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  • ot homemade sewer tester(manometer)

    i took on a job that I regret. I was asked to do a municipal sewer for a house that i am doing the plumbing for.
    The engineer has told me i have to do an air pressure test on the line.
    He at first told me I need to test it at 3.7bar for five minutes and then at 2.5 bar for two minutes.
    This sounds more like a destructive test and I think he has some decimals displaced.

    I suspect it is more like 3.7kpa.How could I test this sewer line to 3.75kpa?
    The sewer is 160mm diameter (6") and is 25meters long.I have heard of a machine called a manometer . Could I use science to make a simple machine.?
    I have been told that for every meter of height the pressure in a pipe is ten kpa so I would think if I had a column of water of 375mm I should obtain a pressure of 3.75 kpa.Its how to hook this up that puzzles me.
    Could I use a compressor?How long would it take to pump a pipe that is already full of air to 3.75kpa?

  • #2
    Drain testing is fairly standard, there's kits over here at builders and plumbers merchants, a pair of screw in 4" pipe plugs, one blank, one with a nipple for the pump, gauge etc, they aren't expensive to be honest, they come with instructions for your particular country or area usually, ours are different
    http://www.screwfix.com/p/bailey-dra...WneBoChS_w_wcB
    It's a manometer one, there are gauge ones for a bit more but the manometer is always useful
    Mark
    Ps, they come in 6" too, if it's a straight run of pipe without joints a basic test will do, it's just to check nothing punctured it that may leak into the ground, even erode the ground around a joint, I've seen a bloody great void around a pipe I dug up recently, amazing where all the dirt went, must have been the size of a washing machine.
    Last edited by boslab; 06-22-2016, 01:28 AM.

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    • #3
      No, you don't need a compressor for this, usually for a manometer air test, you just blow into a rubber tube, till the gauge shows the right reading, then lock it off for the hold period.
      'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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      • #4
        You could make a simple manometer by holding a transparent hose in a U shape and partly filling it with water. Connect one end to your pipe and leave the other end open.
        Like you said, water column pressure is 1 atmosphere (=100kPa) for 10m of water. So 3.75kPa is 38cm of water column.

        Just add air to the pipe until the water level in one tube is 38cm higher than the level in the other tube. Like in this picture (ignore the text)
        Last edited by ikdor; 06-22-2016, 03:12 AM.

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        • #5
          I just made a simple gauge setup for use with an air compressor. Here the test for 6" pipe is 4psi for 5 minutes. For 4" pipe it is 6psi for 5 minutes.



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          • #6
            You are correct that the pressures the guy quotes seem too high by far. More like supply pipe pressures.

            Our "drain/waste/vent" pipe is specifically stated to NOT be pressure pipe. Seems that it should stand the pressure of maybe 25 to 30 feet of water, which might happen in a 3 story building if the vent "stack" filled up due to some blockage at the bottom (under basement floor). Past that, I'd not expect it to have good results......
            Last edited by J Tiers; 06-22-2016, 09:59 AM.
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              The column exerts 0.433 pounds per square inch of pressure. One pound per square inch (psi) of pressure can be created using a 1-in. square column of water nearly 28 inches or 2.31 feet high.

              At one time I knew this, but this was a Google result.
              Retired - Journeyman Refrigeration Pipefitter - Master Electrician - Fine Line Automation CNC 4x4 Router

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              • #8
                Our building code calls for a water column filled with water. At the lowest point exiting the buiding, a test ee is installed and a ball is inflated in the pipe. Then all stub ups are capped and the column filled. A savy inspector will want to see the ball removed and be sure all the pipes drain out.

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                • #9
                  It does not matter what shape the column of what is, round, square, heagonal or what ever. I bar is a bit over ten metres of water head.

                  ! bar is of course 100 kilopascals.

                  3.75Kpa is about 15 inches of water.

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                  • #10
                    For S&G I Googled sewer testing procedures and from the couple I read it seems 3.7 bar is way too high and 3.7 kpa is way too low. One site said "Test Pressure: Joint test pressure shall be 3-psi higher than the groundwater pressure, if any, outside the pipe." and "In the absence of groundwater pressure data, the test pressure shall be equal to 1/2 psi per vertical foot of pipe depth or 3 psi, whichever is greater." (3.7 bar =53.66 psi, 3.7 Kpa =.53 psi, 1/2 psi = 3.48 kpa and 3 psi = 20.6 kpa).

                    I suggest you get an Official copy of the testing requirements that are applicable to your location. If you build any instruments without knowing for sure what the upper and lower limits are you might find out you have just made a nice bit of useless equipment.

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                    • #11
                      The requirements ask for 3.75kpa for a stabalizing period of 2 minutes .Then it needs to be brought to 2.5kpa .Then the machine needs to be switched off and it can drop to no less than 1.5kpa over a three minute period.
                      I made a manometer from 8mm od by 4mm id perspex that I bent into a tube. It is about 700mm long.
                      If the difference between the lower level and the higher level is 375mm does this mean it is 3.75 kpa or is it 7.5kpa ?
                      Why i ask is that I borrowed a 100mm manometer but I see the graduations are in mm but the 100mm graduation is in fact only 50mm.

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                      • #12
                        Ah, so your guy mixed up "bar" and kpa. 1 bar is around atmospheric average pressure, so nearly 4 bar would indeed be a decent water pressure for supply.

                        The test you need is evidently for leakage in/out of the pipe, and that 3.75 kpa is appropriate.

                        yes, water column is measured from water surface to water surface, so if each moves 50mm, total is 100mm difference. As one side goes up 50mm the other goes bown 50, difference 100.
                        1601

                        Keep eye on ball.
                        Hashim Khan

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                        • #13
                          My manometer is a cheap yellow plasticky beast, I use manometer dye in mine, don't use orange squash as it goes manky food dye is ok, the graduation is MM and inches aka inches water gauge as the book says, the brand is "monument", main gas pressure over here is about 10" not high really but the things can be used on vacuum too which is handy.
                          Just about all the plumbing supplies sell them, short ones and long ones, the long beasts are about 700mm long, most of the plumbers use the digital manometers, they come in one and 2 port for differential pressure, usually the guys who work on gas boilers use those, not somthing I touch myself,
                          Gets a bit legal there
                          Btw, if you have 2 of them and a long pipe between they make good water levels I'm told
                          Mark

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