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BOILER SAFETY, TROUBLESHOOTING AND INSPECTION

Safe Operation and Troubleshooting of CB-HAWK Boiler Management Control System

The CB-Hawk boiler management control system ('''Figure 1''') combines the functions of a flame safeguard programmer with those of operating and firing rate controls. It also monitors the fuel pressure and temperature (if required) with solid-state sensors and provides a built-in safety limit control of those functions. This system is used on most types of steam or hot water boilers, including fire-tube, industrial water-tube, and commercial water-tube. The control system is designed to operate a gas, oil, or combination burner using a single modulation motor and provides the best results when used with a fully modulating burner.


'''Figure 1: CB-HAWK Boiler Management Control System'''

The burner and control system are in the starting condition when the following conditions exist:

  • Boiler water is up to the correct level, closing the low-water cutoff switch.
  • The low-water light (panel) is off.
  • The operating limit pressure control (steam boiler) or the operating limit temperature control (hot water boiler) and high limit pressure or temperature control are below their cutoff setting.
  • All applicable limits are correct for burner operation.
  • The load demand light glows.
  • All entrance switches are closed and power is present at the line terminals of:
    • Blower motor starter
    • Air compressor motor starter (if provided)
    • Oil heater relay (if provided)
    • Oil pump motor starter (if provided)
Menu

Circuit and Interlock Controls

The electrical portion of the boiler is made up of individual circuits with controls that are wired in a manner designed to provide a safe workable system. The program relay provides connection points for the interconnection of the various circuits.

The controls used vary depending upon the fuel oil or gas and the specific requirement of applicable regulatory bodies. Refer to the boiler wiring diagram to determine the actual controls provided.

The circuits and controls normally used in the circuits follow and are referred to in the following sequence of operation.

  • Limit Circuit:
    • Burner switch (BS)
    • Operating limit control (OLC) - pressure or temperature
    • High limit control (HLC) - pressure or temperature
    • Low-water cutoff (LWCO)
    • Gas-oil selector switch (GOS) - (Combination burner only)
    • Oil drawer switch (ODS) - Oil burner
    • Low oil temperature switch (LOTS) - (Nos. 5 and 6 oil only)
    • Low gas pressures switch (LGPS)
    • High gas pressure switch (HGPS)
    • L E Proximity switch interlock
  • Fuel Valve Interlock Circuit:
    • Main gas valve auxiliary switch (MGVAS)
    • Oil valve auxiliary switch (OVAS) Blower Motor Starter Circuit
    • Blower motor starter (BMS)
    • Air compressor motor starter (ACMS) (if provided)
    • Air purge valve (APV) (Nos. 5 or 6 oil only)
  • Running Interlock Circuit:
    • Blower motor starter interlock (BMSI)
    • Combustion air proving switch (CAPS)
    • Atomizing air proving switch (AAPS) (if provided)
  • Low Fire Proving Circuit:
    • Low fire switch (LFS)
  • Pilot Ignition Circuit:
    • Gas pilot valve (GPV)
    • Ignition transformer (IT)
    • Gas pilot vent valve (GPVV) (if provided)
  • Flame Detector Circuit:
    • Flame detector (FD)
  • Main Fuel Valve Circuit:
    • Main gas valve (MGV
    • Main gas vent valve (MGVV) (if provided)
    • Oil valve (OV)
    • Main fuel valve light (FVL)
  • Firing Rate Circuit:
    • Damper motor transformer (DMT)
    • Modulating damper motor (MDM)
    • Manual-automatic switch (MAS)
    • Manual flame control (MFC)
    • Modulating control (MC)
  • High Fire Proving Circuit:
    • High fire switch (HFS)
  • Running Interlock and Limit Circuit:
    • Low oil pressure switch (LOPS)
    • High oil pressure switch (HOPS)
    • High oil temperature switch (HOTS)
    • Auxiliary low-water cutoff (ALWCO)

Sequence of Operation – Oil or Gas

On a combination fuel unit, the gas/oil switch must be set for the proper fuel. The following sequence ('''Figure 2''') occurs with power present at the program relay (PR) input terminals and with all other operating conditions satisfied.

