4BE3.5 U3 C2 Obj 2 Easy Medium Hard
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EASY What is the purpose of a thermocouple in a boiler?

  • To control the fuel input
  • To measure the temperature of the furnace
  • To detect flame failure (correct)
  • To generate a large voltage

    • What is the limitation of thermocouple flame safeguards?

  • They are difficult to install
  • They are expensive
  • They have a slow flame failure response time (correct)
  • They are unreliable

    • What is the typical voltage generated by a thermocouple?

  • 100 millivolts
  • 20 to 30 millivolts (correct)
  • 5 volts
  • 1 volt

    • What is the function of the pilotstat in a thermocouple circuit?

    <p>To supervise the pilot flame</p> Signup and view all the answers

    What is the purpose of the cold junction in a thermocouple?

    <p>To provide a reference point for the thermocouple</p> Signup and view all the answers

    What is the material used for the outer sheath of a thermocouple?

    <p>Copper</p> Signup and view all the answers

    What happens when the thermocouple voltage drops below 7 millivolts?

    <p>The SSOV stays open</p> Signup and view all the answers

    What is the maximum input of a boiler that can use a thermocouple flame safeguard?

    <p>120 kW</p> Signup and view all the answers

    What is the name of the valve body that combines a gas pressure regulator, safety shut-off valve, and manual gas valve?

    <p>Combination gas valve</p> Signup and view all the answers

    What is the purpose of a pilotstat?

    <p>To stop the flow of gas to the pilot burner when the pilot flame is extinguished</p> Signup and view all the answers

    What is the typical voltage generated by a thermocouple?

    <p>Up to 30 millivolts</p> Signup and view all the answers

    What is the purpose of a thermopile?

    <p>To develop sufficient voltage to operate an SSOV independently from any external power source</p> Signup and view all the answers

    What is the principle of operation of a flame rod?

    <p>Conduction of electricity by the flame</p> Signup and view all the answers

    What is the purpose of a limit switch in an SSOV circuit?

    <p>To stop the gas flow to the main burner</p> Signup and view all the answers

    What is the advantage of a millivolt system?

    <p>It operates without external power</p> Signup and view all the answers

    What is the purpose of a safety shut-off valve?

    <p>To stop the gas flow to the main burner in case of an emergency</p> Signup and view all the answers

    What is the typical input range of combination gas valves?

    <p>Up to 120 kW</p> Signup and view all the answers

    How does a flame rod detect a flame?

    <p>By conducting electricity through the flame</p> Signup and view all the answers

    What is the purpose of the scanner sight tube in a firetube boiler burner assembly?

    <p>To observe the pilot burner and the main burner</p> Signup and view all the answers

    What type of light is emitted by the igniter sparks in a firetube boiler burner assembly?

    <p>Ultraviolet light</p> Signup and view all the answers

    What is the recommended maximum temperature for mounting a UV scanner in a firetube boiler burner assembly?

    <p>100°C</p> Signup and view all the answers

    What is the function of the cathode in a rectifying photocell?

    <p>To emit electrons when exposed to visible light</p> Signup and view all the answers

    What happens when the flame fails in a rectifying photocell?

    <p>The contact points of the flame relay open</p> Signup and view all the answers

    What is the purpose of the pilot flame in a firetube boiler burner assembly?

    <p>To keep the burner circuit energized</p> Signup and view all the answers

    Why did the scanner detect a flame signal in the case study?

    <p>The igniter spark reflected off the new sight glass back to the scanner</p> Signup and view all the answers

    Where is the rectifying photocell often mounted in small packaged oil burners?

    <p>Inside the combustion air supply tube</p> Signup and view all the answers

    What is the primary direction of electron flow in a flame rod system?

    <p>From the burner to the flame rod</p> Signup and view all the answers

    What causes the DC flow from the burner to the flame rod in a flame rod system?

    <p>The pulsations of the flame</p> Signup and view all the answers

    What happens if the flame rod is accidentally grounded to the burner?

    <p>The burner monitoring circuit opens the SSOVs</p> Signup and view all the answers

    What is the role of the relay in a basic flame rod system?

    <p>To amplify the signal from the flame unit</p> Signup and view all the answers

    What is the advantage of using flame rods over thermocouples and thermopiles?

    <p>They offer faster flame failure response time</p> Signup and view all the answers

    What is the purpose of a photoelectric cell in a flame monitoring system?

