button on the front of the controller.
MEDIUM What is the primary function of the pre-ignition interlocks in a boiler's programming controller?
To check permissives and interlocks
What happens if the pilot flame is deemed inadequate during the pilot trial for ignition period?
The BMS shuts the pilot SSOV and locks out the burner system
What is the purpose of the airflow sensing devices in a boiler's programming controller?
To sense airflow and adjust combustion air damper position
What determines the specific sequence of operation for a boiler's programming controller?
All of the above
What happens when the purge period is completed?
The BMS returns the combustion airflow to low fire
What is the purpose of the purge period in the boiler startup sequence?
To remove unburned fuel and debris from the furnace
What happens during the main flame trial for ignition period?
The main burner ignites, and both pilot and main SSOVs are open
What is the term for the period of time during which the pilot flame is established and proven to be stable?
Pilot trial for ignition period
What is necessary to be satisfied for the boiler to start?
The fuel pumps must be running to satisfy the low fuel pressure cut-off switch.
What happens when the steam pressure or hot water temperature rises above the set point of the operating control?
The programming controller begins a post-purge.
What is the purpose of the low combustion air pressure fuel cut-off switch?
To prevent ignition when combustion air pressure is low.
What happens during the purge period?
The airflow blows through the furnace to purge it of combustible gases.
What must be reset manually after a safety shutdown and lockout?
The manual resets on the cut-offs.
What is the purpose of the flame detector?
To sense the pilot flame.
What happens when the airflow reaches at least 60% of the high-fire airflow?
The low combustion air pressure fuel cut-off switch closes.
What is necessary for oil-fired boilers?
All of the above.
What happens during the post-purge period?
The programming controller returns to its standby mode.
What happens when a condition that can cause unsafe burner operation is detected?
A safety shutdown and lockout occur.
What is the primary purpose of the safe start check in a boiler's programming controller?
To detect any condition that may simulate a flame before the ignition period
What happens if a burner safety limit opens during the run period?
The BMS performs a safety shutdown and lockout
What is the primary function of the airflow sensing devices in a boiler's programming controller?
To detect the presence of combustion air during the purge period
What is the term for the period of time during which the pilot flame is established and proven to be stable?
Pilot trial for ignition
What happens if the power quality is poor during the initiate stage?
The initiate stage is maintained until the supply voltage conditions have normalized
What is the primary purpose of the purge period in a boiler's programming controller?
To remove any combustible gases from the furnace
What happens if the main flame is not established within 10 seconds during the main flame trial for ignition?
The BMS performs a safety shutdown and lockout
What is the purpose of the post-purge period in a boiler's programming controller?
To remove any combustible gases from the furnace
What happens if the permissives are not satisfied during the ignition trials?
The BMS performs a safety shutdown and lockout
What is the purpose of the high airflow step in a boiler's programming controller?
To detect the presence of combustion air during the purge period
What happens to the burner when an operating control opens in an automatically fired boiler?
The burner restarts automatically when the switch closes.
What is the purpose of the primary controller in a natural draft gas-fired boiler?
To initiate the startup sequence and control the purge period.
What happens during the SAFE START CHECK period?
The SSOV proof-of-closure switch is checked.
What is required for a boiler to start?
The operating control must be closed.
What happens when the steam pressure or hot water temperature rises above the set point of the operating control?
The operating control opens.
What is the purpose of a safety shutdown and lockout?
To leave the burner in a safe condition and require manual reset.
During the RUN period, what happens if the airflow proving switch opens?
A safety shutdown and lockout occurs.
What is the purpose of the programming controller in a boiler?
To control the ignition sequence and monitor the boiler's operation.
What is the purpose of the flame detector in a natural draft gas-fired boiler?
To detect the pilot flame.
What happens if the pilot flame is not established during the PILOT TRIAL-FOR-IGNITION PERIOD?
A safety shutdown and lockout occurs.
What happens if the pilot does not light within 15 to 90 seconds?
The primary controller waits for 5 minutes before retrying ignition
What is the purpose of the 5-minute wait before retrying ignition?
To allow the furnace to naturally purge
What happens if the main flame goes out during the run period?
The primary controller goes to safety shutdown and lockout immediately
What is the purpose of the permissives in fully automatic boilers?
To ensure safe startup conditions
What is necessary to reset the primary control after a lockout?
