bbq supply line problems?

I have a 25' - 1/2" natural gas supply line between the back of my house and my bbq. It has been there for 10 years and I've never seen any issues. '

Recently I noticed each of the two independently controlled burners exhibiting a pulsing. The period of this pulsing is 3-4 seconds on, 2-3 seconds off. This seems to repeat indefinitely. THe duration of the off state is long enough that the flame doesn't always re-ignite on its own.

Here is what I've done thus far to debug the problem. I replaced the regulator and that didn't have any effect on the problem. An interesting thing that I noticed when replacing the regulator was that there was some water in there, maybe a teaspoon.

On a related note, a neighbor mentioned that he had problems with his gas line and called a plumber who determined that there was water in the supply pipe. Coincidence? How would the water get in the pipe? How do I determine if there is water in the pipe?

Another thing I thought about was a faulty thermocouple in the bbq? The thing that makes me think that this probably isn't the problem is that the behavior is the same with either of the two burners. I'm thinking that each burner control valve has its own thermocouple. Thoughts??

At this point I need to narrow down the problem to either be in the pipe or in the bbq. I'm planning to build a manometer to test the flow pressure in the line.

If there is water in the pipe, can I just tap into the line at the back of the house and blow it out with a compressor? If I have to do this, what pressure should I use? Are there concerns that an overly high pressure might cause problems with the pipe?

Any thoughts on what might be going wrong here?

Am I on the right track or should I go down some different paths?

thanks in advance for the help!

Chris

Insome places, a gas line is required to have a drip leg. If you have one of those, you should be able to remove the cap and drain any trapped moisture. NG devices run on very low pressures, so you'd have to isolate the pipe from any diaphrams or regulators as pressure high enough to blow out the lines would likely mess them up, plus, it could blow any scale or crud in the lines through, blocking things up.

That's a fairly long run for 1/2", consider putting in a larger one for the next grill which will likely want more gas, depending on the draw of the burners. Since you've replaced the regulator, I'd guess you have something blocking the pipe partly...could be water, rust scale, or something else. You may need to replace the run. If sloped, you could add a drip leg and maybe a sight glass and see if there was an accumulation that needed purging.

gas line

The most common thing is a rusted out gas line and ground water has filled the pipe. The pulsations are when the line develops enough pressure to push through the water and then the water "sloshes" back down and cuts it off again.

gas line

What is the average lifespan of a coated gas pipe? Is it possible that it is rusted thru in 10 years?

If the problem is water in the pipe should I first blow it out or should I do a pressure test on the pipe first to insure that it is still intact? I never gave any thought to the possibility that the pipe has rusted thru.

Is it still wise to confirm that the flow thru the pipe is the problem by using the manometer to measure the pressure while gas is flowing?

thanks,
Chris

If the pipe runs outside, condensation becomes an issue. Have the line pressure tested and blown out. Water will destroy your regulator and gas valve.

gas pipe

Bad news!

I have a shutoff valve between the backyard section of pipe and the house, so I closed that valve and installed my pressure gague on the other end of the pipe. I pumped the line up to 10psi from the bbq side and in a matter of 1 minute the pressure was down to 0. I repeated this a few times with the same results. The only thing that I can see that would invalidate these results is if the shutoff valve between the house and yard gas pipes was the weak link. It seems like these valvles should be able to handle much-much higher pressures without any problem.

I think the line is a gonner. SInce it is run underneath the concrete patio it looks like I'll have to convert to propane.

thanks for all the help!

Chris

thanks for all the help.

pipe

Most of the "approved" coated pipe is not much better than painted black pipe. I have seen it rust through in two years in damp conditions. That is why I NEVER use it unless I also tape wrap it first.