2025/26 POWER ENGINEERING 4TH CLASS - UNIT A6 REVIEW | QUESTIONS | ANSWERED
& RATED 100% CORRECT!!
Explain the purpose of the 2 "red" emergency shutdown buttons - (answer)1 - shuts
down the electricity to plant
1 - trips gas shut off to the plant
Explain a hydrostatic test on a pressure vessel. - (answer)This is where the boiler is
completely filled with water and pressurized to 1.5 times it's MAWP. With no air to
compress, if a failure occurs there is no compressed energy to be released. This is done
to check for leaks and structural integrity of the pressure vessel.
Identify the location of the main gas shut off valve to the building, main electrical panel
and main raw water shut off. - (answer)Outside on the south west corner of the ITTC
building
- In front of the watertube boiler
- Above the firetube boiler on the mezzanine
Explain the water circulation in a watertube boiler. - (answer)There are risers and
downcomers tubes. The riser tubes are the hottest and the downcomers are the cooler
tubes. The change in temp changes the density of the water. The difference in density
between the riser and downcomer tubes drives the water circulation within the boiler.
The water in the riser tubes goes up and that water is replaced by cooler water from the
downcomer tubes.
Explain how the flame scanner works & what maintenance is required? - (answer)The
scanner senses light from the flame and transmits a signal to the burner management
system(BMS) to confirm a flame is in the boiler. If the flame goes out or the sensor fails,
the burner automatically shuts off.The maintenance is to keep the flame scanner clean
and test it periodically. Solid and oil fueled furnaces require the most cleaning due to
higher ash content, natural gas furnaces burn very clean.
,2025/26 POWER ENGINEERING 4TH CLASS - UNIT A6 REVIEW | QUESTIONS | ANSWERED
& RATED 100% CORRECT!!
Explain how the combustion air pressure sensor works. - (answer)An air signal, from the
discharge of the combustion fan, is fed to a circular diaphragm. The diaphragm moves
outward and closes a set of contacts, within the sensor and confirms the combustion air
is at a set pressure. If the pressure goes down the BMS will trip the burner. This is one of
many safety limit switches in the BMS.
Explain the low water cut off devices - float & probe types? - (answer)- The float type is
located within the water column. The float rides up and down with the water level a long
a center shaft. The center shaft senses where the float is and transmits a signal to the
electronic level indictor. If the water level goes below a certain point, the BMS trips the
flame off.
- The probe type is located in the steam drum(WT) or a separate water column(FT). It
consists of two probes that act as a switch, when the probes are both covered in water,
the switch is closed, if the water level drops and uncovers the probes, the switch is
opened, then the BMS trips the flame off.
Are shut off valves allowed between boiler & water column. What is the exception to
this rule and explain why? - (answer)No, if the boiler is an unsupervised boiler. The
exception is if the boiler is supervised and the shut off valves are locked in the open
position.
Name all BMS safety trips and explain their purpose. - (answer)Low water cutoff - trips
burner on low water, automatic reset
Auxiliary low water cutoff - Trips burner on low water, is set below main LWCO, requires
operator reset. This is because the LWCO failed and they want an operator to determine
why.
- High gas pressure trip - if the gas pressure is too high it will trip the flame, high gas
pressure will result in a rich flame and potentially cause soot build up or a possible
furnace explosion.Low gas pressure trip - if the gas pressure is to low it will trip the
flame, low gas pressure can result in an unstable flame.
, 2025/26 POWER ENGINEERING 4TH CLASS - UNIT A6 REVIEW | QUESTIONS | ANSWERED
& RATED 100% CORRECT!!
Flame scanner - to monitor the presence of a flame
- Combustion air pressure sensor - to monitor the minimum combustion air pressure. If
the pressure goes to low it will rip the lame. Low air pressure can result in a furnace
explosion due to insufficient combustion air.
- High steam pressure trip - will trip the flame if the pressure goes above a certain set
point. This point must be below the MAWP and the set point of the safety valves. This
requires a manual operator reset because it means the main pressure controller failed to
shut the burner down when the set point was hit.
Explain how you regulate boiler flame during start up. - (answer)Switch to manual
control and set the flame at low fire until the boiler is at working pressure.
Explain "Swell & "Shrinkage" in a boiler. - (answer)Swell is caused by a sudden increase
in steam flow, this reduces the pressure inside the boiler momentarily, this causes an
increase in boiling inside the boiler. This increases the amount of steam bubbles within
the boiler water, which takes up volume. This increased volume results in the boiler level
rising(swell).
- Shrinkage - As the burner picks up the load, the boiler pressure increases, which
reduces the boiling action inside the boiler. The extra steam bubbles collapse and the
level falls(shrinkage). This is problematic for the level controller because it reduces
feedwater flow during swell because of the increased level, when it should be adding
water because the steam flow increased. When the steam flow stabilizes, it can result in
a low water level and trip the boiler. Boilers with 3 element FW controllers can better
manage large load changes on boilers. This is also more dramatic the larger the boiler.
Who is allowed to change fuel/air ratio on the boiler? - (answer)gasfitter
Explain the importance of monitoring the boiler flame. - (answer)The flame must be
looked at everyday to ensure you have a good and stable flame
& RATED 100% CORRECT!!