Turning off the power to the boiler
What happens if the number of main flame failures in a call for heat cycle reaches 5?
The primary controller performs a 5-minute natural draft purge
What is the purpose of the programming controller in oil-fired boilers?
To sequence the ignition and startup of the boiler
HARD What is the purpose of the boiler pressuretrol or aquastat?
To signal a call for heat when the water temperature or steam pressure drops below the desired set point
What must be satisfied for the boiler to start?
The permissives and pre-ignition interlocks must be satisfied
What happens when the steam pressure or hot water temperature rises above the set point of the operating control?
The programming controller shuts off the fuel oil pump
What is the primary purpose of the BMS checking permissives and pre-ignition interlocks during the startup sequence?
To confirm all necessary conditions are met before proceeding with startup
Why does the BMS open the main SSOVs during the main flame trial for ignition period?
To light the main burner
What is the primary reason for the BMS to lockout the burner system in case of an inadequate pilot flame?
To prevent unsafe burner operation
What determines the specific sequence of operation for a boiler's programming controller?
All of the above
What happens if the pilot flame is not established during the pilot trial for ignition period?
The BMS locks out the burner system
What is the purpose of the high airflow step in the sequence of operation?
To increase the fan speed
What is the term for the period of time during which the pilot flame is established and proven to be stable?
Pilot trial for ignition period
What happens when the BMS detects low airflow during the startup sequence?
The BMS returns the combustion airflow to low fire
What is the primary purpose of the pilot trial for ignition period in a natural draft gas-fired boiler?
To establish and prove the pilot flame
What happens when the operating control opens in an automatically fired boiler?
The burner restarts automatically
What condition can cause a safety shutdown and lockout during the RUN period?
If the airflow proving switch opens
What is required for all fuel-fired boilers?
A burner management system
What happens when a condition that can cause unsafe burner operation is detected?
The BMS performs a safety shutdown and lockout
What is indicated directly on the controller during a safety shutdown?
An alarm light
What must be satisfied for the boiler to start?
The operating control must be closed
What happens when the steam pressure or hot water temperature rises above the set point of the operating control?
The operating control opens
What is the purpose of the airflow sensing devices in a boiler's programming controller?
To sense airflow and prove the furnace is purged
What must an operator do to reset the programming controller after a safety shutdown and lockout?
Press the reset button on the front of the controller
What is the primary reason for the controller to conduct a post-purge of the furnace during the run period?
To ensure the burner is operating within safe limits
During the safe start check, what is the primary condition that the controller is checking for?
The presence of a flame in the furnace
What happens to the pilot SSOV during the main flame trial for ignition period?
It remains energized
What is the primary function of the programming controller during the standby stage?
To wait for a call for heat
What happens if the power quality is poor during the initiate stage?
The initiate stage is maintained until the supply voltage conditions have normalized
What is the primary reason for the controller to perform a safety shutdown and lockout during the pilot trial for ignition period?
The pilot flame is not established within 10 seconds
What happens during the ignition trials if the low-fire proving switch is not closed?
The ignition trials are aborted
What is the primary function of the safe start check during the startup sequence?
To detect the presence of a flame in the furnace
What happens if the controller detects power at any of the fuel SSOV terminals during the safe start check?
The controller performs a safety shutdown and lockout
What is the primary function of the programming controller during the run period?
To ensure the burner is operating within safe limits
What is the primary reason why a primary controller goes into safety shutdown and lockout if the pilot does not light within 15 to 90 seconds?
To prevent unsafe burner operation
What is the significance of the 5-minute wait before retrying ignition in a primary controller?
It allows the furnace to naturally purge
What happens if the number of main flame failures in a call for heat cycle reaches 5 in a primary controller?
The primary controller performs a 5-minute natural draft purge
What is the primary purpose of the programming controller in oil-fired boilers?
To control the ignition sequence
What is the primary function of the pre-ignition interlocks in a boiler's programming controller?
To satisfy the necessary conditions before starting the boiler
What happens if the steam pressure or water temperature rises above the set point of the operating control in a fully automatic boiler?
The boiler stops
What is the primary purpose of the flame detector in oil-fired boilers?
To sense the flame and cause the flame relay to close
What is necessary to reset the primary control after a lockout?
Turning off the power to the boiler
What happens if the pilot is not established on the second attempt in a primary controller?
