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High Risk Work Licence - Standard Boiler (BS) study materials
High Risk Work Licence - Standard Boiler (BS) study resources

High Risk Work Licence - Standard Boiler (BS) practice questions

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Question 1Boiler construction, types and terminology

In a standard fire-tube boiler, which component carries the hot combustion gases through the water space?

  1. The superheater header and attemperator
  2. The economiser and air preheater
  3. The steam drum and downcomers
  4. The furnace tube and fire tubes Correct answer.

Explanation

A fire-tube boiler is defined by hot gases passing inside tubes that are surrounded by water, so the furnace tube and the bank of fire tubes are the gas-side passages. The water surrounds these tubes and absorbs heat through their walls. Components such as economisers and superheaters are separate heat-recovery or steam-conditioning items, not the defining gas passages.

Question 2Boiler construction, types and terminology

Which statement correctly describes the pressure limitation that generally applies to fire-tube boilers compared with water-tube boilers?

  1. Fire-tube boilers are limited to lower pressures because steam cannot form inside a shell
  2. Fire-tube boilers are generally limited to lower pressures because the shell is a large pressure vessel Correct answer.
  3. Fire-tube boilers have no pressure limit provided the tubes are seamless
  4. Fire-tube boilers can safely operate at any pressure because the tubes are in compression

Explanation

In a fire-tube boiler the entire outer shell contains steam at working pressure and is a large-diameter pressure vessel, so shell thickness and cost rise steeply with pressure. This is why fire-tube designs are generally used at lower pressures than water-tube designs, where pressure is contained in smaller tubes. The limit is a structural and economic one, not a thermodynamic one.

Question 3Boiler construction, types and terminology

What is the main purpose of a superheater in a boiler?

  1. To remove dissolved oxygen from the feedwater before it enters the drum
  2. To reduce the pressure of steam before it reaches the turbine
  3. To preheat combustion air using heat from the flue gas
  4. To raise steam temperature above saturation temperature at the same pressure Correct answer.

Explanation

A superheater adds heat to saturated steam at essentially constant pressure, raising its temperature above the saturation value for that pressure. Superheated steam contains more available energy and condenses less readily in the turbine. Deaeration, air preheating and pressure reduction are functions of other equipment.

Question 4Boiler construction, types and terminology

A boiler is described as having a 'D-type' arrangement. Which feature characterises this water-tube configuration?

  1. A horizontal cylindrical shell with the furnace tube running along its axis
  2. A large furnace on one side and a convection bank on the other, enclosed by flat tube walls Correct answer.
  3. A vertical cylindrical shell with a cross-tube grate at the base
  4. A single central furnace surrounded symmetrically by an annular tube nest

Explanation

The D-type or bi-drum water-tube boiler has a refractory-lined or membrane-walled furnace on one side and a convection tube bank on the other, giving a D-shaped cross section. Two drums are connected by generating tubes and water walls. The other descriptions match fire-tube or vertical shell designs.

Question 5Boiler construction, types and terminology

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

  1. To burn fuel and direct the flame into the furnace
  2. To store solid fuel ready for the stoker
  3. To cool the flue gas before it reaches the chimney
  4. To separate steam from water and provide a reservoir for circulation and feedwater control Correct answer.

Explanation

The steam drum sits at the top of the circulation circuit and allows steam to separate from the water before leaving the boiler. It also holds a water reserve that buffers feedwater fluctuations and provides space for chemical dosing and blowdown connections. Combustion and gas cooling occur elsewhere.

Question 6Boiler construction, types and terminology

A boiler component described as an 'economiser' primarily recovers heat from which source?

  1. Combustion air entering the burner, used to preheat fuel
  2. Blowdown water, used to preheat the furnace
  3. Flue gas leaving the boiler, used to preheat feedwater Correct answer.
  4. Steam leaving the superheater, used to reheat feedwater

Explanation

An economiser is a heat exchanger in the flue gas path after the boiler surfaces that transfers residual heat to the incoming feedwater. This lowers the stack temperature and improves overall efficiency. Air preheaters and blowdown heat recovery are separate systems.

Question 7Boiler construction, types and terminology

Why is a fusible plug fitted in the crown sheet of some shell boilers?

  1. To melt and shut off the fuel supply when the steam demand rises
  2. To melt and add water to the boiler if the pressure falls too low
  3. To melt and open the safety valve if the boiler is overfired
  4. To melt and release steam into the furnace if the crown sheet is uncovered by water Correct answer.