    <p>To react to infrared, ultraviolet, or visible light emitted by fire</p> Signup and view all the answers

    What type of photocell is used in the scanner illustrated in Figure 15?

    <p>Infrared scanner</p> Signup and view all the answers

    What happens to the resistance of the lead-sulfide cell when it receives an increase in the amount of infrared light?

    <p>It decreases</p> Signup and view all the answers

    What is the purpose of the electronic amplifier in an infrared scanner?

    <p>To increase the flame signal</p> Signup and view all the answers

    What happens to the power supply to the main SSOV when a flame failure occurs in an infrared scanner system?

    <p>It is cut-off</p> Signup and view all the answers

    MEDIUM What is the reason thermocouples are limited in use to pilot burners for small boilers?

    <p>Because thermocouples have a slow flame failure response time</p> Signup and view all the answers

    What is the function of the cold junction in a thermocouple?

    <p>To act as a reference point for the thermocouple</p> Signup and view all the answers

    What is the purpose of the outer copper sheath in a thermocouple?

    <p>To act as one of the two conductors</p> Signup and view all the answers

    What happens when the thermocouple voltage drops below 7 millivolts?

    <p>The safety shut-off valve opens</p> Signup and view all the answers

    What is the typical voltage generated by a thermocouple?

    <p>20-30 millivolts</p> Signup and view all the answers

    What is the function of the pilotstat in a thermocouple circuit?

    <p>To energize the main SSOV when the thermocouple voltage is above 7 millivolts</p> Signup and view all the answers

    What is the purpose of the inner wire in a thermocouple?

    <p>To act as one of the two conductors</p> Signup and view all the answers

    What occurs when the hot junction is exposed to a flame in a thermocouple?

    <p>The temperature of the hot junction increases, generating a small voltage</p> Signup and view all the answers

    What is the purpose of the scanner sight tube in a firetube boiler burner assembly?

    <p>To observe the pilot and main burner flames</p> Signup and view all the answers

    Why did the scanner detect a flame signal in the case study?

    <p>Because of the spark from the igniter</p> Signup and view all the answers

    What type of light is emitted by the igniter sparks in a firetube boiler burner assembly?

    <p>Ultraviolet</p> Signup and view all the answers

    Where is the rectifying photocell often mounted in small packaged oil burners?

    <p>Inside the combustion air supply tube</p> Signup and view all the answers

    What happens when the flame fails in a rectifying photocell?

    <p>The main safety shut-off valve closes</p> Signup and view all the answers

    What is the function of the cathode in a rectifying photocell?

    <p>To emit electrons when exposed to light</p> Signup and view all the answers

    What is the recommended maximum temperature for mounting a UV scanner in a firetube boiler burner assembly?

    <p>100°C</p> Signup and view all the answers

    What is the principle of operation of a UV scanner?

    <p>It responds to ultraviolet light from the flame</p> Signup and view all the answers

    What is the purpose of a combination gas valve?

    <p>To provide a single valve body for multiple components</p> Signup and view all the answers

    What is the function of a pilotstat?

    <p>To detect the pilot flame</p> Signup and view all the answers

    What is the typical input range of boilers that can use thermocouples or thermopiles?

    <p>Up to 120 kW</p> Signup and view all the answers

    What is the principle of operation of a flame rod?

    <p>Conducting electricity through the flame</p> Signup and view all the answers

    What is the purpose of a limit switch in an SSOV circuit?

    <p>To prevent the burner from operating under unsafe conditions</p> Signup and view all the answers

    What is the advantage of a millivolt system?

    <p>It operates independently of external power</p> Signup and view all the answers

    What is the purpose of the manual reset button on a combination gas valve?

    <p>To reset the pilotstat after a flame failure</p> Signup and view all the answers

    What happens when the thermocouple voltage drops below a certain threshold?

    <p>The pilotstat de-energizes</p> Signup and view all the answers

    What is the purpose of a thermopile?

    <p>To operate an SSOV independently of external power</p> Signup and view all the answers

    What is the typical voltage generated by a thermopile?

    <p>Around 750 millivolts</p> Signup and view all the answers

    What is the reason for pulsating DC current in a flame rod system?

    <p>Pulsations in the flame</p> Signup and view all the answers

    What happens if the flame rod is accidentally grounded to the burner in a flame rod system?

