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Power Eng 5th Class practice questions

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Question 1Boiler and Pressure Vessel Fundamentals

On a low-pressure steam heating boiler, which fitting is required to indicate the water level directly at the boiler shell?

  1. A water column with gauge glass and try cocks Correct answer.
  2. A float switch inside the feedwater tank
  3. A closed-circuit sight glass on the feed line
  4. A level transmitter wired to the burner control

Explanation

A boiler must have a direct, visible means of confirming water level at the shell. The water column with a gauge glass, plus try cocks as a backup check, satisfies that requirement. Remote or indirect devices do not replace the direct reading.

Question 2Boiler and Pressure Vessel Fundamentals

What is the primary function of the safety valve on a steam boiler?

  1. To limit internal pressure by discharging steam Correct answer.
  2. To release air when the boiler is filling
  3. To drain condensate from the steam header
  4. To admit feedwater when the level drops

Explanation

The safety valve is the final pressure-limiting device and opens automatically at its set pressure. It protects the boiler shell from overpressure by discharging steam. It is not a level, drain, or air-venting control.

Question 3Boiler and Pressure Vessel Fundamentals

A gauge glass shows the water level at the normal mark, but the lower connection to the water column is plugged. What is the most likely indication?

  1. The glass reads falsely low because water cannot enter the column
  2. The glass reads correctly because the upper connection is clear
  3. The glass shows no water at all
  4. The glass reads falsely high because steam pressure enters the top only Correct answer.

Explanation

With the lower (water) connection blocked, steam from the upper connection fills the column and glass. The level then appears above the true boiler water line, which is a dangerous false-high reading. A blocked lower connection makes the glass read high, not low.

Question 4Boiler and Pressure Vessel Fundamentals

Which condition must be met before a boiler safety valve can be adjusted or its set pressure changed?

  1. The burner must be at high fire
  2. The boiler must be at normal operating pressure
  3. The feedwater pump must be running
  4. The boiler must be cooled, drained, and depressurized Correct answer.

Explanation

Adjusting a safety valve requires the boiler to be depressurized so the valve can be worked on safely and set with proper test equipment. Working on a valve under pressure risks uncontrolled steam release and injury. Operating conditions such as burner firing are irrelevant to this task.

Question 5Boiler and Pressure Vessel Fundamentals

What is the purpose of the fusible plug installed in the crown sheet area of a fire-tube boiler?

  1. To indicate the water level in the shell
  2. To drain water when the boiler is shut down
  3. To relieve pressure during normal firing
  4. To melt and release steam if water level falls and metal overheats Correct answer.

Explanation

The fusible plug contains a low-melting alloy that fails when the metal around it overheats from low water. Steam then escapes into the furnace, warning the operator and reducing the risk of a crown sheet failure. It is a low-water warning device, not a pressure relief or drain.

Question 6Boiler and Pressure Vessel Fundamentals

A low-water cutoff on a steam boiler is tested by blowing it down. What should the operator observe?

  1. The feedwater pump should stop
  2. The burner should shut off, then relight only after the level is restored Correct answer.
  3. The safety valve should open
  4. The burner should continue firing without change

Explanation

Blowing down the low-water cutoff simulates a low-water condition. The control should trip the burner off, and it must not relight until the water level is restored and the control resets. This confirms the cutoff is protecting the boiler.

Question 7Boiler and Pressure Vessel Fundamentals

Which statement correctly describes the test pressure used in a hydrostatic test of a boiler?

  1. It is half the normal operating pressure
  2. It is the pressure at which the boiler normally runs
  3. It exceeds the maximum allowable working pressure by a specified factor Correct answer.
  4. It is set at the safety valve set pressure

Explanation

A hydrostatic test is performed at a pressure above the maximum allowable working pressure, using a factor set by the applicable code. The test verifies shell and joint integrity beyond normal service. Testing at operating pressure or valve set pressure would not demonstrate the required margin.

Question 8Boiler and Pressure Vessel Fundamentals

During a hydrostatic test, at what temperature should the water generally be introduced?

