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  • w.h. t+p valve

    customers t+p blew off some. will change it out and install expansion tank
    on cold. Here's the questions. there is a hot water circ. pump plumbed off the side of a brass t from the top,not side, tap on the tank. It has a close nipple
    and I wonder if the probe even enters the tank. should i also re plumb this?
    tank is not leaking but must be 20 years old. she is wealthy and said change out tank also if i want to. thank's tool
    I can build anything You want , if you draw a picture of it , on the back of a big enough check .

  • #2
    Originally posted by toolaholic
    customers t+p blew off some. will change it out and install expansion tank
    on cold. Here's the questions. there is a hot water circ. pump plumbed off the side of a brass t from the top,not side, tap on the tank.
    i always plumb the circ. to the botom of the tank by removing the hose bibb and installing a brass nipple,ball valve, hose bibb and pump.

    It has a close nipple
    and I wonder if the probe even enters the tank. should i also re plumb this?

    i would install the t&p valve in it's own tank tap. most new heaters have either a top tap, side tap, or both. it should be on it's own so that the probe will be in direct contact with the tank water.


    tank is not leaking but must be 20 years old. she is wealthy and said change out tank also if i want to. thank's tool
    if the tank is installed indoors where it will do damage, i would change it. most heaters were not built to last much beyond their warranty period.
    although there are still some all copper or monel tanks still out there that are still working today

    back then it was a 5 or 10 year. today it's a 6-12 year.

    a would also change the expansion tank if it is more than 5 years old.

    rick.
    phoebe it is

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    • #3
      I would replace water heater and new expansion tank I would not pipe pump from bottom. In year to come it will get build up in bottom of tank. and mess up pump. No home owner drains these tanks every year to clean. If you have to you can buy longer T&P valves

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      • #4
        Re: w.h. t+p valve

        Plumb circulating from hot out to boiler drain at bottom, remember that cold water enters the tank from the bottom via a dip tube. Expansion tank is pointless unless there is a check valve between meter and domestic water within the house. Check valve will not permit "used" water to go back through the meter. Expansion tank gives a place for the heated, expanded water to go. T+P within 6" of the tank, preferably inside the tank, in any case no further from the tank than 6".

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        • #5
          Re: w.h. t+p valve

          Originally posted by toolaholic View Post
          customers t+p blew off some. will change it out and install expansion tank
          on cold. Here's the questions. there is a hot water circ. pump plumbed off the side of a brass t from the top,not side, tap on the tank. It has a close nipple
          and I wonder if the probe even enters the tank. should i also re plumb this?
          tank is not leaking but must be 20 years old. she is wealthy and said change out tank also if i want to. thank's tool
          If the T&P valve is blowing off, you have a problem with:

          1) The T&P valve is defective. At which point changing the valve should correct the problem.

          2) The heater is over heating, which means the T&P is doing it's job.

          Changing the expansion tank will do nothing. It's job is to absorb pressure differential caused by the expansion of heated water. In my opinion they are useless in a domestic water system, and they are not meant to absorb enough pressure to prevent a T&P valve from activating.
          the dog

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          • #6
            Re: w.h. t+p valve

            another reason for a T&p to blow off is if some has installed a check valve (as scott said). This creates a closed system, and if the water cant expand past the check valve, an expansion tank is what will fix this.he didnt say he is going to change the tank, he is installing one one that didnt previously exist. tool, if there is no check valve, then an expansion wont help, check your temp setting
            West Trail Mechanical Ltd
            Service. Commitment. Expertise.

            www.westtrailmechanical.ca

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            • #7
              Re: w.h. t+p valve

              The dog is speaking simple facts here.

              Also the t&p must be in the tank within 6" of the top of the tank. The expansion tank, like the others have said is not required. If there is a check valve instaled then just take it out and drill a 3/32 hole in the check. this will allow the pressure to leave.

