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MT Boiler Operator practice questions

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Question 1Boiler Construction, Design, and Fittings

A boiler fitting that automatically admits feedwater to maintain a set water level is called a:

  1. Feedwater regulator Correct answer.
  2. Steam trap
  3. Blowdown valve
  4. Safety valve

Explanation

A feedwater regulator senses water level and modulates feedwater flow to hold the drum level at the setpoint. Safety valves limit pressure, blowdown valves remove water, and steam traps remove condensate.

Question 2Boiler Construction, Design, and Fittings

In a fire-tube boiler, the hot gases:

  1. Circulate through an external economizer only
  2. Pass over tubes containing water
  3. Pass through tubes surrounded by water Correct answer.
  4. Surround a water-filled shell only

Explanation

In a fire-tube design, combustion gases travel through tubes that are immersed in the surrounding water. Water-tube boilers reverse this arrangement, with water inside tubes and gases outside.

Question 3Boiler Construction, Design, and Fittings

The main purpose of a safety valve on a boiler is to:

  1. Indicate the water level in the gauge glass
  2. Drain condensate from the steam header
  3. Regulate the burner firing rate
  4. Release pressure before it exceeds the maximum allowable working pressure Correct answer.

Explanation

A safety valve is the final overpressure protection and must open at or below the set pressure to prevent exceeding the maximum allowable working pressure. It does not perform level, drain, or firing-control functions.

Question 4Boiler Construction, Design, and Fittings

A boiler gauge glass is normally fitted with:

  1. A pressure gauge only
  2. A safety valve at its lower fitting
  3. Two try cocks and a single shutoff valve
  4. Isolating valves at the top and bottom connections plus a drain or blowdown valve Correct answer.

Explanation

The gauge glass has isolating valves at both the steam and water connections so it can be secured, and a drain cock to blow it down and prove the connections are clear.

Question 5Boiler Construction, Design, and Fittings

The maximum allowable working pressure stamped on a boiler is best described as the:

  1. Highest pressure at which the boiler may be operated under its design Correct answer.
  2. Pressure reached during a hydrostatic test
  3. Normal operating pressure shown on the gauge
  4. Pressure at which the safety valve is factory tested only

Explanation

The maximum allowable working pressure is the design limit for normal operation established by the code and the boiler's construction. Safety valves are set at or below it, and hydrostatic test pressure is higher than operating pressure.

Question 6Boiler Construction, Design, and Fittings

A fusible plug is installed in a boiler to:

  1. Prevent backflow of feedwater
  2. Relieve pressure when steam demand drops
  3. Indicate the steam temperature
  4. Warn of low water by melting and releasing steam or water into the furnace Correct answer.

Explanation

The fusible plug contains a low-melting alloy that melts when the metal overheats from low water, releasing steam or water to alert the operator and reduce the hazard. It is a low-water warning device, not a pressure or temperature control.

Question 7Boiler Construction, Design, and Fittings

Water-tube boiler designs are generally preferred over fire-tube designs for:

  1. Systems where the furnace must be submerged in the shell
  2. Applications requiring a large water storage volume
  3. Very low initial cost in small heating plants
  4. High pressure and high steam capacity applications Correct answer.

Explanation

Water-tube boilers contain water in smaller tubes that can be built for higher pressures and larger capacities than fire-tube shells. Fire-tube boilers are typically favored for lower pressures and smaller capacities.

Question 8Boiler Construction, Design, and Fittings

The fitting that prevents boiler water from flowing backward into the feedwater supply is a:

  1. Pressure-reducing valve
  2. Globe valve
  3. Gate valve
  4. Check valve Correct answer.

Explanation

A check valve permits flow in one direction only, protecting the feedwater source from backflow of hot boiler water. Gate and globe valves are manually operated and do not stop reverse flow on their own.

Question 9Boiler Construction, Design, and Fittings

A boiler is rated at 500 boiler horsepower. What is the approximate equivalent heat output in Btu/hr?

  1. 33,450 Btu/hr
  2. 16,700,000 Btu/hr Correct answer.
  3. 5,000,000 Btu/hr
  4. 1,670,000 Btu/hr

Explanation

One boiler horsepower is defined as 33,450 Btu/hr of heat output. Multiplying 500 by 33,450 gives about 16,725,000 Btu/hr, which rounds to 16,700,000 Btu/hr.

Question 10Boiler Construction, Design, and Fittings

A safety valve on a boiler is set to open at 150 psig. The maximum allowable working pressure is 150 psig. Which arrangement satisfies standard practice?