  1. As cold as the supply allows
  2. At or above normal operating temperature
  3. At boiling point
  4. Near the ambient air temperature or slightly warm Correct answer.

Explanation

Test water is normally near ambient or slightly warm to avoid thermal shock to the shell and to reduce the risk of brittle behaviour in cold metal. Very cold water can stress the material, and hot water creates handling hazards. Boiling water would make the test meaningless.

Question 9Boiler and Pressure Vessel Fundamentals

What is the main reason for blowing down a boiler?

  1. To warm the boiler shell evenly
  2. To test the safety valve
  3. To increase the steam pressure
  4. To remove dissolved and suspended solids from the water Correct answer.

Explanation

Blowdown removes concentrated dissolved solids and sludge that accumulate as steam is produced. Controlling these impurities prevents carryover, scale, and corrosion. It does not raise pressure or test the safety valve.

Question 10Boiler and Pressure Vessel Fundamentals

A boiler operator notices the bottom blowdown valve is leaking steam continuously. What is the correct action?

  1. Increase feedwater to compensate
  2. Open the valve fully to clear debris
  3. Ignore it because the leak is small
  4. Shut down and repair the valve as soon as safely possible Correct answer.

Explanation

A leaking blowdown valve allows water and steam to escape and can worsen, leading to low water or erosion of the seat. The correct action is to arrange repair, shutting down if needed for safety. Opening the valve fully will not fix a damaged seat and increases loss.

Question 11Boiler and Pressure Vessel Fundamentals

Which type of boiler is classified as a fire-tube boiler?

  1. A once-through coil boiler
  2. A boiler with water passing through tubes surrounded by hot gas
  3. A waterwall boiler with tubes around the furnace
  4. A boiler with hot gases passing through tubes surrounded by water Correct answer.

Explanation

In a fire-tube boiler, hot combustion gases travel through tubes that are surrounded by water in the shell. The other arrangements describe water-tube or once-through designs. The distinction is which fluid is inside the tubes.

Question 12Boiler and Pressure Vessel Fundamentals

What is the function of the steam drum in a water-tube boiler?

  1. To condense exhaust steam
  2. To filter feedwater
  3. To separate steam from water and provide storage Correct answer.
  4. To burn fuel and generate heat

Explanation

The steam drum provides space for steam and water to separate and acts as a reservoir to smooth level changes. It also houses internal separators and connections for water level indication. It is not a combustion or filtration device.

Question 13Boiler and Pressure Vessel Fundamentals

Why is a boiler furnace maintained at a slight negative pressure in balanced-draft operation?

  1. To prevent hot gases from escaping into the boiler room Correct answer.
  2. To force air into the furnace to increase pressure
  3. To raise the steam temperature
  4. To cool the refractory

Explanation

A slight negative pressure keeps combustion gases inside the furnace and flue rather than leaking into the operating space. It also supports stable combustion airflow. Positive pressure would risk gas leakage into the room.

Question 14Boiler and Pressure Vessel Fundamentals

Which instrument indicates the pressure inside the boiler shell?

  1. The flow meter
  2. The pressure gauge Correct answer.
  3. The thermometer
  4. The water column

Explanation

The pressure gauge displays the internal pressure of the boiler shell so the operator can compare it with the safety valve setting. Thermometers measure temperature and the water column shows level. A flow meter measures flow rate.

Question 15Boiler and Pressure Vessel Fundamentals

A pressure gauge on a boiler is required to have which feature to protect it from steam?

  1. A relief valve
  2. A check valve
  3. A strainer
  4. A siphon or pigtail loop Correct answer.

Explanation

A siphon (pigtail) loop traps condensate so live steam does not enter the gauge mechanism. The condensate protects the Bourdon tube from high-temperature damage. Check valves, strainers, and relief valves serve other purposes.

Question 16Boiler and Pressure Vessel Fundamentals

What does the term maximum allowable working pressure (MAWP) mean for a boiler?

  1. The average pressure over a normal shift
  2. The pressure at which the safety valve is factory set
  3. The pressure at which the boiler was last tested
  4. The highest pressure at which the boiler may be operated under its design Correct answer.