Explain the purpose of the 2 "red" emergency shutdown buttons - (answer)1 - shuts
down the electricity to plant
1 - trips gas shut off to the plant
Explain a hydrostatic test on a pressure vessel. - (answer)This is where the boiler is
completely filled with water and pressurized to 1.5 times it's MAWP. With no air to
compress, if a failure occurs there is no compressed energy to be released. This is done
to check for leaks and structural integrity of the pressure vessel.
Identify the location of the main gas shut off valve to the building, main electrical panel
and main raw water shut off. - (answer)Outside on the south west corner of the ITTC
building
- In front of the watertube boiler
- Above the firetube boiler on the mezzanine
Explain the water circulation in a watertube boiler. - (answer)There are risers and
downcomers tubes. The riser tubes are the hottest and the downcomers are the cooler
tubes. The change in temp changes the density of the water. The difference in density
between the riser and downcomer tubes drives the water circulation within the boiler.
The water in the riser tubes goes up and that water is replaced by cooler water from the
downcomer tubes.
Explain how the flame scanner works & what maintenance is required? - (answer)The
scanner senses light from the flame and transmits a signal to the burner management
system(BMS) to confirm a flame is in the boiler. If the flame goes out or the sensor fails,
the burner automatically shuts off.The maintenance is to keep the flame scanner clean
and test it periodically. Solid and oil fueled furnaces require the most cleaning due to
higher ash content, natural gas furnaces burn very clean.
,2025/26 POWER ENGINEERING 4TH CLASS - UNIT A6 REVIEW | QUESTIONS | ANSWERED
& RATED 100% CORRECT!!
Explain how the combustion air pressure sensor works. - (answer)An air signal, from the
discharge of the combustion fan, is fed to a circular diaphragm. The diaphragm moves
outward and closes a set of contacts, within the sensor and confirms the combustion air
is at a set pressure. If the pressure goes down the BMS will trip the burner. This is one of
many safety limit switches in the BMS.
Explain the low water cut off devices - float & probe types? - (answer)- The float type is
located within the water column. The float rides up and down with the water level a long
a center shaft. The center shaft senses where the float is and transmits a signal to the
electronic level indictor. If the water level goes below a certain point, the BMS trips the
flame off.
- The probe type is located in the steam drum(WT) or a separate water column(FT). It
consists of two probes that act as a switch, when the probes are both covered in water,
the switch is closed, if the water level drops and uncovers the probes, the switch is
opened, then the BMS trips the flame off.
Are shut off valves allowed between boiler & water column. What is the exception to
this rule and explain why? - (answer)No, if the boiler is an unsupervised boiler. The
exception is if the boiler is supervised and the shut off valves are locked in the open
position.
Name all BMS safety trips and explain their purpose. - (answer)Low water cutoff - trips
burner on low water, automatic reset
Auxiliary low water cutoff - Trips burner on low water, is set below main LWCO, requires
operator reset. This is because the LWCO failed and they want an operator to determine
why.
- High gas pressure trip - if the gas pressure is too high it will trip the flame, high gas
pressure will result in a rich flame and potentially cause soot build up or a possible
furnace explosion.Low gas pressure trip - if the gas pressure is to low it will trip the
flame, low gas pressure can result in an unstable flame.
, 2025/26 POWER ENGINEERING 4TH CLASS - UNIT A6 REVIEW | QUESTIONS | ANSWERED
& RATED 100% CORRECT!!
Flame scanner - to monitor the presence of a flame
- Combustion air pressure sensor - to monitor the minimum combustion air pressure. If
the pressure goes to low it will rip the lame. Low air pressure can result in a furnace
explosion due to insufficient combustion air.
- High steam pressure trip - will trip the flame if the pressure goes above a certain set
point. This point must be below the MAWP and the set point of the safety valves. This
requires a manual operator reset because it means the main pressure controller failed to
shut the burner down when the set point was hit.
Explain how you regulate boiler flame during start up. - (answer)Switch to manual
control and set the flame at low fire until the boiler is at working pressure.
Explain "Swell & "Shrinkage" in a boiler. - (answer)Swell is caused by a sudden increase
in steam flow, this reduces the pressure inside the boiler momentarily, this causes an
increase in boiling inside the boiler. This increases the amount of steam bubbles within
the boiler water, which takes up volume. This increased volume results in the boiler level
rising(swell).
- Shrinkage - As the burner picks up the load, the boiler pressure increases, which
reduces the boiling action inside the boiler. The extra steam bubbles collapse and the
level falls(shrinkage). This is problematic for the level controller because it reduces
feedwater flow during swell because of the increased level, when it should be adding
water because the steam flow increased. When the steam flow stabilizes, it can result in
a low water level and trip the boiler. Boilers with 3 element FW controllers can better
manage large load changes on boilers. This is also more dramatic the larger the boiler.
Who is allowed to change fuel/air ratio on the boiler? - (answer)gasfitter
Explain the importance of monitoring the boiler flame. - (answer)The flame must be
looked at everyday to ensure you have a good and stable flame