  1. A safety valve set at 150 psig plus a plugged second opening
  2. A single safety valve set at 155 psig
  3. One or more safety valves with total capacity set to relieve at or below 150 psig Correct answer.
  4. A safety valve set at 165 psig with a rupture disc

Explanation

Safety valves must be set to open at or below the maximum allowable working pressure and must have enough relieving capacity to prevent pressure from rising above the permitted accumulation. Setting a valve above the working pressure defeats the protection.

Question 11Boiler Construction, Design, and Fittings

A boiler drum has an inside diameter of 60 inches and a straight shell length of 12 feet. What is the approximate volume of the shell in cubic feet?

  1. 157 cu ft
  2. 236 cu ft Correct answer.
  3. 942 cu ft
  4. 314 cu ft

Explanation

The radius is 30 inches, or 2.5 feet. Using volume equal to pi times radius squared times length: 3.1416 times 6.25 times 12 equals about 236 cubic feet.

Question 12Boiler Construction, Design, and Fittings

The primary reason a boiler is fitted with a bottom blowdown valve is to:

  1. Remove concentrated dissolved solids and sludge from the lowest part of the boiler Correct answer.
  2. Increase the feedwater temperature
  3. Provide a second path for steam leaving the drum
  4. Control steam temperature

Explanation

Bottom blowdown discharges water from the lowest point where sludge and concentrated solids collect, controlling dissolved solids and preventing carryover. It does not affect steam temperature directly or heat feedwater.

Question 13Boiler Construction, Design, and Fittings

A pressure gauge on a steam boiler should be connected:

  1. To the water column below the gauge glass drain
  2. Directly to the steam space with no accessory
  3. To the feedwater line downstream of the check valve
  4. Through a siphon or pigtail loop that traps condensate Correct answer.

Explanation

A siphon loop fills with condensate and keeps live steam from reaching the gauge mechanism, protecting it from high temperature. The gauge still senses drum pressure through the loop.

Question 14Boiler Construction, Design, and Fittings

A boiler is described as having a 'wet-back' reversal chamber. This means the reversal chamber is:

  1. Refractory-lined and dry on the gas side
  2. Surrounded by water on its gas-side surface Correct answer.
  3. Externally insulated with no water contact
  4. Cooled only by combustion air

Explanation

A wet-back design places the turnaround chamber in contact with boiler water, which improves heat transfer and reduces refractory maintenance compared with a dry-back arrangement.

Question 15Boiler Construction, Design, and Fittings

A boiler operator observes that the gauge glass shows a normal level, but the low-water cutoff has tripped. Which condition should be investigated first?

  1. The burner nozzle is worn
  2. The feedwater pump is oversized
  3. The steam pressure is too low
  4. The gauge glass connections are clogged, giving a false reading Correct answer.

Explanation

A clogged gauge glass connection can trap water and display a false level while the actual drum level is low, which would explain a legitimate low-water trip. The glass should be blown down and proven clear before assuming the cutoff is faulty.

Question 16Boiler Construction, Design, and Fittings

The water column attached to a boiler serves to:

  1. Dampen level fluctuations and provide a stilling point for level controls and the gauge glass Correct answer.
  2. Separate moisture from steam before the superheater
  3. Increase steam storage capacity
  4. Preheat feedwater before it enters the drum

Explanation

The water column provides a calm column of water so that level devices read a steady value rather than the turbulent surface inside the drum. It also provides mounting points for the gauge glass and level controls.

Question 17Boiler Construction, Design, and Fittings

A boiler is to be fitted with two safety valves. Which arrangement of set pressures is typical for a boiler with a maximum allowable working pressure of 200 psig?

  1. One valve set at 200 psig and one set slightly higher within the permitted accumulation Correct answer.
  2. Both valves set at 180 psig with no capacity calculation
  3. Both valves set at 210 psig
  4. One valve set at 150 psig and one at 250 psig

Explanation

Standard practice sets the first valve at or below the maximum allowable working pressure and permits additional valves to be set somewhat higher within the allowed accumulation, so the total capacity protects the boiler.

Question 18Boiler Construction, Design, and Fittings

Which fitting is required to protect a boiler from overpressure caused by a failure of the pressure-reducing valve on a superheated steam supply?

  1. An additional check valve on the feedwater line
  2. An extra blowdown valve
  3. A larger gauge glass
  4. A safety valve on the low-pressure side of the reducing station Correct answer.