Pre-Purge Cycle

When the burner switch (BS) is turned "on," and controls wired in the "limit" and "fuel valve interlock" circuits are closed and no flame signal is present, the "blower motor start circuit" is powered, energizing the blower motor starter (BMS). The load demand light (LDL) turns on. When firing oil, the air compressor motor starter (ACMS) (if provided) is also powered. The air purge valve (APV) (Nos. 5 and 6 oil only) remains de-energized.

At the same time, the program relay signals the modulating damper motor (MDM) to open the air damper. The damper begins to open and drives to its full open or high fire position. Opening the damper motor allows a flow of purging air through the boiler prior to the ignition cycle.

On certain boilers, the circuitry will include a high fire switch (HFS). The purpose of the switch is to prove that the modulating damper motor (MDM) has driven the damper to the open position during the prepurge cycle. In this instance, the "high fire proving circuit" is used.

The controls wired into the "running interlock circuit" must be closed within 10 seconds after the start sequence. In the event any of the controls are not closed at this time, or if they subsequently open, the program relay will go into a safety shutdown.

At the completion of the high fire purge period, the program relay signals the modulating damper motor (MDM) to drive the air damper to its low fire position.

To ensure that the system is in low fire position prior to ignition, the low fire switch (LFS) must be closed to complete the "low fire proving circuit." The sequence will stop and hold until the modulating damper motor (MDM) has returned to the low fire position and the contacts of the low fire switch (LFS) are closed. Once the low fire switch is closed, the sequence is allowed to continue.

NOTE:

The ignition trial cannot be started if flame or a flame simulating condition is sensed during the pre-purge period. A safety shutdown will occur if flame is sensed at this time.


'''Figure 3: 833-2416 Sequence'''

Ignition Cycle

The ignition transformer (IT) and gas pilot valve (GPV) are energized from the appropriate pilot ignition terminal.

NOTE:

An oil-fired burner may be equipped with an oil pilot tather than a gas pilot. The ignition sequence of both is identical.

The pilot flame must be established and proven by the flame detector (FD) within a 10 second period in order for the ignition cycle to continue. If for any reason this does not happen, the system will shut down and safety lockout will occur.

With a proven pilot, the main fuel valve(s) (OV or MGV) is/are energized and the main fuel valve light (FVL) in the panel is lighted. The main flame is ignited and the trial period for proving the main flame begins. It lasts 10 seconds for light oil and natural gas, and 15 seconds for heavy oil. At the end of the proving period, if the flame detector still detects main flame, the ignition transformer and pilot valve are de-energized and pilot flame is extinguished.

NOTE:

If the main flame does not light, or stay lit, the fuel valve will close. The safety switch will trip to lock out the control. Refer to flame loss sequence (section D) for description of action.

WARNING!

The cause for loss of flame or any other unusual condition should be investigated and corrected before attempting to re-start. Failure to follow these instructions could result in serious personal injury or death!

Run Cycle

With main flame established, the program relay releases the modulating damper motor (MDM) from its low fire position to control by either the manual flame control (MFC) or the modulating control (MC), depending upon the position of the manual-automatic switch (MAS). This allows operation in ranges above low fire.

With the manual-automatic switch (MAS) set at automatic, subsequent modulated firing will be at the command of the modulating control (MC), which governs the position of the modulating damper motor (MDM). The air damper and fuel valves are actuated by the motor through a linkage and cam assembly to provide modulated firing rates.

Normal operation of the burner should be with the switch in the Manual-Automatic position and under the direction of the modulating control. The Manual position is provided for initial adjustment of the burner over the entire firing range. When a shutdown occurs while operating in the Manual position at other than low fire, the damper will not be in a closed position, thus allowing more air than desired to flow through the boiler. Excess airflow subjects the pressure vessel metal and refractory to undesirable conditions. The effectiveness of nozzle purging is lost on a No. 6 oil burner.

The burner starting cycle is now complete. The (LDL) and (FVL) lights on the panel remain lit. Demand firing continues as required by load conditions.

Burner Shutdown-Post Purge

The burner will fire until steam pressure or water temperature in excess of demand is generated. With modulated firing, the modulating damper motor (MDM) should return to the low fire position before the operating limit control (OLC) opens. When the limit control circuit is opened, the following sequence occurs:

The main fuel valve circuit is de-energized, causing the main fuel valve (MGV) or (OV) to close. The flame is extinguished. The control panel lights (LDL) and (FVL) are turned off. The blower motor continues to run to force air through the boiler for the post-purge period.

