Gas Line Filter?

I don't know if this is appropriate for this board or not, but I figured that most plumbers have some experience with gas lines too. Anyway, I have a commercial natural gas stove with a pilot on each burner (6 total). The pilots slowly get lower and lower over several months until they refuse to stay lit. I took out one of the pilot lights and cleaned out the supply tube for it with an air compressor. I had a bunch of black material come out. Since then, that pilot has been working great.

I've got a feeling that the offending foreign material might be coming through the supply line. The lines are quite old. Also, there was some recent construction work that had to connect to the existing lines. Does anybody know of any in-line natural gas filter I can put in place before this stove in case this is the problem?

If anybody has any other ideas on the source of this black material, I'm game. My initial instinct was it was carbon buildup, but wouldn't that be at the pilot tip itself and not back in the supply tube?

It has been close to forty years since I saw a gas line filter and I think that maintaining one would be as much trouble as maintaining the pilot burners on your range. The filters that I saw way back then were in-line units that had a felt-like material in them.

I think that what you may be finding in your pilot burners is compressor oil. Do you have a "drip leg" assembly on the gas line just prior to the range connection? This would be a Tee fitting with the gas entering the side tapping and exiting the top tapping. The lower tapping would have a nipple (usually 4 to 6 inches long) with a cap on the bottom. If you do have this fitting then you might want to turn off the gas prior to this fitting and then remove the nipple or cap to be sure the nipple is clear of foreign material. Use proper sealing materials when replacing the nipple and cap.

If you do not have the drip leg then install one.

filter

Drip leg debris traps should cure your problem if it is coming from the gas line, rather than building up externally from deposits in the air.