The primary controller goes into safety shutdown and lockout
What is the primary purpose of the purge period in the boiler startup sequence?
To allow the furnace to naturally purge
What is the primary function of the low combustion air pressure fuel cut-off switch?
To ensure proper combustion air flow
What is the purpose of the atomizing medium in an oil-fired boiler?
To create a stable flame
What happens when the combustion airflow reaches at least 60% of the high-fire airflow?
The programming controller begins counting the purge
What is the purpose of the manual resets on the cut-offs?
To ensure safe startup
What happens during the post-purge period?
The airflow is reduced to low-fire position
What is the purpose of the programming controller in a boiler?
To manage the startup and shutdown sequences
What happens if the main flame is not established within 10 seconds?
The programming controller retries ignition
What is the purpose of the fuel selector switch in a dual fuel boiler?
To select the fuel source
What happens if the pilot flame is interrupted during the run period?
The programming controller opens the circuit to de-energize the igniter and pilot gas valve
What is the purpose of the flame detector in a boiler?
To sense the presence of a flame
Study Notes
Power Engineers and Programming Controllers
- Power engineers must familiarize themselves with the programming controller installed on each boiler they operate.
- Different types of flame amplifiers, purge timers, pre-ignition interlocks, airflow sensing devices, and permissives may vary depending on the fuel used, burner input, furnace volume, fuel pressure, and age of the equipment.
Typical Sequence of Operation for Programming Controllers
- Pre-ignition interlocks and permissives are checked, and if satisfied, the startup sequence proceeds.
- The draft fan starts, and the fan speed or combustion air damper position is increased to high-fire position.
- High airflow is detected, and the purge counter begins.
- When the purge is complete, the combustion airflow returns to low-fire position.
- The pilot is ignited, and the pilot SSOV is opened. The pilot flame must be proven within 10 seconds, otherwise, a safety shutdown occurs.
- The main burner is lit, and the main SSOV is opened. The main flame must be established within 10 seconds, otherwise, a safety shutdown occurs.
- The burner runs until a burner limit or boiler operating limit switch opens, and a post-purge is conducted.
Operating Sequence Charts
- The sequence of operation can be illustrated using charts, such as those shown in Figures 22 and 23.
- The chart shows the events during each stage of the sequence, including initiate, standby, safe start, ignition trials, pilot trial for ignition, main flame trial for ignition, run, and shutdown.
Safety Shutdown and Lockout
- A safety shutdown is a built-in feature of every programming controller that closes all SSOVs and locks out the controller when a condition that can cause unsafe burner operation is detected.
- Safety shutdown occurs under various conditions, including:
- INITIATE period: power error, low voltage, or poor power quality.
- STANDBY period: flame signal present, ignition transformer or SSOV energized, or SSOV proof-of-closure switch opens.
- SAFE START CHECK: ignition transformer, pilot SSOV, or main SSOVs energized, or SSOV proof-of-closure switch opens.
- PILOT TRIAL-FOR-IGNITION PERIOD: airflow proving switch opens, ignition transformer and pilot SSOV not energized, or main SSOV energized.
- RUN period: airflow proving switch opens, ignition transformer energized, main SSOV not energized, or no flame present.
Burner Management Systems
- Burner management systems (BMS) must have built-in self-diagnostics and perform a safety shutdown and lockout if an internal fault is detected.
- Shutdown without lockout occurs when an operating control opens, and the burner shuts off, but the BMS does not lockout.
- BMS are required for all fuel-fired boilers, and smaller natural draft boilers with atmospheric burners may not require controllers with the ability to start draft fans and prove purge conditions.
Natural Draft Gas-Fired Boilers
- The operating control initiates a startup, and the primary controller opens the uptake damper, permitting natural draft to purge the furnace for 30 seconds.
- The primary controller energizes the ignition transformer and pilot SSOV to light the pilot flame.
- The pilot flame is established, and the primary control energizes the main gas SSOV.
- The main burner is lit, and the ignition transformer is de-energized.
- The primary control keeps the main burner in operation until the desired preset operating steam pressure or water temperature is reached.
Oil-Fired Boilers with No Pilot
- The programming controller energizes the motor that drives the draft fan and fuel oil pump, and purges the furnace.
- The programming controller energizes the ignition transformer and fuel oil SSOV.
- The spark ignites the main burner, and the flame detector senses the flame.
