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5th Class Power Engineer Practice Exam

SOPEEC-aligned · Class 5

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    Class 5 Power Engineer — Sample Questions (50 free preview questions of 50)

    Q1. A hot water boiler relief valve discharges each time the boiler fires. What is a typical cause?

    1. A system thermometer reading lower than actual
    2. An operating control set too low for the system
    3. A ruptured diaphragm tank or flooded expansion tank ✓
    4. A circulating pump that is running faster than designed

    Explanation: A ruptured diaphragm tank or flooded expansion tank leaves no room for expansion, so the relief valve typically discharges when the boiler fires.

    Q2. A steam boiler operates at 120 kPa. Under which ASME Code section must it be built?

    1. Section IV, Heating Boilers, because steam temperature is below 121°C
    2. Section IV, Heating Boilers, because steam pressure is below 1100 kPa
    3. Section I, Power Boilers, because steam pressure exceeds 103 kPa ✓
    4. Section VIII, because it is a pressure vessel below 1100 kPa

    Explanation: A steam boiler is a heating boiler only if its pressure does not exceed 103 kPa (14.7 psi). At 120 kPa it is a power boiler under Section I. The 1100 kPa and 121°C limits apply to hot water boilers.

    Q3. In a closed hot water system, the pressure pointer reads lower than the altitude pointer. What does this indicate?

    1. The relief valve setting is too low
    2. The system is no longer full of water ✓
    3. The circulating pump is producing too much pressure
    4. The expansion tank is waterlogged

    Explanation: In closed systems the pressure pointer should always read higher than the altitude pointer during operation. A lower reading means the system is no longer full of water.

    Q4. On a high pressure boiler with a quick-opening and a slow-opening blowdown valve, what is the correct sequence?

    1. Open inside valve first, blow with outside valve, close outside first, inside last ✓
    2. Open outside valve first, blow with inside valve, close the inside valve first
    3. Open both valves together, blow, then close both valves together at the end
    4. Open inside valve first, blow with the inside valve, close the outside valve last

    Explanation: Open the inside (quick) valve first, then open the outside valve and blow. Close the outside valve first and the inside valve last, so the outside valve takes the wear.

    Q5. Why should a high water level not be lowered by opening the blowdown valves first?

    1. The blowdown water would scald the operator
    2. The safety valve would lift from the pressure surge
    3. The low water cut-off would trip immediately
    4. The pressure drop can cause the boiler water to swell ✓

    Explanation: Opening blowdown can drop pressure, causing water "swell". Stopping cool feedwater raises pressure slightly, causing "shrink", which helps.

    Q6. A boiler shuts down because the low water fuel cut-off opens. What happens when the water level is restored?

    1. It restarts automatically; the lockout switch is not actuated ✓
    2. It restarts only after the high limit control is reset
    3. It restarts directly on high fire to recover the pressure
    4. It stays locked out until the operator manually resets it

    Explanation: When the operating control or a limit switch such as the low water cut-off shuts the boiler down, or power fails, the boiler restarts automatically. Only flame failure causes a lockout needing manual reset.

    Q7. How does water hammer occur when steam is admitted into a cold steam line?

    1. Condensate waves trap a steam pocket that condenses, and water rushes into it ✓
    2. Steam pushes slugs of water ahead at high velocity until they hit the line end
    3. Air in the cold line is compressed by the steam and then suddenly released
    4. The cold pipe contracts sharply when the steam hits it and cracks the fittings

    Explanation: A wave of condensate may rise behind steam, isolating a steam pocket. The steam condenses suddenly, creating low pressure, and water rushing in causes severe shock.

    Q8. What happens if the blowdown ring of a pop safety valve is screwed up toward the portholes?

