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  • Expansion tanks

    I don't have much experience with them. Since our city water meters don't have check valves in them, there is not much need for them because the heated water can push back through the cold lines when the pressure builds (apparently even past the heat traps installed in the tank.)
    Of course we them in the systems with circ pumps and tankless.
    My question: is there a scenario where an old or faulty expansion tank can cause a knocking in the pipes when the hot water is turned on or when a circ pump is running? It is not water hammer and the knocking is about 2 beats/sec. Also, it is not loose pipes. And it is sporadic. It sounds localized near the ex.tank. Perhaps it could be the flap in the check valve slamming. The other time this occurred there wasn't a check valve,just a pressure regulating valve.
    Last edited by SlimTim; 03-04-2014, 10:12 PM.
    "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

  • #2
    Re: Expansion tanks

    Is the Ex. tank full of water ! rubber bladder blown out ?
    I can build anything You want , if you draw a picture of it , on the back of a big enough check .

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    • #3
      Re: Expansion tanks

      Two beats per second kinda' sounds like a flat washer loose and vibrating. Not sure that helps, but I have heard it before in weird situations.

      I don't think a faulty expansion tank would cause the sound when opening something.

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      • #4
        Re: Expansion tanks

        The tank I replaced today had 0 pressure, so yes, the bladder must have been leaking. I am still curious if that could be the cause of the knocking. I guess I will find out if the knocking stops. But, I still want to know why.
        "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

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        • #5
          Re: Expansion tanks

          I don't think it is a loose washer in this case. New addition (3 or 4 yrs), all washerless faucets and no outside faucets. There is a tankless water heater in the closet with the expansion tank.
          "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

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          • #6
            Re: Expansion tanks

            I'm getting confused. Are there check valves and/or a circulating pump in the system now?

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            • #7
              Re: Expansion tanks

              Both a check valve and a circulating pump.
              "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

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              • #8
                Re: Expansion tanks

                I've traced knocking sounds back to faulty water meters before.

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                • #9
                  Re: Expansion tanks

                  Originally posted by SlimTim View Post
                  Both a check valve and a circulating pump.

                  could be the check valve making noise. could be a bad pump cartridge.
                  ~~

                  ... it was plumbed by Ray Charles and his helper Stevie Wonder

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                  • #10
                    Re: Expansion tanks

                    We had an issue with a chattering concealed water pipe on a remodel we did a few years ago. I was getting pretty worried about it because the stretch of pipe that was vibrating was concealed and finished over before the problem was discovered. We tried to isolate and solve the problem in different ways, but it wasn't until I spoke to a friend at the supply house who gave me a good tip that we found and fixed the problem.

                    We had installed a new Bradford/White water heater and the problem turned out to be a rubber washer which acted as a sort of heat trap in the cold inlet of the water heater. At just the right flow this washer would flutter and create a pipe chatter that resonated throughout the house. Pulling that factory installed heat trap and replacing it with an in-line spring check solved the problem.
                    Last edited by GreatLakesPlumber; 03-06-2014, 10:07 AM.

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                    • #11
                      Re: Expansion tanks

                      Originally posted by GreatLakesPlumber View Post
                      We had an issue with a chattering concealed water pipe on a remodel we did a few years ago. I was getting pretty worried about it because the stretch of pipe that was vibrating was concealed and finished over before the problem was discovered. We tried to isolate and solve the problem in different ways, but it wasn't until I spoke to a friend at the supply house that we found a fixed the problem.

                      We had installed a new Bradford/White water heater and the problem turned out to be a rubber washer which acted as a sort of heat trap in the cold inlet of the water heater. At just the right flow this washer would flutter and create a pipe chatter that resonated throughout the house. Pulling that factory installed heat trap and replacing it with an in-line spring check solved the problem.
                      thanks ,that's awesome Info. !
                      I can build anything You want , if you draw a picture of it , on the back of a big enough check .

                      Comment


                      • #12
                        Re: Expansion tanks

                        Originally posted by GreatLakesPlumber View Post
                        We had an issue with a chattering concealed water pipe on a remodel we did a few years ago. I was getting pretty worried about it because the stretch of pipe that was vibrating was concealed and finished over before the problem was discovered. We tried to isolate and solve the problem in different ways, but it wasn't until I spoke to a friend at the supply house who gave me a good tip that we found and fixed the problem.

                        We had installed a new Bradford/White water heater and the problem turned out to be a rubber washer which acted as a sort of heat trap in the cold inlet of the water heater. At just the right flow this washer would flutter and create a pipe chatter that resonated throughout the house. Pulling that factory installed heat trap and replacing it with an in-line spring check solved the problem.

                        we had a similar problem with rheem/ruud tanks that used the ceramic check balls. rattle rattle rattle at certain flows.
                        ~~

                        ... it was plumbed by Ray Charles and his helper Stevie Wonder

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                        • #13
                          Re: Expansion tanks

                          OMG!!!! I swear, lawyers can be the most difficult people to work for sometimes (this homeowners profession).
                          I picked up another expansion tank and replaced the old one. The old one had completely lost its charge. I was still trying to parse out how it could cause the knocking sound. To me, the water forces inside a pipe can be downright mysterious what with eddies and cavatations (sp?) aspirations, diffused oxygen, heat, pressure, physics, etc.
                          Mind you, this owner told me the knocking only occurs when they use the hot water and it would always stop when he turned the water off to the water heater.
                          I had just decided to live with the mystery of why it happened -then he said," while your here, please check our toilet. It seems to run sometime.... I just shook my head in disbelief that I could be so stupid! Of course, it had to be the fill valve. And it was.
                          The lesson I learned- Listen attentively to the homeowner, then check everything no matter how many times they say "it can't be that".
                          Thanks for all your suggestions. Sorry to waste your time with this one.
                          "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

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                          • #14
                            Re: Expansion tanks

                            Originally posted by SlimTim View Post



                            The lesson I learned- Listen attentively to the homeowner,
                            .
                            Can I just act like I'm listening attentively.

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                            • #15
                              Re: Expansion tanks

                              Originally posted by saysflushable View Post
                              Can I just act like I'm listening attentively.
                              Of course! That goes without saying.
                              "Man will do many things to get himself loved, he will do all things to get himself envied." Mark Twain

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