Explanation

When a reducing valve fails open, high-pressure steam can enter the lower-pressure side. A safety valve sized for that side relieves the overpressure and protects the downstream equipment.

Question 19Boiler Construction, Design, and Fittings

A boiler's steam drum is fitted with an internal feedwater distributing pipe. Its purpose is to:

  1. Increase the steam velocity leaving the drum
  2. Provide a mounting point for the safety valve
  3. Inject feedwater away from the gauge glass connections and mix it with drum water to reduce thermal shock Correct answer.
  4. Measure the drum water level

Explanation

The feedwater distributor introduces cooler feedwater along the drum length and away from level fittings, promoting mixing and limiting localized thermal stress. It does not increase steam velocity or measure level.

Question 20Boiler Construction, Design, and Fittings

A fire-tube boiler has a shell outside diameter of 72 inches, a wall thickness of 0.5 inch, and a design pressure of 150 psi. Using the hoop-stress relationship for a thin cylindrical shell, what is the approximate longitudinal seam stress?

  1. 2,700 psi
  2. 10,800 psi
  3. 5,400 psi Correct answer.
  4. 1,350 psi

Explanation

For a thin cylinder, the hoop stress equals pressure times inside diameter divided by twice the thickness. The inside diameter is 72 minus 1, or 71 inches; 150 times 71 divided by 1.0 gives about 10,650 psi, and the longitudinal stress is half the hoop stress, about 5,400 psi.

Question 21Boiler Construction, Design, and Fittings

A boiler is rated at 20,000 lb/hr of steam at 100 percent rating. If the boiler produces 15,000 lb/hr, what is the approximate percentage of rating?

  1. 75 percent Correct answer.
  2. 80 percent
  3. 133 percent
  4. 60 percent

Explanation

Percentage of rating equals actual output divided by rated output times 100. Dividing 15,000 by 20,000 gives 0.75, or 75 percent of rating.

Question 22Boiler Construction, Design, and Fittings

A water-tube boiler shows a steam drum, a mud drum, and generating tubes connecting them. The mud drum primarily:

  1. Provides the mounting surface for the safety valve
  2. Houses the burner and combustion air fan
  3. Stores superheated steam for peak demand
  4. Collects sludge and provides a lower distribution header for the generating tubes Correct answer.

Explanation

The mud drum sits at the bottom of the generating circuit, where solids settle and can be blown down, and it distributes water to the tube bank. It does not store superheated steam or house the burner.

Question 23Boiler Construction, Design, and Fittings

Two identical boilers operate in parallel. One is fitted with a feedwater regulator that responds to drum level only, while the other responds to level with a steam-flow feedforward signal. During a sudden large steam demand increase, which behavior is expected?

  1. The feedforward regulator will not respond until level deviates
  2. Both regulators will behave identically because level is the controlled variable
  3. The feedforward regulator will begin adding feedwater sooner, reducing level swell and shrink effects Correct answer.
  4. The level-only regulator will respond faster and more accurately

Explanation

A feedforward signal from steam flow lets the regulator anticipate the feedwater requirement before the level deviates, improving response to sudden demand changes and reducing swell and shrink effects. A level-only regulator must wait for a measurable level error.

Question 24Boiler Construction, Design, and Fittings

A boiler shell is made from plate rolled and joined by a longitudinal seam. Why is the longitudinal seam typically required to be stronger, or at least as strong, as the circumferential seam?

  1. Circumferential seams are only for alignment
  2. Circumferential seams carry no pressure load
  3. The longitudinal seam is exposed to higher temperature
  4. The longitudinal seam carries approximately twice the stress of the circumferential seam Correct answer.

Explanation

In a thin cylindrical shell under internal pressure, the hoop stress acting on the longitudinal seam is about twice the longitudinal stress acting on the circumferential seam. The longitudinal seam must therefore resist the higher stress.

Question 25Boiler Construction, Design, and Fittings

An operator finds that a safety valve on a boiler has been gagged. What is the correct action and rationale?

  1. Remove the gag immediately and place the boiler in a safe condition, because a gagged valve cannot relieve overpressure Correct answer.
  2. Leave it gagged until the next scheduled outage to avoid nuisance trips
  3. Replace the safety valve with a pressure gauge
  4. Loosen the gag slightly so the valve can open at a higher pressure

Explanation

A gag holds a safety valve closed and defeats the boiler's final overpressure protection, so it must be removed and the boiler secured until the valve is proven functional. Operating with a gagged valve creates an immediate hazard.