    1. Escape port area decreases, the valve closes sooner, and blowdown decreases
    2. Escape port area increases, the popping pressure rises, and blowdown is unchanged
    3. Escape port area increases, the valve closes sooner, and blowdown decreases
    4. Escape port area decreases, the valve stays open longer, and blowdown increases ✓

    Explanation: Screwing the ring up decreases port area, directing more steam against the lip. The greater lifting force keeps the valve open longer and it closes at a lower pressure, increasing blowdown.

    Q9. In an electrode boiler, what happens when steam generation exceeds demand?

    1. Regulating zone pressure pushes water into the generating zone, so more electrode is covered
    2. The salinity feeder adds more electrolyte, which reduces the current through the water
    3. The pressure regulator opens wider, lowering the generating zone pressure and the level
    4. Generating zone pressure pushes water into the regulating zone, so less electrode is covered ✓

    Explanation: When generation exceeds demand, the regulator closes, generating zone pressure rises and forces water out the bottom into the regulating zone. Less electrode is submerged, less current flows and less steam is made.

    Q10. A single large heating boiler is sized for the coldest weather. About how much of the time will it run near full capacity?

    1. 90%
    2. 10% ✓
    3. 60%
    4. 40%

    Explanation: Since 60% or less of capacity is needed for 90% of the season, a single large boiler runs near full capacity only about 10% of the time.

    Q11. A hot water boiler's relief valve is set at 250 kPa. What is the highest recommended operating pressure?

    1. 188 kPa
    2. 181 kPa ✓
    3. 225 kPa
    4. 200 kPa

    Explanation: 25% of 250 kPa is 62.5 kPa, which is less than 69 kPa. The 69 kPa minimum applies, so the maximum is 250 − 69 = 181 kPa.

    Q12. The steam connection to a gauge glass becomes plugged. What will the glass show?

    1. A lower level than the true boiler level
    2. An empty glass
    3. A higher level than the true boiler level ✓
    4. The true level, but slower to respond

    Explanation: With the steam connection blocked, steam trapped in the top of the glass condenses, and boiler pressure pushes water higher, so the glass reads high.

    Q13. A pressure control has its main scale set at 55 kPa and its differential at 20 kPa. At what pressures does the burner start and stop?

    1. Starts at 55 kPa, stops at 75 kPa ✓
    2. Starts at 45 kPa, stops at 65 kPa
    3. Starts at 55 kPa, stops at 95 kPa
    4. Starts at 35 kPa, stops at 55 kPa

    Explanation: On the control described, the main scale shows the cut-in pressure and the differential is added to get cut-out: 55 + 20 = 75 kPa.

    Q14. On a hot water boiler, what may happen if the fuel valve sticks open after the low water cut-off trips?

    1. The flow switch senses the low water and shuts the burner down
    2. Temperature and pressure rise until the relief valve opens ✓
    3. The automatic fill valve refills the boiler and prevents damage
    4. The expansion tank absorbs the rise until the burner cycles off

    Explanation: If the fuel valve sticks open, firing continues and temperature and pressure rise until the relief valve opens, letting water and steam escape.

    Q15. A fuel needs 15 kg of theoretical air per kg, and 18 kg of air per kg is actually supplied. What is the excess air?

    1. 20% ✓
    2. 17%
    3. 83%
    4. 30%

    Explanation: Excess = 18 − 15 = 3 kg. As a percentage of theoretical air: 3 ÷ 15 × 100 = 20%. (3 ÷ 18 = 17% is the common error of dividing by actual air.)

    Q16. Why can't the low water fuel cut-off on a hot water boiler be tested by opening its float chamber drain during normal operation?

    1. The float is fixed in its upper position in hot water service
    2. The drain valve on the chamber is locked closed by Code
    3. The system is full of water, so the chamber will not empty ✓
    4. Opening the drain would trip the flow switch before the cut-off

    Explanation: The boiler and system are full of water with no intervening valves, so opening the drain will not empty the chamber. Testing needs the boiler shut down and isolated.

    Q17. Why do dissolved solids in an electrode boiler tend to form sludge rather than hard scale?