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              • #8
                Re: w.h. t+p valve

                guy's, a little about thermal expansion.

                true a check valve will create a closed system, and thus requires an expansion tank. but so will a system with an inlet pressure prior to the pressure regulator that is more than the setting of the relief valve.

                an example: most pressure relief valves are set to open at 150 psi. if the city main pressure prior to the pressure regulator is higher than 150 psi, even though you are regulating the discharge pressure to 65psi, will require an expansion tank. this is because the regulator has an internal thermal bypass. the issue is that the relief valve will open since the high pressure side of the regulator is more than the relief setting of the pressure relief valve.

                if the city side is less than the relief setting, (less than 125-150psi) then the regulator will allow for thermal expansion back into the city system, assuming that there is no form of a backflow preventer, check valve at the main.

                it's also very important to precharge the expansion tank to the static inlet pressure too.

                then there is the temperature relief setting too.

                a very simple example, test is to fill the heater and system compleatly with water. screw a pressure guage to the hose bibb drain at the bottom of the heater. then without opening any faucets in the house, let the heater come up to the proper temperature. you will see the pressure guage climb too. once a faucet is opened the pressure will drop back to the regulator setting. if nothing is opened, then the pressure will climb to the level of the high pressure side of the regulator. if it's more than 125-150, the relief valve will open.

                water is a hydraulic. it will not compress like air does. that's the whole purpose of an expansion tank.

                there is a toilet ballcock that was designed to allow for thermal expansion. it actually dripped the excess pressure into the toilet tank.

                hope this helped the readers that were confused about thermal expansion.

                rick.
                phoebe it is

                Comment


                • #9
                  Re: w.h. t+p valve

                  " T+P within 6" of the tank, preferably inside the tank, in any case no further from the tank than 6". "

                  I don't believe the above to be 100% correct. AFAIK a T&P valve must be installed so the temperature element is immersed in the hottest water in the top 6 inches of the tank. That's not the way the above statement reads to me.
                  ---------------
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                  Comment


                  • #10
                    Re: w.h. t+p valve

                    Have'nt had much to say on this site for a while but I have to comment on this. I am a residential service plumber and I get this call all the time. What amazes me, and I thought for a moment Rick was going to, is that nobody has mentioned what the actual problem is here. Whenever anyone calls me and says anything like "I think my water heater's shot 'cause water won't stop running out of this valve ..." I always check my truck and make sure I have'nt used my last prv because 9 times out of 10 that's what the problem is.

                    Did you check the pressure at the water heater drain?

                    Think about this for a minute. HO's t&p is actuating which means the temp at the probe is either 210 deg. F (I've never witnessed or even heard of this happening) or the pressure has reached 150 psi. Since your standard 2 gal. expansion tank has an operating range not exceeding 150 psi then if your t&p is allowing water to pass it means the entire system is at that pressure.
                    So if you have a pressure of 150 psi it almost always means that the prv has failed to do its job.

                    Now all of this may depend on the code your area observes but for any area observing the IPC, no check valve is required and so everything above applies. I don't know what the UPC says but for any system that has a check valve anywhere between the prv and wh this obviously would not necessarily apply and the prv may not be but still could be (and probably is) at fault.

                    Having said all that, it sounds as if the HO realizes she has a very elderly tank (the oldest I ever saw was 32 years) and I would go ahead and replace it, because it can't be long for this world anyway, but not without checking out the exact cause of the pressure problems first.

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                    • #11
                      Re: w.h. t+p valve

                      Are we talking about a residential water heater for domestic hot water, or a heating boiler with a small expansion tank?

                      If you look at any tank style hot water heater for residential use that was made in the USA for use here in the USA you'll see that it has a special port that is just for the T & P relief valve and nothing else. You are to screw the T & P valve directly into this port which is normally on the side and close to the top, but is sometimes on the top of the tank. The next time any of you are in a plumbing supply house or a home center, take a good look at the different tank style water heaters.

                      As for needing an expansion tank, that would be if there is either a pressure regulator for the feed water (most likely the whole house) or a check valve or both. In addition to the T & P valve (on water heater) there should be a pressure relief valve just after any check valves or pressure regulators.

                      Please see picture for example, and please be sure to properly pipe the discharge so it's a few inches above the floor and aimed at the floor. This is for safety reasons.
                      Attached Files
                      Last edited by Woussko; 01-28-2007, 03:54 AM.

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