Technical Reports
Maintenance of a Gas Burner

Gas Burner Maintenance

Flame adjustment and all operating safeties are a vital part of an efficient and safe gas burner performance. The flame should be a billowing type, blue with yellowish orange tips.

Warning: A lazy loafing type flame, colored yellow, red, or orange, is very unsafe and may lead to an explosion. Stop the oven, obtain qualified service people and adjust the flame properly. This should only be done with the oven doors fully opened and the area completely vented.

Warning: Never, should any safety device be wired out (by-passed) or eliminated from the system. All components should be kept free of tar and creosote which can freeze the safeties. The combustion air fan should be kept clean. Gas pressure and make up (combustion air) should remain constant. Gas burner assemblies are manufactured to operate very safely. Lack of good maintenance and sanitation practices causes accidents, yet it is lacking in many plants.

Burner Maintenance Program

An adequate preventive maintenance program, periodic inspections of gas burning equipment and controls is necessary to assure continued safe operation of important production units. The exact schedule for inspection of equipment should be carefully developed and rigidly adhered to.

Burner supervision is the responsibility of plant management. They may delegate responsibility to a qualified engineer who has received special training and who has experience with an intimate knowledge of the entire burner installation.

Instructions should be prepared by the manufacturer or installer for maintenance of the burner equipment. Safe burner operation requires the testing of burner safety devices at least weekly - more often if deemed advisable. General practice is to prepare a checklist to be followed when making maintenance checks.

Such a checklist will cover at least the following items.

  • Gas safety shut off valve
  • Flame failure control response
  • Burner gas control system
  • Time delay timers
  • Electric ignition system
  • Pilot burner assembly
  • Motor starter interlocks
  • Supervisory pressure switches
  • Damper limit switches
  • Supervisory temperature switches

After completion of the daily pre-operating checklist proceed to the following operation instructions.

Caution: If your food-processing oven is gas heated, do not attempt to by-pass any of the combustion safeguards interlocks.

  1. Prove food processing oven doors open microswitch N.C. contact, opens when door is closed. Fixed non-adjustable.

  2. Prove fresh air damper open micro-switch N.O. contact, closed when damper is full open. Fixed non-adjustable.

  3. Prove exhaust damper open micro-switch N.O. contact, closes when damper is full open. Fixed non-adjustable.

  4. Prove exhaust fan running, auxiliary contact on start N.O. contact, closes when starter is energized. Fixed non-adjustable.

  5. Prove recirculating fan running, auxiliary contact on start N.O. contact, closes when starter is energized. Fixed non-adjustable.

  6. Low gas pressure cut-off, (Mercoid switch #PRL-153 and Honeywell on ovens after 1995) N.O. contact, closed with range of 1" to 6" W.C. Set cut-off point 25% less than pressure when burner is firing at maximum rate. Example: Manometer reading 4.50 W.C. x 0.80 = 3.6" W.C. (maximum operating pressure - 1 PSIG).
    Check your low gas pressure cut-off setting.
    Check your gas pressure at burner maximum firing.

  7. High temperature limit switch supply air located in discharge of main fan range 350°F to 550°F to meet FM, IRI, AGA, NFRA, AND CSA approval. Is your setting changed?
    Normally closed contact open when temperature rises above setting.

  8. Prove safety valves closed. Honeywell 133569 IRI Proof of Closure SW. contact closes when safety valves are closed. Non-adjustable, on the safety valve.

  9. Prove low fire start, micro-switch. Normally open contact, closes when burner control operating is in low fire position. Non-adjustable.

  10. Airflow switch Chicago Safety #JD-2. Normally contact, closes with pressure of main recirculating fan. Range .07" to 4.0" W.C. factory setting of .10" W.C. (can be adjusted).

  11. Low combustion air cut-off Chicago Safety #JD-2. Normally open contact, closes with rise of pressure range .07" to 4.0" W.C. Set cut off point 25% less than pressure when burner is firing at maximum rate.
    Example: 3.50" W.C. x 0.75 = 2.6" W.C. setting
    Low combustion air cut off setting
    Combustion air pressure

  12. High gas pressure cut off (later food processing ovens use Mercoid switch #PR-153 also Honeywell on ovens after 1995).

    • Normally closed contact opens with range of 2" to 16" W.C.

    • Set cut off point 25% above pressure when burner is on low fire start.

    • Example: 6.3" W.C. x 1.25 = 7.88" W.C. setting

    • Maximum operating pressure 1 PSIG

    • High gas range spring adjustable 5" to 27" W.C.

    • High gas pressure cut off setting

    • Gas pressure at burner minimum firing

  13. Purge timer Eagle #HD32A622 5.5 minutes to permit pre-purge of unit prior to light-off of burner.
    Setting of purge timer (three minutes minimum). 1995

  14. Ignition timer Eagle #HD32A621 55 seconds.
    Set at 15 seconds - required by Insurance Company IRI (limited time for ignition).

  15. Combustion safeguard safety check for proper response. Shut gas off at cock closest to burner. Combustion safeguard should respond in 4 seconds or less - refer to manual on type of unit used can be found in section of this manual.

Use of Test Meter Testing UVM and TFM controls requires the use of an AC-DC multi meter, with a 20,000 ohm/volt DC rating.

With the test meter leads inserted into the test jacks, a steady DC voltage reading of 4.0 to 5.5 volts (UVM) and 14 to 17 volts (TFM) should be obtained when the controls are detecting a flame, and zero when no flame is present.

On TFM controls only, a micrometer may be connected in series with the wire to Terminal S2. Normal flame will produce a meter reading between 4 and 10 microamps.

Flame Signal Testing

  • Manually shut off the main fuel valve.
  • Set the test meter on the IC scale and insert the meter leads into the test jacks (if meter reads backwards, reverse the meter leads).
  • Indicate a normal start up.
  • When flame is established, the test meter reading should be 4.0 to 5.5 volts (UVM) and 14 to 17 volts TFM should be obtained when the controls are detecting a flame, and zero when no flame is present.
  • Inadequate flame signal may be improved by:

     

    • Assure that the flame detector is clean and within the ambient temperature limits.
    • Assure that the flame is sufficiently large enough to detect.
    • If UV scanner is used, make sure sight pipe is not clogged.

Flame Failure Test

  • Initiate a normal start up.
  • Manually shut off all fuel and observe the loss of flame signal on the test meter.
  • If flame signal does not reduce to zero within flame response time of the control, verify that the UV flame detector is not actuated by the spark.