On a No. 6 oil burner, the air purge valve (APV) is powered from the blower motor start circuit via the contacts of the air purge relay (APR) to provide an air purge of the oil nozzle. The damper motor returns to the low fire position if it is not already in that position.

WARNING!

The lockout switch must be manually reset following a safety shutdown. The cause for loss of flame or any unusual condition should be investigated and corrected before attempting to re-start. Failure to follow these instructions could result in serious personal injury or death!

The blower motor start circuit is de-energized at the end of the post purge cycle and the shutdown cycle is complete.

The program relay is now ready for subsequent recycling, and when steam pressure or water temperature drops to close the contacts of the operating control, the burner again goes through its normal starting and operating cycle.

Flame Loss Sequence

The program relay will recycle automatically each time the operating control closes, or after a power failure. It will lockout following a safety shutdown caused by failure to ignite the pilot, or the main flame, or by loss of flame. Lockout will also occur if flame or flame simulating condition occurs during the pre-purge period.

The control will prevent startup or ignition if limit circuit controls or fuel valve interlocks are open. The control will lock out upon any abnormal condition affecting air supervisory controls wired in the running interlock circuit.

WARNING!

The lockout switch must be manually reset following a safety shutdown. The cause for loss of flame or any unusual condition should be investigated and corrected before attempting to re-start. Failure to follow these instructions could result in serious personal injury or death!

  1. '''NO PILOT FLAME'''The pilot flame must be ignited and proven within a 10-second period after the Troubleshooting and ignition cycle begins. If not proven within this period, the main fuel valve circuit will not be powered and the fuel valve(s) will not be energized. The ignition circuit is immediately de-energized and the pilot valve closes, the reset switch lights and lockout occurs immediately.The blower motor will continue to operate. The flame failure light and the alarm bell (optional) are energized 10 seconds later.The blower motor will be de-energized.'''The lockout switch must be manually reset before operation can be resumed.'''
  2. '''PILOT BUT NO MAIN FLAME'''When the pilot flame is proven, the main fuel valve circuit is energized. Depending upon the length of the trial-for-ignition period, the pilot flame will be extinguished 10 or 15 seconds later. The flame detecting circuit will respond to de-energize the main fuel valve circuit within 2 to 4 seconds to stop the flow of fuel. The reset switch lights and lockout occurs immediately. The blower motor will continue to operate.The flame failure light and alarm bell (optional) are energized 10 seconds later.The blower motor will be de-energized. '''The lockout switch must be manually reset before operation can be resumed.'''
  3. '''LOSS OF FLAME'''If a flame outage occurs during normal operation and/or the flame is no longer sensed by the detector, the flame relay will trip within 2 to 4 seconds to de-energize the fuel valve circuit and shut off the fuel flow. The reset switch lights and lockout occurs immediately. The blower motor continues operation. The flame failure light and alarm bell (optional) are energized 10 seconds later.The blower motor will be de-energized. '''The lockout switch must be manually reset before operation can be resumed.'''

If the burner will not start, or upon a safety lockout, the trouble shooting section in the operating manual and the technical bulletin should be referred to for assistance in pinpointing problems that may not be readily apparent.

The program relay has the capability to self-diagnose and to display a code or message that indicates the failure condition. Refer to the control bulletin for specifics and suggested remedies. Familiarity with the program relay and other controls in the system can be obtained by studying the contents of the manual and this bulletin.

Knowledge of the system and its controls will make troubleshooting much easier. Costly down time or delays can be prevented by systematic checks of the actual operation against the normal sequence to determine the stage at which performance deviates from normal. Following a routine may possibly eliminate overlooking an obvious condition, often one that is relatively simple to correct.

Remember, a safety device, for the most part, is doing its job when it shuts down or refuses to operate. Never attempt to circumvent any of the safety features.

