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pressure drop/test

steve gates
steve gates Member Posts: 329
in a gas line test. Rather large line, filled durring heat of the day/ How much pressure drop is allowed for the cold of the night, or in some cases day? If it comes back up the next day fine But if the temps have dropped it won't come back up. Course if it goes to 0...

On my residentials I allow 1 or 2psi. and still don't trust it till it comes back or I don't see it drop any more.

Inspector have no liability, I do.


  • hot_rod
    hot_rod Member Posts: 21,866
    Hard to say

    depends on how much piping, and the "good old Delta T" again. I'll bet an engineer could calculate that knowing the volume and temp change.

    I have seen some of my pex tubing jobs move 10- 15 pounds from a hot sunny day to a cool nightime temperature.
    Fill a large exposed pex layout up in the early morning and check back at noon!

    Nothing like that feeling of a gauge at zero with the inspector pulling up the driveway, to make your heart skip a beat :)

    Check out this piece of pex I foolishly used to connect two solar panels on my roof. The pump quit, and I suspect this went well over 200 degrees. The neighbors said it sounded like a gun shot. Amazingly the crimp rings still held fast and I had to cut the rings to remove the piece!

    hot rod

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  • Gary Fereday
    Gary Fereday Member Posts: 427

    a 60# + gauge pressure has to hold for 15 minutes with no loss! for residential. That alone stops the temperature from lowering the pressure. The pressure guage must be have increments of 2#'s or less. It also prevents the Gas Co. from having to return, and someone fooling around with the loss if it happenes.
  • Glen
    Glen Member Posts: 855

    Eventhough we all know that temp changes pressure - how can you be certain that it is temp. If it comes back up - OK, our code up to 2 psi service and house/building gas pressure, 200 feet or less, 15 psi/15 min zero pressure drop. But you are wise to have complate comfidence in your system before isnp gets there.
  • Paul_6
    Paul_6 Member Posts: 88
    Ah yes, ruptured pex.

    It probably went Waaay over 200. I have used pex to connect water source heat pumps and if you are unfortunate enough to suffer defered maintanence, they can run with low water flow, and not quite cause the high head pressure switch to open, and at 380 psi r22 can get quite hot. first the pex will begin to bulge, and then it will begin to look like a fat happy snake, and then bang it will split. Ive also seen this happen to sched 80 pvc ( it won't burst it just softens the threads and "pops" apart.) But I digress the original question deals with pressure drop in a piping system and the real culprit there is grains of moisture per lb of air in relation to volumn/ temperature. fill up a system on a warm humid day and let it sit over a cool evening and you will see a pressure drop by morning. If I have a crucial application I will purge and pressure test with nitrogen. If you purge the line well and run up to test pressure you will not see any significant pressure drop. usually if I see more than 1 psi out comes the soap.

    Hope this helps Paul.

    P.S. that 1psi would be over a 24 hour period.
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