Explanation

MAWP is the maximum pressure the boiler is designed and stamped to withstand in service. It is established by design and code rules, not by the last test or a factory setting. Operating above it is prohibited.

Question 17Boiler and Pressure Vessel Fundamentals

A boiler nameplate shows a maximum allowable working pressure of 1035 kPa. The safety valve is set at 1035 kPa. What does this arrangement indicate?

  1. The safety valve setting is consistent with the design limit Correct answer.
  2. The boiler may be operated at 1200 kPa
  3. The safety valve should be removed
  4. The safety valve is set too high and must be reduced

Explanation

The safety valve must be set at or below the maximum allowable working pressure so the boiler cannot be operated above its design limit. A setting equal to the MAWP is acceptable and consistent. Operating above the MAWP is never permitted.

Question 18Boiler and Pressure Vessel Fundamentals

What is the purpose of the refractory lining in a boiler furnace?

  1. To insulate and protect the casing from high furnace temperatures Correct answer.
  2. To hold the water in the drum
  3. To conduct heat away from the shell
  4. To filter combustion gases

Explanation

Refractory withstands high temperatures and protects the casing and structure from heat. It also helps maintain furnace temperature for stable combustion. It does not conduct heat away or filter gases.

Question 19Boiler and Pressure Vessel Fundamentals

A boiler has been idle and the water level in the gauge glass is not visible. What is the correct first action?

  1. Open the safety valve
  2. Secure the fuel and investigate the water level using try cocks Correct answer.
  3. Add water rapidly through the feed pump
  4. Start the burner immediately

Explanation

When the level is not visible, the boiler must be treated as potentially low on water. Fuel must be secured before any investigation, and try cocks used to confirm conditions. Starting the burner or adding water quickly can be dangerous if the crown sheet is overheated.

Question 20Boiler and Pressure Vessel Fundamentals

Which device automatically regulates the water level in a steam boiler?

  1. The feedwater regulator Correct answer.
  2. The draft fan
  3. The safety valve
  4. The blowdown valve

Explanation

The feedwater regulator senses level and adjusts the feedwater flow to maintain the normal operating level. The safety valve controls pressure and the draft fan controls airflow. Blowdown valves are used to remove water and solids.

Question 21Boiler and Pressure Vessel Fundamentals

Why must a boiler be vented while it is being filled with water?

  1. To warm the water
  2. To test the safety valve
  3. To allow air to escape so the boiler fills completely Correct answer.
  4. To increase the fill rate

Explanation

Air trapped in the shell can prevent complete filling and can cause uneven heating or false level readings. Venting allows the air to escape as water enters. It does not increase fill rate or test the safety valve.

Question 22Boiler and Pressure Vessel Fundamentals

What is the main hazard of operating a boiler with a faulty water level control?

  1. Excessive steam pressure
  2. Corrosion of the chimney
  3. Overheating of pressure parts from low water Correct answer.
  4. Excessive feedwater temperature

Explanation

A faulty level control can allow the water level to fall below safe limits. Uncovered pressure parts can overheat and fail, which is a serious hazard. Excessive pressure is controlled by the safety valve, not the level control.

Question 23Boiler and Pressure Vessel Fundamentals

Which statement about the try cocks on a boiler is correct?

  1. They are used to drain the boiler completely
  2. They are used to sample feedwater
  3. They are used to relieve excess pressure
  4. They are used to confirm water level independently of the gauge glass Correct answer.

Explanation

Try cocks are small valves at different heights on the water column that let the operator confirm the water level directly. They serve as a backup when the gauge glass is suspect. They are not pressure relief or drain valves.

Question 24Boiler and Pressure Vessel Fundamentals

A boiler is being prepared for internal inspection. Which step is essential before entry?

  1. Start the draft fan for ventilation only
  2. Leave the safety valve in place under pressure
  3. Cool, drain, vent, and isolate the boiler and lock out energy sources Correct answer.
  4. Fill the boiler with water

Explanation

Before internal inspection, the boiler must be cooled, drained, vented, and isolated from all energy and water sources, with lockout applied. This ensures the space is safe for entry. Filling with water or leaving it pressurized is incompatible with inspection.