Preventive maintenance and scheduled inspection of all components should be followed. Periodic checking of the relay is recommended to see that a safety lockout will occur under conditions of failure to ignite either pilot or main flame,

Safety shutdown (lockout) occurs if:

PERIOD

LOCKOUT OCCURS IF:

1. Standby Period

  • Incorrect fuel selection input
  • Pre-ignition interlock open
  • Flame signal is present continuous for more than 40 seconds
  • Pilot/ignition terminal energized
  • Main oil valve terminal energized
  • Main gas valve terminal energized
  • Internal system fault
  • Damper motor fault

2. Pre-Purge Period

  • Incorrect fuel selection input
  • Pre-ignition interlock open
  • Lockout interlock open (after 10 seconds into the pre-purge period)
  • Flame present, after 10 seconds into the pre-purge period.
  • Oil pressure fault:

- 833-2417 Program Module; lock out if pressure is not within limit values, after 10 seconds into the prepurge period.

- 833-2418 Program Module; lock out if oil pressure is not within limit values.

  • Oil temperature fault:

- 833-2417 Program Module; lock out if high oil temperature limit exceeded, after 10 seconds into the ignition period.

- 833-2418 Program Module; lock out if oil temperature is not within limit values, after 10 seconds into the pre-purge period.

  • Damper motor fault
  • Pilot valve/ignition terminal energized
  • Main oil valve terminal energized
  • Main gas valve terminal energized
  • Internal system fault
  • Faulty gas pressure sensor

3. Pilot Flame Establishing Period

  • Incorrect fuel selection input
  • Pre-ignition interlock open or shorted
  • Lockout interlock open
  • No flame established
  • Gas pressure limit or sensor fault
  • Oil pressure limit fault, heavy oil only
  • Oil temperature limit fault
  • Damper motor fault
  • Pilot valve or ignition terminal not energized
  • Main oil valve energized
  • Main gas valve energized
  • Internal system fault

4. Main Flame Establishing Period

  • Incorrect fuel selection input
  • Lockout interlock open
  • No flame present
  • Gas pressure limit fault
  • Oil pressure limit fault, heavy oil only
  • Oil temperature limit fault
  • Atomizing air pressure switch open, oil selected fuel
  • Damper motor fault
  • Pilot/ignition transformer terminal de-energized
  • Main oil valve de-energized, oil selected fuel
  • Main gas valve de-energized, gas selected fuel
  • Internal system fault

5. Run Period

  • Incorrect fuel select input.
  • No flame present.
  • Lockout interlocks open.
  • Gas pressure limit fault.
  • Oil pressure limit fault, heavy oil only.
  • Oil temperature limit fault.
  • Atomizing air de-energized, oil selected fuel.
  • Damper motor fault.
  • Pilot/ignition terminal energized.
  • Main valve terminal de-energized, selected fuel.
  • Main valve terminal energized, main valve of fuel series not selected.
  • Internal system fault.

6. Post-purge Period

  • Pre-ignition interlock open after five seconds.
  • Atomizing air terminal de-energized; oil selected fuel
  • Pilot/ignition terminal energized
  • Main oil valve terminal energized
  • Main gas valve terminal energized
  • Internal system fault
  • Damper motor fault

Troubleshooting

If the burner will not start or operate properly, refer to the troubleshooting chart below ('''Table 1''') for assistance in pinpointing problems that may not be readily apparent.

The program relay has the capability to self-diagnose and to display a code or message that indicates the failure condition. Knowledge of the system and its controls will make trouble shooting much easier. Costly down-time or delays can be prevented by systematic checks of actual operation against the normal sequence to determine the stage at which performance deviates from normal. Following a routine may possibly eliminate overlooking an obvious condition, often one that is relatively simple to correct.

If an obvious condition is not apparent, check the continuity of the circuits with a voltmeter or test lamp. Each circuit can be checked and the fault isolated and corrected.

Table 1: Burner Troubleshooting Problems and Solutions

PROBLEM

SOLUTION

BURNER DOES NOT START

1. No voltage at program relay power input terminals

A. Main disconnect switch open

B. Blown control circuit fuse

C. Loose or broken electrical connection

2. Program relay safety switch requires resetting.

3. Limit circuit not completed-no voltage at end of limit circuit program relay terminal.

A. Pressure or temperature is above setting of operation control. (Load demand light will not glow.)

B. Water below required level

1) Low-water light (and alarm horn) should indicate this condition.

2) Check manual reset button, if provided, on low-water control.

