Flame safety timing

Servicewiz_3

Does anyone have any good resources on finding out what is the acceptable safety timing for flame lockout on a gas or oil burner when you know the BTU input? Any help is greatly appreciated!

Tim McElwain

Flame Lockout

I assume you are talking about the safe shutdown of a burner. On most gas ignition systems today it is .8 of a second or slightly higher to maybe 2 seconds it depends on the system. On older systems such as a thermocouple it can be up to 180 seconds. On a bi metal pilot 25 to 30 seconds and on a mercury pilot 30 to 45 seconds. On some new decorative appliances they have a quick drop out of about 30 seconds. The trial for ignition times however are different for each system and you must look at the module or integrated controls for those times.



On oil each burner system may be slightly different, I am sure some of the oil guys will help with those.



On commercial industrial burners you have to check the specs on the burner system.

Steamhead

On oil

There have been controls with up to 70 second TFI (trial for ignition). All the new residential ones are coming thru with 15-second TFI and we upgrade to these wherever possible. If you use an oil valve with a built-in delay (such as the PD Timer on a CleanCut fuel unit) with a 15-second control, you effectively drop your TFI to 10 seconds or so.



Commercial jobs go by whatever the manufacturer says to use.



If the flame fails while running, most controls would immediately stop the burner and either try to re-start it or just lock out. Some might run thru a purge cycle before restarting.



Personally I'd like to see a 5-second TFI on oil. If a burner doesn't light off in a second or so, that's a PROBLEM!