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Thread: Pressure Testing Gas Line

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  1. #1
    DIY Junior Member cloves's Avatar
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    Question Pressure Testing Gas Line

    Hi everyone, wondering if anyone had any insight here. I just had some gas line installed by a plumber. When he finished he put air into the line (25PSI). A day later the pressure has dropped to (11PSI). He mentioned it should be anything to worry about because air changed and expands based on temp and he also mentioned that his valve maybe leaking. So my question is does that make much sense? If the PSI is dropping doesn't that mean there is a leak in the system and when gas gets connected isn't it going to leak out as well?

    I think the local inspector uses 5PSI for 24hrs for final inspection.

  2. #2
    DIY Member Lightwave's Avatar
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    I'm not a plumber, but that smells like BS to me. Air pressure in a confined volume will change with temperature but a 14 PSI drop over one day sounds far too big to be entirely a thermal issue. There's probably a hole somewhere.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Thermal pressure changes go BOTH ways, down when it cools and up when it gets hot, but the air does not "disappear". He has a slight leak, possibly at his gauge, but he should FIND it. He may be counting on the fact that it appears to be a "small" leak, and since the gas will be at 1/100 of the test pressure it MIGHT not leak out, or if it does, it would be in such a small concentration that it would not be dangerous, if it cannot collect in a closed space.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Normally when we test gas, we pull the shutoff valve and cap it.

    Then after inspection, we reinstall the shutoff and soap test.

  5. #5
    In the Trades Wally Hays's Avatar
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    2.5 x working pressure. No permissible drop. Should hold forever.
    Perception is 3/4 of reality

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    Master Plumber-Gas Fitter shacko's Avatar
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    You will get a difference in the drop of a gas test, but that's too much.

    Thats why I liked the mercury test (not allowed anymore) as soon as the test was on you knew if there was a leak or not by viewing the shape of the column.

  7. #7
    In the Trades Wally Hays's Avatar
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    Shacko, you can still buy a manometer that uses water. Very accurate,, PITA to set up though. I like the old mercury ones also but I suppose time marches on.
    Perception is 3/4 of reality

  8. #8
    Moderator & Master Plumber hj's Avatar
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    using a water manmeter at the required test pressure would require a water column about 10' tall, and maybe 20' if they wanted a 10 psi test.

  9. #9
    In the Trades Wally Hays's Avatar
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    Not useable for high pressure testing. Very good for in./wc.
    Perception is 3/4 of reality

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