C. Fuel pressure must be within settings of low-pressure and high-pressure switches.

D. Oil fired unit - burner gun must be in full forward position to close oil drawer switch.

E. Heavy oil fired unit - oil temperature below minimum settings.

4. Fuel valve interlock circuit not completed.

A. Fuel valve auxiliary switch not enclosed.

NO IGNITION

1. Lack of spark

A. Electrode grounded or porcelain cracked

B. Improper electrode setting

C. Loose terminal on ignition cable; cable shorted

D. Inoperative ignition transformer

E. Insufficient or no voltage at pilot ignition circuit terminal

2. Spark but no flame

A. Lack of fuel: no gas pressure, closed valve, empty tank, broken line, etc

B. Inoperative pilot solenoid

C. Insufficient or no voltage at pilot ignition circuit terminal

D. Too much air

3. Low fire switch open in low fire proving circuit

A. Damper motor not closed, slipped cam, defective switch

B. Damper jammed or linkage binding

4. Running interlock circuit not completed

A. Combustion or atomizing air proving switches defective or not properly set

B. Motor starter interlock contact not closed

5. Flame detector defective, sight tube obstructed, or lens dirty

PILOT FLAME, BUT NO MAIN FLAME

1. Insufficient pilot flame

2. Gas Fired Unit:

A. Manual gas cock closed

B. Main gas valve inoperative

C. Gas pressure regulator inoperative

3. Oil Fired Unit:

A. Oil supply cut off by obstruction, closed valve, or loss of suction

B. Supply pump inoperative

C. No fuel

D. Main oil valve inoperative

E. Check oil nozzle, gun, and lines

4. Flame detector defective, sight tube obstructed or lens dirty

5. Insufficient or no voltage at main fuel valve circuit terminal

BURNER STAYS IN LOW FIRE

1. Pressure or temperature above modulating control setting

2. Manual-automatic switch in wrong position

3. Inoperative modulating motor

4. Defective modulating control

5. Binding or loose linkage, cams, setscrews, etc

SHUTDOWN OCCURS DURING FIRING

1. Loss or stoppage of fuel supply

2. Defective fuel valve; loose electrical connection

3. Flame detector weak or defective

4. Lens dirty or sight tube obstructed

5. If the programmer lockout switch has not tripped, check the limit circuit for an opened safety control.

6. If the programmer lockout switch has tripped:

A. Check fuel lines and valves.

B. Check flame detector.

C. Check for open circuit in running interlock circuit.

D. The flame failure light is energized by ignition failure, main flame failure, inadequate flame signal, or open control in the running interlock circuit.

7. Improper air/fuel ratio (lean fire)

A. Slipping linkage

B. Damper stuck open

C. Fluctuating fuel supply:

1) Temporary obstruction in fuel line

2) Temporary drop in gas pressure

3) Orifice gate valve accidentally opened (heavy oil)

8. Interlock device inoperative or defective

MODULATING MOTOR DOES NOT OPERATE

1. Manual-automatic switch in wrong position

2. Linkage loose or jammed

3. Motor does not drive to open or close during pre-purge or close on burner shutdown.

A. Motor defective

B. Loose electrical connection

C. Damper motor transformer defective

4. Motor does not operate on demand.

A. Manual/automatic switch in wrong position

B. Modulating control improperly set or inoperative

C. Motor defective

D. Loose electrical connection

E. Damper motor transformer defective

Basic Flame Safeguard Burner Control System

  • Automatic operation, self-checking circuits.
  • Self-checking ultraviolet flame detectors, Infrared flame detectors with self-checking amplifiers permitted on fire tube boilers.
  • Provide one spare scanner and control chassis for each type used.
  • Combustion Control System: Automatic control of steam pressure or water temperature, with provision for manual control.

Types of Flame Detectors

Most fire detection technology focuses on detecting heat, smoke (particle matter) or flame (light) – the three major characteristics of fire. All of these characteristics also have benign sources other than fire, such as heat from steam pipes, particle matter from aerosols, and light from the sun. Other factors such as air temperature and air movement further confound the process of fire detection by masking the characteristic of interest. In addition, smoke and heat from fires can dissipate too rapidly or accumulate too slowly for effective detection. In contrast, because flame detectors are optical devices, they can respond to flames in less than a second. This optical quality also limits the flame detector as not all fires have a flame. As with any type of detection method, its use must match the environment and the risk within the environment.

