917 Bacon St. Erie, PA 16511

Combustion Quiz Answers

Test Your Knowledge

1 What components are in the main gas train?

  • Lock out Tag out ball valve
  • Drip Leg
  • Wye Strainer
  • Regulator
  • Gas Block Valves
  • Low gas switch
  • High gas switch
  • Test port for setting main gas regulator
  • Test ports for leak test
  • Ball valve for leak testing

2 What is needed for the limits complete circuit?

  • Blower starter auxiliary contacts
  • Air Pressure switch
  • Low gas switch
  • High gas switch
  • High Temperature limit controller output

3 Why is the purge timer so long? What is required before it starts?

  • The purge timer is calculated from the Area inside the furnace multiplied by 4 (to get 4 air changes). Then the total is divided by the total amount of air that is flowing through the burner.
  • Limits Complete
  • Purge permissive

4 What does the limiting orifice do?

  • The limiting orifice is used to set the high fire gas flow to a burner.

5 What does the ratio regulator do?

  • The ratio regulator is used to maintain a ratio to a burner when the air valve is being modulated.

6 How do you set the ratio regulator at low fire? High fire?

  • The low fire is set by adjusting the stem on the regulator which adjust the pressure on the diaphragm. There may be a small by-pass adjustment around the regulator that can be set for a low fire light off but that is a different discussion.
  • The high fire setting is accomplished with the Limiting orifice

7 How do you adjust the gas flow at 100% output to the burner?

  • By adjusting the Limiting Orifice!

8 How do you verify the flow and what instrument is used for measuring?

  • The flow to a burner is accomplished by either an external metering orifice or from an orifice that is built into the burner.
  • A manometer either a U tube or Incline is used for measuring the flows.

9 How does the flame rod work?

  • Not to get into the whole theory but the Flame acts as a path for current to flow between the flame rod and ground on the burner. This does not mean the flame rod must glow red as long as the flame is touching ground and the flame rod there will be a micro amp. Current to be measured.

10 How can you verify operation of the UV sensor?

  • With Honeywell UV sensors you can be test with a lighter.

11 How do you know the number of burners in a zone?

  • Typically you can look at the air header or gas header and determine the number of burners in a zone.

12 Are the control motors 4-20mA or position proportional drive?

  • This will be determined from the controller or the control motor model # .

13 Can you verify the controller output to the valve position?

  • If the controller output is at 50% can you look at the valve to verify it moved 50%?
  • The change in the controller output should move the valve and then it can be verified by the air tap to the inlet of the burner.

14 Do you know how to balance the burners in a zone?

  • This is a question to test if you know how. This would be connecting U tube manometers to every burner in a zone and verifying they all read the same value.

15 What effect can a dirty combustion blower filter have on the burners?

  • The dirty filter can restrict the amount of are available for the burner to use so the high fire capability could be limited.

16 How can you identify a failed thermocouple?

  • A failed thermocouple, if open, should read a max value or on some controllers will tell you there is a thermocouple failure. If shorted the reading will be ambient temperature. The best way is to verify with a test instrument.

17 Why is pressure control needed?

  • Pressure control is used to help prevent cold air from infiltrating through the cracks in the furnace.

18 Why is the high temperature limit set where it is and what happens if the set point is exceeded?

  • The High Temperature Limit controller is there to protect the furnace from running over the temperature it was designed for. When the setpoint is exceeded the main gas valves will shut down as it is a part of the Limits Complete circuit.

19 What can cause flame distortion?

  •  wrong settings
  • broken tile
  • internal burner part failure
  • blockage

20 Is there routine cleaning of the igniter, flame rod or UV sensor?

  • There should be a routine but that is set by the company.


Now what?

If you failed, don’t worry we’re here for you! Call Onex to schedule your onsite training session to gain the comprehensive knowledge of your combustion systems.


Erie Location

917 Bacon Street
Erie, PA 16511
P. 814.838.9638
E. info@onexinc.com

Pittsburgh Location

3711 West 3rd Avenue
Beaver Falls, PA 15010
E: info@onexinc.com

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