Question 26Boiler Construction, Design, and Fittings

The main steam stop valve on a boiler is typically mounted on which part of the boiler?

  1. The mud drum at the lowest point
  2. The feedwater inlet line near the check valve
  3. The bottom blowdown header
  4. The highest point of the steam drum or shell Correct answer.

Explanation

The main steam stop valve is located at the highest point of the steam space so that the driest steam is drawn off and condensate does not collect at the valve. Mounting it at the top of the drum or shell also keeps it clear of water level surges.

Question 27Boiler Construction, Design, and Fittings

A boiler is fitted with a spring-loaded safety valve. Which component determines the pressure at which the valve begins to open?

  1. The compression of the spring Correct answer.
  2. The diameter of the discharge pipe
  3. The temperature of the steam
  4. The adjusting ring position

Explanation

The spring load balances the steam force on the disc, so changing spring compression changes the set pressure at which the valve lifts. Adjusting rings affect blowdown and simmer, and discharge piping must be sized so it does not influence set pressure.

Question 28Boiler Construction, Design, and Fittings

A boiler is equipped with a water column and gauge glass. The lower connection of the water column becomes plugged with scale while the upper connection stays clear. What will the gauge glass most likely indicate?

  1. A level that remains steady while the true drum level falls Correct answer.
  2. A level that rises steadily as the boiler is fired
  3. A level that drops immediately to the bottom of the glass
  4. A level that fluctuates violently with each burner cycle

Explanation

The gauge glass reflects the pressure difference between its two connections. If the lower water connection is plugged, steam pressure can push water up and hold a false high level, so the glass can read steady or high while the actual water level drops. This is why water column connections must be blown down and kept clear.

Question 29Boiler Construction, Design, and Fittings

A boiler is to be fitted with a main steam stop valve and a feedwater check valve. Which statement correctly describes the required arrangement of these two fittings?

  1. The steam stop valve controls outflow and the feedwater check valve permits flow in one direction only Correct answer.
  2. Both valves must be of the gate type to allow full flow
  3. Both valves must be installed on the steam drum
  4. The steam stop valve must be a check valve and the feedwater valve a globe valve

Explanation

The main steam stop valve is a manually operated valve that isolates or regulates steam leaving the boiler, while the feedwater check valve is a one-way valve that prevents boiler water from flowing back into the feed line. Each fitting performs a distinct function and is selected for that duty.

Question 30Boiler Construction, Design, and Fittings

A fire-tube boiler shell is built with a longitudinal riveted seam and a circumferential riveted seam. Under internal pressure, which seam carries the higher unit stress and therefore needs the greater joint efficiency?

  1. The longitudinal seam, because it resists the hoop stress Correct answer.
  2. The circumferential seam, because it resists the end thrust
  3. The seam nearest the fired end, because it is hottest
  4. Both seams carry equal stress because pressure acts equally in all directions

Explanation

Internal pressure produces hoop stress around the circumference, which acts on the longitudinal seam, and this stress is twice the longitudinal stress acting on circumferential seams. The longitudinal seam therefore governs shell thickness and requires the higher joint efficiency.

Question 31Boiler Accessories and Safety Devices

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

  1. To preheat combustion air before it enters the furnace
  2. To add feedwater when the level drops
  3. To release pressure automatically before it exceeds the maximum allowable working pressure Correct answer.
  4. To drain water from the boiler during blowdown

Explanation

A safety valve is the final overpressure protection device; it opens automatically at its set pressure to discharge steam and prevent the boiler from exceeding its maximum allowable working pressure. It is not a level or water-handling device and does not affect combustion air.

Question 32Boiler Accessories and Safety Devices

A boiler operator notices the water level in the gauge glass is dropping steadily and the low-water cutoff has not yet tripped. What is the correct immediate action?

  1. Increase the firing rate to raise steam output
  2. Verify the actual level and restore feedwater before the level reaches the cutoff point Correct answer.
  3. Open the bottom blowdown valve to lower the level further
  4. Ignore it because the low-water cutoff will handle it

Explanation

A falling level must be confirmed and corrected promptly by restoring feedwater; relying on the low-water cutoff as an operating control is unsafe because it is a protective last resort. Raising firing or blowing down would worsen the condition.

Question 33Boiler Accessories and Safety Devices

The low-water fuel cutoff on a steam boiler is designed primarily to:

  1. Maintain a constant steam pressure
  2. Regulate the feedwater flow to the boiler
  3. Automatically restart the burner after a flame failure
  4. Shut off the fuel and burner when the water level falls below a safe point Correct answer.