There are three types of flame detectors currently available: ''infrared (IR)'', ''ultraviolet (UV)'', and a ''combination of UV and IR''. The spectrum below shows the relationship between these frequencies and visible light.

Infrared Flame Detectors

Infrared detectors have been available for many years; however, it has only been in recent times that technology has allowed for stable, accurate detection to occur. There are two types of infrared detectors: ''single frequency'' and ''multi-spectrum''.

Infrared Single Frequency Flame Detectors

The basic principles of operation for a single frequency IR detector are:

  • The detector is sensitive to a narrow band of radiation around the 4.4 micron range which is a predominant emission band for hydrocarbon fuelled fires. Additionally, the sun’s radiation at this band is absorbed by the earth’s atmosphere, making the IR flame detector solar blind.
  • Single frequency detectors use a pyroelectric sensor, which responds to changes in IR radiation intensity. In addition, they incorporate a low frequency band pass filter, which limits their response to those frequencies that are characteristic of a flickering fire.
  • In response to a fire signal from the sensor, electronic circuitry in the detector generates an output signal.

Strengths of the single frequency IR detector are:

  • Highly immune to optical contaminants like oil, dirt, and dust
  • High speed response under 30 milliseconds for some brands
  • Insensitive to solar, welding, lightning, X-rays, sparks, arcs, and corona

Limitations of the single frequency IR detector are:

  • Generally not suitable for non-carbon fires
  • Some brands will respond to modulated infrared sources.
  • Rain, ice, and water vapor on the detector lens will inhibit detection.

Infrared Multi Spectrum Flame Detectors

The basic principle of operation for a multi spectrum IR detector is:

  • The detector has three sensors, each sensitive to a different frequency of radiation.
  • The IR radiation emitted by a typical hydrocarbon fire is more intense at the wavelength accepted by one sensor than the other two.
  • Electronic circuitry in the detector translates the difference in intensity of the three sensors to a ratio that, along with a synchronous flicker, must be present before a fire signal is produced. This allows the detector to reject high intensity flickering black body radiation sources since these sources will not meet the proper ratio criteria.

Strengths of the multi-spectrum IR detector are:

  • Virtually immune to false alarms
  • Fire response in the presence of modulated infrared black body radiation with some brands
  • Long detection range (60 meters to some fires)

Limitations of multi spectrum IR detector are:

  • Typical response time is longer when compared to single frequency detectors.

IR detectors are sensitive to most hydrocarbon fires (liquids, gases, and solids). Fires such as burning metals, ammonia, hydrogen and sulphur do not emit significant amounts of IR in the detector’s sensitivity range to activate an alarm. IR detectors are suitable for applications where hydrocarbon fires are likely to occur and high concentrations of airborne contaminants and/or UV radiation sources may be present. The detector should be used with caution when the presence of hot objects and the potential for ice buildup on the detector are likely.

Ultraviolet Flame Detectors

A UV detector uses a sensor tube that detects radiation emitted in the 1,000 to 3,000 angstrom (one ten-billionth of a meter) range. It is important to note that ultraviolet radiation from the sun that reaches earth starts at 2,800 angstroms. If the detector’s sensor has a wide range, then it will be triggered by the sun’s rays, which means it is only suitable for indoor use. There are sensors available with a range of 1,800 to 2,500 angstroms. Virtually all fires emit radiation in this band, while the sun’s radiation at this band is absorbed by the earth’s atmosphere. The result is that the UV flame detector is solar blind. The implication of this feature is that the detector can be used indoors and outdoors. In response to UV radiation from a flame that falls within the narrow band, the sensor generates a series of pulses that are converted by the detector electronics into an alarm output.

Strengths of the UV detector are:

  • Responds to hydrocarbon, hydrogen, and metal fires
  • High speed response – under 10 milliseconds
  • Solar insensitive

Limitations of the UV detector are:

  • Will respond to welding at long range
  • May respond to lightning, X-rays, sparks, arcs, and corona
  • Some gases and vapors will inhibit detection.
  • Some UV sensors have a wide detection range resulting in solar false alarms.

UV detectors are sensitive to most fires, including hydrocarbon (liquids, gases, and solids), metals (magnesium), sulphur, hydrogen, hydrazine, and ammonia. The UV detector is the most flexible general purpose optical fire detector available. They are fast, reliable, have few false alarm sources, and respond to virtually any fire.