Explanation

A fusible plug contains a low-melting alloy that fails when the metal around it overheats, which happens if the crown sheet loses water cover. The failure releases steam and water into the furnace, giving a loud warning and helping to cool the plate. It is a last-resort protection against overheating, not a normal control device.

Question 8Boiler construction, types and terminology

Which term describes the water-and-steam mixture circuit that relies on density differences to move water through a boiler without a pump?

  1. Once-through flow
  2. Natural circulation Correct answer.
  3. Positive displacement
  4. Forced circulation

Explanation

Natural circulation occurs because the steam-water mixture in the heated tubes is less dense than the water in the downcomers, producing a driving head. This density difference keeps water moving around the circuit without a circulation pump. Forced circulation uses a pump and once-through designs have no recirculating drum circuit.

Question 9Boiler construction, types and terminology

What does the term 'saturation temperature' mean for water at a given pressure?

  1. The temperature at which water boils and steam condenses at that pressure Correct answer.
  2. The temperature at which the safety valve is set to lift
  3. The temperature at which water has its maximum density
  4. The temperature at which dissolved solids begin to precipitate

Explanation

At any given pressure, saturation temperature is the boiling point of water and equally the condensation temperature of steam. Adding heat at constant pressure converts saturated water to saturated steam without changing temperature. Maximum density, precipitation and valve set points are unrelated concepts.

Question 10Boiler construction, types and terminology

A boiler gauge glass shows the water level at the bottom of the visible range while the plant is steaming normally. What is the most appropriate interpretation?

  1. The drum water level is dangerously low and immediate action is required Correct answer.
  2. The boiler is operating at maximum efficiency
  3. The level is normal because the glass is only for pressure indication
  4. The gauge glass is simply reading the level of the steam space

Explanation

The gauge glass is a direct indication of the water level in the drum, and a reading at the bottom of the visible range indicates a low-water condition that threatens the heated surfaces. Immediate action is needed to confirm the reading and protect the boiler. A gauge glass never indicates pressure, and a low reading is never a sign of good efficiency.

Question 11Boiler construction, types and terminology

What is the purpose of the crown sheet in a locomotive-type or firebox boiler?

  1. It forms the top of the firebox and is directly exposed to radiant heat from the fire Correct answer.
  2. It separates the steam space from the superheater header
  3. It supports the boiler shell on the foundation frame
  4. It forms the bottom of the chimney and supports the blast pipe

Explanation

The crown sheet is the upper plate of the firebox and is exposed to radiant heat from the fuel bed, with water on its upper side. It must remain covered by water to avoid overheating, which is why crown sheet level is critical. Chimney, superheater and support functions belong to other parts.

Question 12Boiler construction, types and terminology

In boiler terminology, what is 'blowdown'?

  1. The purging of fuel gas from the burner before ignition
  2. Deliberate discharge of water from the boiler to control dissolved solids and sludge Correct answer.
  3. The draining of condensate from the steam mains
  4. The release of steam through the safety valve during overpressure

Explanation

Blowdown is the controlled release of boiler water to remove concentrated dissolved solids and settled sludge, protecting against foaming, carryover and scale. Bottom blowdown removes sludge while surface blowdown controls dissolved solids concentration. Safety valve discharge, burner purging and condensate drainage are separate operations.

Question 13Boiler construction, types and terminology

Which design feature distinguishes a water-tube boiler from a fire-tube boiler?

  1. Hot gas is inside the tubes and water surrounds them
  2. The furnace is always immersed in a separate water bath outside the shell
  3. Water is inside the tubes and hot gas surrounds them Correct answer.
  4. Both water and gas pass through a single large tube

Explanation

In a water-tube boiler, water and steam flow inside the tubes while hot combustion gas passes over the outside of the tubes. This is the reverse of the fire-tube arrangement, where gas is inside the tubes and water surrounds them. The naming always refers to what is inside the tubes.

Question 14Boiler construction, types and terminology

What is the role of the furnace in a boiler?

  1. To cool and condense exhaust steam returning from the plant
  2. To store the steam produced until demand arises
  3. To provide the combustion space where fuel burns and heat is released to the surrounding surfaces Correct answer.
  4. To filter suspended solids from the feedwater

Explanation

The furnace is the combustion chamber where fuel and air react to release heat, and its walls and exit pass that heat to the water or steam circuits. Its volume and shape affect combustion completion and flame stability. Steam storage, steam condensation and water filtration belong to other equipment.