Question 25Boiler and Pressure Vessel Fundamentals

Which condition would most likely cause scale buildup on boiler heating surfaces?

  1. Hard feedwater with high calcium and magnesium content Correct answer.
  2. High steam demand
  3. Low firing rate
  4. Properly treated feedwater

Explanation

Scale forms when hardness minerals such as calcium and magnesium precipitate on hot surfaces. Proper treatment removes or controls these minerals. Firing rate and steam demand affect load but not the mineral content causing scale.

Question 26Boiler and Pressure Vessel Fundamentals

A safety valve on a boiler is set to open at 1000 kPa. What is the primary purpose of this valve?

  1. To isolate the boiler from the plant steam header during a shutdown
  2. To limit steam pressure by releasing steam before the pressure exceeds the maximum allowable working pressure Correct answer.
  3. To regulate the water level in the steam drum
  4. To drain condensate from the steam header during start-up

Explanation

A safety valve is an overpressure protection device that opens automatically when the boiler pressure reaches its set point, discharging steam to prevent the pressure from exceeding the maximum allowable working pressure. It is not used for routine control of pressure, water level, or flow. The valve must be set at or below the MAWP and have sufficient capacity to relieve the maximum steaming rate.

Question 27Boiler and Pressure Vessel Fundamentals

Which statement correctly describes the function of a fusible plug in a boiler?

  1. It indicates the water level in the gauge glass
  2. It melts at a predetermined temperature to release steam and warn of low water
  3. It melts at a predetermined temperature to allow water to extinguish the fire Correct answer.
  4. It opens when the steam pressure exceeds the set point

Explanation

A fusible plug contains a low-melting-point alloy that melts when the metal around it becomes overheated, usually because the water level has fallen below the top of the crown sheet or tubes. When it melts, water and steam are released into the firebox, extinguishing the fire and warning the operator. It is not a pressure relief device and does not indicate water level.

Question 28Boiler and Pressure Vessel Fundamentals

A boiler operator observes that the water in the gauge glass appears discolored and foamy, and the indicated water level is difficult to read. Which condition does this most likely indicate?

  1. The gauge glass is incorrectly connected
  2. The safety valve is leaking
  3. The boiler is being fired too slowly
  4. The boiler water is contaminated with dissolved solids or organic matter Correct answer.

Explanation

Foamy or discolored water in the gauge glass typically indicates high dissolved solids, organic contamination, or improper chemical treatment, which causes the water to foam and makes the level difficult to read. The remedy is to blow down the boiler and review the water treatment program. Firing rate, gauge glass connections, and a leaking safety valve do not cause foaming.

Question 29Boiler and Pressure Vessel Fundamentals

A boiler has a maximum allowable working pressure of 1200 kPa. The safety valve is set at 1200 kPa. During operation, the boiler pressure gauge reads 1250 kPa and the safety valve has not opened. What is the most likely explanation?

  1. The safety valve is stuck closed or its set pressure has drifted higher Correct answer.
  2. The boiler is operating normally because safety valves only open at 110% of MAWP
  3. The safety valve is correctly set and the extra pressure is due to a faulty gauge
  4. The pressure gauge is inaccurate and the boiler is actually at 1200 kPa

Explanation

If the pressure gauge reads above the safety valve set pressure and the valve has not opened, the valve is likely stuck, obstructed, or its set pressure has drifted. The operator should reduce firing immediately and investigate. A safety valve must open at or below its set pressure, and the set pressure must not exceed the MAWP.

Question 30Boiler and Pressure Vessel Fundamentals

Which statement correctly describes the purpose of a boiler blowdown separator?

  1. It increases the pressure of the blowdown to assist drainage
  2. It cools the blowdown water before it enters the sewer
  3. It separates steam from the blowdown water so that steam can be vented and water drained safely Correct answer.
  4. It filters suspended solids from the boiler water

Explanation

A blowdown separator receives high-pressure blowdown water and allows the flash steam to separate and vent safely while the remaining water drains to the sewer. It protects the sewer system from high pressure and temperature. It does not cool the water, filter solids, or increase pressure.