Ultraviolet / Infrared Flame Detectors

A UV/IR detector consists of an UV and single frequency IR sensor paired to form one unit. The two sensors individually operate the same as previously described, but additional circuitry processes signals from both sensors. This means the combined detector has better false alarm rejection capabilities than the individual UV or IR detectors.

Strengths of the UV/IR detector are:

  • Virtually immune to false alarms
  • High speed response – under 500 milliseconds
  • Solar, welding, lightning, X-rays, sparks, arcs, and corona insensitive

Limitations of UV/IR detector are:

  • Not recommended for non-carbon fires
  • Some gases and vapors will inhibit detection due to blinding of the UV sensor.

Since the UV/IR detector pairs two sensor types, it will typically only detect fires that emit both UV and flickering IR radiation. UV detectors will respond to virtually all fires including hydrocarbon (liquids, gases, and solids), metals (magnesium), sulfur, hydrogen, hydrazine and ammonia. IR detectors typically only respond to hydrocarbon fires. Since the IR detector is not sensitive to burning metals, ammonia, hydrogen, and sulfur, the combined unit will not respond to these fires.

The detector is suitable for applications where hydrocarbon fires are likely and other sources of radiation may be present (X-rays, hot surfaces, and arc welding). They maintain constant protection while arc welding takes place. The UV/IR detectors are highly reliable with fast response times and low propensity to false alarms

Boiler Inspections

Boilers are inspected annually to ensure they are safe to operate. The inspector checks safety controls to make sure they work properly and inspects inside the boiler, both the waterside and fireside. The inspector looks for signs of problems that should be investigated, such as:

  • Overheating
  • Excessive scale
  • Corrosion
  • Deformed or damaged pressure vessel components

Before the inspector arrives, you can take the following steps to ensure the boiler passes the inspection:

  1. Perform an operational check of the boiler’s interlock controls. Required controls vary with fuel type, burner capacity, number of burners, and whether the burner is forced draft or natural draft. Minimum controls found on all burners are:
    • Safety valve (steam) or safety relief valve (hot water) - make sure the safety relief valve is not stuck but lifts freely; leaking valves may indicate dirt on the valve seat that can be cleaned or a worn valve seat that must be replaced
    • Low-level cutoff - cuts off fuel in the event of low water level and requires manual reset to resume boiler firing
    • Flame scanner - shuts off fuel flow if burner flame is lost and requires manual reset to resume fuel flow
    • Temperature control (hot water) - turns burner on and off to maintain a set-point temperature
    • High-temperature cutoff (hot water) - if water temperature exceeds the high-temperature safety setpoint, shuts off fuel flow to the burner and requires manual reset to resume boiler firing
    • Pressure control (steam) - similar to the temperature control, but maintains a steam pressure setpoint
    • High-pressure cutoff (steam) - if steam pressure exceeds the high-pressure safety setpoint, shuts off fuel flow to the burner and requires manual reset to resume boiler firing.
  2. Make sure the boiler will pass the pressure test. Prior to draining the boiler for cleaning, fill it with water. With the boiler at operating pressure, close the valves to isolate the boiler from the system. If the pressure drops, the boiler will fail the inspection; so, fix the leaks. Start by checking the valves (isolation, drain, and water level) because they are most susceptible to small leaks that can cause the boiler to fail the test.
  3. Make sure the pressure gauges have been calibrated and are marked with the calibration date.
  4. Clean the boiler waterside. Draining and flushing the boiler will help remove scale and sediment.
  5. Make sure the proper American Society of Mechanical Engineers (ASME) stamp is installed on the boiler. ASME designators shown on the stamp are "U" for unfired pressure vessels, "H" for heating boilers, and "S" for power boilers.
  6. Make sure the water treatment system is working properly. Water treatment helps prevent problems resulting from scale buildup, sediment, and oxygen or carbon dioxide corrosion. Water from boilers that have been laid up for the summer months should he tested prior to putting the boiler back online. Boilers should not be drained during summer lay up to avoid corrosion. If a significant amount of water is added at any time, the water must be immediately heated to at least 180 degrees Fahrenheit to drive off dissolved gases from the water to avoid corrosion.
  7. Check for obvious defects, problems that should be identified and corrected such as unusual noises, deformed door gaskets, damaged insulation, or stains indicating leaks. Drains should be clean and clear and run freely.