    1. The electric current breaks the solids into fine particles
    2. The electrolyte dissolves any scale as it forms
    3. The water circulates too quickly for scale to settle
    4. The metal surfaces never get hotter than the water temperature ✓

    Explanation: In fuel-fired boilers the metal can be much hotter than the water, making solids adhere as scale. In electric boilers the metal never gets hotter than the water, so solids tend to end up as sludge.

    Q18. In a burner with two fixed capacity nozzles, when can the secondary oil solenoid valve be opened?

    1. At the same moment as the primary oil valve, on every start-up
    2. Before the primary valve opens, so the furnace is warmed first
    3. Only after the primary nozzle has lit and its flame is recognized ✓
    4. Whenever the pump discharge pressure reaches 690 kPa

    Explanation: The secondary valve cannot be opened unless fuel from the primary nozzle has ignited and the flame is recognized by the combustion control.

    Q19. A low pressure steam boiler's safety valve is set at 103 kPa. What is the highest ideal high limit cut-out setting?

    1. About 77 kPa
    2. About 93 kPa ✓
    3. About 103 kPa
    4. About 98 kPa

    Explanation: Ideally the high limit should not exceed 90% of the safety valve setting: 0.9 × 103 = about 93 kPa.

    Q20. Why are the floor tubes of "D" and "O" type furnaces covered with refractory tile?

    1. The tile reflects heat upward and raises the furnace temperature
    2. The floor tubes are made of copper, which cannot withstand flame contact
    3. The floor tubes carry feedwater that would flash to steam if heated directly
    4. Steam formed would flow along the top of the tube and not cool it the way water does ✓

    Explanation: Steam generated in horizontal floor tubes would flow along the top of the tube and not act as a coolant, so the tubes could overheat. Tile protects them.

    Q21. Why must all air be removed from a boiler before a hydrostatic test?

    1. Air left inside will corrode the boiler metal at test pressure
    2. Air left inside will make the safety valve lift during the test
    3. With nothing compressible inside, any leak shows as a pressure drop ✓
    4. Air left inside stops the test pump from reaching test pressure

    Explanation: A hydrostatic test is a still water test with no air or gas present. With nothing compressible, the slightest change in water volume causes a large pressure change.

    Q22. A hot water boiler's relief valve is set at 200 kPa. Which gauge dial range is acceptable?

    1. 0–250 kPa
    2. 0–800 kPa
    3. 0–400 kPa ✓
    4. 0–200 kPa

    Explanation: The dial must be graduated to not less than 1.5 and not more than 3.5 times the relief valve setting: 300 to 700 kPa. Only 400 kPa falls in that range.

    Q23. Why is the water in a copper-tubular boiler pumped from the top of the tubing downwards?

    1. So the pump works against less pressure because the gas flow helps it
    2. So cold water never enters the hottest section, preventing excessive stresses ✓
    3. So steam bubbles are swept downward and separated in the lower coil
    4. So sediment drops into the combustion chamber and is burned off

    Explanation: With water flowing top-down and gases rising, cold water is not pumped into the hottest section. This prevents excessive stresses and gives longer life.

    Q24. A low pressure steam boiler's high limit has locked out. What does this indicate?

    1. The low water cut-off has failed and let the level drop
    2. The burner is overfiring because of a fuel pressure fault
    3. The safety valve is set too high for the boiler's MAWP
    4. The operating control is malfunctioning and must be repaired ✓

    Explanation: The high limit only trips if the operating control fails to stop the burner at its cut-out. The lockout tells the operator the operating control is malfunctioning.

    Q25. A hot water boiler at operating temperature is suddenly flooded with cool water from a system that has been out of service. What is the risk?

    1. A low water condition from water contraction
    2. Water hammer from steam collapsing in the boiler
    3. Uneven expansion from a rapid rise in temperature
    4. Thermal shock from a rapid drop in temperature ✓

    Explanation: Thermal shock is also caused by a rapid temperature drop, such as when hot boiler water (90–115°C) is replaced in minutes by cool water from an idle system.