Question 31Boiler and Pressure Vessel Fundamentals

A boiler is equipped with a low-water fuel cutoff and a feedwater regulator. During normal operation, the water level drops below the lowest visible level in the gauge glass. What should happen first?

  1. The low-water fuel cutoff should shut off the fuel supply to the burner Correct answer.
  2. The feedwater regulator should increase feedwater flow to restore level
  3. The safety valve should open to relieve pressure
  4. The operator should manually open the bottom blowdown valve

Explanation

The low-water fuel cutoff is a safety device that shuts off the fuel supply when the water level falls below a safe point, preventing overheating of the boiler. The feedwater regulator is a control device and may respond, but the safety function of the cutoff takes precedence. The safety valve and blowdown valve are not involved in low-water protection.

Question 32Boiler and Pressure Vessel Fundamentals

Which statement correctly describes the function of a steam trap in a steam heating system?

  1. It measures the steam flow rate to the heating unit
  2. It removes condensate and non-condensable gases while preventing steam loss Correct answer.
  3. It adds water to the boiler to maintain the water level
  4. It reduces the steam pressure before it reaches the heating unit

Explanation

A steam trap automatically discharges condensate and air from the steam system while closing against live steam, allowing the steam to do useful work. It does not reduce pressure, feed water, or measure flow. Proper trap operation is essential for efficient heat transfer and preventing water hammer.

Question 33Boiler and Pressure Vessel Fundamentals

A boiler operator is preparing to hydrostatically test a boiler after repairs. Which statement correctly describes a required precaution?

  1. The boiler should be filled with hot water to speed the test
  2. The test should be performed with the burner firing to maintain temperature
  3. The safety valve must be removed or blanked off during the test Correct answer.
  4. The test pressure should be maintained for at least 30 minutes before inspection

Explanation

During a hydrostatic test, the safety valve must be removed or isolated because the test pressure may exceed the valve set pressure, which could damage the valve or cause it to lift. The test is performed with the boiler cold and the burner off. The test pressure is typically held for a specified time, often 10 to 30 minutes, but the key precaution is isolating the safety valve.

Question 34Boiler and Pressure Vessel Fundamentals

Which statement correctly describes the purpose of a boiler inspection opening such as a handhole or manhole?

  1. To provide access for cleaning, inspection, and repair of internal surfaces Correct answer.
  2. To allow steam to escape during normal operation
  3. To mount the safety valve on the boiler shell
  4. To drain water from the boiler during blowdown

Explanation

Handholes and manholes are openings that allow personnel to inspect, clean, and repair the internal surfaces of the boiler and pressure vessel. They are closed and sealed during normal operation. They are not used for steam release, blowdown, or mounting safety valves.

Question 35Boiler and Pressure Vessel Fundamentals

A fire-tube boiler exhibits a bulge in the crown sheet above the fire. Which condition is the most likely cause?

  1. Improper safety valve setting
  2. Too much feedwater
  3. Excessive steam pressure
  4. Low water level allowing the crown sheet to overheat Correct answer.

Explanation

A bulge in the crown sheet is typically caused by overheating due to low water level, which allows the metal to weaken and deform under pressure. Excessive pressure would more likely cause a rupture than a localized bulge. Safety valve setting and feedwater quantity do not directly cause crown sheet bulging.

Question 36Boiler and Pressure Vessel Fundamentals

Which statement correctly describes the function of a boiler feedwater check valve?

  1. It regulates the flow rate of feedwater to match steam demand
  2. It measures the quantity of feedwater entering the boiler
  3. It reduces the feedwater pressure before it enters the boiler
  4. It prevents backflow of water from the boiler into the feedwater line Correct answer.

Explanation

A feedwater check valve allows water to flow into the boiler but prevents it from flowing back into the feedwater line when the feed pump stops or pressure drops. It is a safety device that protects the feedwater system from boiler pressure and contamination. It does not regulate flow, reduce pressure, or measure quantity.

