slow gas line leak - how to detect?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by kmuddzy, Oct 14, 2012.

  1. kmuddzy

    kmuddzy New Member

    Messages:
    41
    Location:
    New Jersey
    Hi. I have a combination csst and black pipe gas line system and it has a leak. At 10psi it will drop 4 psi in an 18hr period but at 5psi it will only drop .5psi in the same amount of time. Either way, there doesn't seem to be enough air leaking to make bubbles using a detergent/water mix. Is there a better way to detect such a slow leak?

    I've taken apart the black pipe, put the appropriate pipe putty on it and retightened it very hard. Every time there is still a leak this is driving me nuts.

    Thanks for your help!! Keith
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,830
    Location:
    New England
    The gas company, and probably some HVAC or plumbers, generally have a gas sniffer probe that can detect very small leaks. Never looked for one to buy, but a tool rental place might have one.

    It could be a porous cast fitting or a valve (don't trust the stuff from China!, but it could happen from anywhere) and not in the threaded connection.
  3. Killer95Stang

    Killer95Stang New Member

    Messages:
    46
    Location:
    Southern CA
    I'm no plumber... but I have had a similar situation.. and I did stay in a Holiday Inn once...

    First.. I'm assuming you are testing your gas line with your gas meter disconnected from the system. If not, you are most likely loosing the gas from the vent on the meter. Most meters cannot handle that much pressure in the line past the regulator.

    My second tip... call your gas company!! They will come out typically for free to test for gas leaks... even at midnight on a Sunday. Socal Gas had not problem coming out on off hours to test when I had leak near my meter. Once he fixed the meter issue, he used his gas sniffer to test around the the new tankless water heater that was put in.
  4. kmuddzy

    kmuddzy New Member

    Messages:
    41
    Location:
    New Jersey
    Thanks everyone. this is a new LP gas line install for a new heating system, dryer and hot water heater. The LP tank hasn't been installed yet and I am just testing this for the rough-in inspection. There isn't a regulator on the lines - the black pipe is simply capped as it runs outside.

    I thought that maybe the valves were bad (or even the guage) but obviously the only way I can figure this all out is to replace them one at a time and retest, which is time consuming. That is why I was looking for a way to detect the leak so I could actually fix the problem rather than spend more time on something I have already spent way too much time on. I've already pushed back my inspection 3x thinking I would easily be able to solve this by the next day only to see it lose psi again. I'm sure the inspectors don't like me doing that....

    I will see if a plumber or rental place has something I could rent. Thanks for the suggestions - if anyone has any others let me know.

    Keith
  5. kevink1955

    kevink1955 New Member

    Messages:
    31
    Location:
    L.I. New York
    What are you using to air it up, I have a small oil less compressor that I use and once the system under test is up to pressure and I shut the compressor down the air will leak back thru the compressor. It's a slow leak but it will screw up the test.

    I now use a schrrader fitting so I can disconnect the compressor, I also leak test the schrader fitting so I know it's leak free.

    Just a thought
  6. kmuddzy

    kmuddzy New Member

    Messages:
    41
    Location:
    New Jersey
    Good thought & thanks. I use a bicycle pump on a schrader valve. It only takes 15 seconds to get the piping to 10psi. I used to keep it connected but I've disconnected it once I reach pressure and still get the same leaking. I read that the union fittings are very prone to leak and also that one shouldn't use dope with teflon in it on these unions. I first used dope with teflon so I'm going to go back and either clean or replace the union fitting using non-teflon dope. I will update this thread once I figure this out.
  7. Rich B

    Rich B DIY Senior Member

    Messages:
    283
    Location:
    New Jersey
    Air up the line with 10-15lbs of air.....Get some Dawn dishwashing liquid....thin it with a little water.....paint the solution onto every fitting and let it sit......You can find the smallest leak with this technique....I had a line I was testing and it had avery slow leak......It was the cap I bought from Home Depot just to test the line.....Made in China and porous.....leaked right thru the metal and this was not the first time for this issue with something from H-D
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,311
    Location:
    Cave Creek, Arizona
    quote; call your gas company!! They will come out typically for free to test for gas leaks...

    In this area, if you call the gas company, they will come out and check the meter to see if you have a gas leak in the house. If you do, they "LOCK" the meter and red tag it. Then you MUST call a licensed plumber. He locates the gas leak, obtains a city repair permit, gets an inspection, THEN the city calls the gas company so the gas is turned back on. THis is usually about a one week process. IF you call the plumber first, he will locate and repair the leak in about a day.
  9. bluebinky

    bluebinky Member

    Messages:
    383
    Location:
    Santa Clara, CA
    Double check the gauge and the immediate surroundings with soapy water (try the kids bubble making stuff). I almost always seem to get leaks there.
  10. kmuddzy

    kmuddzy New Member

    Messages:
    41
    Location:
    New Jersey
    THANKS! for some reason I didn't think about increasing the air. I googled this problem and found that you shouldn't use teflon pipe dope in a union. Not sure if this is true but I cleaned out the union, used some non-teflon pipe dope, and really tightened it. I then jacked up the PSI to over 15lbs and coated the joints. A Tee hub had a very small leak and the union was still leaking a small amount so I tightened both as hard as I could using big plumbers wrenches and I am now good.

    The lessons I learned doing my first LP gas line rough-in installation:

    1) CSST is coslty but much simpler and easier than black pipe.
    2) Stop by the plumbers supply and get good pipe dope and don't be shy with it (on the male threads only).
    3) Use some big plumbers wrenches and tighten the joints harder than you think is necessary. I was straining at times.
    4) The black pipe and fixtures made in China can be defective so don't rule that out.
    5) If you have a slow leak, jack up the PSI (make sure your guage can handle it) and coat the joints with a thick slurry of dish detergent and water and watch for subtle foaming.

    Thanks to all that replied and helped!!!
    Keith
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,311
    Location:
    Cave Creek, Arizona
    Use kid's soap bubble solution instead of soap and water. It will "stick" to the joint a lot longer and any bubbles will also be more visible for a longer time.
  12. kmuddzy

    kmuddzy New Member

    Messages:
    41
    Location:
    New Jersey
    Good to know - thanks!
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