Fuel oil-fired boilers are especially susceptible to corrosion on the fireside and leaks in the fuel train. If the boiler firing level is too low, condensation can occur in the stack and cause corrosion.

When bringing a boiler online with other boilers, make sure the operating temperature and pressure are the same as the other boilers online before opening the supply and return isolation valves. When bringing a boiler online, crack the valves and check for unusual noises or vibrations prior to fully opening the valves. For steam boilers, be sure to drain condensate from the steam feed line prior to opening the steam outlet valve to avoid slugging condensate into the steam main.

Combustion Analysis

MODEL 300 COMBUSTION ANALYZER

WARNINGS – BURN HAZARDS!

DO NOT touch the Model 300 Combustion Analyzer probe after it is removed from a stack. Allow the probe to cool before handling.

When emptying filter/trap bowl and particulate trap, be aware that both traps may contain hot and mildly corrosive water. Take the necessary precautions to avoid being burned.

All of the sensors contain corrosive chemicals. DO NOT puncture or take them apart.

CAUTIONS!

To avoid damaging the probe assembly due to excessive heat, remove probe from stack at or before the prescribed time listed below. Allow probe to cool to room temperature before reinserting it back into the stack.

100–1,000°F (38–538°C)...........

Unlimited

1,000–1,200°F (538–649°C)......

30 mins. per exposure

1,200–1,400°F (649–760°C)......

10 mins. per exposure

Note that the high-temperature extended-probe options have unlimited exposure times up to 2,000°F (1,093°C).

  • Allow probe to cool before placing it in case.
  • DO NOT store the Model 300 Combustion Analyzer at temperatures below –4°F (–20°C).

Perform testing using the operating instructions that come with the analyzer.

Causes of Boiler Failures

Automatic low-high water control equipment must be serviced on a daily basis when the boiler is in operation. A high frequency of boiler failures is the result of low water, and can be attributed to a careless boiler operator. A procedure must be established at your facility to regularly clean the glass gauge column by "blowing down" the column at the start of the facility day, during non-peak operating periods, and at the conclusion of the facility day or shift. This ensures ability to determine the level of water in the boiler.

Low Water

A major reason for damages incurred to low-pressure steam boilers is the low water within the boiler. If the condition of low water exists it can seriously weaken the structural members of the boiler, and result in needless inconvenience and cost. Low-pressure boilers can be protected by installing an automatic water level control device.

Steam boilers are usually equipped with automatic water level control devices. It must be noted, however, that most failures occur due to low water on boilers equipped with automatic control devices. The water control device will activate water supply or feedwater pumps to introduce water at the proper level, interrupt the gas chain and ignition process when the water reaches the lowest permissible level, or perform both functions depending on design and interlocking systems. No matter how automatic a water control device may be, it is unable to operate properly if sediment scale and sludge are allowed to accumulate in the float chamber.

Accumulations of matter will obstruct and interfere with the proper operation of the float device, if not properly maintained. To ensure for the reliability of the device, procedures must be established in your daily preventive maintenance program to allow "blow-down" the float chamber at least once a day. Simply open the drain for three to five seconds, making certain that the water drain piping is properly connected to a discharge line in accordance with city building codes. This brief drainage process will remove loose sediment deposits, and at the same time, test the operation of the water level control device. If the water level control device does not function properly it must be inspected, repaired, and retested to guarantee proper operation.

Low Water Cutoff - Tests and Maintenance

There are two very effective tests for low water controls on steam boilers. The first is the quick drain or blowdown test, which should be performed at a time other than a peak steam generating period. As the water is drained from the column the firing sequence is interrupted, the low water alarm signal activates, and the boiler operation shuts down.

The second and more costly method is the slow-drain test. By opening the blowdown valves, the water level can be checked to determine the water level in the column, gauge glass, and boiler. The boiler should shut down while you determine the level in the gauge glass.

As a safety precaution, the low water float chamber of hot water boilers should be tested daily, at the beginning of the shift, at the end of the shift, and once during non-peak firing periods. Time of tests and the boiler controls tested should be recorded on your boiler room log.

Annually, or as required, a thorough inspection of all low water control parts shall be performed. The annual inspection should include opening and cleaning the water chamber.