Question 37Boiler Operation, Combustion, and Controls

On a packaged fire-tube boiler, what is the primary function of the low-water fuel cutoff?

  1. To reduce feedwater temperature before it enters the boiler
  2. To add makeup water when the gauge glass level drops
  3. To open the main steam stop valve automatically
  4. To stop the burner when the water level falls below a safe point Correct answer.

Explanation

The low-water fuel cutoff is a safety device that senses water level and cuts off the fuel supply to the burner before the crown sheet or tubes are exposed to flame. It does not add water or control steam flow; feedwater control is a separate function.

Question 38Boiler Operation, Combustion, and Controls

A boiler operator observes a steady, sharply defined blue flame with a short, intense inner cone at the burner. This appearance most nearly indicates which condition?

  1. Excess combustion air with a properly adjusted flame Correct answer.
  2. A flame impinging on the boiler tubes
  3. Insufficient combustion air
  4. A rich mixture with incomplete combustion

Explanation

A short, well-defined blue flame with an intense inner cone is characteristic of good air-fuel mixing and adequate but not excessive air. Yellowing, a long lazy flame, or a smoky tail would suggest air deficiency or other trouble.

Question 39Boiler Operation, Combustion, and Controls

What is the purpose of the purge (pre-purge) period before a burner is ignited?

  1. To test the flame scanner sensitivity
  2. To warm the furnace refractory gradually
  3. To drive out combustible gases from the furnace and flue passages Correct answer.
  4. To pressurize the fuel oil line

Explanation

Pre-purge moves air through the furnace and passes for a set time to clear any accumulated combustible gases before ignition, reducing the risk of a furnace explosion. It is a safety interlock step in the burner sequence, not a warm-up or fuel-line function.

Question 40Boiler Operation, Combustion, and Controls

A steam boiler safety valve is set to open at the maximum allowable working pressure. What is the operator's correct response when the valve lifts during normal operation?

  1. Increase the firing rate to stabilize the draft
  2. Investigate and correct the cause of the overpressure Correct answer.
  3. Hold the valve open until pressure falls well below the setpoint
  4. Close the valve by hand to prevent steam loss

Explanation

A safety valve lifting signals that pressure has reached the setpoint, so the operator must find and correct the cause, such as a stuck burner, faulty pressure control, or excessive firing. The valve must never be blocked, held open, or manually closed while under pressure.

Question 41Boiler Operation, Combustion, and Controls

Which device converts the boiler's steam pressure into a signal used by the modulating burner control?

  1. The low-water cutoff float
  2. The pressuretrol (pressure control) Correct answer.
  3. The draft gauge
  4. The flame scanner

Explanation

A pressuretrol senses steam pressure and sends a signal to the burner control to modulate or cycle firing to hold the setpoint. The flame scanner proves flame, the low-water cutoff protects against low water, and the draft gauge indicates furnace pressure.

Question 42Boiler Operation, Combustion, and Controls

During a routine check, the operator finds the modulating damper stuck fully open while the burner is at low fire. What is the most likely immediate effect on combustion?

  1. Insufficient air and heavy smoke
  2. Loss of flame signal
  3. A rich mixture with high CO
  4. Excess air and a cooling effect on the furnace Correct answer.

Explanation

A damper stuck open at low fire delivers far more air than the fuel requires, producing excess air that cools the furnace and lowers efficiency. It does not cause smoke or a rich mixture, which would come from too little air.

Question 43Boiler Operation, Combustion, and Controls

The gauge glass on a steam boiler shows a level that stays steady while the burner is firing hard and the feedwater valve is closed. Which conclusion is most reasonable?

  1. The gauge glass connections may be plugged and the indication is unreliable Correct answer.
  2. The safety valve is leaking
  3. The boiler is being overfed with cold water
  4. The steam demand has dropped to zero

Explanation

A gauge glass that does not respond to firing and feedwater changes is a warning sign that its connections may be plugged, giving a false reading. The glass should be blown down and checked before trusting the level.