Question 15Boiler construction, types and terminology

A boiler is fitted with a superheater that is described as 'convection type'. Where is it normally located?

  1. In the steam line after the main stop valve
  2. In the flue gas path downstream of the furnace, where gas flow over the tubes dominates heat transfer Correct answer.
  3. Inside the furnace, directly facing the flame and radiant heat
  4. In the feedwater line before the economiser

Explanation

A convection superheater is placed in the gas path where the gas flows across its tubes, so heat transfer is dominated by convection from the gas. Radiant superheaters are placed in the furnace where they receive direct radiation. Placing a superheater in the feedwater or downstream of the stop valve would defeat its purpose.

Question 16Boiler construction, types and terminology

What is meant by the 'heating surface' of a boiler?

  1. The area of the grate on which solid fuel burns
  2. The floor area occupied by the boiler house
  3. The internal volume of the steam drum available for steam storage
  4. The total area of the surfaces on one side of which heat passes to the water or steam Correct answer.

Explanation

Heating surface is the measured area of tubes, plates and other surfaces through which heat is transferred to the working fluid. It is a key measure of a boiler's evaporative capacity and is quoted as a defined area. Grate area, drum volume and floor area are different quantities.

Question 17Boiler construction, types and terminology

Why are water walls used in the furnace of a water-tube boiler?

  1. They provide a path for flue gas to bypass the superheater
  2. They absorb radiant heat and protect the furnace structure from high temperatures Correct answer.
  3. They increase the pressure rating of the steam drum
  4. They store water to supply the boiler during shutdown

Explanation

Water walls are tubes lining the furnace that absorb intense radiant heat from the flame, generating steam and lowering furnace exit gas temperature. This protects the refractory and structure and improves efficiency. They do not change drum pressure rating, bypass gas, or act as shutdown storage.

Question 18Boiler construction, types and terminology

A boiler is described as 'packaged'. What does this term indicate?

  1. The unit is built on site from loose plates and tubes
  2. The unit uses only solid fuel fired on a chain grate
  3. The unit is factory-assembled and delivered as a complete unit ready for connection Correct answer.
  4. The unit has no pressure vessel and operates at atmospheric pressure

Explanation

A packaged boiler is assembled and tested at the factory, then transported as a complete or near-complete unit for rapid site installation. This reduces site work and commissioning time compared with site-erected boilers. It says nothing about pressure rating or fuel type.

Question 19Boiler construction, types and terminology

What is the function of downcomers in a natural circulation water-tube boiler?

  1. They carry cooler water from the drum to the lower headers to feed the heated tubes Correct answer.
  2. They vent combustion gas from the furnace to the chimney
  3. They carry steam from the drum to the superheater outlet
  4. They drain condensate from the steam mains back to the feed tank

Explanation

Downcomers are unheated or lightly heated pipes that take relatively cool water from the steam drum down to the lower headers. From there the water rises through heated generating tubes, and the density difference between the two legs drives natural circulation. They do not carry steam, condensate or flue gas.

Question 20Boiler construction, types and terminology

Which boiler type has a furnace tube running longitudinally through a cylindrical shell, often with a corrugated section to allow for expansion?

  1. D-type water-tube boiler
  2. Locomotive-type or Cornish-type shell boiler Correct answer.
  3. Once-through forced circulation boiler
  4. Vertical cross-tube boiler

Explanation

Locomotive and Cornish type shell boilers contain a longitudinal furnace tube within a cylindrical shell, and corrugations accommodate differential expansion. The D-type is a water-tube design, once-through units have no large shell, and vertical cross-tube boilers have a different orientation.

Question 21Boiler construction, types and terminology

What is the purpose of the steam space above the water level in a boiler drum?

  1. To allow steam to separate from water droplets and to accommodate level fluctuations Correct answer.
  2. To house the burner and ignition equipment
  3. To store feedwater for the next shift
  4. To contain the superheater tubes

Explanation

The steam space provides residence time and a large area for gravity separation of water droplets from steam, reducing carryover. It also gives room for the water level to rise and fall without wetting the steam outlet. Feedwater storage, burner housing and superheater location are separate.

Question 22Boiler construction, types and terminology

A boiler nameplate states a 'design pressure' of 1200 kPa. What does this value represent?