    Q26. A steam boiler's water level is found below the gauge glass. After shutting it down, what must NOT be done?

    1. Feed water into the boiler or open the safety or vent valve ✓
    2. Drain and open the boiler to inspect for overheating
    3. Find why the low water cut-off failed
    4. Let the boiler cool slowly to hand-touch temperature

    Explanation: Do not feed water to raise the level or open the safety or vent valve; any such action may shock or damage the boiler. Let it cool slowly, then drain and inspect.

    Q27. If a boiler tube ruptures in a plant with several boilers on a common header, what does the non-return stop valve do?

    1. It opens fully to relieve the damaged boiler's pressure into the header
    2. It must be closed by hand by the operator to isolate the damaged boiler
    3. It closes automatically, keeping header steam out of the damaged boiler ✓
    4. It locks in the open position so the other boilers can supply the damaged one

    Explanation: Pressure in the damaged boiler drops, header pressure becomes greater, and the free disc closes, preventing steam from other boilers entering it.

    Q28. Why is a second low water cut-off required by Code on a steam boiler whose cut-off also controls the feedwater?

    1. Because feedwater control is now the primary function of the first device ✓
    2. Because the first device is a float type and the second must be a probe type
    3. Because the first device cannot sound an alarm
    4. Because the first device is wired in series with the high limit

    Explanation: When the cut-off's primary function becomes feedwater control, a second, dedicated low water cut-off is required by Code.

    Q29. In a two-probe low water fuel cut-off, when does the fuel shut off?

    1. When the water level drops below the lower probe
    2. When both probes are covered with water
    3. When the water level drops below the upper probe ✓
    4. When the water level rises above the upper probe

    Explanation: When the level drops below the upper probe, current to the solenoid stops, the switch opens and the fuel supply is interrupted.

    Q30. The water connection to a gauge glass becomes plugged. What will the glass show over time?

    1. A level that drops to the bottom of the glass
    2. A lower level than the true boiler level
    3. The true level, because steam still reaches the glass
    4. A higher level than the true boiler level ✓

    Explanation: Steam condenses in the glass, and the water cannot drain back to the boiler, so the level in the glass rises above the actual boiler level.

    Q31. When opening the drums of a watertube boiler for inspection, which manhole covers are removed first, and why?

    1. The lower drum covers first, so fresh air can enter from below
    2. The steam drum covers first, to prevent steam burns from convection ✓
    3. The lower drum covers first, so the last of the water drains out
    4. The steam drum covers last, so they hold in the remaining heat

    Explanation: Remove the steam drum manhole covers first, then the lower drum. If the top cover were removed last, convection would force steam out of the steam drum manway.

    Q32. When starting a cold high-low fire boiler, why is the manual high-low switch set to low?

    1. The low fire nozzle cannot light unless the high fire switch is turned off first
    2. Below its cut-in the high-low control calls for high fire, which is unsafe at start-up ✓
    3. The damper motor will not move to high fire until the steam pressure is up
    4. The high fire nozzle cannot light until the boiler reaches its operating pressure

    Explanation: Below 72 kPa the high-low control would be on high fire. Starting on high fire is unsafe, so the switch is set to low until the boiler is warm and circulation is established.

    Q33. A plant has five small boilers instead of one large one. If the cycling boiler's efficiency drops 10%, about how much does overall plant efficiency drop?

    1. About 2% ✓
    2. About 10%
    3. About 8%
    4. About 5%

    Explanation: The cycling boiler is only a fraction of plant capacity. In the textbook example, a 10% drop in the cycling boiler gives only about a 2% drop overall (10% ÷ 5 boilers).

    Q34. A hot water boiler operates at 900 kPa with water at 130°C. How is it classified?