    <p>The burner monitoring circuit does not accept the AC signal and shuts off the SSOVs</p> Signup and view all the answers

    What is the function of the relay in a basic flame rod system?

    <p>To provide power to the main SSOV</p> Signup and view all the answers

    What is the advantage of using flame rods over thermocouples and thermopiles?

    <p>Faster flame failure response time</p> Signup and view all the answers

    What is the purpose of a photoelectric cell in a flame monitoring system?

    <p>To detect the presence of flames</p> Signup and view all the answers

    What type of photocell is used in the scanner illustrated in Figure 15?

    <p>Infrared scanner</p> Signup and view all the answers

    What happens to the resistance of the lead-sulfide cell when it receives an increase in the amount of infrared light?

    <p>It decreases</p> Signup and view all the answers

    What is the purpose of the electronic amplifier in an infrared scanner?

    <p>To amplify the flame signal</p> Signup and view all the answers

    What happens when a flame failure occurs in an infrared scanner system?

    <p>The power supply to the main SSOV is cut off</p> Signup and view all the answers

    What is the purpose of the sighting tube in a photoelectric cell?

    <p>To mount the scanner</p> Signup and view all the answers

    HARD What is the primary reason for the limitation of thermocouple flame safeguards to small boilers?

    <p>Thermocouples have a slow flame failure response time.</p> Signup and view all the answers

    What is the purpose of the reference junction in a thermocouple circuit?

    <p>To provide a stable temperature reference for the hot junction.</p> Signup and view all the answers

    What is the effect of the hot junction being exposed to a flame in a thermocouple?

    <p>The voltage generated by the thermocouple increases.</p> Signup and view all the answers

    What is the function of the outer copper sheath in a thermocouple?

    <p>To act as an electrical conductor.</p> Signup and view all the answers

    What is the purpose of the pilotstat in a thermocouple circuit?

    <p>To energize the main SSOV when the thermocouple voltage is sufficient.</p> Signup and view all the answers

    What happens when the thermocouple voltage drops below 7 millivolts in a thermocouple circuit?

    <p>The main SSOV opens.</p> Signup and view all the answers

    What is the purpose of the inner wire in a thermocouple?

    <p>To form a hot junction with the copper sheath.</p> Signup and view all the answers

    What is the primary advantage of using thermocouples over other flame detection methods?

    <p>They are less expensive than other flame detection methods.</p> Signup and view all the answers

    What is the primary reason why flame rods are used in burners over 120 kW input?

    <p>Because they offer fast flame failure response time</p> Signup and view all the answers

    What is the effect of soot bridging on a flame rod system?

    <p>It causes a nuisance outage</p> Signup and view all the answers

    What is the purpose of the threaded ring in a photoelectric cell installation?

    <p>To secure the scanner on the sight tube</p> Signup and view all the answers

    What happens to the resistance of the lead-sulfide cell when it receives an increase in the amount of infrared light?

    <p>It decreases</p> Signup and view all the answers

    What is the purpose of the electronic amplifier in an infrared scanner system?

    <p>To amplify the flame signal</p> Signup and view all the answers

    What happens when the flame rod is accidentally grounded to the burner?

    <p>The burner monitoring circuit shuts off the SSOVs</p> Signup and view all the answers

    What is the primary function of the relay in a basic flame rod system?

    <p>To control the power supply to the main SSOV</p> Signup and view all the answers

    What is the effect of carbon deposits on a flame rod system when used with oil-fired burners?

    <p>It causes a nuisance outage</p> Signup and view all the answers

    What is the primary advantage of using flame rods over thermocouples and thermopiles?

    <p>They offer faster flame failure response time</p> Signup and view all the answers

    What is the purpose of the sight tube in a photoelectric cell installation?

    <p>To allow the scanner to see the flame</p> Signup and view all the answers

    What is the primary reason for using a thermopile instead of a thermocouple in a millivolt system?

    <p>To provide sufficient power to operate an SSOV directly</p> Signup and view all the answers

    Which of the following components is NOT typically included in a combination gas valve?

    <p>Water pressure regulator</p> Signup and view all the answers

    What is the primary function of the pilotstat manual reset button?

    <p>To re-energize the pilotstat after a flame failure</p> Signup and view all the answers

    What is the primary advantage of a millivolt system over a traditional electrical power source?

    <p>Ability to operate during a power failure</p> Signup and view all the answers

    What is the primary function of the flame rod in a flame detection system?