  1. The pressure at which the safety valve must be removed for testing
  2. The normal operating pressure at which the boiler is always run
  3. The pressure of the feedwater pump discharge
  4. The maximum pressure the boiler is designed to withstand under its approval conditions Correct answer.

Explanation

Design pressure is the maximum pressure used in the mechanical design of the pressure parts and is the basis for approval and safety valve setting. Normal operating pressure is usually below the design pressure, and safety valves are set at or below the approved limit. Feedwater pump discharge pressure is a separate system value.

Question 23Boiler construction, types and terminology

Which statement best explains why a corrugated furnace tube is used in some shell boilers?

  1. The corrugations increase the tube's resistance to internal steam pressure only
  2. The corrugations provide flexibility to absorb thermal expansion and improve heat transfer Correct answer.
  3. The corrugations prevent water from entering the furnace tube
  4. The corrugations allow the tube to be rolled into the shell without welding

Explanation

A corrugated furnace tube acts like a flexible bellows, accommodating the differential expansion between the hot furnace tube and the cooler shell. The corrugations also disturb gas flow and increase surface area, improving heat transfer. They are not primarily a pressure-strength, fixing or water-exclusion feature.

Question 24Boiler construction, types and terminology

In a boiler with a two-drum water-tube arrangement, what is the usual function of the lower drum?

  1. It separates steam from water before the superheater
  2. It stores superheated steam for the turbine
  3. It acts as a water header that distributes water to the generating tubes and collects sludge for blowdown Correct answer.
  4. It preheats combustion air before the burner

Explanation

The lower drum of a two-drum boiler serves as a water header, receiving cooler water from the downcomers and distributing it to the generating tubes. Sludge tends to settle there, so it is fitted with blowdown connections. Steam separation occurs in the upper drum, and air preheating is separate.

Question 25Boiler fittings, valves, gauges and safety devices

On a standard boiler, what is the primary function of the safety valve?

  1. To release steam automatically when pressure exceeds the set limit Correct answer.
  2. To isolate the boiler from the plant steam main on shutdown
  3. To regulate the feedwater flow into the boiler drum
  4. To drain condensate from the steam header during warm-up

Explanation

The safety valve is the final overpressure protection device on the boiler. It opens automatically at its set pressure to discharge steam and prevent the boiler pressure from rising above the design limit, then reseats as pressure falls. It is not used for routine control of steam flow, condensate removal or feedwater regulation.

Question 26Boiler fittings, valves, gauges and safety devices

A boiler has two independently mounted safety valves. What is the standard requirement for their set pressures?

  1. Both valves must be set at exactly the same pressure
  2. The lower-set valve must be set no higher than the design pressure and the other slightly above it Correct answer.
  3. Only one valve needs setting; the second acts as a spare
  4. Both valves must be set above the design pressure to avoid nuisance lifting

Explanation

Where multiple safety valves are fitted, one valve is set at or below the boiler design pressure so it protects the vessel, and the remaining valve or valves are set slightly above that figure but still within the permitted accumulation. Setting both identically causes them to lift together and chatter, while setting both above design pressure defeats the protection.

Question 27Boiler fittings, valves, gauges and safety devices

What does the water level gauge glass on a boiler indicate to the operator?

  1. The temperature of the feedwater entering the drum
  2. The steam pressure inside the boiler drum
  3. The level of water inside the boiler drum Correct answer.
  4. The rate of steam leaving the superheater

Explanation

The gauge glass is connected to the steam space and water space of the drum so that the water finds its own level in the glass. It therefore gives a direct visual indication of the water level in the boiler, which is critical for safe operation. Pressure, temperature and steam flow are shown by separate instruments.

Question 28Boiler fittings, valves, gauges and safety devices

Why are gauge glass fittings on a boiler fitted with isolation cocks and a drain valve?

  1. To permit the boiler to be filled through the gauge glass
  2. To allow the glass to be blown through and isolated for maintenance while the boiler is in service Correct answer.
  3. To provide an additional steam outlet for the safety valve
  4. To allow steam to be sampled for purity testing

Explanation

The top and bottom isolation cocks let the operator shut off the glass from the boiler, and the drain cock lets the glass be blown through to clear blockages and prove the connections are open. This allows routine proving and replacement of the glass without taking the boiler offline. The fittings have no role in steam sampling, filling or safety valve discharge.