Explanation

The low-water fuel cutoff is a safety device that stops combustion when the water level drops below the safe minimum, preventing overheating and possible explosion. It does not regulate feedwater, pressure, or flame restart.

Question 34Boiler Accessories and Safety Devices

What is the purpose of the try cocks on a boiler water column?

  1. To sample steam quality for purity testing
  2. To measure the boiler's internal pressure
  3. To provide a manual backup check of water level if the gauge glass fails Correct answer.
  4. To vent air from the boiler during startup

Explanation

Try cocks are manually operated valves at the water column that let the operator confirm water level by observation when the gauge glass is broken or unreliable. They do not measure pressure, vent air, or test steam purity.

Question 35Boiler Accessories and Safety Devices

A pressure gauge on a steam boiler should be connected to the boiler by:

  1. A direct rigid pipe with no isolation valve
  2. A flexible hose rated for water only
  3. A siphon (pigtail) and a shutoff valve Correct answer.
  4. A line shared with the safety valve

Explanation

The gauge is connected through a siphon loop, which traps condensate to protect the Bourdon tube from high-temperature steam, and a shutoff valve for isolation. A shared or unprotected connection is unsafe.

Question 36Boiler Accessories and Safety Devices

The main steam stop valve is normally located:

  1. On the feedwater line before the economizer
  2. At the bottom of the mud drum
  3. On the combustion air duct
  4. Between the boiler and the main steam header Correct answer.

Explanation

The main steam stop valve isolates the boiler from the plant steam header and is located on the main steam outlet. Feedwater, blowdown, and air duct components serve other functions.

Question 37Boiler Accessories and Safety Devices

A feedwater regulator's function is to:

  1. Control the fuel-to-air ratio
  2. Limit the maximum steam pressure
  3. Discharge excess steam to atmosphere
  4. Maintain the boiler water level within the desired range by modulating feedwater flow Correct answer.

Explanation

The feedwater regulator modulates feedwater flow to hold the drum level at setpoint, commonly using a level signal (single- or three-element control). Fuel/air ratio, pressure limiting, and steam discharge are separate functions.

Question 38Boiler Accessories and Safety Devices

Which device prevents steam from escaping through the feedwater line and protects the feedwater system from backflow of steam?

  1. The economizer bypass valve
  2. The steam separator
  3. The air preheater
  4. The feed check valve and feed stop valve arrangement Correct answer.

Explanation

The feed check valve permits flow only into the boiler and blocks reverse flow of steam or hot water back into the feedwater line; the feed stop valve provides isolation. The other devices serve different purposes.

Question 39Boiler Accessories and Safety Devices

The purpose of a bottom blowdown valve is to:

  1. Add chemicals to the boiler water
  2. Remove dissolved gases from the feedwater
  3. Discharge water and sludge from the lowest point of the boiler to control dissolved solids and sediment Correct answer.
  4. Reduce steam pressure during peak demand

Explanation

Bottom blowdown removes sludge and sediment and helps control dissolved solids concentration in the boiler water. It does not deaerate, reduce steam pressure, or dose chemicals.

Question 40Boiler Accessories and Safety Devices

A boiler is equipped with both a slow-opening and a quick-opening blowdown valve in series. Which arrangement is correct?

  1. Slow-opening valve nearest the boiler, quick-opening valve downstream Correct answer.
  2. Only the quick-opening valve is required
  3. Both valves must be the same type
  4. Quick-opening valve nearest the boiler, slow-opening valve downstream

Explanation

The slow-opening (screw) valve is placed next to the boiler so it can be opened gradually against full pressure, while the quick-opening valve downstream provides rapid full-flow operation. This sequence protects piping and the operator.

Question 41Boiler Accessories and Safety Devices

What is the primary purpose of a flame safeguard control on a boiler burner?

  1. To prove the presence of flame and shut off fuel if flame is not established or is lost Correct answer.
  2. To monitor the stack temperature
  3. To regulate the steam pressure setpoint
  4. To control the feedwater level

Explanation

The flame safeguard programmer supervises the burner sequence, proves flame with a scanner, and closes the fuel valves on flame failure or failure to light. Pressure, level, and stack temperature are handled by other controls.