    1. As a heating boiler, because the pressure is below 1100 kPa
    2. As a hot water supply boiler, because it heats water rather than making steam
    3. As a power boiler, because the water temperature exceeds 121°C ✓
    4. As a heating boiler, because the pressure is below 1100 kPa and temperature below 150°C

    Explanation: To be a heating boiler, a hot water boiler must not exceed 121°C (250°F) and must not exceed 1100 kPa (160 psi). Exceeding either limit makes it a power boiler; 130°C exceeds the temperature limit.

    Q35. If the huddling chamber escape ports of a pop safety valve were closed off, what would happen?

    1. The valve would fail to open at its set pressure
    2. The valve would chatter open and closed rapidly
    3. Boiler pressure would have to drop quite low before the valve closed ✓
    4. The valve would close with very little drop in boiler pressure

    Explanation: With the huddling chamber outlet closed, pressure under the lip is greater, so boiler pressure must fall quite low before the spring can close the valve, giving a large blowdown.

    Q36. Before a pop test on a hot water boiler, how high may the boiler pressure be?

    1. Not more than 50% of the relief valve set pressure ✓
    2. Not more than 75% of the relief valve set pressure
    3. Not more than 90% of the relief valve set pressure
    4. At the normal operating pressure

    Explanation: Pressure must be not more than 50% of the set pressure. Reduce excess pressure with the boiler drain, not the try lever, which would defeat the test's accuracy.

    Q37. When a motor-driven pump trips on power failure, what causes the severe water hammer shock?

    1. The pump overspeeding as the motor stops
    2. The relief valve lifting on the discharge line
    3. Air entering the suction line
    4. Reverse flow slamming the check valve shut ✓

    Explanation: Discharge pressure drops, the water stops and reverses, and rapid closing of the check valve violently expends the reverse flow energy against the disc.

    Q38. In a vertical firetube boiler, why should firing be very slow during warm-up?

    1. The draft hood can spill flue gases into the room until the stack is warm
    2. The water column cannot show the true level until the steam pressure is up
    3. The lower tubesheet is exposed to cold feedwater and can crack if heated too fast
    4. The upper tubes are cooled only by steam and, with the top tubesheet, can overheat ✓

    Explanation: The upper part of the tubes passes through the steam space and is cooled by steam, not water. Fire slowly until steam is produced to avoid overheating the tubes and upper tubesheet.

    Q39. An inclined gauge shows a furnace draft of 25 mm of water. About what pressure is this?

    1. 2.45 kPa
    2. 24.5 Pa
    3. 255 Pa
    4. 245 Pa ✓

    Explanation: 1 mm of water = 9.81 Pa, so 25 mm × 9.81 = about 245 Pa.

    Q40. After shutting down a steam boiler for a suspected tube leak, what should be done with the water level while it cools?

    1. Raise the level to the top of the glass
    2. Lower the level below the tubes
    3. Drain the boiler immediately to stop the leak
    4. Maintain the normal water level ✓

    Explanation: Shut down, close the steam stop valve, and maintain the normal water level until the boiler has cooled. Then open the doors to locate the leak.

    Q41. In the oil-fired bar graph example, why must the flame relay be open at 10 seconds?

    1. An open flame relay is needed to energize the ignition transformer at 37 seconds
    2. A closed relay during purge is a false flame signal, so the timer stops and locks out ✓
    3. An open flame relay restarts the timer motor after the low air switch proves
    4. An open flame relay shows the fuel valve is closed, so the purge can continue

    Explanation: At 10 seconds the timer stops if the flame relay is not open, and the lockout switch is energized. No flame should be detected before ignition.

    Q42. An NPS 4 pipe has an outside diameter of 114.30 mm and a Schedule 40 wall of 6.02 mm. What is its inside diameter?

    1. 108.28 mm
    2. 97.18 mm
    3. 120.32 mm
    4. 102.26 mm ✓

    Explanation: d = D − 2t = 114.30 − (2 × 6.02) = 102.26 mm. Subtracting the wall once gives 108.28 mm, a common error.