Question 29Boiler fittings, valves, gauges and safety devices

What is the purpose of the low-water cutoff device on a boiler?

  1. To sound an alarm only, without affecting combustion
  2. To reduce steam pressure when the water level is high
  3. To add water automatically when the level drops
  4. To cut off the fuel supply when the water level falls to an unsafe point Correct answer.

Explanation

The low-water cutoff is a protective interlock that stops the fuel and combustion air supply when the water level falls below a safe limit. This prevents overheating and catastrophic failure of the boiler due to low water. It is a safety trip, not a level control or pressure control device.

Question 30Boiler fittings, valves, gauges and safety devices

An operator notices the water level in the gauge glass is steady and the glass looks clean, but suspects a blocked water connection. Which action best proves the lower connection is clear?

  1. Open the drain cock after closing both top and bottom cocks
  2. Close the top cock and watch whether the level falls
  3. Close the bottom cock and open the drain cock Correct answer.
  4. Blow down the glass with all cocks open and leave them open

Explanation

Closing the bottom cock and opening the drain cock tests the upper steam connection, while closing the top cock and opening the drain tests the lower water connection. If the water connection is clear, water will flow down and appear at the drain when the top cock is shut. Correct proving sequence checks each connection separately.

Question 31Boiler fittings, valves, gauges and safety devices

What is the normal function of the main steam stop valve on a boiler?

  1. To isolate the boiler from the steam main Correct answer.
  2. To control the boiler pressure automatically
  3. To drain water from the superheater
  4. To act as a non-return valve against backflow

Explanation

The main steam stop valve is a manually operated isolating valve that connects the boiler to the plant steam main. It is used to bring the boiler on line, take it off line and isolate it for maintenance. Pressure control and non-return duties are performed by other devices.

Question 32Boiler fittings, valves, gauges and safety devices

Why is a non-return valve often fitted between the boiler and the steam main?

  1. To measure the quantity of steam leaving the boiler
  2. To prevent steam from the main flowing back into the boiler when the boiler pressure falls Correct answer.
  3. To reduce the steam pressure supplied to the plant
  4. To allow the boiler to be filled with water from the main

Explanation

A non-return valve permits steam to leave the boiler but blocks flow in the reverse direction. If the boiler pressure drops below the main pressure, the valve closes and prevents steam and condensate from the main entering the boiler, which could contaminate it or cause damage. It does not regulate pressure, admit water or meter flow.

Question 33Boiler fittings, valves, gauges and safety devices

A pressure gauge on a boiler is fitted with a siphon (pigtail) tube. What is the purpose of this tube?

  1. To dampen pressure pulsations from the safety valve
  2. To increase the gauge reading for greater accuracy
  3. To protect the gauge mechanism from high-temperature steam by trapping condensate Correct answer.
  4. To allow the gauge to be isolated for calibration without shutting down

Explanation

The siphon loop fills with condensed steam, and this water seal keeps live steam away from the Bourdon tube and mechanism. It protects the gauge from overheating and gives a steadier reading. Isolation for calibration is done by a separate gauge cock.

Question 34Boiler fittings, valves, gauges and safety devices

What does the red line or mark on a boiler pressure gauge indicate?

  1. The pressure at which the feed pump starts
  2. The pressure at which the gauge was last calibrated
  3. The normal operating pressure of the plant
  4. The maximum permissible working pressure of the boiler Correct answer.

Explanation

The gauge is marked with a prominent line at the maximum permissible working pressure so the operator can see at a glance when the boiler is approaching its limit. Normal operating pressure is normally below this mark. Feed pump settings and calibration dates are recorded elsewhere.

Question 35Boiler fittings, valves, gauges and safety devices

A pressure gauge is connected to the boiler by a cock and a siphon. How should the gauge be checked for correct operation while the boiler is in service?

  1. Remove the gauge and compare it with a master gauge
  2. Open the gauge cock fully and watch the needle rise
  3. Close the gauge cock and note that the needle stays put
  4. Close the gauge cock and confirm the needle falls to zero Correct answer.

Explanation

Closing the gauge cock isolates the gauge from the boiler, and a serviceable gauge needle should fall back to zero. If the needle remains stuck at the working pressure, the gauge or its connection is blocked or faulty and must be investigated. Gauges are not removed for comparison while the boiler is live.

Question 36Boiler fittings, valves, gauges and safety devices

What is the role of the feedwater check valve on a boiler?