Question 42Boiler Accessories and Safety Devices

During a burner startup sequence, the purpose of the prepurge is to:

  1. Drive out combustible gases from the furnace and flue before ignition Correct answer.
  2. Test the low-water cutoff
  3. Pressurize the fuel oil line
  4. Warm the boiler water before firing

Explanation

Prepurge introduces air through the furnace and flue for a set time to purge any accumulated combustible gases, preventing a furnace explosion at light-off. It does not warm water, test level devices, or pressurize fuel lines.

Question 43Boiler Accessories and Safety Devices

A flame scanner on a burner fails to detect flame during the trial-for-ignition period. The flame safeguard should:

  1. Increase the fuel supply to establish flame
  2. Open the main steam stop valve
  3. Continue firing for another full cycle
  4. Close the fuel valves and lock out the burner until reset Correct answer.

Explanation

If flame is not proven within the trial-for-ignition time, the programmer must shut off fuel and go to lockout to prevent unburned fuel accumulation. The operator then investigates before resetting.

Question 44Boiler Accessories and Safety Devices

What is the function of an economizer in a boiler system?

  1. To remove moisture from steam before it reaches the turbine
  2. To store steam for peak demand
  3. To preheat boiler feedwater using heat from the exiting flue gas Correct answer.
  4. To cool the combustion air supply

Explanation

An economizer recovers sensible heat from the flue gas to preheat feedwater, improving overall efficiency. Moisture removal, air cooling, and steam storage are handled by other equipment.

Question 45Boiler Accessories and Safety Devices

An air preheater on a boiler recovers heat from flue gas to:

  1. Heat the incoming combustion air, improving combustion efficiency Correct answer.
  2. Heat the feedwater before it enters the economizer
  3. Cool the boiler water during low-fire operation
  4. Pressurize the fuel oil supply

Explanation

The air preheater transfers heat from the flue gas to combustion air, raising furnace temperature and improving efficiency. Feedwater heating is the economizer's role, and the other functions are unrelated.

Question 46Boiler Accessories and Safety Devices

A deaerator in the feedwater system primarily removes:

  1. Scale from the boiler tubes
  2. Dissolved oxygen and other noncondensable gases from feedwater Correct answer.
  3. Suspended solids by filtration
  4. Excess boiler water during high level

Explanation

The deaerator heats feedwater and strips dissolved oxygen and other gases to reduce corrosion in the boiler and feedwater system. It does not filter solids, remove water, or descale tubes.

Question 47Boiler Accessories and Safety Devices

Why must the gauge glass blowdown (drain) valve be opened carefully during a gauge glass cleaning procedure?

  1. To prevent steam and hot water from injuring the operator and to avoid damaging the glass Correct answer.
  2. To test the safety valve setpoint
  3. To increase the boiler firing rate
  4. To avoid tripping the main circuit breaker

Explanation

Opening the drain valve on a hot gauge glass releases high-temperature steam and water; careful operation with proper PPE prevents burns and thermal shock to the glass. It has no bearing on electrical breakers, firing rate, or safety valve setpoint.

Question 48Boiler Accessories and Safety Devices

The operating pressure control on a boiler is set to cut the burner off at a pressure below the safety valve setpoint. Why is this arrangement required?

  1. To allow the boiler to exceed its maximum allowable working pressure briefly
  2. To ensure the safety valve never operates during normal service Correct answer.
  3. To reduce the feedwater temperature
  4. To increase the safety valve's relieving capacity

Explanation

The operating control cycles the burner to hold pressure below the safety valve setpoint so the safety valve remains a last-resort device and does not seat-leak from frequent operation. It does not change valve capacity, permit overpressure, or affect feedwater temperature.

Question 49Boiler Accessories and Safety Devices

A high-pressure limit control on a boiler differs from the operating pressure control in that the high limit:

  1. Controls the draft fan speed
  2. Cycles the burner on and off during normal operation
  3. Provides a manual reset safety shutdown if pressure exceeds a set limit Correct answer.
  4. Regulates feedwater flow

Explanation

The high-pressure limit is a protective device that trips the burner and requires manual reset, while the operating control cycles the burner during normal service. Feedwater and draft control are separate systems.

Question 50Boiler Accessories and Safety Devices

The fusible plug in a fire-tube boiler is intended to:

  1. Automatically add water when the level is low
  2. Melt and release steam/water to warn of low water or overheating of the crown sheet Correct answer.
  3. Provide a permanent pressure relief path
  4. Indicate steam temperature

Explanation

The fusible plug has a low-melting alloy that melts when the metal around it overheats, typically from low water, releasing steam/water as a warning and cooling effect. It is not a pressure relief device, thermometer, or automatic feeder.