    Q43. During a pop test, a low pressure steam safety valve opens at 112 kPa. How should this be judged?

    1. Unacceptable, because it must open at exactly 103 kPa
    2. Unacceptable, because it exceeds the 108 kPa limit
    3. Acceptable, because it is within plus or minus 15 kPa of 103 kPa ✓
    4. Acceptable, but only if the blowdown is less than 15 kPa

    Explanation: The valve should open at 103 kPa (15 psi), with a variation of plus or minus 15 kPa (2 psi) acceptable. 112 kPa is within that range.

    Q44. During a pop test, the safety valve has not opened at 117 kPa. What should be done?

    1. Keep firing slowly until the valve finally opens, then record that pressure
    2. Screw the adjusting nut up to lower the set pressure, then continue firing
    3. Strike the valve body lightly with a hammer to free the disc, then continue
    4. Shut off the burner, bleed pressure off slowly, try lever the valve, then retest ✓

    Explanation: Shut off the burner and release pressure slowly through the vent or into the header. Below popping pressure, try lever the valve a few times and repeat. If it still fails, repair or replace it. Never hammer a valve.

    Q45. A steam boiler's water level climbs out of sight because the level control has failed. What should be done first?

    1. Lower the boiler pressure to reduce carryover
    2. Shut down the feedwater supply immediately ✓
    3. Open the gauge glass drain to lower the level
    4. Open the bottom blowdown valve to lower the level

    Explanation: Stop the feedwater first. Lowering the level before stopping feed lets the control keep feeding, and blowdown can drop pressure and cause swell.

    Q46. There is a spark but no flame at start-up. Which is a likely cause?

    1. A loose terminal on the ignition cable at the transformer
    2. Grounded ignition electrodes or a cracked electrode porcelain
    3. An inoperative ignition transformer with an open winding
    4. No fuel, from a closed manual valve or a clogged oil filter ✓

    Explanation: Spark but no flame points to fuel: closed manual valves, clogged filter, empty tank, wrong pilot gas pressure, or an inoperative pilot or low-fire solenoid. The other options cause no spark.

    Q47. If a heater tube splits and hot oil sprays into the furnace, what must be done immediately?

    1. Stop the fuel gas only, and keep the hot oil circulating through the coils
    2. Stop both the oil flow to the coils and the fuel gas to the burners ✓
    3. Increase the oil flow through the coils so the split tube is cooled
    4. Open the stack damper fully and keep firing so the oil burns away safely

    Explanation: The oil ignites and overheats the furnace. Unless both oil flow and fuel gas are immediately stopped, the heater will burn up in a large fire.

    Q48. In the main flame failure test, what causes the lockout?

    1. After the main trial the pilot shuts off, and no main flame is seen ✓
    2. The fan stops when the programmer finds the main fuel cock closed
    3. The pilot fails to light, so the main fuel valve is never energized
    4. The scanner sees the pilot, but the main valve then fails to open

    Explanation: The main burner cannot light with its cock closed. After the main trial period the pilot shuts off, no flame is detected, the main valve de-energizes and the lockout switch trips.

    Q49. An operator finds a boiler firing but cannot see any water level in the gauge glass. What is the first action?

    1. Open the bottom blowoff to trip the low water cut-off
    2. Shut down the boiler and open the safety valve to cool it
    3. Start the feed pump at once to raise the level into the glass
    4. Open the glass drain quickly to see if the glass is full or empty ✓

    Explanation: The glass may be completely full or empty. Check quickly by opening the glass drain. If the level is below the glass, shut the boiler down immediately.

    Q50. Why must an ultraviolet scanner not be able to sight the igniter spark?

    1. The spark would block the scanner's view of the pilot
    2. The spark interferes with the scanner's electrical supply
    3. The spark would damage the scanner lens
    4. It reacts to the spark and could falsely show a flame ✓

    Explanation: The UV scanner reacts to the igniter spark as well, so it must not sight it, or it could falsely prove a flame.

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