Flames at End of Tubes near Manifold


  #1  
Old 01-04-10, 09:23 AM
W
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Flames at End of Tubes near Manifold

Last Saturday on my HydroTherm Model VGA150 BS gas fired steam furnace I changed a defective thermocouple for the standing gas pilot. I have been going through 2 thermocouples a year for the past several years.

Thinking the pilot assembly was too close to one of the tubes and the heat from the flames coming out of the tube was causing the thermocouples to burn out so often I moved the position of the pilot assembly slightly away from the tube I thought it was too close to. When I lit the pilot and turned the knob on the controller to the on position flames appeared at the end of all four tubes near the manifold. When this happens I turn off the electric power to the furnace and restarted it. Flames again appeared at the end of the tubes near the manifold.

I then positioned the pilot assembly closer to the tube I had moved it away from and it appears to be operating normally again.

Could it be that when I reinstalled the thermocouple and positioned the pilot assembly further away from one of the tubes and it is taking too long for the gas to ignite? Or perhaps the flame on the pilot was too low? Not sure why the gas was igniting at the end of the tubes and at times space between manifold and the tubes. There was also a "roaring noise" when this happened. Iím also not sure why the thermocouples are burning out so frequently.

Thanks for your help

Wally
 
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Old 01-04-10, 10:16 AM
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If the pilot is moved far enough away from the burner, ignition will be delayed - with more than the usual amount of gas getting into the burners before ignition. This can cause flame rollout back to the burner-tube inlets and a "whoosh" sound. Best not to monkey with the original pilot's location.

Maybe your pilot flame is set too high and/or enveloping too much of the thermocouple's tip? That can cause overheating of the T/C and shortened life.

A photo or two would help. Upload to one of the free image hosting sites, and link here.
 
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Old 01-06-10, 06:46 AM
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Thanks Mike that is a good explanation. I was concerned enough to call our local gas company and they sent out a technician to look at the problem. Using a device that sensed gas leaks he found the valve controller was not working properly. That is, when he set the knob on the controller to the pilot position a small amount of gas was leaking out of the openings in the manifold that lead to the tubes. Apparently the valve that controls the main gas flow was leaking. He replaced the controller, adjusted the pilot and main gas flow.

I think the controller issue is seperate from the issue you described. When the pilot was repositioned away from the tubes and the old controller was in pilot position there were no flames at the ends of the tubes even though a small amount of gas was leaking from the manifold openings. It was not until I turned the knob on the controller to on position that the flames appeared at the end of the tubes and the roaring sound started. When I moved the pilot back to its original position the furnace operated normally.

The problem I decscribed I believe was caused, as you said, by delayed ignition from moving the pilot from its original location. The leaking control valve had nothing to do with the flames at the end of the tubes or the roaring sound. It was however something that needed to be replaced.

I hope the technician adjusted the pilot flame correctly - I've burned out too many thermocouples
 
  #4  
Old 01-06-10, 09:22 AM
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Burning back at the orifices is usually due to excessive manifold pressure, too low of manifold pressure, plugged burners or missaligned burner manifold with burners.
 
 

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