- The ignition transformer de-energizes, and the flame relay closes.
- In case of ignition failure, the programming control locks out, and the operator must correct the problem and reset the control.
Programming Controller Sequence of Fully Automatic Boilers
- Fully automatic packaged boilers use highly sophisticated programming controls that include one or more timers, and several relays.
- The programming controller sequence varies depending on the type of burner, fuel, method of ignition, and operating controls used.
- The boiler or burner manufacturer's operations manual must be consulted for specific instructions.
Pre-Start Conditions
- Before a steam or hot water boiler can be started, several conditions, known as permissives and pre-ignition interlocks, must be satisfied.
- Typical permissives include:
- Water level in the boiler drum above the cut-off point of each low water fuel cut-off.
- Steam pressure or water temperature at or below the cut-in setting of the operating control.
- Fuel supply pressure to the burner valves above the cut-out point of the low fuel pressure cut-off switch.
- Low combustion air pressure fuel cut-off switch open.
- Combustion air damper or air supply interlocks satisfied.
- Oil pumps running to satisfy the low fuel pressure cut-off switch.
- Atomizing medium at the proper pressure to satisfy the low atomizing medium cut-off switch.
Startup Sequence
- The boiler ignition sequence is initiated when the on-off and operating control switches are closed.
- The programming controller starts the draft fans, and the airflow to the burner is established.
- The purge period is completed, and the combustion airflow returns to the low-fire position.
- The programming controller energizes the ignition transformer, and opens the pilot gas valve.
- The pilot flame is established, and the programming controller energizes the main SSOV.
- The main burner is lit, and the flame detector senses the main flame.
- The burner runs until a permissive, a manual on-off switch, or a burner safety switch shuts it off.
Shutdown Sequence
- When the steam pressure or hot water temperature rises above the set point of the operating control, the call for heat ends.
- The programming controller de-energizes the SSOVs, and extinguishes the flame.
- The programming controller begins a post-purge.
- The programming controller returns to its standby mode.
- If there is a call for heat, and all permissives and pre-ignition interlocks are satisfied, the programming controller repeats the startup sequence.
Power Engineers and Programming Controllers
- Power engineers must familiarize themselves with the programming controller installed on each boiler they operate.
- Different types of flame amplifiers, purge timers, pre-ignition interlocks, airflow sensing devices, and permissives may vary depending on the fuel used, burner input, furnace volume, fuel pressure, and age of the equipment.
Typical Sequence of Operation for Programming Controllers
- Pre-ignition interlocks and permissives are checked, and if satisfied, the startup sequence proceeds.
- The draft fan starts, and the fan speed or combustion air damper position is increased to high-fire position.
- High airflow is detected, and the purge counter begins.
- When the purge is complete, the combustion airflow returns to low-fire position.
- The pilot is ignited, and the pilot SSOV is opened. The pilot flame must be proven within 10 seconds, otherwise, a safety shutdown occurs.
- The main burner is lit, and the main SSOV is opened. The main flame must be established within 10 seconds, otherwise, a safety shutdown occurs.
- The burner runs until a burner limit or boiler operating limit switch opens, and a post-purge is conducted.
Operating Sequence Charts
- The sequence of operation can be illustrated using charts, such as those shown in Figures 22 and 23.
- The chart shows the events during each stage of the sequence, including initiate, standby, safe start, ignition trials, pilot trial for ignition, main flame trial for ignition, run, and shutdown.
Safety Shutdown and Lockout
- A safety shutdown is a built-in feature of every programming controller that closes all SSOVs and locks out the controller when a condition that can cause unsafe burner operation is detected.
- Safety shutdown occurs under various conditions, including:
- INITIATE period: power error, low voltage, or poor power quality.
- STANDBY period: flame signal present, ignition transformer or SSOV energized, or SSOV proof-of-closure switch opens.
- SAFE START CHECK: ignition transformer, pilot SSOV, or main SSOVs energized, or SSOV proof-of-closure switch opens.
- PILOT TRIAL-FOR-IGNITION PERIOD: airflow proving switch opens, ignition transformer and pilot SSOV not energized, or main SSOV energized.
- RUN period: airflow proving switch opens, ignition transformer energized, main SSOV not energized, or no flame present.
Burner Management Systems
- Burner management systems (BMS) must have built-in self-diagnostics and perform a safety shutdown and lockout if an internal fault is detected.