  1. To measure the quantity of feedwater added
  2. To reduce feedwater pressure before it enters the drum
  3. To prevent boiler water from flowing back into the feed line Correct answer.
  4. To control the rate of feedwater flow

Explanation

The feedwater check valve allows water to enter the boiler but closes to stop reverse flow. This protects the feed line and pump from hot boiler water and steam if the pump stops or pressure falls. Flow rate and quantity are handled by the regulator and flowmeter.

Question 37Boiler fittings, valves, gauges and safety devices

Why must the feedwater stop valve and check valve be arranged so that the check valve is between the stop valve and the boiler?

  1. So the check valve protects the stop valve from steam pressure
  2. So the feed pump can be run without the stop valve open
  3. So the stop valve can regulate the feed flow more accurately
  4. So the check valve can be serviced while the stop valve isolates the boiler Correct answer.

Explanation

With the check valve nearest the boiler and the stop valve outboard of it, closing the stop valve isolates both the check valve and the feed line for maintenance. The check valve then still guards against backflow whenever the stop valve is open. This arrangement gives both protection and serviceability.

Question 38Boiler fittings, valves, gauges and safety devices

What is the function of the blowdown valve on a boiler?

  1. To drain the steam main of condensate
  2. To discharge water from the boiler to control dissolved solids and remove sludge Correct answer.
  3. To admit air to the boiler during cooling
  4. To release steam to the atmosphere when pressure is high

Explanation

Blowdown valves allow water to be discharged from the boiler, either from the bottom to remove sludge or from the surface to control dissolved solids concentration. Regular blowdown keeps the boiler water chemistry within limits. Steam release and condensate drainage are separate functions.

Question 39Boiler fittings, valves, gauges and safety devices

Why are two blowdown valves often fitted in series on a boiler bottom blowdown line?

  1. To allow the blowdown line to be used for feedwater filling
  2. To allow blowdown from two points at once
  3. To provide a safety barrier so that one valve can be kept closed while the other is worked Correct answer.
  4. To increase the blowdown flow rate beyond a single valve's capacity

Explanation

The two valves in series give a double barrier between the boiler and the atmosphere. One valve is kept fully open while the other is used to start and stop the blowdown, so a single valve failure does not leave an uncontrolled opening. This arrangement is a safety requirement on high-pressure boilers.

Question 40Boiler fittings, valves, gauges and safety devices

What does the term 'accumulation of pressure' mean when testing a boiler safety valve?

  1. The pressure at which the valve reseats after lifting
  2. The pressure rise above the set pressure that occurs when the valve is discharging at full capacity Correct answer.
  3. The total steam discharged during a test
  4. The gradual build-up of scale on the valve seat over time

Explanation

Accumulation is the amount by which the boiler pressure exceeds the safety valve set pressure when the valve is passing its rated capacity with the boiler at maximum firing. Codes limit this accumulation to a small percentage of design pressure. It is not related to scale, total discharge or reseating pressure.

Question 41Boiler fittings, valves, gauges and safety devices

What is the purpose of the boiler vent valve on top of the steam drum?

  1. To provide a secondary steam outlet to the plant
  2. To allow air to escape when filling and to admit air when draining Correct answer.
  3. To release steam to the atmosphere during normal running
  4. To supply steam for soot blowing

Explanation

The vent valve is opened during filling so air can escape and closed once steam forms, and it is opened during draining or cooling so air can enter and prevent a vacuum. It is not used for continuous steam release or as a process steam supply.

Question 42Boiler fittings, valves, gauges and safety devices

An operator finds the safety valve on a boiler weeping slightly at normal operating pressure. What is the most appropriate response?

  1. Tap the valve body with a hammer to reseat it
  2. Increase the boiler pressure until the valve seats firmly
  3. Ignore it because a slight weep is normal
  4. Report the fault and have the valve inspected and reseated by a competent person Correct answer.

Explanation

Weeping at normal pressure indicates the valve is not seating correctly, which can lead to seat damage and loss of protection. The fault must be reported and the valve examined and reseated by an authorised person. Operating pressure must never be raised to force a valve to seat.

Question 43Boiler fittings, valves, gauges and safety devices

Which instrument provides the most direct indication that the boiler is approaching its maximum permissible working pressure?