Question 44Boiler Operation, Combustion, and Controls

Which statement correctly describes the relationship between boiler draft and combustion air supply?

  1. Draft has no effect on the quantity of air entering the furnace
  2. Draft is only needed when the burner is off
  3. Draft is created solely by the feedwater pump
  4. Draft draws combustion air into the furnace and carries flue gases out Correct answer.

Explanation

Draft is the pressure difference that pulls combustion air into the furnace and moves flue gases through the passes and up the stack. Without adequate draft, the burner cannot get enough air and products of combustion cannot leave properly.

Question 45Boiler Operation, Combustion, and Controls

A boiler is firing natural gas at a steady rate, and the flue gas oxygen reading is 9 percent. What does this reading most likely indicate?

  1. The mixture is fuel-rich and CO is likely high
  2. The burner is at maximum capacity
  3. There is substantial excess air and stack losses are elevated Correct answer.
  4. The flame scanner is misaligned

Explanation

A flue gas oxygen reading near 9 percent is well above the typical 2 to 5 percent target for gas firing, indicating excess air that carries heat up the stack and lowers efficiency. Fuel-rich firing would show low oxygen, not high.

Question 46Boiler Operation, Combustion, and Controls

What is the correct sequence of events in a typical automatic gas burner startup?

  1. Pre-purge, pilot ignition and proving, main flame proving Correct answer.
  2. Pilot ignition, pre-purge, main flame, flame proving
  3. Main flame, pre-purge, pilot ignition, proving
  4. Pre-purge, main flame, pilot ignition, proving

Explanation

The burner control runs a pre-purge to clear the furnace, then ignites and proves the pilot, and only then opens the main fuel valve and proves main flame. Igniting main fuel before proving a pilot would be unsafe.

Question 47Boiler Operation, Combustion, and Controls

An operator must blow down a boiler gauge glass. Which procedure is correct?

  1. Open the drain first, then close the top valve, then reopen
  2. Close the top and bottom valves, then open the drain
  3. Open the drain, close the bottom valve, then reopen it after the glass clears Correct answer.
  4. Open the bottom valve fully and leave the drain open

Explanation

Blowing down the glass means opening the drain to flush the passages, then closing the bottom valve so steam from the top clears the glass, and finally reopening the bottom valve to restore the normal level. This confirms both connections are clear.

Question 48Boiler Operation, Combustion, and Controls

A steam boiler shows rising stack temperature and falling efficiency while firing rate and steam load are unchanged. Which cause is most likely?

  1. A lower feedwater temperature
  2. A decrease in excess air
  3. Scale or soot buildup on heat transfer surfaces Correct answer.
  4. A higher steam pressure setpoint

Explanation

Scale or soot acts as an insulating layer that reduces heat transfer, so more heat leaves with the flue gas and stack temperature rises. Cleaning the fireside and waterside restores heat transfer and efficiency.

Question 49Boiler Operation, Combustion, and Controls

What is the function of the flame scanner (flame detector) in a burner management system?

  1. To prove that flame is present and shut off fuel if it is lost Correct answer.
  2. To measure the temperature of the furnace refractory
  3. To regulate the fuel oil pressure
  4. To control the feedwater valve

Explanation

The flame scanner continuously proves flame presence and signals the control to close the fuel valves if flame is lost, preventing unburned fuel from accumulating. It does not measure temperature or regulate fuel pressure.

Question 50Boiler Operation, Combustion, and Controls

A boiler operator notices the furnace pressure is running positive and hot gases are escaping around the burner plate. Which action is most appropriate?

  1. Increase forced draft fan speed to push more air in
  2. Raise the firing rate to burn off the gases
  3. Open the furnace door to relieve pressure
  4. Reduce excess draft by adjusting the induced draft or stack damper to restore slight negative pressure Correct answer.

Explanation

A positive furnace pressure at the burner plate means draft is insufficient, so the induced draft or stack damper should be adjusted to restore the slight negative pressure that keeps gases inside the furnace. Opening doors or increasing forced draft worsens the condition.