- Shutdown without lockout occurs when an operating control opens, and the burner shuts off, but the BMS does not lockout.
- BMS are required for all fuel-fired boilers, and smaller natural draft boilers with atmospheric burners may not require controllers with the ability to start draft fans and prove purge conditions.
Natural Draft Gas-Fired Boilers
- The operating control initiates a startup, and the primary controller opens the uptake damper, permitting natural draft to purge the furnace for 30 seconds.
- The primary controller energizes the ignition transformer and pilot SSOV to light the pilot flame.
- The pilot flame is established, and the primary control energizes the main gas SSOV.
- The main burner is lit, and the ignition transformer is de-energized.
- The primary control keeps the main burner in operation until the desired preset operating steam pressure or water temperature is reached.
Oil-Fired Boilers with No Pilot
- The programming controller energizes the motor that drives the draft fan and fuel oil pump, and purges the furnace.
- The programming controller energizes the ignition transformer and fuel oil SSOV.
- The spark ignites the main burner, and the flame detector senses the flame.
- The ignition transformer de-energizes, and the flame relay closes.
- In case of ignition failure, the programming control locks out, and the operator must correct the problem and reset the control.
Programming Controller Sequence of Fully Automatic Boilers
- Fully automatic packaged boilers use highly sophisticated programming controls that include one or more timers, and several relays.
- The programming controller sequence varies depending on the type of burner, fuel, method of ignition, and operating controls used.
- The boiler or burner manufacturer's operations manual must be consulted for specific instructions.
Pre-Start Conditions
- Before a steam or hot water boiler can be started, several conditions, known as permissives and pre-ignition interlocks, must be satisfied.
- Typical permissives include:
- Water level in the boiler drum above the cut-off point of each low water fuel cut-off.
- Steam pressure or water temperature at or below the cut-in setting of the operating control.
- Fuel supply pressure to the burner valves above the cut-out point of the low fuel pressure cut-off switch.
- Low combustion air pressure fuel cut-off switch open.
- Combustion air damper or air supply interlocks satisfied.
- Oil pumps running to satisfy the low fuel pressure cut-off switch.
- Atomizing medium at the proper pressure to satisfy the low atomizing medium cut-off switch.
Startup Sequence
- The boiler ignition sequence is initiated when the on-off and operating control switches are closed.
- The programming controller starts the draft fans, and the airflow to the burner is established.
- The purge period is completed, and the combustion airflow returns to the low-fire position.
- The programming controller energizes the ignition transformer, and opens the pilot gas valve.
- The pilot flame is established, and the programming controller energizes the main SSOV.
- The main burner is lit, and the flame detector senses the main flame.
- The burner runs until a permissive, a manual on-off switch, or a burner safety switch shuts it off.
Shutdown Sequence
- When the steam pressure or hot water temperature rises above the set point of the operating control, the call for heat ends.
- The programming controller de-energizes the SSOVs, and extinguishes the flame.
- The programming controller begins a post-purge.
- The programming controller returns to its standby mode.
- If there is a call for heat, and all permissives and pre-ignition interlocks are satisfied, the programming controller repeats the startup sequence.
Power Engineers and Programming Controllers
- Power engineers must familiarize themselves with the programming controller installed on each boiler they operate.
- Different types of flame amplifiers, purge timers, pre-ignition interlocks, airflow sensing devices, and permissives may vary depending on the fuel used, burner input, furnace volume, fuel pressure, and age of the equipment.
Typical Sequence of Operation for Programming Controllers
- Pre-ignition interlocks and permissives are checked, and if satisfied, the startup sequence proceeds.
- The draft fan starts, and the fan speed or combustion air damper position is increased to high-fire position.
- High airflow is detected, and the purge counter begins.
- When the purge is complete, the combustion airflow returns to low-fire position.
- The pilot is ignited, and the pilot SSOV is opened. The pilot flame must be proven within 10 seconds, otherwise, a safety shutdown occurs.
- The main burner is lit, and the main SSOV is opened. The main flame must be established within 10 seconds, otherwise, a safety shutdown occurs.
- The burner runs until a burner limit or boiler operating limit switch opens, and a post-purge is conducted.
Operating Sequence Charts
- The sequence of operation can be illustrated using charts, such as those shown in Figures 22 and 23.
