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Posted by Jack, CVMS on December 18, 2003 at 06:53:29:
In Reply to: electrodes posted by Tim on December 17, 2003 at 21:57:55:
The distance apart, or gap, on most burners is 1/8"
The distance above the nozzle centerline on the most common Becketts (AF, AFG, AF15, AF II) has been 7/16", but they recently began recommending lowering that to as little as 5/16".
The distance forward of the nozzle face is somewhat related to the nozzle angle, but that variation diminishes as the gap is brought closer to the nozzle centerline.
For a 90° nozzle, you can have the gap flush with the nozzle face. With an 80° nozzle, it can be flush to 1/16" forward. For a 70° nozzle, 1/16" to 1/8".
The distance forward, while it should be adjusted carefully, isn't as critical as some would suggest, as the spark is blown forward into the fuel spray in a horseshoe pattern. It is important to get quick, sure, ignition at each startup.
With most modern flame retention burners, the flame will sustain itself after a few seconds of running, and newer burner primary controls "interrupt" (they turn it off) the ignition cycle within 30 seconds of startup.
As with any service work on the burner, it is important to make any adjustments with the aid of combustion analysis for proper, efficient burning, and minimum CO production.