    <p>To conduct electricity between the flame rod and the burner</p> Signup and view all the answers

    What is the primary reason for using a limit switch in an SSOV circuit?

    <p>To prevent the main burner from operating under unsafe conditions</p> Signup and view all the answers

    What is the primary function of the thermocouple in a thermocouple circuit?

    <p>To generate a voltage signal in response to a flame</p> Signup and view all the answers

    What is the primary disadvantage of using a thermocouple in a millivolt system?

    <p>Limited voltage output</p> Signup and view all the answers

    What is the primary function of the pilotstat in a combination gas valve?

    <p>To interrupt the gas flow to the pilot burner</p> Signup and view all the answers

    What is the primary advantage of using a flame rod over a thermocouple or thermopile?

    <p>Ability to detect both pilot and main flames</p> Signup and view all the answers

    What is the reason for placing the UV scanner as close as possible to the flame?

    <p>To detect ultraviolet rays emitted by the flame.</p> Signup and view all the answers

    What was the likely cause of the scanner detecting a flame signal in the case study?

    <p>The new sight glass was too shiny.</p> Signup and view all the answers

    What is the primary function of the cathode in a rectifying photocell?

    <p>To emit electrons when exposed to visible light.</p> Signup and view all the answers

    What is the purpose of angling the scanner sight tube?

    <p>To observe the pilot and main burner flames.</p> Signup and view all the answers

    What happens when the flame fails in a rectifying photocell?

    <p>The flame relay closes the contact points.</p> Signup and view all the answers

    Why do newer burner management systems distinguish between sparks and flames?

    <p>To prevent false flame signals.</p> Signup and view all the answers

    What is the benefit of using a UV scanner over other flame detection methods?

    <p>It is less prone to false flame signals.</p> Signup and view all the answers

    What is the purpose of the curved metal cathode in a rectifying photocell?

    <p>To emit electrons when exposed to visible light.</p> Signup and view all the answers

    Study Notes

    Flame Failure Detection Methods

    • Various methods are used to detect flame failure in boilers, including:
    • Thermocouples
    • Thermopiles
    • Flame rods
    • Photoelectric cells

    Thermocouples

    • A thermocouple consists of two dissimilar wires welded together at one end to form a measuring (or “hot”) junction.
    • The opposite ends are connected to an electric circuit, called the reference (or “cold”) junction.
    • When the hot junction is exposed to a flame, its temperature increases above that of the cold junction, generating a small voltage (about 20 to 30 millivolts).
    • This voltage energizes a sensitive relay, called a pilotstat, which may be built into an SSOV (Safety Shut-Off Valve).
    • Thermocouples are limited to pilot burners up to 120 kW input due to their slow flame failure response time (up to 90 seconds).

    Thermopiles

    • A thermopile is a flame detector that develops sufficient voltage to operate an SSOV independently from any external power source.
    • It consists of multiple thermocouples in series, generating around 750 millivolts.
    • Thermopiles are also limited to burners not exceeding 120 kW input.
    • They offer the advantage of operating without external power, making them suitable for small residential boilers.

    Flame Rods

    • A flame rod is a flame detection device that operates on the principle that flames can conduct electricity.
    • It consists of two electrodes (the flame rod and the burner) and the flame, which conducts electricity between them.
    • The flame rod is a heat-resistant, small diameter metal rod, supported by a ceramic holder that keeps the rod electrically insulated from the burner.
    • Flame rods are commonly used with gas burners and are suitable for burners over 120 kW input due to their fast flame failure response time.

    Photoelectric Cells

    • A photoelectric cell is a device that reacts to infrared, ultraviolet, or visible light emitted by fire.
    • Common types of photocells include:
    • Infrared scanner
    • Ultraviolet scanner
    • Rectifying photocell
    • A scanner is mounted on the boiler in such a way that it can observe the flame, and its resistance decreases with an increase in the amount of infrared light it receives from the flame.
    • When a flame failure occurs, the scanner does not sense a flame, and its resistance increases, causing the flame relay to open, which shuts off the fuel to the burner.

    Case Study

    • A case study highlights the importance of proper installation and maintenance of flame safeguard controls to avoid false readings and potential explosions.