- The chart shows the events during each stage of the sequence, including initiate, standby, safe start, ignition trials, pilot trial for ignition, main flame trial for ignition, run, and shutdown.
Safety Shutdown and Lockout
- A safety shutdown is a built-in feature of every programming controller that closes all SSOVs and locks out the controller when a condition that can cause unsafe burner operation is detected.
- Safety shutdown occurs under various conditions, including:
- INITIATE period: power error, low voltage, or poor power quality.
- STANDBY period: flame signal present, ignition transformer or SSOV energized, or SSOV proof-of-closure switch opens.
- SAFE START CHECK: ignition transformer, pilot SSOV, or main SSOVs energized, or SSOV proof-of-closure switch opens.
- PILOT TRIAL-FOR-IGNITION PERIOD: airflow proving switch opens, ignition transformer and pilot SSOV not energized, or main SSOV energized.
- RUN period: airflow proving switch opens, ignition transformer energized, main SSOV not energized, or no flame present.
Burner Management Systems
- Burner management systems (BMS) must have built-in self-diagnostics and perform a safety shutdown and lockout if an internal fault is detected.
- Shutdown without lockout occurs when an operating control opens, and the burner shuts off, but the BMS does not lockout.
- BMS are required for all fuel-fired boilers, and smaller natural draft boilers with atmospheric burners may not require controllers with the ability to start draft fans and prove purge conditions.
Natural Draft Gas-Fired Boilers
- The operating control initiates a startup, and the primary controller opens the uptake damper, permitting natural draft to purge the furnace for 30 seconds.
- The primary controller energizes the ignition transformer and pilot SSOV to light the pilot flame.
- The pilot flame is established, and the primary control energizes the main gas SSOV.
- The main burner is lit, and the ignition transformer is de-energized.
- The primary control keeps the main burner in operation until the desired preset operating steam pressure or water temperature is reached.
Oil-Fired Boilers with No Pilot
- The programming controller energizes the motor that drives the draft fan and fuel oil pump, and purges the furnace.
- The programming controller energizes the ignition transformer and fuel oil SSOV.
- The spark ignites the main burner, and the flame detector senses the flame.
- The ignition transformer de-energizes, and the flame relay closes.
- In case of ignition failure, the programming control locks out, and the operator must correct the problem and reset the control.
Programming Controller Sequence of Fully Automatic Boilers
- Fully automatic packaged boilers use highly sophisticated programming controls that include one or more timers, and several relays.
- The programming controller sequence varies depending on the type of burner, fuel, method of ignition, and operating controls used.
- The boiler or burner manufacturer's operations manual must be consulted for specific instructions.
Pre-Start Conditions
- Before a steam or hot water boiler can be started, several conditions, known as permissives and pre-ignition interlocks, must be satisfied.
- Typical permissives include:
- Water level in the boiler drum above the cut-off point of each low water fuel cut-off.
- Steam pressure or water temperature at or below the cut-in setting of the operating control.
- Fuel supply pressure to the burner valves above the cut-out point of the low fuel pressure cut-off switch.
- Low combustion air pressure fuel cut-off switch open.
- Combustion air damper or air supply interlocks satisfied.
- Oil pumps running to satisfy the low fuel pressure cut-off switch.
- Atomizing medium at the proper pressure to satisfy the low atomizing medium cut-off switch.
Startup Sequence
- The boiler ignition sequence is initiated when the on-off and operating control switches are closed.
- The programming controller starts the draft fans, and the airflow to the burner is established.
- The purge period is completed, and the combustion airflow returns to the low-fire position.
- The programming controller energizes the ignition transformer, and opens the pilot gas valve.
- The pilot flame is established, and the programming controller energizes the main SSOV.
- The main burner is lit, and the flame detector senses the main flame.
- The burner runs until a permissive, a manual on-off switch, or a burner safety switch shuts it off.
Shutdown Sequence
- When the steam pressure or hot water temperature rises above the set point of the operating control, the call for heat ends.
- The programming controller de-energizes the SSOVs, and extinguishes the flame.
- The programming controller begins a post-purge.
- The programming controller returns to its standby mode.
- If there is a call for heat, and all permissives and pre-ignition interlocks are satisfied, the programming controller repeats the startup sequence.
Learn about the programming controllers used in boiler operation, including flame amplifiers, purge timers, and airflow sensing devices. Understand the sequence of operation for most programming controllers.
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