  1. The water level gauge glass
  2. The pressure gauge with its red marking Correct answer.
  3. The steam temperature thermometer
  4. The feedwater flowmeter

Explanation

The pressure gauge shows the internal pressure, and the red mark at the maximum permissible working pressure lets the operator judge how close the boiler is to its limit. The gauge glass shows level, the flowmeter shows feed rate and the thermometer shows temperature, none of which indicate pressure margin.

Question 44Boiler fittings, valves, gauges and safety devices

What is the function of a fusible plug fitted in some boiler crowns?

  1. To support the crown plate against pressure
  2. To melt and release steam if the boiler pressure is too high
  3. To melt and warn of low water or overheating of the crown plate Correct answer.
  4. To act as a drain for the boiler during shutdown

Explanation

A fusible plug contains a low-melting alloy that melts if the metal around it becomes overheated, which typically happens when the water level falls and the crown is uncovered. The melting opens a passage that releases steam and alerts the operator. It is not a pressure relief device or a structural support.

Question 45Boiler fittings, valves, gauges and safety devices

Why should the water level gauge glass be blown through at the start of a shift?

  1. To reduce the boiler pressure slightly before firing
  2. To test the safety valve setting
  3. To confirm that both steam and water connections are clear and the indicated level is true Correct answer.
  4. To warm the glass so it does not crack

Explanation

Blowing through the glass proves that the steam and water passages are open and that the level shown is genuine. A blocked connection can give a false steady level and lead to a dangerous low-water condition going unnoticed. The test is about proving clear passages, not warming the glass or testing other devices.

Question 46Boiler fittings, valves, gauges and safety devices

A boiler pressure gauge is reading a steady value but the gauge cock is found to be partly closed. What is the risk to the operator?

  1. The gauge may show a lower pressure than actual, giving a false sense of safety Correct answer.
  2. The gauge may show a higher pressure than actual, causing unnecessary alarm
  3. The safety valve will automatically compensate for the error
  4. The gauge accuracy is unaffected by the cock position

Explanation

A partly closed cock restricts the pressure signal reaching the gauge, so the indicated pressure can lag or read lower than the true boiler pressure. The operator may then believe there is more margin to the limit than actually exists. The safety valve protects against overpressure but does not correct a misleading gauge.

Question 47Boiler fittings, valves, gauges and safety devices

What is the purpose of the superheater drain valves on a boiler with a superheater?

  1. To remove condensate from the superheater during start-up and prevent water carryover to the turbine Correct answer.
  2. To reduce superheated steam temperature during normal running
  3. To drain the boiler drum during blowdown
  4. To supply steam for the safety valve

Explanation

During start-up the superheater contains condensate that must be drained before steam is admitted to the plant. Removing this water prevents carryover and thermal shock to downstream equipment. The drains are not used to control steam temperature or for drum blowdown.

Question 48Boiler fittings, valves, gauges and safety devices

What does the term 'set pressure' of a boiler safety valve mean?

  1. The pressure at which the valve reseats after discharge
  2. The pressure at which the feed pump stops
  3. The pressure at which the valve begins to open and discharge steam Correct answer.
  4. The pressure at which the boiler normally operates

Explanation

Set pressure is the pressure at which the safety valve starts to lift and pass steam, and it is stamped on the valve and recorded on its certificate. Reseating pressure is a lower figure at which the valve closes again. Normal operating pressure and feed pump settings are separate values.

Question 49Boiler fittings, valves, gauges and safety devices

An operator is asked to check that the low-water cutoff is working. Which test best confirms the interlock functions correctly?

  1. Raise the water level and confirm the feed pump stops
  2. Lower the water level in a controlled way and confirm the fuel supply is cut off and an alarm sounds Correct answer.
  3. Open the safety valve slightly and listen for discharge
  4. Close the main stop valve and watch the pressure rise

Explanation

Testing the low-water cutoff requires simulating a low-water condition and confirming that the interlock trips the fuel supply and gives an alarm. This proves the protective function, not just the level indication. Safety valve and stop valve tests check different systems.

Question 50Boiler fittings, valves, gauges and safety devices

What is the main purpose of a boiler safety valve?

  1. To regulate the burner firing rate
  2. To indicate the water level in the drum
  3. To release steam automatically when pressure exceeds the set point Correct answer.
  4. To drain condensate from the steam main

Explanation

A safety valve is the final protective device on a boiler. It opens automatically at its set pressure and discharges steam so that pressure cannot rise beyond the maximum permissible working pressure, then reseats when pressure falls.