    Flame Failure Detection Methods

    • Various methods are used to detect flame failure in boilers, including:
    • Thermocouples
    • Thermopiles
    • Flame rods
    • Photoelectric cells

    Thermocouples

    • A thermocouple consists of two dissimilar wires welded together at one end to form a measuring (or “hot”) junction.
    • The opposite ends are connected to an electric circuit, called the reference (or “cold”) junction.
    • When the hot junction is exposed to a flame, its temperature increases above that of the cold junction, generating a small voltage (about 20 to 30 millivolts).
    • This voltage energizes a sensitive relay, called a pilotstat, which may be built into an SSOV (Safety Shut-Off Valve).
    • Thermocouples are limited to pilot burners up to 120 kW input due to their slow flame failure response time (up to 90 seconds).

    Thermopiles

    • A thermopile is a flame detector that develops sufficient voltage to operate an SSOV independently from any external power source.
    • It consists of multiple thermocouples in series, generating around 750 millivolts.
    • Thermopiles are also limited to burners not exceeding 120 kW input.
    • They offer the advantage of operating without external power, making them suitable for small residential boilers.

    Flame Rods

    • A flame rod is a flame detection device that operates on the principle that flames can conduct electricity.
    • It consists of two electrodes (the flame rod and the burner) and the flame, which conducts electricity between them.
    • The flame rod is a heat-resistant, small diameter metal rod, supported by a ceramic holder that keeps the rod electrically insulated from the burner.
    • Flame rods are commonly used with gas burners and are suitable for burners over 120 kW input due to their fast flame failure response time.

    Photoelectric Cells

    • A photoelectric cell is a device that reacts to infrared, ultraviolet, or visible light emitted by fire.
    • Common types of photocells include:
    • Infrared scanner
    • Ultraviolet scanner
    • Rectifying photocell
    • A scanner is mounted on the boiler in such a way that it can observe the flame, and its resistance decreases with an increase in the amount of infrared light it receives from the flame.
    • When a flame failure occurs, the scanner does not sense a flame, and its resistance increases, causing the flame relay to open, which shuts off the fuel to the burner.

    Case Study

    • A case study highlights the importance of proper installation and maintenance of flame safeguard controls to avoid false readings and potential explosions.

    Flame Failure Detection Methods

    • Various methods are used to detect flame failure in boilers, including:
    • Thermocouples
    • Thermopiles
    • Flame rods
    • Photoelectric cells

    Thermocouples

    • A thermocouple consists of two dissimilar wires welded together at one end to form a measuring (or “hot”) junction.
    • The opposite ends are connected to an electric circuit, called the reference (or “cold”) junction.
    • When the hot junction is exposed to a flame, its temperature increases above that of the cold junction, generating a small voltage (about 20 to 30 millivolts).
    • This voltage energizes a sensitive relay, called a pilotstat, which may be built into an SSOV (Safety Shut-Off Valve).
    • Thermocouples are limited to pilot burners up to 120 kW input due to their slow flame failure response time (up to 90 seconds).

    Thermopiles

    • A thermopile is a flame detector that develops sufficient voltage to operate an SSOV independently from any external power source.
    • It consists of multiple thermocouples in series, generating around 750 millivolts.
    • Thermopiles are also limited to burners not exceeding 120 kW input.
    • They offer the advantage of operating without external power, making them suitable for small residential boilers.

    Flame Rods

    • A flame rod is a flame detection device that operates on the principle that flames can conduct electricity.
    • It consists of two electrodes (the flame rod and the burner) and the flame, which conducts electricity between them.
    • The flame rod is a heat-resistant, small diameter metal rod, supported by a ceramic holder that keeps the rod electrically insulated from the burner.
    • Flame rods are commonly used with gas burners and are suitable for burners over 120 kW input due to their fast flame failure response time.

    Photoelectric Cells

    • A photoelectric cell is a device that reacts to infrared, ultraviolet, or visible light emitted by fire.
    • Common types of photocells include:
    • Infrared scanner
    • Ultraviolet scanner
    • Rectifying photocell
    • A scanner is mounted on the boiler in such a way that it can observe the flame, and its resistance decreases with an increase in the amount of infrared light it receives from the flame.
    • When a flame failure occurs, the scanner does not sense a flame, and its resistance increases, causing the flame relay to open, which shuts off the fuel to the burner.

    Case Study

    • A case study highlights the importance of proper installation and maintenance of flame safeguard controls to avoid false readings and potential explosions.

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    Description

    This quiz covers various methods used to detect flame failure in boilers, including thermocouples, thermopiles, flame rods, and photoelectric cells.

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