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Acceptable gas pressure reduction

cabbydog | Posted in General Discussion on November 1, 2015 09:12am

I’m installing gas line in my Lake Tahoe cabin for the first time. Gas company has installed the service line to the house.

I have installed the main 1-1/4″ line, and 3 branch lines (range, fireplace, water heater).

No appliances are connected. branch lines end with caps after valves.

On October 26 at 1pm the line was pressurized to 20 psi with compressed air.

The temperature was 61 degrees.

Today, Nov 1 at 12:30pm, I returned to find the pressure had dropped to 17.6 psi.

It was 44 degrees.

A decrease of 2.4psi over 7 days.

A temperature decrease of 17 degrees.

Gas Pressure Law: P1/T1 = P2/T2 

20/61=.328

17.6/44=.4

Doesn’t sound like much, but this is my first gas line install.

Is this acceptable.

Is it safe?

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Replies

  1. junkhound | Nov 01, 2015 11:15pm | #1

    You have leak(s)

    First, use absolut temp (Rankine) for gas law calcs, not F.

    Also, volume of pipe will decrease due to TCE of pipe, so less pressure drop due to temp than strictly by gas law.  

    3rd, have seen cheap water pipe reducer fittings as shown porous to gasses.

    Pressureize to 100 psi, and find your leak(s) with soap bubbles. Be patient, dont expect big bubbles right off. 

    1. User avater
      Mike_Mahan | Nov 02, 2015 09:31am | #4

      Black iron water pipe fittings??????

      Since never.

  2. user-1116010 | Nov 02, 2015 06:05am | #2

    operating pressure

    2 psi is considered high pressure for piping systems connected to a natural gas supply and where systems use 2psi delivery pressure, a step down regulator is required to reduce the pressure at appliances which typically operate at 12 - 15 inches water column ( 27" water column equals 1 psi ). 

    The IRC requires new gas piping to withstand a minimum test pressure of 3 psi for ten minutes; we prefer to test for 24 hours with a minimum test pressure of 1/3 of the pressure gauge max reading - we use a 30lb gauge.

    Nice to see you using iron pipe, we will not install or service csst.............

    1. cabbydog | Nov 02, 2015 11:27am | #5

      Thank you.

      The drop is over 7 days.

      Wont be back in tahoe for at least another 5 days.

      Cheers!

  3. DanH | Nov 02, 2015 07:11am | #3

    It's simple enough to watch the gauge for another 24 hours.  If it continues to drop you have a leak.  If not then the pressure change was due to temperature effects, oxygen reacting with the metal in the pipe, etc.

  4. User avater
    Mongo | Nov 06, 2015 09:05pm | #6

    You're in trouble.

    I forwarded this to Roger Goodell.

    He's going to send an inspector named Ted Wells out to investigate. You don't need to talk to Wells, as he'll already have the report written before he lands in Tahoe.

    The gist of it is...the temperature change has nothing to do with your loss of pressure. Someone let the pressure out, and that someone happens to be YOU.

    You are hereby prohibited from working on your house for the next four Sundays.

    Is there any chance you've beaten up a women over the last few weeks? If so, let me know and we can get that 4-week suspension revoked. If you've beaten up more than one women, there might be a pay raise in there for you somewhere.

    1. mark122 | Nov 07, 2015 08:25am | #7

      how do you feel about Floyd Mayweather Jr.?

      1. User avater
        Mongo | Nov 07, 2015 10:24am | #8

        ??

        I have no idea how you could go feeling about Floyd Mayweather Jr. 

        He might punch you if you try.

        1. mark122 | Nov 07, 2015 09:55pm | #9

          or his wife if he cant hit you...

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