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Thread: How reliable is a Pressure Test?

  1. #1

    Default How reliable is a Pressure Test?

    Home is new. 1500SF on slab, one level with two baths. W&D in garage. Plumbing still under warranty.

    Water meter indicated a leak (1.5 gallons/day) recently and a leak was found and repaired between street/meter and home. Meter stabilized for a few days and then began to move again. Now losing about 1 gallon per day.

    Plumber reluctantly came back but didn't care to look at meter this time but chose a pressure test. The small guage, a bit larger than a silver dollar indicated 120 psi. The guage, attached to one of two outside bibs, was watched for about 20 minutes and indicated no leak so plumber feels I have no leak.

    Toilets were off, ice maker off, hot water off (for 10 days) during meter checks. Dishes were washed in cold water to let hot water tank stabilize.

    Assuming there's a leak of less than two ounces per 20 minutes, how reliable is a pressure test? How much would the needle move and could you even see it?

  2. #2
    Plumber/Owner Norcal's Avatar
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    I don't see any way that they could detect that small of a leak with a pressure gauge.

    Doesn't your meter spin to show that the water is running. The meters in my area can detect a small toilet leak.

    Is there a main water shutoff valve on the outside of the house that you can shut off to see if the leak is under ground or inside the house.

    Good luck

  3. #3
    Plumber Cass's Avatar
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    Turn off the main shutoff to the house and if there is a leak the leak detector on the meter will move showing the leak. What material was used for the water line from meter to house.

  4. #4
    Commercial Plumber markts30's Avatar
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    Quote Originally Posted by scooter11
    The small guage, a bit larger than a silver dollar indicated 120 psi. The guage, attached to one of two outside bibs, was watched for about 20 minutes and indicated no leak so plumber feels I have no leak.
    Did the plumber pump up the system to 120?
    If not and if that is the static pressure at your house, you need a PRV...(and then an expansion tank...)

  5. #5

    Default Misc

    I think the regular pressure is 60. Plumber did pump it up to 120. I don't know what the water line material is. There is no other shutoff valve other than the one about two feet after the meter, out in the lawn.

    I wish I had just drained a 1/4 cup of water before he shut his test down just to see if he noticed a drop in pressure, just to satisfy myself.

  6. #6
    Plumber jimbo's Avatar
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    I am not clear on this. You say you washed dishes, albeit in cold water, for 10 days. ( Plenty of Right Guard, I assume!). So, your water was not turned off, and that pressure test was completely meaningless.

    As others have pointed out, most meters have a dial hand, or a little triangular indicator, and in a mater of a few minutes you can determine if any water is flowing through the meter.

    As far as the pressure, I hope you have a regulator between the point where you are measuring 120 PSI, and the house. 120 would be way too high for in the house.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default test

    Where did he turn the system off to make the pressure test. Unless he shut down the valve ahead of the meter, he did not test your entire line.

  8. #8
    DIY Senior Member TedL's Avatar
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    Quote Originally Posted by hj
    Where did he turn the system off to make the pressure test. Unless he shut down the valve ahead of the meter, he did not test your entire line.
    Unless he shut that valve, he didn't test anything, as the supply would maintain the pressure even in the presence of a leak many times the one suspected to be present.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    Default valve

    If he turned off a valve at the house, then he would have tested the house piping, but not the main from the meter to that valve. It was indicated that he pumped the system to 120 psi, so he had to have sealed the system somewhere.

  10. #10

    Default More Misc

    The problem, as I see it, is the plumber doesn't want to act in an honorable manner. He wants me to go away and stop bothering him.

    I've been running my own tests. When I shut the house valve off ... I hope there's no snake in there and turn the valve 90 degrees clockwise ... the meter stops moving ... that little red wheel stops turning. (Two revolutions of the little red wheel = 1/10th tick on the sweep hand which has to turn one full revoultion to indicate 10 gallons.)

    When I turn the house valve ON, the meter (little red wheel with a head, four legs, and a tail - I call it the "turtle") moves.

    One "explain it away" from the plumber was that the water loss was evaporation in the hot water tank. So I shut the hot water off and took showers at the gym and washed dishes in cold water (ever been camping? perfectly acceptable) for days and days ... so he wouldn't have that excuse. The same with toilets and ice maker.

    Not to confuse anyone, when I collect data on the meter, I'm not using the water. For example, I shut the toilets off at 10:00pm, take a reading, and then in the morning, I'll take another reading at 7:00am and then turn the toilets back on, satisfied that those nine hours worth of data (meter readings) tell me something. I even went 24 hours on one test.

    I think the pressure test, where the plumber shut the main house valve OFF, was just an attempt to blow smoke up my rear but what do I know. That's why I've been asking. Can a 20 minute pressure test (WITH THE MAIN HOUSE VALVE OFF) indicate anything on a 2 oz loss typically in that time frame?

    To me the METER is the gold standard, not a pressure test.
    Last edited by scooter11; 01-19-2007 at 08:57 PM.

  11. #11
    Plumber Cass's Avatar
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    Try this unless you have already. Place a pressure gage on a hose bib and be sure there is no leak there where it is connected when turned on. Close every valve going to every fixture in the whole house Water heater, toilets, washing machine, everything. Then close the main valve coming into the house. Record pressure. Let it sit over night and record pressure again. See what you get.

    You can purchase a pressure gage at Low*s.
    Last edited by Cass; 01-20-2007 at 03:41 AM.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default leak

    If the meter is moving there is a leak, but if there is a leak, and the valves hold tightly, then the pressure should also drop when the system is isolated from the meter's supply. You are indicating two different things, that the meter is running but the pressure does not drop, so we cannot determine which is "real", of if the testing is being done properly. But, water does not "evaporate" from the water heater, and if he really believes that then you need to have the contractor send a different plumber.

  13. #13

    Default Cass

    Re: Pressure test to outside bib ... Yes, that's what the plumber's two workmen did, except they pumped it up to 120 psi and then they waited ... but only 20 minutes, not overnight.

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